The Dark Side of the Universe DSU2022

5 Dec 2022, 08:30 → 9 Dec 2022, 17:00 Australia/Sydney

^{Conference photo courtesy of Frank Yourong Wang. See here for more impressions of the meeting.}

The 16th International Workshop on the Dark Side of the Universe/2nd Gordon Godfrey Workshop on Astroparticle Physics took place on 5-9 Dec 2022 at The University of New South Wales (UNSW) in Sydney, Australia, hosted by the Sydney Consortium for Particle Physics and Cosmology.  It brought together a wide range of theorists and experimentalists to discuss current ideas on models of the dark sector of the Universe and to relate them to ongoing and future experiments.

The meeting featured invited plenary talks covering topics of recent interest, as well as a number of parallel sessions to provide an opportunity for junior scientists to present their work.

The workshop was preceded by the 3rd Sydney Spring School, aimed at graduate students and young postdocs, held on 30 Nov-2 Dec 2022 at the University of Sydney.

 

We thank everyone for their contributions and look forward to seeing you again in Sydney in the future.

 

 

Plenary speakers:

Jenni Adams (U. Canterbury)

Elisabetta Barberio (U. Melbourne)

Csaba Balazs (Monash U.)

Roland Crocker (ANU)

Valentina De Romeri (IFIC Valencia)

Cora Dvorkin (Harvard U.)

Theresa Fruth (U. Sydney)

Tony Gherghetta (U. Minnesota)

Jinn-Ouk Gong (Ewha Womans U.)

Julia Harz (Mainz U.)

Bin Hu (Beijing Normal U.)

Joerg Jaeckel (Heidelberg U.)

Pyungwon Ko (KIAS, Seoul)

Florian Kühnel (MPP, Munich)

Sachiko Kuroyanagi (IFT, Madrid)

Geraint Lewis (U. Sydney)

Yann Mambrini (CNRS IJCLab, U. Paris-Saclay)

Shinji Mukohyama (Kyoto U.)

Natsumi Nagata (Tokyo U.)

Keith Olive (U. Minnesota)

Adam Ritz (U. Victoria)

Gavin Rowell (U. Adelaide)

Seon-Hee Seo (IBS, Daejeon)

Tracy Slatyer (MIT, Cambridge)

Alexander Vikman (FZU, Prague)

Aaron Vincent (Queen's U.)

Ray Volkas (U. Melbourne)

Meng-Ru Wu (National Taiwan U.)

Yu-Feng Zhou (ITP, Beijing)

Monday 5 December

Registration

Plenary

Livestream link: https://tinyurl.com/DSU2022plenary

Convener: Prof. Matthew Dolan (University of Melbourne)

1 Opening

Wong.pdf

2 News from sub-GeV FI(N)Ps

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Speaker: Joerg Jaeckel (Institut fuer theoretische Physik, Heidelberg University)

Sydney5.pdf

3 Primordial Black Holes as Dark Matter

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Speaker: Dr Florian Kühnel (LMU Munich)

Kuhnel-Florian - Syndey - DSU - December 2022.pdf

10:30 Coffee break

Plenary

Livestream link: https://tinyurl.com/DSU2022plenary

Convener: Ciaran O'Hare (Sydney)

4 Light sub-GeV dark matter at accelerators

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Speaker: Adam Ritz

DSU_DM_2022.pdf

5 Status and prospects of dark matter direct detection

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Speaker: Theresa Fruth (University of Sydney)

DSU_DirectDetection_Fruth.pdf

6 Dark matter searches in the southern hemisphere

Speaker: Elisabetta Barberio

DM_SH_DSU_final.pdf

12:30 Lunch break

Dark matter

Convener: Theresa Fruth (University of Sydney)

7 First results from the LUX-ZEPLIN (LZ) dark matter experiment

Dark matter is still one of the greatest mysteries of the Universe. The detection and the properties of dark matter particles, which make up about 86% of the mass of our Universe, are still elusive. LUX-ZEPLIN (LZ) is a direct detection dark matter experiment located at the 4850 ft. level of the Sanford Underground Research Facility in Lead, South Dakota, United States. The LZ experiment employs a dual-phase xenon time projection chamber (TPC), in combination with an active neutron veto, to detect Weakly Interacting Massive Particles (WIMPs), a highly motivated dark matter candidate. With an exposure of 60 live days and a fiducial mass of 5.5 t, LZ has set new limits on the spin-independent WIMP-nucleon cross-sections for WIMP masses above 9 GeV/c^2. This presentation will provide an overview of the detector design and the first dark matter search results.

Speaker: Nishat Parveen (SUNY Albany)

DSU2022_nishat.pdf

8 XENONnT Dark Matter Experiment: Recent Status and Latest Results

One of the open questions in modern physics today concerns the nature of Dark Matter (DM). The XENONnT experiment, the successor of XENON1T, is the latest of the XENON project primarily conceived for DM direct detection and it is currently taking data for the second science run at the underground Laboratori Nazionali del Gran Sasso, in Italy. It consists in a dual-phase time projection chamber containing 5.9-tonne of liquid xenon as active target. Thanks to the increased target compared to its predecessor, it reached an unprecedented purity and background level which allows for different rare events searches. This talk will focus on an overview of the XENONnT experiment and its performance as well as on the latest results and future projections.

Speaker: Dr Yajing Xing (SUBATECH)

DSU2022_yajing.pdf

9 Direct dark matter searches in XMASS-I

Results of various WIMP direct dark matter searches using full data set of XMASS-I are reported. The XMASS-I is multi-purpose experiment using single phase liquid xenon at the Kamioka Observatory (2700 m.w.e.) in Japan. Stable XMASS-I data taking accumulated a total live time of 1590.9 days between Nov. 20, 2013 and Feb. 1, 2019.
The analysis thrshold was 1.0 keV (for electron recoil) for whole data set, and 0.5 keV for latter half of data set owing to improvement of a trigger system.
We will describe results from searching for WIMP signal in the detector's fiducial volume (97 kg) and WIMP induced annual modulation signatures in the detectos's whole target volume (832 kg).

Speaker: Atsushi Takeda

221205-cnf-takeda-DSU2022.pdf

10 DARWIN: a liquid xenon observatory for rare events physics searches

Shedding light on the nature of dark matter and studying properties of neutrinos are among the main priorities of modern particle and astroparticle physics today. Worldwide, numerous direct detection experiments are prepared to observe rare signals induced by dark matter candidates and neutrinos in ultra-sensitive, low-background detectors. One of the leading technologies today are Liquid Xenon Dual Phase Time Projection Chambers. This technology is evolving rapidly and is expected to continue leading the field in the future years. In the context of this evolution, the DARWIN collaboration aims at the realisation of a future liquid xenon observatory. With about 40 tons of liquid xenon in its active volume, the detector will be designed to push the sensitivity of direct dark matter searches far beyond existing limits. Its low background and large target mass will also make it ideally suited for a large number of other rare event searches. In this talk I will present the concept of the DARWIN detector and discuss its physics reach, the main sources of backgrounds and the ongoing R&D efforts to overcome a multitude of challenges related to this ambitious project.

Speaker: Dr Sara Diglio (SUBATECH/CNRS/In2p3)

DSU2022_Sydney_SaraD_final_with_backup.pdf

11 DarkSide-20k and the Direct Dark Matter Search with Liquid Argon

Dual-phase noble liquid Time Projection Chambers (TPCs) and single-phase scintillation-only detectors offer competitive ways to search for dark matter directly via elastically scattering off of detector target nuclei and electrons. Argon possesses an intrinsic property allowing for powerful discrimination between electron (background) and nuclear (signal) recoils. The Global Argon Dark Matter Collaboration (GADMC) has undertaken an ambitious program from the extraction and purification of Underground Argon (UAr), depleted in $^{39}$Ar reducing the radioactive background, to the development of large arrays of Silicon Photo Multiplier (SiPM) modules capable of resolving single photoelectrons. DarkSide-20k (dual-phase TPC) is the next stage of this program, and it has entered the construction phase at the Gran Sasso underground laboratory (LNGS) in central Italy. An exposure goal of ≈ 200 tonne-years with near-zero instrumental background has been set for sensitivity to a WIMP-nucleon cross section of $\approx 10^{-47} \textrm{cm}^2$ for a WIMP mass of 1 TeV/c$^2$ over a 10-year run. An overview of the DarkSide-20k experimental program, along with recent UAr cryogenic system testing results and other progress will be presented.

Speaker: Thomas Nathan Thorpe (University of California Los Angeles (US))

Thorpe_dsu22.pdf

Early Universe

Convener: Sachiko Kuroyanagi (IFT UAM-CSIC)

12 CP-violating inflation

I introduce the novel phenomena of CP-violating inflation in a non-minimal Higgs framework where the inflaton has a complex non-minimal coupling to gravity leading to CP-violation - a necessary source of the baryon asymmetry. I discuss the inflationary dynamics of such a framework and its implications for baryogenesis.

Speaker: Venus Keus (Dublin Institute for Advanced Studies (DIAS))

VKeus_DSU2022.pdf

13 Type II Seesaw Leptogenesis

The Type II Seesaw Mechanism provides a minimal framework to explain the neutrino masses involving the introduction of a single triplet Higgs to the Standard Model. We have demonstrated that this triplet Higgs alone can simultaneously generate the observed baryon asymmetry of the universe and the neutrino masses while playing a role in setting up Inflation. This is achievable with masses as low as 800 GeV, and predicts that the neutral component obtains a small vacuum expectation value v_∆< 10 keV. I will discuss the rich phenomenology of our model which can be tested by various terrestrial experiments as well as by cosmological observations. In particular, the successful parameter region may be probed at a future 100 TeV collider, upcoming lepton flavor violation experiments such as Mu3e and COMET, and neutrinoless double beta decay experiments.

Speaker: Neil Barrie

TIILep_DSU_Barrie.pdf

14 Universe with a large lepton asymmetry

The recent observation of ${}^4$He implies that our universe has a large lepton asymmetry. We consider the Affleck-Dine (AD) mechanism for lepton number generation. In the AD mechanism, non-topological solitons called L-balls are produced, and the generated lepton number is confined in them. We study the formation and evolution of the L-balls and find that the universe with large lepton asymmetry suggested by the recent $^4$He measurement can be realized. Furthermore, the produced L-balls dominate the Universe and their rapid decay enhances the background gravitational waves through the Poltergeist mechanism.

Speaker: Masahiro Kawasaki

kawasaki_large_lepton.pdf

15 Constraining Phase Transitions in Grand Unified Theories with Gravitational Waves

The era of gravitational wave (GW) astronomy offers a new avenue to explore the early universe and with it an energy scale that may never be accessible to terrestrial colliders. This provides a fresh new way to investigate the phenomenology of grand unified theories (GUT). We construct an $SO(10)$ inspired Pati-Salam model encompassing an intermediate minimal left-right symmetric model. We calculate the stochastic GW background associated with the $SU(4)$ symmetry breaking phase transition and find that, in general, the spectrum peaks well above the sensitivity windows of any current or proposed GW detector. However, for some regions of the parameter space, the signal peaks close to LIGO and VIRGO's most sensitive region. We assess to what extent the LIGO-VIRGO network can already be used as a way to constrain GUT models and to what extent future observatories such as the Einstein Telescope could improve on this.

Speaker: Matthew Pearce (Monash University)

PhaseTransitionsInGUTs.pdf

16 Gravitational production during reheating phase: the possibility of purely Gravitational reheating

My talk will mainly focus on an interesting reheating scenario where minimal gravitational interaction plays an important role that was ignored in the literature due to its supposedly weak strength. We take a systematic approach toward building a reheating scenario that can provide model-independent observable predictions. I shall start the discussion with the dark matter (DM) sector first, where it is assumed to be produced from both inflaton and radiation bath through minimal gravitational interaction only. Since the gravitational production process is always present, we can't ignore this. However, we introduce arbitrary coupling between inflaton and standard model particles to achieve the radiation-dominated universe. After successfully generating the present dark matter abundance through gravitational production during the reheating phase, a natural question we can ask: is it possible to reheat our universe purely gravitationally? Surprisingly, such a scenario has turned out to be possible because the energy scale of any physical processes during reheating could be as large as $10^{15}$ GeV, and that leads gravity mediated decay process to become strong enough to reheat the universe. This is the possibility we will also explore in this talk. We will name it gravitational reheating (GRe). Therefore here, we remove all arbitrary couplings between inflaton and daughter fields, which implies the inflaton sector is coupled with the observable sector only through gravitational interaction. Interestingly, only gravitational interaction turned out to be enough to reheat our universe successfully. In this phase, DM mass is the only free parameter except for the inflationary parameters. We will see how such less freedom naturally makes GRe a unique mechanism compared to reheating scenarios discussed so far in the literature. All the massless decay products from inflaton will be collectively called radiation, and massive ones are DM. Given the present state of the universe, the GRe scenario is consistent with a very limited class of inflation models and a narrow range of DM masses. However, if DM couples with the radiation bath, gravitational production sets the maximum limit on the DM mass. It is the s-channel graviton exchange process through which inflaton converts its energy to radiation and DM during reheating.
References. 1. Phys.Rev.D 106 (2022) 2, 023506,
2. e-Print: 2201.02348.

Speaker: MD RIAJUL Haque (Indian Institute of Technology Guwahati)

DSU2022_Riajul.pdf

Ultralight dark matter

Convener: Benjamin Roberts

17 Proposals for searches of scalar field dark matter using cavity resonators and capacitors

We consider scalar field dark matter model with a dilaton-like interaction with the electromagnetic field. If the mass of this scalar field falls within the range of hundreds of MHz, it may be detected using cavity resonator techniques similar to those used in the search of the axion dark matter in the ADMX and ORGAN experiments. We show that existing cavity resonators employed in experiments like ADMX have a low but nonvanishing sensitivity to the scalar-photon coupling. As a result, by repurposing the results of the ADMX experiment, we find new limits on the scalar-photon coupling constant in the frequency band from 630 MHz to 1 GHz. We propose new cavity resonators with enhanced sensitivity and a novel capacitor-based experiment featuring broadband detection possibilities of the scalar field dark matter.

Speaker: Dr Igor Samsonov (UNSW)

Samsonov1.pdf

18 Dark matter detection via atomic interactions

The mystery of dark matter (DM) is a long-standing issue in physics, with numerous dedicated experiments returning no confirmed detections. With the constantly increasing sensitivity of direct detection experiments, much of the parameter space for Weakly Interacting Massive Particles (WIMPs) has been ruled out. However, low mass (sub-GeV) WIMP-like particles are less researched and yet to be excluded as a possibility, despite their potential for direct detection via atomic interactions. Due to these particles having masses comparable to or lower than nucleons, detection of any nuclear recoil in scintillation experiments proves difficult. Instead, a DM-electron interaction could be detected in conventional scintillators due to an enhanced scattering rate. Considering this possibility is important for assessing recent experimental results and upcoming scintillator-based DM searches. In this work, I will present atomic excitation factors and calculated event rates for DM-electron scattering, and how they can inform experimental searches.

Speaker: Ashlee Caddell (The University of Queensland)

DSU_DMAtomic_Caddell.pdf

19 New optical clocks based on Cu II, Yb III, Hf II, Hf IV, and W VI ions which may be used to search for dark matter and variation of the fine structure constant

We study the prospects of using several metastable excited states of Cu II, Yb III, Hf II, Hf IV, and W VI ions as clock transitions in optical clocks. The transitions between ground and metastable states in these systems are the $s-d$ transitions which ensure high sensitivity to the variation of the fine structure constant. Cooling E1 transitions are available. Energy levels, $\text { Landé g-factor }$, transition amplitudes for electric dipole (E1), electric quadrupole (E2), and magnetic dipole (M1) transitions, lifetimes, and electric quadrupole moments are investigated using a combination of several methods of relativistic many-body calculations including the configuration interaction (CI), linearized coupled-cluster single-doubles (SD) and many-body perturbation theory (CI+SD), and also the configuration interaction with perturbation theory (CIPT). Scalar polarizabilities of the ground states and the clock states have been calculated to determine the black body radiation (BBR) shifts. We have found that the relative BBR shifts for these transitions range between 10$ ^{-16} $ $-$ 10$ ^{-18} $. The second-order Zeeman shifts of Cu II and Yb III, whose stable isotopes have non-zero nuclear spins ($I$), have also been calculated. A linear combination of two clock transition frequencies allows one to further suppress BBR. Studying possible variation of the fine structure constant may be used to search for dark matter causing this variation. The enhancement coefficient for $\alpha$ variation reaches K = 8.3. As these atomic systems have multiple isotopes, King plots can be made and new interactions may be found mediated by scalar particles or other mechanisms.

Speaker: Saleh Allehabi

20 Searching for new bosons in atomic spectra

We shall explain why we expect atomic spectra to be sensitive to new bosons, like Z' boson and axion. Such bosons can be exchanged between the known particles. We will present new bounds on the properties of such bosons, using spectra of antiprotonic helium, muonium, positronium, helium, and hydrogen. We will show how to construct such bounds, including one using pseudovector interaction which is inversely proportional to the boson's mass squared.
Phys. Rev. A 105, 022812 (2022).
Combining results from different experiments, we compare bounds on spin-dependent interactions from a review in the making.

Speaker: Pavel Fadeev (Helmholtz Institute Mainz, Johannes Gutenberg University, 55128 Mainz, Germany)

Potentials DSU2022.pdf

Potentials DSU2022.pptx

21 Searching for scalar field dark matter with hyperfine transitions in alkali atoms

Fundamental constants such as masses and coupling constants of elementary particles can have small temporal and spatial variations in the scalar field dark matter model. These variations entail time oscillations of other constants, such as the Bohr and nuclear magnetons, Bohr radius and the hyperfine structure constant. In the presence of an external magnetic field, these oscillations induce hyperfine transitions in atoms and molecules. We determine the probability of magnetic dipole hyperfine transitions, caused by the oscillating fundamental constants, and propose an experiment that could detect the scalar field dark matter through this effect. This experiment may be sensitive to the scalar field dark matter with mass in the range $1 \ \mu \text{eV} < m_{\phi} < 100 \mu \text{eV}$

Speaker: Andrew Mansour

15:40 Coffee break

Dark matter

Convener: Sara DIGLIO (SUBATECH/CNRS/In2p3)

22 ANAIS-112: testing the DAMA/LIBRA signal beyond 3 sigma

To the date, the only positive signal of presence of dark matter (DM) in the Milky Way halo by direct observation of its interaction with a detector comes from the DAMA/LIBRA experiment in the Gran Sasso National Laboratory (LNGS). For more than 20 years it has observed an annual modulation in the low energy counting rate compatible with that expected due to the rotation of the Earth around the Sun. For most WIMP candidates this result is incompatible with the negative results of other experiments, remaining as one of the most intriguing puzzles in the field.
The goal of ANAIS-112 is to provide a direct and independent check of the DAMA/LIBRA DM positive result using the same type of detector: NaI(Tl) scintillators. The experiment was installed in August 2017 in the Canfranc Underground Laboratory (LSC) and is taking data since then with excellent performance. The results published so far, corresponding to 1.5 and 3 years of data collection, show no modulation and are incompatible with DAMA/LIBRA for a sensitivity of 2.5-2.7$\sigma$ C.L. In this talk I will present a reanalysis of the 3 years data using new filtering protocols based on machine learning techniques, which notably increases the experimental sensitivity. New sensitivity prospects and preliminary modulation results will also be presented.

Speaker: Maria Martinez

DSU_22_MMartinez.pdf

23 Cryogenic NaI based remoTES calorimeters for direct dark matter detection in COSINUS

The COSINUS experiment (Cryogenic Observatory for SIgnals seen in Next generation Underground Searches) is a low-threshold, cryogenic experiment being set up at Laboratori Nazionali Del Gran Sasso, Italy. It aims to provide a model independent cross-check of the DAMA/LIBRA findings of a potential dark-matter like modulating signal.
COSINUS utilizes a two-channel readout system based on transition edge sensors(TESs) that allows for particle discrimination. It consists of ultrapure scintillating sodium iodide (NaI) crystals read out using a novel remoTES scheme to measure the phonon signal of a particle interaction. A silicon beaker surrounding the crystals is used to measure the light signal from the same particle interaction. Results from the latest prototypes and updates on the setup will be presented in this contribution.

Speaker: Mukund Raghunath Bharadwaj

DSU_2022_Mukund.pdf

24 Impact of quenching factor models on tests of DAMA

For nearly two decades the DAMA Collaboration has been observing a modulating signal compatible with that expected from a dark matter presence in our galaxy. However, interpretations of this with the standard assumptions for dark matter particles are strongly ruled out by a large number of other experiments. This tension can be relaxed somewhat by making more tailored choices for the dark matter model and properties of interest, but expanding the models of interest in such a way makes it impossible to test the DAMA modulation conclusively. In order to understand the exact nature of this signal, we need to use a detector based on the same target (NaI(Tl)), which would be sensitive to exactly the same particle interaction models as DAMA.
There are a number of such experiments in the data taking or commissioning stages designed to do just this, two of which (ANAIS and COSINE) recently released their results after 3 years of data taking. Interestingly, the modulation observed by the two experiments deviate from each other by 2𝜎, while being within 3𝜎 of the DAMA result. This talk addresses potential differences between NaI(Tl) based detectors that could lead to the differing results to date, with a particular focus on the quenching factor.

Speaker: Madeleine Zurowski

dsu-zurowski.pdf

25 Radio-impurity studies for dark matter detection with the SABRE South experiment

The aim of the SABRE (Sodium-iodide with Active Background REjection) experiment is to detect an annual rate modulation from dark matter interactions in ultra-high purity NaI(Tl) crystals in order to provide a model independent test of the signal observed by DAMA/LIBRA. The scientific program includes the deployment of two separate detectors: SABRE South located at the Stawell Undergrond Physics Laboratory (SUPL) in Australia and SABRE North at the Laboratori Nazionali del Gran Sasso (LNGS) in Italy.

Ultra-high purity of the NaI(Tl) crystals are a crucial feature of the SABRE South detector. Radiation from both intrinsic and cosmogenic processes in the detector material must be studied and quantified in order to distinguish it from dark matter events. NaI(Tl) crystals are immersed in a liquid scintillator veto, further surrounded by passive steel and polyethylene shielding and a plastic scintillator muon veto. Furthermore, the SABRE collaboration develops ultra-sensitive techniques to measure radionuclides that could mimic dark matter events. Currently the focus is being put on radionuclides potassium-40 and lead-210, which are expected to be the dominant radio-impurities in the crystal background. Chemical procedures, sample preparation as well as sample measurements via accelerator mass spectrometry and inductively coupled plasma mass spectrometry are under development in order to understand the sensitivity of SABRE South.

In this talk the current status of the radioimpurity-studies and their importance for the SABRE South experiment are conferred. The chemical methods, sample preparation as well as measurement techniques under investigation to be used to quantify the radio-impurities in the NaI(Tl) crystals are addressed.

Speaker: Dr Zuzana Slavkovska (Australian National University)

DSU2022_Zuzana_Slavkovska_Radioimpurity_Talk.pdf

26 R11065 Crystal Photomultiplier Contribution to the SABRE South Experimental Background

The DAMA experiments have detected a modulating signal compatible with dark matter for 20 years with a combined significance of 12.9~$\sigma$. A result in tension for a spin independent WIMP with null results from large noble gas experiments. This is the motivation for SABRE (Sodium iodide with Active Background Rejection) South experiment. A NaI(Tl) based replication studies of the DAMA experiment, and the Southern Hemispheres first dark matter direct detection experiment. It is designed to test the DAMA modulation results the same NaI(Tl) crystal target readout by 14 Hamamatsu R11065 photomultiplier tubes (PMTs) with a 1~keV$_{\text{ee}}$ threshold.

This threshold corresponds to $\sim13$ detected photons, this makes separating genuine scintillation events from PMT noise difficult. Thus PMT noise is a significant component of the low energy background model that is difficult to include in time dependent background models as it cannot be modelled in Monte Carlo simulations. This makes accurate measurement of the low energy noise important for both understanding and minimising its contribution to the overall background.

This talk will report on the photomultiplier characterisation test bench developed for the crystal detector photomultipliers of SABRE South and preliminary results from the first test batch of PMTs. This includes studies of the single photon response, quantum efficiency, and dark noise. A specific focus is on correlated dark noise between two photomultipliers above the random coincidence rate, due to its significant contribution to the low energy background, we provide estimates of this effect also utilising studies of photomultipliers noise from underground measurements at LNGS. The results of the photomultiplier characterisation are crucial to model and understand the low energy performance of the SABRE South experiment. This is crucial to ensure that SABRE South can provide and accurate and untactful measurement of the DAMA signal.

Speaker: William Melbourne (The University of Melbourne)

DSU22 - R11065 PMT SABRE South- W. Melbourne.pdf

Early Universe

Convener: Alexander Vikman (Czech Academy of Sciences (CZ))

27 Analyzing the Hubble tension through hidden sector dynamics in the early universe

We propose a particle physics model that can alleviate the observed Hubble tension via an out-of-equilibrium hidden sector coupled to the visible sector. The particles that populate the dark sector consist of a dark fermion, which acts as dark matter, a dark photon, a massive scalar and a massless pseudo-scalar. Assuming no initial population of particles in the dark sector, feeble couplings between the visible and the hidden sectors via kinetic mixing populate the dark sector even though the number densities of hidden sector particles never reach their equilibrium distribution and the two sectors remain at different temperatures. A cosmologically consistent analysis is presented where a correlated evolution of the visible and the hidden sectors with coupled Boltzmann equations involving two temperatures, one for the visible sector and the other for the hidden sector, is carried out. The relic density of the dark matter constituted of dark fermions is computed in this two-temperature formalism. As a consequence, BBN predictions are upheld with a minimal contribution to ΔNeff. However, the out-of-equilibrium decay of the massive scalar to the massless pseudo-scalar close to the recombination time causes an increase in ΔNeff that can help weaken the Hubble tension.

Speaker: Michael Klasen

klasen.pdf

28 De Sitter space as coherent state of gravitons

Not a long ago, it was argued that the quantum gravity only tolerates de Sitter as a state on top of a valid vacuum. So, we construct the de Sitter state as a coherent state of gravitons on top of the Minkowski vacuum. To make the construction consistent, we use BRST quantization. As an example, first we study such construction in QED, and then we generalise it in linear gravity. Coupling the gravity with large number of soft scalars give us possibility to take double-scale, so-called species limit, in which gravity linearize and the construction is exact. In this theory, only collective quantum phenomena, like Gibbons-Hawking radiation, survive. We also double-check consistency of our construction using the above processes.

Speaker: Dr Otari Sakhelashvili (The University of Sydney)

talk.pdf

29 Massive neutrino self-interactions and inflation

Based on: arXiv 2207.07142
Certain inflationary models like Natural inflation (NI) and Coleman-Weinberg inflation (CWI) are disfavoured by cosmological data in the standard ΛCDM+r model (where r is the scalar-to-tensor ratio), as these inflationary models predict the regions in the n_s−r parameter space that are excluded by the cosmological data at more than 2σ (here n_s is the scalar spectral index). The same is true for single-field inflationary models with an inflection point that can account for all or majority of dark matter in the form of PBHs (primordial black holes). Cosmological models incorporating strongly self-interacting neutrinos (with a heavy mediator) are, however, known to prefer lower n_s values compared to the ΛCDM model. Considering such neutrino self-interactions can, thus, open up the parameter space to accommodate the above inflationary models. In this work, we implement the massive neutrino self-interactions with a heavy mediator in two different ways: flavour-universal (among all three neutrinos), and flavour-specific (involving only one neutrino species). We implement the new interaction in both scalar and tensor perturbation equations of neutrinos. Interestingly, we find that the current cosmological data can support the aforementioned inflationary models at 2σ in the presence of such neutrino self-interactions.

Speaker: Shouvik Roychoudhury

Talk_Shouvik.pdf

30 (The) Wiggles going non-linear

Features in the primordial power spectrum (PPS) can provide indications of the physics of the early Universe. We aim to analyse non-linear wave-mode coupling in models with global, logarithmic features through high-resolution dark-matter N-body simulations to calibrate a semi-analytic fitting function and apply Gaussian process regression to the results to obtain a continuous "map" of the expected non-linear dampening of global features in the PPS.

Speaker: Nathan Cohen

DSU_2022_Conference_Talk (1).pdf

N1024_L256_4K_24Snap.mov

31 Signatures of Light Massive Relics on nonlinear structure formation

Cosmologies with Light Massive Relics (LiMRs) as a subdominant component of the dark sector are well-motivated from a particle physics perspective, and can also have implications for the $\sigma_8$ tension between early and late time probes of clustering. The effects of LiMRs on the Cosmic Microwave Background (CMB) and structure formation on large (linear) scales have been investigated extensively. In this paper, we initiate a systematic study of the effects of LiMRs on smaller, nonlinear scales using cosmological $N$-body simulations; focusing on quantities relevant for photometric galaxy surveys. For most of our study, we use a particular model of nonthermal LiMRs but the methods developed generalize to a large class of LiMR models --- we explicitly demonstrate this by considering the Dodelson-Widrow velocity distribution. We find that, in general, the effects of LiMR on small scales are distinct from those of a $\Lambda$CDM universe, even when the value of $\sigma_8$ is matched between the models. We show that weak lensing measurements around massive clusters, between $\sim 0.1\hmpc$ and $\sim 10 \hmpc$, should have sufficient signal-to-noise in future surveys to distinguish between $\Lambda$CDM and LiMR models that are tuned to fit both CMB data and linear scale clustering data at late times. Furthermore, we find that different
LiMR cosmologies indistinguishable by conventional linear probes can be distinguished by nonlinear probes if their velocity distributions are sufficiently different. LiMR models can, therefore, be best tested by jointly analyzing the CMB and late-time structure formation on both large \textit{and} small scales.

Speaker: Ravi Kumar Sharma (Indian Institute of Astrophysics bangalore)

DSU_Sharma.pdf

Ultralight dark matter

Convener: Igor Samsonov (UNSW)

32 Searching for ultralight scalar dark matter with muonium and muonic atoms

Ultralight scalar dark matter may induce apparent oscillations of the muon mass, which may be directly probed via temporal shifts in the spectra of muonium and muonic atoms. Existing datasets and ongoing spectroscopy measurements with muonium are capable of probing scalar-muon interactions that are up to 8 orders of magnitude feebler than astrophysical bounds. Ongoing free-fall experiments with muonium can probe forces associated with the exchange of virtual ultralight scalar bosons between muons and standard-model particles, offering up to 5 orders of magnitude improvement in sensitivity over complementary laboratory and astrophysical bounds.

Reference: Yevgeny V. Stadnik, arXiv:2206.10808.

Speaker: Yevgeny Stadnik (The University of Sydney)

Stadnik_DSU_2022-Dec.pdf

33 Searches for axion dark matter at IBS-CAPP

Axions have been considered the most favored solution to both the strong-CP problem and the dark matter mystery. Many experimental searches that rely on the axion-photon conversion under a strong magnetic field utilize the haloscope technique that is sensitive in the microwave region. We, the Center for Axion and Precision Physics Research (CAPP) of the Institute for Basic Science (IBS), have recently reached the theoretically interesting regions in various mass ranges. In particular, an experiment with a 12T superconducting magnet, a high-cooling power dilution refrigerator, and quantum-noise-limited devices enabled us to achieve unprecedented experimental sensitivities, exploring the DFSZ axion model above 1 GHz. We are also developing state-of-the-art technologies in a variety of areas to enhance performance to investigate the axion physics over a wider frequency range. In this talk, we present the current status of axion search experiments and R&D activities at IBS-CAPP, and discuss the future prospects.

Speaker: Dr SungWoo Youn (Institute for Basic Science)

DSU2022_YOUN.pdf

DSU2022_YOUN.pptx

34 Axions in the post-inflationary scenario

In the scenario in which the axion is born after inflation, understanding the abundance and distribution of axion dark matter requires dedicated numerical simulations. We study the complex dynamics of the axion field's evolution, including the scaling of the axion cosmic string network, the decay of domain walls, and the gravitational formation of miniclusters by means of lattice and N-body simulations. Given the expanding experimental campaign to search for axions and axion-like particles, these simulations have potentially wide implications for present-day searches.

Speaker: Giovanni Pierobon

dsu_pierobon.pdf

35 Dynamical Friction from Ultralight Dark Matter

We simulate the gravitational dynamics of a massive object interacting with ultralight/fuzzy dark matter (ULDM/FDM), nonrelativistic quantum matter described by the Schrödinger-Poisson equation.

We first consider a point mass moving in a uniform background, and then a supermassive black hole (SMBH) moving within a ULDM soliton. After replicating simple dynamical friction scenarios to verify our numerical strategies, we demonstrate that the wake induced by a moving mass in a uniform medium may undergo gravitational collapse that dramatically increases the drag force, albeit in a scenario unlikely to be encountered astrophysically. We broadly confirm simple estimates of dynamical friction timescales for a black hole at the center of a halo but see that a large moving point mass excites coherent “breathing modes” in a ULDM soliton. These can lead to “stone skipping” trajectories for point masses which do not sink uniformly toward the center of the soliton, as well as stochastic motion near the center itself. These effects will add complexity to SMBH-ULDM interactions and to SMBH mergers in a ULDM universe.

This talk will also discuss ongoing work in the quantitative analysis of nonlinear oscillations of a range of systems made up of ULDM solitons and point particles.

Speaker: You-Rong Frank Wang (The University of Auckland)

DSU22_YWan.pdf

36 Search for a Variation of the Fine Structure Constant around the Supermassive Black Hole in Our Galactic Centre

Searching for space-time variations of the constants of Nature is a promising way to search for new physics beyond general relativity and the standard model motivated by unification theories and models of dark matter and dark energy. We propose a new way to search for a variation of the fine-structure constant using measurements of late-type evolved giant stars from the S star cluster orbiting the supermassive black hole in our Galactic Center. A measurement of the difference between distinct absorption lines (with different sensitivity to the fine structure constant) from a star leads to a direct estimate of a variation of the fine structure constant between the star’s location and Earth.
In our recent work [1], using spectroscopic measurements of five stars, we obtained a constraint on the relative variation of the fine structure constant below $10^{−5}$. This is the first time a varying constant of nature is searched for around a black hole and in a high gravitational potential. This analysis shows new ways the monitoring of stars in the Galactic Center can be used to probe fundamental physics.
Now, with dedicated telescope time we except to improve on these results by several orders of magnitude. The improved sensitivity comes from improved statistics from dedicated observations, data from stars closer to the black hole (and thus in higher gravitational potential), and from the observation of lines from atomic transitions that have higher sensitivity to the variation of the fine structure constant.

[1] A. Hees, T. Do, B. M. Roberts, Andrea M. Ghez, S. Nishiyama, R. O. Bentley, A. K. Gautam, S. Jia, T. Kara, J. R. Lu, H. Saida, S. Sakai, M. Takahashi, and Y. Takamori, Phys. Rev. Lett. 124, 081101 (2020).

Speaker: Benjamin Roberts

DSU-talk-Roberts.pdf

18:00 Reception

Tuesday 6 December

Plenary

Livestream link: https://tinyurl.com/DSU2022plenary

Convener: Prof. Nicole Bell (The University of Melbourne)

37 Neutron Star Heating: WIMP DM vs others

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Speaker: Natsumi Nagata

20221206.pdf

38 Dark matter and dark sectors in stars

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Speaker: Aaron Vincent (Queen's University)

DSU_DM_Stars_noAnim.pdf

39 The light of a Billion Stars: Dark matter and the stellar halo

Our view of the stellar halos of large galaxies is being revolutionised as deep surveys reveal a wealth of stellar streams and shells.As the remnants of progenitors that have been tidally disrupted in the galactic potential, this stellar debris offers the promise of determining the dark matter properties of the halo. Here, I will review the current state of the field, and provide a panoramic view of our Local Group. As Gaia and spectroscopic observations unveil the full phase-space properties of numerous stellar streams, I will explore just what stellar halos can reveal about the properties of dark matter.

Speaker: Geraint Lewis

BillionStars.pdf

10:30 Coffee break

Plenary

Livestream link: https://tinyurl.com/DSU2022plenary

Convener: Prof. Archil Kobakhidze

40 Lower than freeze-in portal couplings can still generate DM and be measured via Gravitational Waves

I will discuss a recently proposed class of models where Dark Matter (DM) is produced via an inverse phase transition. The inverse phase transition can be caused by coupling to some cosmological field. For instance, this field can be a primordial magnetic field, as in e-Print: 2010.03383 or thermal fluctuations of other fields, as in e-Print: 2104.13722. In the latter work DM is modelled as a real scalar, which interacts with the hot primordial plasma through a portal coupling to another scalar field. For a particular sign of the coupling, this system exhibits an inverse phase transition. The latter leads to an abundant DM production, even if the portal interaction is so weak that the freeze-in mechanism is inefficient. The model predicts domain wall formation in the early Universe, long before the inverse phase transition. These domain walls have a tension decreasing with time, and completely disappear at the inverse phase transition, so that the problem of overclosing the Universe is avoided. The domain wall network emits gravitational waves with the peak frequency falling in the observable range of currently planned observational missions.

Speaker: Alexander Vikman (Czech Academy of Sciences (CZ))

DSU_2022_Vikman.pdf

41 Dark energy, black holes and effective field theory

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Speaker: Shinji Mukohyama

221206Mukohyama.pdf

42 Lensing reconstruction of AliCPT-1

Speaker: Bin Hu (Beijing Normal University)

AliCPTLensing2.pdf

12:30 Lunch break

Dark matter

Convener: Giorgio Busoni (The Australian National University)

43 CYGNUS-Oz development of directional dark matter detection capabilities using a gaseous time projection chamber for the Cygnus experiment

As dark matter detectors continue to probe into increasingly lower mass and cross-section regions of the phase space for Weakly Interacting Massive Particles (WIMPs), coherent scattering of solar neutrinos from the neutrino floor (increasingly termed the ‘neutrino fog’ [1]), will pose an irreducible background that needs to be overcome. Directional detectors such as gaseous time projection chambers (TPCs) are an attractive means of overcoming this background by using directional information to distinguish solar neutrinos from dark matter in the galactic halo. To date, however, the gaseous TPCs, have not been demonstrated to be able to meet the performance criteria required to probe the neutrino fog [2].

The Australian National University is part of the international CYGNUS effort that aims to demonstrate the viability of gaseous TPCs as a WIMP detector capable of exploring the neutrino fog, amongst other potential physics uses. To this end, the CYGNUS-Oz collaboration has been initiated to unify the Australian contributions to CYGNUS. This presentation will provide a general overview of the CYGNUS-Oz experimental work underway at the ANU, which centres around a prototype gas TPC with 7 L of sensitive volume. The current experimental status and an overview of the potential physics reach of CYGNUS will also be presented.

[1] C.A.J. O’Hare, New definition of the neutrino floor for direct dark matter searches, Physical Review Letters 127 (2021)

[2] S.E. Vahsen, C.A.J. O’Hare, D. Loomba, Directional Recoil Detection, Annual Review of Nuclear and Particle Science 71 (2021).

Speaker: Ferdos Dastgiri

FD_DSU_2022_Cygnus2.pdf

44 Precise predictions and new insights for the Migdal effect

The scattering of neutral particles by an atomic nucleus can lead to electronic ionisation and excitation through a process known as the Migdal effect. We revisit and improve upon previous calculations of the Migdal effect, providing accurate predictions for large nuclear recoil velocities and demonstrating the importance of multiple ionisation. Our calculations provide the theoretical foundations for future measurements of the Migdal effect using neutron sources, and searches for dark matter in direct detection experiments.

Speaker: Peter Cox (The University of Melbourne)

PeterCox-DSU-2022.pdf

45 Light dark matter: Theory and Chemistry

The search for light dark matter (with a mass below a GeV) is entering an exciting phase. New experiments based on light dark matter interactions with collective modes in various types of condensed matter systems will probe pristine parameter space. Alongside this, new calculational techniques, particularly employing the use of effective field theory, are being developed to accurately describe the dark matter interaction and detector response. On the theory side, I will present curious features that show up in the calculations of dark matter interacting with condensed matter. I will also present new effective field theories and techniques that have been developed to describe these non-relativistic interactions from a spontaneously-broken relativistic point-of-view. Finally, I will present developments from an ongoing experimental effort to utilise a novel type of chemical crystal — single molecule magnets — as a ‘magnetic bubble chamber’ for detecting light dark matter.

Speaker: Tom Melia (Kavli IPMU)

LDM.pdf

46 Scintillating Bubble Chambers for GeV-Scale Dark Matter Searches

The Scintillating Bubble Chamber (SBC) collaboration in developing physics-capable noble-liquid bubble chambers with potential physics reach in the search for GeV-scale dark matter, as well as in detecting reactor neutrino CEvNS. A small-scale liquid xenon prototype has demonstrated the potential of this technique to detect sub-keV nuclear recoils while remaining effectively electron-recoil blind. Currently, two devices with 10-kg liquid argon active volumes are under construction: one at Fermilab to be used to calibrate the response to electron recoils and nuclear recoils down to 100-eV, and one to be deployed at SNOLAB for a low-background dark matter search. I will discuss the status and plans for these devices.

Speaker: Prof. Russell Neilson (Drexel University)

DSU_2022.pdf

47 GLIMPSE: Graphene-based Light Invisible Matter Particle SEarch

We introduce a new dark-matter detection experiment that will enable the search of keV-range super-light dark matter, representing an improvement of the minimum detectable mass by more than three orders of magnitude over the ongoing experiments. This is possible by integrating intimately the target material, π-bond electrons in graphene, into a Josephson junction to achieve a high sensitivity detector that can resolve a small energy exchange from dark matter as low as ~0.1 meV. We investigate detection prospects with pg-, ng-, and 𝜇g-scale detectors by calculating the scattering rate between dark matter and the free electrons confined in two-dimensional graphene. We find not only that the proposed detector can serve as a complementary probe of super-light dark matter but also achieve higher experimental sensitivities than other proposed experiments, i.e. in having a low detectable threshold provided the same target mass, thanks to the extremely low energy threshold of our graphene-based Josephson junction sensor.

Speaker: Jong-Chul Park

GLIMPSE_DSU2022_JCPark.pdf

Early Universe

Convener: Jan Hamann (The University of New South Wales)

48 Constraining primordial tensor features with the anisotropies of the Cosmic Microwave Background

It is commonly assumed that the stochastic background of gravitational waves on cosmological scales follows an almost scale-independent power spectrum, as generically predicted by the inflationary paradigm. However, it is not inconceivable that the spectrum could have strongly scale-dependent features, generated, e.g., via transient dynamics of spectator axion-gauge fields during inflation. Using the temperature and polarisation maps from the Planck and BICEP/Keck datasets, we search for such features, taking the example of a log-normal bump in the primordial tensor spectrum at CMB scales. We do not find any evidence for the existence of bump-like tensor features at present, but demonstrate that future CMB experiments such as LiteBIRD and CMB-S4 will greatly improve our prospects of determining the amplitude, location and width of such a bump. We also highlight the role of delensing in constraining these features at angular scales $\ell > 100$.

Speaker: Ameek Malhotra

DSU_Malhotra.pdf

49 Non-Gaussianity in CMB lensing

CMB lensing is one of the most powerful techniques to describe the large-scale structures in the Universe. It extends our sight of structure evolution to very high redshift and can be used to constrain fundamental physical quantities, such as matter density and neutrino masses. Several competitive constraints have been achieved from the Planck CMB lensing power spectrum. However, the power spectrum method is inadequate to characterize all the information, especially the non-Gaussian information from small-scale non-linear evolution, which can be gleaned from ongoing and upcoming high-resolution ground-based CMB observations, such as AdvACT and CMB Stage-IV surveys. In this talk, I will discuss the feasibility of Minkowski functionals as morphological descriptors of CMB lensing and explore the impact given by the non-Gaussian reconstruction noise. I will also introduce a pipeline for full-sky CMB lensing simulations.

Speaker: Yuqi Kang

dsu2022.pdf

50 Enhancing Bispectrum Estimators for Photometric Galaxy Redshift Survey with Velocities

Primordial non-Gaussanities can provide valuable information about the primordial universe. We explore the possibility of constraining them with photometric galaxy redshift surveys. Further, I will discuss how the inclusion of velocity maps via the kinetic Sunyaev Zeldovich effect can improve the estimator. Finally, I will comment on the prospects of reaching fnl<1 in the future.

Speaker: Mr Julius Wons (UNSW)

DSU_Wons.pdf

51 GPry: Fast Bayesian inference using Gaussian Processes

In modern physics, with an increasing number of experiments, more available data will open a window towards testing new, increasingly complex-to-compute theories. Often, comparing this data against theory requires expensive computations arising from the sheer size of the dataset as well as numerical simulations required to go from theory to observables.
This in turn makes Bayesian inference using such codes prohibitively expensive, as typical sampling algorithms like Markov chain Monte Carlo usually take many tens of thousands of evaluations of the likelihood/posterior distribution, hence requiring a large amount of theory-simulations. Likelihood-free approaches circumventing this problem have lately gained some attention, however these come with their own set of challenges like managing biases and often require methods which need to be tailored to the problem at hand. With our Python package “GPry” we introduce a new tool which keeps the simplicity and robustness of likelihood-based inference, while drastically reducing the number of samples that are needed to get an MC sample of the posterior. This approach is based on interpolating the posterior distribution with a suitable Gaussian process and a deterministic, sequential acquisition of likelihood samples inspired by Bayesian optimization. To enable parallelization of the algorithm, we have also developed a batch acquisition procedure which allows the likelihood function to be evaluated in parallel. We also avoid a common problem in many similar approaches where vanishing posterior values or errors in the analysis chain cannot be correctly interpreted by supplementing the Gaussian process with a support vector machine classifier to define a finite region of interest. We show the performance of the algorithm on both test distributions as well as cosmological and binary inspiral problems.

Speaker: Jonas El Gammal (University of Stavanger)

GPry DSU Sydney.pdf

52 Connecting the dark Universe and artificial intelligence

As numerical complexities of cosmological models are increasing in recent years, so too are the demands for resources when computing solutions to the Einstein-Boltzmann equations with codes like \textsc{class} and \textsc{camb}. A solution to this demand is, of course, more computational power through increasingly better and faster hardware, but perhaps another and more sustainable approach is emulating the Einstein-Boltzmann solver codes using a neural network. In doing so, we heavily decrease the time for each model evaluation, and a whole new world of parameter inference beyond Markov chain Monte Carlo opens.
In this talk I will present the new code \textsc{connect} introduced in Nygaard et al. (arXiv: 2205.15726), which is a framework for sampling training data and training a neural network of custom architecture to emulate the outputs of \textsc{class}. We found that the naïve approach of using a latin hypercube as training data leads to erroneous results in certain cases of complex likelihood shapes and it often requires a huge amount of data points, i.e. individual \textsc{class} computations, of orders $10^5$ to $10^6$. We thus propose another sampling method of training data based on an iterative process where we start from a rough latin hypercube and use the network trained on this to perform a high-temperature MCMC sampling resulting in new points in the parameter space to be included as training data for the next iteration. This process builds a representative set of training data and halts when the data reaches convergence. We can thus limit the number of class computations with one or two orders of magnitude, and by not having to accommodate regions of vanishing likelihood in the parameter space, the network is trained to be good only in the region of interest.

Speaker: Andreas Nygaard (Aarhus University)

Presentation.pdf

Neutrino physics

Convener: Prof. Raymond Volkas (The University of Melbourne)

53 Detecting Dark Matter Annihilation to Neutrinos

Considering dark matter annihilation to neutrinos in the Galactic halo, we discuss the prospects for the indirect detection of dark matter using the Hyper-Kamiokande neutrino experiment. We also quantify the extent to which the annihilation of low-mass dark matter to neutrinos could confuse the interpretation of the diffuse supernova neutrino background signal. Finally, we consider a neutrino signal produced via the annihilation of dark matter captured in the Sun and present projected limits on the dark matter spin-dependent scattering cross-section. [Based on arXiv:2005.01950 (JCAP 2020); arXiv:2107.04216 (JCAP 2021); arXiv:2205.14123.]

Speaker: Nicole Bell

DSU_Sydney_2022_Bell.pdf

54 Searching for Dark Matter Annihilation with IceCube and P-ONE

We present a new search for weakly interacting massive particles utilizing neutrino telescopes. We consider galactic and extra-galactic dark matter and perform an analysis on ten years of public IceCube data. In addition, we compare these results to the potential sensitivity of a new neutrino observatory, P-ONE. Assuming extremely heavy dark matter self-annihilates and produces neutrinos indirectly or directly, it would produce unique signatures differening from the typical power-law of the atmospheric and astrophysical background. We use these signatures to show that P-ONE and IceCube can exceed current limits set by gamma-ray experiments, especially when considering extra-galactic dark matter.

Speaker: Dr Stephan Meighen-Berger (The University of Melbourne)

DSU_2022.pdf

55 Leptogenesis in gauged U(1)_{Lμ-Lτ} model

A neutral vector boson $Z′$ associated with the gauged $U(1)_{L_\mu−L_\tau}$ can explain the muon g − 2 anomaly without conflicting with experimental searches for the new particle. Under extensions of the Standard Model with the symmetry relating to lepton flavor, neutrino mass generation has been studied through the type-I seesaw mechanism with right-handed neutrinos. In this framework, it is natural to inquire if the introduced particles can also be responsible for the baryon asymmetry of the Universe. In this talk, we will discuss the breaking of $U(1)_{L_\mu−L_\tau}$ symmetry in cosmological history and the viability of leptogenesis with the decay of right-handed neutrinos.

Speaker: Shintaro Eijima

DSU2022_SEijima.pdf

56 Riding the (Type-I) Seesaw: Neutrinos and New Physics

The Type-I Seesaw model is a simple and elegant way of extending the Standard Model to accommodate neutrino masses. Through quantum effects, massive neutrinos can influence physics in other sectors, leading to various potential observational channels for constraining the parameter space of the Seesaw model. We study a number of these channels.

Speaker: Adam Lackner

DSU2022 Lackner.pdf

57 Seesaw Models and Higgs Physics

We study the feasibility to test Seesaw models via precision Higgs measurements at next-generation lepton colliders, and compare the relevant sensitivities to existing constraints from electroweak precision measurements, lepton-flavour non-universality and lepton-flavour violation.

Speaker: Tobias Felkl (University of New South Wales)

dsu2022.pdf

15:40 Coffee break

BSM physics

Convener: Dr Venus Keus (Dublin Institute for Advanced Studies (DIAS))

58 Correlated signals of first-order phase transitions in dark sectors

I will describe how gravitational waves from a cosmological first-order phase transition can be correlated with microlensing signals of Fermi balls (or gamma-ray signals of primordial black holes) produced during the phase transition. A measurable amount of dark radiation is also typically expected.

Speaker: Danny Marfatia

FB-PBH.pdf

59 Improved stellar limits on a light CP-even scalar

We derive improved stellar luminosity limits on a generic light CP-even scalar field S mixing with the Standard Model (SM) Higgs boson from the supernova SN1987A, the Sun, red giants (RGs) and white dwarfs (WDs). For the first time, we include the geometric effects for the decay and absorption of S particles in the stellar interior. For SN1987A and the Sun, we also take into account the detailed stellar profiles. We find that a broad range of the scalar mass and mixing angle can be excluded by our updated astrophysical constraints. For instance, SN1987A excludes 1.0×10−7≲sinθ≲3.0×10−5 and scalar mass up to 219 MeV, which covers the cosmological blind spot with a high reheating temperature. The updated solar limit excludes the mixing angle in the range of 1.5×10−12<sinθ<1, with scalar mass up to 45 keV. The RG and WD limits are updated to 5.3×10−13<sinθ<0.39 and 2.8×10−18<sinθ<1.8×10−4, with scalar mass up to 392 keV and 290 keV, respectively.

Speaker: Shyam Balaji (LPTHE)

Shyam_DSU.pdf

60 Complementarity of Direct Detection experiments and Collider searches

The electroweak sector of the MSSM is in agreement with DM relic density measurements, direct detection (DD) limits, LHC searches, as well as the 4.2 $\sigma$ deviation found for the anomalous magnetic moment of the muon. Taking all constraints into account we derive upper and lower bounds on several SUSY mass scales. We investigate the prospects for DD experiments. We demonstrate that searches at current and future colliders (HL-LHC, e+e- colliders) are complementary to the prospects of DD experiments and can completely probe this kind of scenario.

Speaker: Sven Heinemeyer (CSIC (Madrid, ES))

sven.pdf

61 Electroweak corrections to Dark Matter Direct Detection

Dark matter direct searches place very stringent constraints on the possible DM candidates proposed in extensions of the Standard Model. There are however models where these constraints are avoided. One of the simplest and most striking examples comes from a straightforward Higgs portal pseudoscalar DM model with a softly broken U(1) symmetry. In this model the tree-level DM-nucleon scattering cross section vanishes in the limit of zero momentum-transfer. Furthermore, adding doublets while keeping the pseudoscalar with the softly broken U(1) symmetry leads to the same result. We have calculated the exact cross section at the one-loop level in two of these scenarios, which is several orders of magnitude larger than the tree-level one. I will also compare these results with scalar DM models where the cancellation at tree-level does not occur. Finally I will present results for a simple model with a vector dark matter particle.

Speaker: Rui Santos (ISEL and CFTC-UL)

DSU2022_santos.pdf

62 Classification of CP-violating operators in SMEFT

In particle physics, the Standard Model makes extremely accurate predictions, but experimental and observational facts like neutrino oscillation or baryon number asymmetry suggest the existence of physics beyond the Standard Model (BSM). If the BSM exists at energy scales higher than the Standard Model, its effects can be approximately described by the Standard Model Effective Field Theory (SMEFT). However, such effects are small and difficult to observe in general. One effective way to search for BSM is to measure CP symmetry breaking. Since the degree of CP violation in the Standard Model is very small, the contribution from the BSM can be detected without being buried in the Standard Model effects. Furthermore, since the BSM is required to break CP symmetry more strongly than the Standard Model to explain the asymmetry of the baryon number in the current universe, CP violation is expected to provide a clue to the detection of the BSM. Therefore, we need to investigate CP-violating operators in the SMEFT Lagrangian.
In 2015, a method was proposed to systematically list independent SMEFT operators using the Hilbert series technique. Moreover, for theories where parity transformations (P) and charge conjugate transformations (C) can be defined, an extended method was proposed that lists the EFT operators based on P and C symmetries respectively. However, since P and C cannot be defined independently for the Standard Model, it is necessary to consider CP transformation. Therefore, we have developed a method to systematically classify SMEFT operators based on the CP symmetry. In this talk, I will explain how to apply the Hilbert series in this method. In addition, I will introduce that the charge conjugate transformation $\mathcal{C}$ has the nontrivial property as an outer automorphism of $SU(N)$:

$\hspace{30pt} \mathcal{C}^2 = \left\{ \begin{array}{2} &+1 && (N: \text{odd}) \\ &\pm 1 && (N: \text{even}) \end{array} \right.\, .$

Speaker: Risshin Okabe (Kavli IPMU)

DSU2022.pdf

Dark matter

Convener: Michael Klasen

63 Impact of precision calculations in Simplified t channel Dark Matter models

Precision calculations can impact the parameter space of well motivated dark matter models significantly. In this talk I will discuss the impact of loop calculations, Sommerfeld enhancement and bound state formation effects for t channel dark matter models. I will demonstrate that the combined effect of precision calculations has a significant impact in constraining as well as opening up new regions of parameter space within these models. Finally I will talk about the future prospects of this class of simplified models.

Speaker: Dipan Sengupta

DSU_Dipan.pdf

64 Improved theoretical predictions of the dark matter relic abundance

In the standard approach, theoretical predictions of the dark matter relic abundance for freeze-out scenarios are performed by only using (effective) tree-level annihilation cross sections as input for the 0-moment of the Boltzmann equation, i.e. the number density equation. To allow for the future automatization of next-to-leading order calculations to the relic density, we present a general extension of the Catani-Seymour dipole subtraction method to massive initial-states and highlight the importance of higher-order corrections for relevant (co)annihilation scenarios in the Minimal Supersymmetric Standard Model. In addition, we discuss the impact on the relic density when the Boltzmann equation is solved on the level of the phase space distribution instead, taking into account the effect of elastic (self)-scattering processes.

Speaker: Luca Paolo Wiggering (University of Münster)

DSU-2022_Wiggering.pdf

65 Global Fits of vector-mediated simplified models for Dark Matter

Dark matter candidates can arise from a wide range of extensions to the Standard Model. Simplified models with a small number of new particles allow for the optimisation and interpretation of dark matter and collider experiments, without the need for a UV-complete theory. In this talk, I will discuss the results from a recent GAMBIT study of global constraints on vector-mediated simplified dark matter models. I will cover several models with differing spins of the dark matter candidate. Along with these constraints, I will provide new unitarity bounds from the self-scattering of vector dark matter and discuss their effect on collider constraints.

Speaker: Christopher Chang

DSU 2022.pdf

66 Radiative Neutrino Mass with GeV Scale Majorana Dark Matter in Scotogenic Model

The experimental observations from the colliders established the standard model (SM), is the most successful phenomenological framework to explain the non-gravitational interactions of fundamental particles at high energy. Non-zero neutrino mass and dark matter cast a shadow over its success. This necessitates the extension of the SM. The most straightforward and elegant extension of the SM to explain these two phenomena is the Scotogenic model, where the SM particle spectrum extends with three isospin singlet right-handed neutrinos and one doublet scalar while all of these being odd under Z2 symmetry. In this work, we have considered the lightest right-handed neutrino as the dark matter candidate and freeze-out mechanism for producing observed dark matter relic density.The charged lepton flavour violation decay processes constrain the upper side of Yukawa coupling while observed relic density limits the lower side. We have performed a unique parameterization to attain the highest possible Yukawa coupling while satisfying LFV and DM constraints. The reduced number of free parameters and large Yukawa coupling make the model predictability at lepton colliders very high. Collider phenomenology for possible signatures performed at lepton colliders and the required luminosities estimated for detection.

Speaker: Avnish .

DSU2022.pdf

67 Composite dark matter from non-abelian gauge theories with real representations

We present a class of composite dark matter models with matter fields in a real representation under the non abelian gauge group. As an exemplary theory we present an Sp(4) gauge theory, with fermions transforming in the antisymmetric representation. We analyze the structure of these theories in the UV and discuss the building blocks of the low energy effective theory in the IR, describing the dynamics of the cold dark matter. We put special focus on the construction of topological terms responsible for 3→2 cannibalization processes within the dark sector and on the physics of the pseudo scalar singlet related to the axial anomaly. We show that both these aspects significantly affect the freeze out calculation of the dark matter relic abundance and thus are relevant for investigations of the parameter space of such theories.

Speaker: Joachim Pomper (University of Graz)

Early Universe

Convener: Jinn-Ouk Gong

68 Constraining astrophysics and cosmology via the kinematic Sunyaev-Zel’dovich effect using SPT and DES data

The kinematic SZ Sunyaev-Zel’dovich (kSZ) effect is produced by the peculiar motion of electrons in galaxy cluster when they scatter with cosmic microwave background (CMB) photons. As such, the kSZ effect carries information about the cosmic velocity field on large-scales and the gastrophysics of galaxy clusters, providing potentially powerful tests of gravity and structure formation. Measuring this signal is challenging due to its small amplitude (compared to primary CMB and other foregrounds) and spectral degeneracy with the CMB temperature fluctuations, however the kSZ imprint can be isolated by cross-correlating CMB maps with large-scale structure datasets.
In this talk, I will present a 4.1$\sigma$ measurement of the kSZ effect using a catalog of optically-selected galaxy clusters from the Year-3 Dark Energy Survey data and CMB temperature maps from SPT-3G, the third generation receiver on the South Pole Telescope. This measurement is based on a pairwise statistical approach that allows to extract the kSZ signal as function of the comoving separation between clusters pairs. By comparing the recovered signal to theoretical expectations, we can infer the mean optical depth of the cluster sample, an important quantity that relates to the clusters' mean thermal SZ (tSZ) effect. Finally, I will also provide a comparison between the optical depths inferred from the tSZ effect, showing that external measurements of the optical depth will enable accurate cosmological constraints from future surveys.

Speaker: Eduardo Schiappucci

pkSZ-DSU.pdf

69 High-resolution SZ observations for cluster cosmology with NIKA2

As the largest gravitationally bound objects in the Universe, galaxy clusters are key tools to study large-scale structure formation processes and to constrain cosmological models. These studies, however, require the mass of clusters to be calibrated, for example with a mass-observable scaling relation. Systematic effects, in particular at high redshift, have an impact on this calibration and are currently the main limitation of cluster-based cosmology.

NIKA2, a millimeter camera installed at the IRAM 30-m telescope is a key experiment to extend our understanding of galaxy clusters. Combining sub-arcminute (17.2’’ at 150 GHz) angular resolution and a 6.5 arcmin diameter field of view, NIKA2 is resolving the Sunyaev-Zel'dovich (SZ) effect towards clusters up to high redshifts. Combined with X-ray data from XMM-Newton satellite, we can infer with high precision the thermodynamical properties and the hydrostatic masses of such objects within the NIKA2 SZ Large Program (LPSZ), which covers a representative sample of 45 galaxy clusters at redshifts from 0.5 to 0.9.

In this talk I will present the latest results of the LPSZ and I will show for the first time preliminary results on the LPSZ sample characteristics, including the cluster masses and mean pressure profile. Based on these results, I will discuss the systematic effects impacting the mass reconstruction, such as the presence of sub-structures and the deviation from the spherical hypothesis, and their implication for cluster cosmology.

Speaker: Mr Corentin Hanser (CNRS)

Slides_DSU_Hanser.pdf

70 Probing dark matter microphysics with gravitational waves and 21cm emission

The microphysics of dark matter remains a mystery, with current data only setting upper bounds on interaction cross sections, or lower bounds on the mass in the case of a thermal relic. Going to higher redshift and smaller scales will let us improve these bounds, but more importantly, may allow us to distinguish between models with otherwise similar signals. In particular, I will present a novel method for constraining models with suppressed small scale structure using gravitational waves, along with forecasts for complementary constraints from 21cm intensity mapping. The latter is especially important regarding what is necessary to distinguish interacting dark matter from warm dark matter.

Speaker: Markus Rasmussen Mosbech

DSU-presentation.pdf

71 Constraints on decaying dark matter from lensing and magnification of cosmic voids

Direct and indirect detection of decaying dark matter models often rely on an assumption of the generation of a standard model particle in the chain of decay channels. This however leads to some ambiguity on the origin of the standard model particles as there is an overlap with processes within baryonic physics. If, however, the decay is assumed to take place wholly within the dark sector then the influence of this processes can be constrained by investigating modifications to the formation of large-scale structure and the underlying cosmology.

Perhaps the ideal cosmological structure to investigate the effect of dark matter decays are the cosmic voids as these are environments with minimal baryonic contamination. We have developed relativistic 1 + 3 hydrodynamical models of cosmic void evolution. By studying the gravitational lensing and Doppler magnification of cosmic voids it is possible to probe the presence and influence of decaying dark matter, and explore the possibility of future surveys to observe this. We present theoretical and numerical work on this area.

In my talk I will present published results as well as some new, unpublished results, which show that future lensing surveys such as Euclid or LSST should be able to constrain the parameter space and confirm or ruled or dark matter decay models with a half-life time on the order of 10 Gyr or shorter.

Speaker: Earl Lester (University of Tasmania)

ESL_DSU_22.pdf

72 Discovering a new well: Decaying dark matter with profile likelihoods

A large number of studies, all using Bayesian parameter inference from Markov Chain Monte Carlo methods, have constrained the presence of a dark matter component decaying to invisible radiation. All such studies find a strong preference for either very long-lived or very short-lived dark matter.

In this talk, I will present our recent work, to appear on the arXiv in the coming weeks, in which we show that this preference is entirely driven by parameter volume effects. Using profile likelihoods, we instead find that the best-fitting parameters correspond to an intermediate regime where $\sim 3 \%$ of cold dark matter decays around recombination, residing in a $\Delta \chi^2$ well of depth $\Delta \chi^2 \approx -6.2$ relative to $\Lambda$CDM with Planck and BAO data and $\Delta \chi^2 \approx -9.9$ with a Gaussian likelihood on the SH0ES $H_0$ measurement.

Ultimately, our results reveal that decaying dark matter is substantially more viable than previously assumed, and illustrate the importance of combined Bayesian/frequentist statistical methods for a fully nuanced analysis.

Speaker: Emil Brinch Holm

emil_brinch_holm.pdf

emil_brinch_holm.ppsx

Wednesday 7 December

Plenary

Livestream link: https://tinyurl.com/DSU2022plenary

Convener: Alejandro Ibarra

73 Seeking the mechanism of neutrino mass generation: a brief review

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Speaker: Prof. Raymond Volkas (The University of Melbourne)

Volkas-DSU-2022.pdf

74 Charting the leptogenesis landscape

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Speaker: Julia Harz

DSU_OverviewLG_2022.pdf

75 Neutrino oscillation experiments

Placeholder title

Speaker: Sunny Seo

Seo_NuOsc-Exp_DSU2022.pdf

10:30 Coffee break

Plenary

Livestream link: https://tinyurl.com/DSU2022plenary

Convener: Danny Marfatia

76 Physics potential of CEvNS in the Standard Model and beyond

I will present the physics potential of the coherent elastic neutrino-nucleus scattering (CEvNS) process. I will first briefly review the status of current observations. Then I will comment about their implications for both precision tests of the Standard Model and for new physics in the neutrino sector. Finally I will discuss the relevance of these measurements for direct dark matter detection probes.

Speaker: Valentina De Romeri

De_Romeri.pdf

77 Supernova neutrinos: probing physics within and beyond the Standard Model

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Speaker: Meng-Ru Wu (Institute of Physics, Academia Sinica)

221207_DSU_MRW.pdf

78 Neutrino astronomy

Placeholder title

Speaker: Jenni Adams (University of Canterbury)

dsu_2022_adams.pdf

Thursday 8 December

Plenary

Livestream link: https://tinyurl.com/DSU2022plenary

Convener: Osamu Seto

79 5D perspectives on the QCD axion

Speaker: Tony Gherghetta (University of Minnesota (US))

Gherghetta_DSU2022.pdf

80 Production of (dark) matter in the early stage of the Universe

I will present in this talk recent works concerning the production of
particles in the earliest stage of the Universe, between the preheating phase and the reheating time. I will insist on the subtleties of backreactions from scattering of the inflaton and apply it to the mechanism to the dark matter production in minimal extensions of the Standard Model, especially gravitational production.

Speaker: Yann MAMBRINI

81 Role of dark Higgs boson in DM physics and Higgs inflation

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Speaker: Prof. Pyungwon Ko (KIAS)

DSU2022_ko.pdf

10:30 Coffee break

Plenary

Livestream link: https://tinyurl.com/DSU2022plenary

Convener: Masahiro Kawasaki

82 Multi-field inflation

Placeholder title

Speaker: Jinn-Ouk Gong

2022-12-08_dsu2022_jgong.pdf

83 Early universe cosmology with the stochastic gravitational wave background

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Speaker: Sachiko Kuroyanagi (IFT UAM-CSIC)

DSU_Kuroyanagi.pdf

84 Cosmic ray boosted dark matter

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Speaker: Prof. Yu-Feng Zhou

boostdm_yfzhou_DSU22.pdf

12:30 Lunch break

BSM physics

Convener: Otari Sakhelashvili (Sydney University)

85 Quantum gravity, the strong CP problem and the companion axion solution

I argue that quantum gravity effects due to the coloured gravitational instantons compromise the standard axion solution to the strong CP problem. I propose a new solution within a theory that requires two axion fields and is dubbed the companion axion model. Some phenomenological and cosmological implications of this model are discussed.

Speaker: Archil Kobakhidze

dsu2022.pdf

86 Dark radiation constraints on hidden gauge-axion system

The dynamics of hidden gauge fields coupled with an axion field during inflation is an interesting source of primordial gravitational wave perturbations. For a large axion decay constant, the subdominant energy density of the axion field would be transformed to that of the extra radiation of the hidden gauge bosons by the axion decay. Part of parameter space of such a model will be tested by future measurements.

Speaker: Osamu Seto

dsu2022.pdf

87 Fake GUT

It is remarkable that the matter fields in the Standard Model (SM) are apparently unified into the SU(5) representations. A straightforward explanation of this fact is to embed all the SM gauge groups into a simple group containing SU(5), i.e., the grand unified theory (GUT). Recently, however, a new framework “fake GUT” has been proposed. In this new framework, the apparent matter unification can be explained by a chiral gauge group G, G ⊃ SU(5). We emphasize that the SM matter fields are not necessarily embed- ded into the chiral representations to explain the apparent unification. In this presentation, we talk about the fake GUT model based on SU(5) × U(2)H. Here, SU(3)c in the SM is from SU(5) while SU(2)L × U(1)Y are from the diagonal subgroups of SU(5) × U(2)H. We also show that this framework predicts rather different decay patterns of the proton, compared to the conventional GUT.

Speaker: Keiichi WATANABE

DSU_2022.pdf

88 Renormalization group effects in non-universal DFSZ axion models

It has been recently pointed out that in certain axion models it is possible to suppress simultaneously both the axion couplings to nucleons and electrons, realising the so-called astrophobic axion scenarios, wherein the tight bounds from SN1987A and from stellar evolution of red giants and white dwarfs are greatly relaxed. So far, however, the conditions for realising astrophobia have only been set out in tree-level analyses. In this talk, we study whether these conditions can still be consistently implemented once renormalization group effects are included in the running of axion couplings. We find that axion astrophobia keeps holding, albeit within fairly different parameter space regions, and we provide analytical insights into this result.
This talk is based on Phys. Rev. D 106, 055016 (2022).

Speaker: Shohei Okawa (ICCUB, Universitat de Barcelona)

DSU2022_Okawa.pdf

89 Exploring the cosmological dark matter coincidence using infrared fixed points

The asymmetric dark matter (ADM) paradigm is motivated by the apparent coincidence between the cosmological mass densities of visible and dark matter, $\Omega_\mathrm{DM} \simeq 5\Omega_\mathrm{VM}$. However, most ADM models only relate the number densities of visible and dark matter, and do not motivate the similarity in their particle masses. One exception is a framework introduced by Bai and Schwaller, where the dark matter is a confining state of a dark QCD-like gauge group, and the confinement scales of visible and dark QCD are related by a dynamical mechanism utilising infrared fixed points of the two gauge couplings. We build upon this framework by properly implementing the dependence of the results on the initial conditions for the gauge couplings in the UV. We then reassess the ability of this framework to naturally explain the cosmological mass density coincidence, and find a reduced number of viable models. We identify features of the viable models that allow them to naturally relate the masses of the dark baryon and the proton while also avoiding collider constraints on the new particle content introduced.

Speaker: Alex Ritter (The University of Melbourne)

DSU22_Ritter.pdf

Dark matter

Convener: Dr Peter Cox (The University of Melbourne)

90 Observational evidence of dark matter within the quark nugget model

Dark matter particles may be represented by compact composite objects of quark matter with macroscopic parameters of mass, charge, and effective temperature. Such particles remain cosmologically and observationally dark if they possess a small cross section to mass ratio. A new feature of the Quark Nugget dark matter model is the prediction of existence of anti-quark nuggets (anti-QNs) built of antimatter and, thus, strongly interacting with visible matter. We study various types of radiation which such anti-QNs can produce, including thermal radiation and gamma photons from matter-antimatter annihilation. Assuming that these particles constitute the dominant dark matter fraction in our galaxy, we then estimate their radiation in our galaxy and compare it with various satellite and terrestrial observations. New detection approaches of this type of dark matter are proposed.

Speaker: Dr Igor Samsonov (UNSW)

Samsonov2.pdf

91 The effects of source morphology on machine learnings ability to identify dark matter substructure in strong gravitational lenses.

Warm and cold dark matter models predict very different abundancies of dark matter substructure within the halos of galaxies. Strong gravitational lensing has shown, in theory, to be a useful probe to measure the parameters of the subhalo mass function which describes these abundancies. In recent years, the focus has been primarily in utilising machine learning to identify substructure properties using simulated photometric data, but often these datasets are rudimentary and not representative of real images. In particular, there is little focus on the influence of the source light galaxies morphology on machine learnings ability to identify substructure signatures. In this talk I will explore the degree to which structure in the source light galaxy is degenerate with substructure signals in the lensing galaxy, comparing a convolutional neural networks ability to accurately classify lenses with and without substructure using increasingly more complex source morphologies. This is done in both the cold and warm dark matter regimes.

Speaker: Tyler Hughes (Swinburne University of Technology)

DSU2022_presentation_TylerHughes_1.pdf

92 Merging clusters as a test-bed for self-interacting dark matter

Self-interacting dark matter (SIDM) has been proposed as a means to alleviate tensions on small scales between observations and simulations. A possible avenue for constraining the interaction cross-section is to study the major mergers of galaxy clusters. These mergers are defined by three components: galaxies, which act as collisionless test particles, gas, which is dissociated from the galaxies through ram pressure stripping, and DM. If the DM is collisionless, as it is in the cold DM (CDM) paradigm, it should remain coincident with the galaxies. However, if the DM is able to interact, it can be offset from the galaxies due to drag from the DM self-interactions. In my current project, I compare the offsets between the galaxies and DM in hydrodynamical simulations of clusters run with both CDM and SIDM physics. My first results show that, as expected, these offsets indeed increase with SIDM cross-section.

Speaker: Ellen Sirks

Ellen Sirks.pdf

93 Thermal WIMPs and the Scale of New Physics

In this talk, I’ll present results from a global fit of Dirac fermion dark matter (DM) effective field theory using the GAMBIT software. We include operators up to dimension-7 that describe the interactions between gauge-singlet Dirac fermion and Standard Model quarks, gluons, and the photon. Our fit includes the latest constraints from the Planck satellite, direct and indirect detection experiments, and the LHC. For DM mass below 100 GeV, we find that it is impossible to simultaneously satisfy all constraints while maintaining EFT validity at high energies. For higher masses, large regions of parameter space exist where EFT remains valid and reproduces the observed DM abundance.

Speaker: Dr Ankit Beniwal (King’s College London)

AB_DSU_2022.pdf

Gravity - Dark Energy

Convener: Shinji Mukohyama

94 Fixing cosmological constant on the event horizon

Standard cosmological equations are written for the Hubble volume, while the real boundary of space-time is the event horizon. Within the thermodynamic approach to gravity, the dark energy term in cosmological equations appears as an integration constant, which we fix at the event horizon and obtain the observed value for the cosmological constant.

Speaker: Prof. Merab Gogberashvili (Javakhishvili State University)

M.Gogberashvili.pdf

95 Probing interacting Dark Energy models and scattering of baryons with Dark Matter in the light of 21cm signal

The EDGES experiment has observed an excess trough in the brightness temperature of the 21cm absorption line of neutral Hydrogen atom (HI) from the era of cosmic dawn. We consider possible interaction of Dark Matter and Dark Energy fluid along with the cooling off of the baryon matter by its collision with Dark Matter to explain the EDGES like excess absorption feature of the 21cm signal. We make use of three different Dark Matter-DarkEnergy (DM-DE) interaction models to test the viability of those models in explaining the EDGES like results. The modification of the evolution of Hubble parameter due to DM-DE interactions influences the optical depth of HI 21cm line as well as the baryon temperature and thus effects brightness temperature of 21cm signal. In addition we also find that DM-DE interaction enables us to explore Dark Matter with varied mass regimes and their viabilities in terms of satisfying the above mentioned EDGES result.

Speaker: upala mukherjee (Saha Institute of Nuclear Physics)

Upala_slides.pdf

96 Hunting Dark Energy on astrophysical scales

State-of-the-art observations tightly constrain the properties of Dark Energy on Cosmological scales, where its behaviour is very close to the one of a cosmological constant. Whilst several Dark Energy candidates are capable of mimicking such a behaviour within the experiments' precision, they may be very distinguishable on smaller astrophysical scales. A rather common feature is that they couple with the gravitational field or other particles, from which an effective variation of some fundamental constants of nature (i.e. couplings) arise. In particular, we assess the drift they induce on astrophysical observables such as time delay between multiple lensed images, the size of Black Hole shadows and the frequency of their photon rings, as well as the shift on the spectral lines of stars in proximity of a supermassive black hole.

Speaker: Leonardo Giani

DSU2022Giani.pdf

97 Holography for extended theories of gravity

The nonextremal Kerr black holes have been considered to be holographically dual to two- dimensional (2D) conformal field theories (CFTs). In this talk, we present the holography for the asymptotically anti-de Sitter (AdS) rotating charged black holes in extended theories of gravity. We find that the scalar wave radial equation at the near-horizon region implies the existence of the 2D conformal symmetries. We note that the 2π identification of the azimuthal angle φ in the black hole line element, corresponds to a spontaneous breaking of the conformal symmetry by left and right temperatures TL and TR, respectively. We show that choosing proper central charges for the dual CFT, we produce exactly the macroscopic Bekenstein-Hawking entropy from the microscopic Cardy entropy for the dual CFT. These observations suggest that the rotating charged black holes in extended theories of gravity, are dual to a 2D CFT at finite temperatures.

Speaker: Masoud Ghezelbash

Ghezelbash.pdf

98 Matter Bounce Scenario in Extended Symmetric Teleparallel Gravity

In this paper, we have shown the matter bounce scenario of the Universe in an extended symmetric teleparallel gravity, the $f(Q)$ gravity. Motivated by the bouncing scenario and loop quantum cosmology (LQC), the form of the function $f(Q)$ has been obtained at the backdrop of Friedmann-Lema$\hat{i}$tre-Robertson Walker (FLRW) space-time. Considering the background cosmology dominated by dust fluid, the e-folding parameter has been expressed, which contains the nonmetricity term. The dynamics of the model have been studied through the phase space analysis, where both the stable and unstable nodes are obtained. Also, the stability analysis has been performed with the first-order scalar perturbation of the Hubble parameter and matter energy density to verify the stability of the model.

Speaker: Mr Amarkumar Agrawal (BITS-Pilani, Hyderabad Campus, India.)

Amarkumar.pdf

15:40 Coffee break

BSM physics

Convener: Tobias Felkl (University of New South Wales)

99 LEvitated MAgnets for QUantum MEtrology

The coupling between the magnetization and the lattice of a ferromagnet gives rise to interesting dynamics. Specifically, in low magnetic fields a levitated magnet should precess, like a spinning top. Such behaviour will enable the use of a ferromagnet as a gyroscope, as a system to test for exotic bosons, and, in the future, to test experimentally the gyrogravitational ratio.
Recently, a collaboration arose to build a proof of principle prototype: LEMAQUME is a European Union’s QuantERA project. In my talk, I will present the motivation to explore such a magnet's dynamics and the ongoing experimental efforts and plans of the collaboration.
https://www.lemaqume.org/
https://arxiv.org/abs/2010.08731
https://arxiv.org/abs/2006.09334

Speaker: Pavel Fadeev (Helmholtz Institute Mainz, Johannes Gutenberg University, 55128 Mainz, Germany)

Gravity Probe Spin DSU2022.pdf

Gravity Probe Spin DSU2022.pdf

Gravity Probe Spin DSU2022.pptx

100 Recent Belle II results related to lepton-flavor universality and violation

The rate of semitauonic B decays has been consistently above theory expectations since these decays were first measured. Also, there are various anomalies in flavour-changing neutral current decays b->sll. The low-background collision environment along with the possibility of partially or fully reconstructing one of the two B mesons in the event offer high precision measurements of semileptonic B decays. This talk presents recent Belle II results related to lepton flavor universality tests based on B decays. In addition, a search for the lepton number violating decay in tau decay is presented.

Speaker: Marco Milesi (The University of Melbourne)

mmilesi_DSU2022.pdf

101 Recent dark-sector results at Belle II

Belle has unique reach for a broad class of models that postulate the existence of dark matter particles with MeV—GeV masses. This talk presents recent world-leading physics results from Belle II searches for dark Higgstrahlung and Z′ decays; as well as the near-term prospects for other dark-sector searches.

Speaker: Chia-Ling Hsu (University of Sydney)

dark_belle2_DSU2022.pdf

102 A Proposed Australian Facility for Particle and Nuclear Physics at the MeV-scale

Determining the nature of New Physics extensions to the Standard Model is one of the most pressing issues for Particle Physics. Well-motivated theories employ New Physics to solve the strong CP, hierarchy or axion quality problems by introducing new pseudoscalar particles which are weakly coupled to the standard model. These axion-like particles can have MeV – GeV masses and predominantly decay to photons and leptons [1, 2]. Recently, the ATOMKI group found evidence [3–5] for a new fundamental boson, named the X17, observed via p + $^{7}$Li → $^{8}$Be + (X17→(e$^{+}$e$^{–}$)), p + $^{3}$H → $^{4}$He + (X17→(e$^{+}$e$^{–}$)), and p + $^{11}$B → $^{12}$C + (X17→(e$^{+}$e$^{–}$)) reactions with a mass of 17 MeV and high statistical significance. There are now numerous searches for weakly coupled bosons, including the X17, using particle physics experiments [6–8]. However, only the ATOMKI group have utilized nuclear reactions in a competitive way to date. We intend to employ the Pelletron accelerator in Melbourne to initiate nuclear reactions of the kind: p + $^{z}$X → $^{z+1}$Y + (e$^{+}$e$^{–}$) and to build a low mass, high precision, Time Projection Chamber (TPC) with a micropatterned readout and magnetic field. The invariant mass resolution of the TPC to the (e$^{+}$e$^{–}$) final state is expected to be 0.1 MeV. This provides a substantially more sensitive search for anomalous (e$^{+}$e$^{–}$) production than any other experiment and 200 times more sensitivity than ATOMKI. Accordingly, we will either observe the ATOMKI anomaly or exclude it at very high significance. Following this, we propose a program to search for anomalous (e$^{+}$e$^{–}$) production with world-leading sensitivity in the 5-25 MeV mass region. In addition, the very large acceptance, and excellent angular and energy resolution of the TPC enables more sensitive investigations of nuclear internal pair conversion decays, enabling a range of novel nuclear physics investigations. The presentation will describe the proposed TPC, its expected performance, together with its application and anticipated impact in particle and nuclear physics investigations.

[1] D. Alves Phys. Rev. D103 055018 (2021)
[2] M. Bauer et al. arXiv:2110.10698
[3] A.J. Krasznahorkay, et al., Phys. Rev. Lett. 116, 042501 (2016)
[4] A.J. Krasznahorkay, et al., Phys. Rev. C104, 044003 (2021)
[5] A.J. Krasznahorkay, et al., arXiv:2209.10795
[6] A. M. Baldini et al. (MEG II Collaboration), Eur. Phys. J. C 78, 380 (2018)
[7] J. Balewski et al. (DarkLight), arXiv:1412.4717
[8] C. Ahdida et al. (SHiP Collaboration), arXiv:2010.11057

Speaker: Dr Lindsey Bignell (Department of Nuclear Physics and Accelerator Applications, The Australian National University)

DSU2022talk.pdf

Dark matter

Convener: Dr Ankit Beniwal (King’s College London)

103 Observational signatures of compact dark stars

Asymmetric dark matter is generically expected to form compact dark stars, which can be searched for through their strong gravitational effects on the light from background stars or on the dynamics of other celestial objects in their vicinity. In this paper we analyze the possible signatures of compact dark stars in asymmetric dark matter scenarios with a portal to the Standard Model. We argue that compact dark stars could capture protons and electrons from the interstellar medium, which then accumulate in the core of the dark star, forming a very hot gas that emit X-rays or $\gamma$-rays. For dark matter parameters compatible with current laboratory constraints, compact dark stars could be sufficient luminous to be detected at the Earth as point source in the X-ray or $\gamma$-ray sky.

Speaker: Alejandro Ibarra

Ibarra.pdf

104 Capture of DM in Compact Stars

Neutron stars harbour matter under extreme conditions, providing a unique testing ground for fundamental interactions.
Dark matter can be captured by neutron stars via scattering, where kinetic energy is transferred to the star.
This can have a number of observational consequences, such as theheating of old neutron stars to infra-red temperatures.
Previous treatments of the capture process have employed various approximation or simplifications.
We present here an improved treatment of dark matter capture, valid for a wide dark matter mass range, that correctly incorporates all relevant physical effects.
We provide general expressions that enable the exact capture rate to be calculated numerically, and derive simplified expressions that are valid for particular interaction types or mass regimes and that greatly increase the computational efficiency.
We find that the potential neutron star sensitivity to DM-lepton scattering cross sections greatly exceeds electron-recoil experiments, particularly in the sub-GeV regime, with a sensitivity to sub-MeV DM well beyond the reach of future terrestrial experiments.
We present results for DM-Baryons scatterings in Neutron stars, were the sensitivity is expected to greatly exceed current DD experiments for the spin-dependent case in the whole masse range, and for spin-independent in the low and high mass range.

Speaker: Giorgio Busoni (The Australian National University)

105 Neutron Star Heating and the (g-2)_muon Discrepancy

The observed value of the muon magnetic dipole moment can be explained in models with weakly-interacting massive particles (WIMPs) coupled to muons. However, a considerable range of parameter space in such models will remain unexplored in future LHC experiments and dark matter (DM) direct searches. Here I will discuss the temperature observation of neutron stars (NSs) as a promising way to probe such models, given that WIMPs are efficiently captured by NSs through DM-muon or spin-dependent DM-nucleon scattering. We consider two classes of representative models, where the DM couples or does not couple to the Higgs field at the tree level, and show that the maximal DM heating is realised in both scenarios.

Speaker: Maura Elizabeth Ramirez Quezada (University of Tokyo)

DSU2022MQuezada.pdf

106 Dark Matter in Compact Objects

Dark Matter capture in compact objects has garnered considerable interest over recent years. This renewed interest is driven primarily by the prospect that the energy deposited by the dark matter can heat these objects potentially to infra-red temperatures, which may soon be observed. Such observations can constrain dark matter interactions complementary to modern direct detection experiments. To gain reliable insight into the reach these objects can offer, correctly incorporating the unique physics relevant to these objects into the capture process is necessary. Key among these are the effects of gravitational focusing, relativistic kinematics for targets and dark matter, Pauli blocking due to degenerate targets, and multiple scattering effects. Additionally, we incorporate the internal structure of the objects in a self consistent manner. Specifically for Neutron stars, baryonic targets have additional physics which needs to be accounted for. These are the effects of strong interactions which induce an effective mass, and accounting for their finite size. We can then project realistic sensitivities for dark matter-lepton and nucleon cross sections using dimension-6 effective operators, which are competitive and potentially stronger than those obtained from direct detection searches.

Speaker: Michael Virgato

DSU 2022 M Virgato.pdf

Particle astrophysics

Convener: Roland Crocker

107 Extending pulsar timing sensitivity below the nanohertz range

We present a first search for continuous ultra-low-frequency gravitational wave sources using secular variations of pulsar parameters. This new methodology extends the sensitivity of pulsar timing arrays well below the nanohertz range. The results are complementary to the typical analysis and provide competitive sensitivity, with the potential to observe supermassive black hole binaries within the next ten years

Speaker: William DeRocco

sydney_2022.pdf

108 Assessing the Impact of Hydrogen Absorption on the Characteristics of the Galactic Center Excess

We present a new reconstruction of the distribution of atomic hydrogen in the inner Galaxy that is based on explicit radiation-transport modelling of line and continuum emission and a gas-flow model in the barred Galaxy that provides distance resolution for lines of sight toward the Galactic Center. The main benefits of the new gas model are, a), the ability to reproduce the negative line signals seen with the HI4PI survey and, b), the accounting for gas that primarily manifests itself through absorption. We apply the new model of Galactic atomic hydrogen to an analysis of the diffuse gamma-ray emission from the inner Galaxy, for which an excess at a few GeV was reported that may be related to dark matter. We find with high significance an improved fit to the diffuse gamma-ray emission observed with the Fermi-LAT, if our new HI model is used to estimate the cosmic-ray induced diffuse gamma-ray emission. The fit still requires a nuclear bulge at high significance. Once this is included there is no evidence for a dark-matter signal, be it cuspy or cored. But an additional so-called boxy bulge is still favoured by the data. This finding is robust under the variation of various parameters, for example, the excitation temperature of atomic hydrogen, and a number of tests for systematic issues.

Speaker: Chris Gordon (University of Canterbury)

DSU2022.pdf

109 Axion electrodynamics in dense neutron star matter

Axions are pseudo-Nambu-Goldstone bosons that provide a cogent solution to the strong CP problem. They are expected to have a rich phenomenology, stemming from their postulated couplings to Standard Model particles.
In this talk, we focus on neutron star (NS) astrophysics and on the axion-photon coupling, which modifies Maxwell’s equations. We show that the expectation value of the axion field can become large at the typical densities expected in NS cores, compared to the vacuum case. Such shift affects the magnetic and thermal evolution of NSs, leading to potentially observable effects. By performing state-of-the-art magneto-thermal simulations of NSs, we show that axion-induced perturbations to
the NS magnetic field grow rapidly. The electric currents circulating in the resistive crustal layers become more intense, causing enhanced ohmic dissipation, heating the crust and increasing the observable NS thermal luminosity. The growth of axion-induced magnetic field perturbations and
the consequent internal heating effect are controlled by axion parameters such as the axion decay constant and axion couplings. By preventing the uncontrolled growth of axion-induced magnetic
field perturbations, we place constraints on axion parameters and couplings with our magneto-thermal simulations, in agreement with the latest data from the population of thermally-emitting NSs and magnetars.

Speaker: Filippo Anzuini (Monash University)

Anzuini_Axions.pdf

110 Advancing Globular Cluster Constraints on the Axion-Photon Coupling

For decades stellar evolution has been a rich source of constraints on physics beyond the Standard Model. In this talk I will discuss our recent improvement of the upper bound on the axion-photon coupling from stellar evolution, which has been derived using the $R_2$ parameter, the ratio of stellar populations on the Asymptotic Giant Branch to Horizontal Branch in Globular Clusters. I will compare observed limits on $R_2$ with data from simulations using the stellar evolution code $\texttt{MESA}$ which include the effects of axion production. The benefits of considering $R_2$ over the traditionally employed $R$-parameter will be discussed, with particular attention given to quantifying in detail the effects of uncertainties on these parameters due to the modelling of convective core boundaries. Using a semiconvective mixing scheme we constrain the axion-photon coupling to be $g_{a\gamma\gamma} < 0.47 \times 10^{-10}~\mathrm{GeV}^{-1}$. This rules out new regions of QCD axion and axion-like particle parameter space. Complementary evidence from asteroseismology suggests that this could improve to as much as $g_{a\gamma\gamma} < 0.34 \times 10^{-10}~\mathrm{GeV}^{-1}$ as the uncertainties surrounding mixing across convective boundaries are better understood.

Speaker: Fred Hiskens (The University of Melbourne)

FJH_DSU.pdf

19:00 Conference dinner

Friday 9 December

Plenary

Livestream link: https://tinyurl.com/DSU2022plenary

Convener: Dr Chris Gordon (University of Canterbury)

111 Detection of the Sagittarius Dwarf Spheroidal Galaxy in Gamma-Rays

The Fermi Bubbles are giant, γ-ray emitting lobes emanating from the nucleus of the Milky Way discovered in ∼1-100 GeV data collected by the Large Area Telescope on board the Fermi Gamma-Ray Space Telescope. Previous work has revealed substructure within the Fermi Bubbles that has been interpreted as a signature of collimated outflows from the Galaxy’s super-massive black hole. Here we show via a spatial template analysis that much of the γ-ray emission associated to the brightest region of substructure – the so-called cocoon – is likely due to the Sagittarius dwarf spheroidal (Sgr dSph) galaxy. This large Milky Way satellite is viewed through the Fermi Bubbles from the position of the Solar System. As a tidally and ram-pressure stripped remnant, the Sgr dSph has no on-going star formation, but we nevertheless demonstrate that the dwarf’s millisecond pulsar (MSP) population can plausibly supply the γray signal that our analysis associates to its stellar template. The measured spectrum is naturally explained by inverse Compton scattering of cosmic microwave background photons by high-energy electron-positron pairs injected by MSPs belonging to the Sgr dSph, combined with these objects’ magnetospheric emission. This finding plausibly suggests that MSPs produce significant γ-ray emission amongst old stellar populations, potentially confounding indirect dark matter searches in regions such as the Galactic Centre, the Andromeda galaxy, and other massive Milky Way dwarf spheroidals.

Speaker: Roland Crocker

Crocker_DSU_2022_UNSW.pdf

112 High-energy astrophysics with gamma-ray telescopes

Gamma-rays are a high effective tracer of extreme particle acceleration in the cosmos and can also be used to probe fundamental, beyond-standard-model and exotic physics in the present and in the early Universe. In this talk, I will summarise some recent results in gamma-ray astronomy from the current generation of ground-based facilities (e.g. HESS, MAGIC, VERITAS, HAWC, LHAASO) focusing on the multi-GeV to PeV energy regime. These facilities have provided exciting new information on the potential for supernova remnants, supernovae, stellar clusters, pulsar wind nebulae, and accreting systems to accelerate electrons and/or cosmic-ray hadrons. I will also discuss constraints on dark matter properties and some other fundamental physics insights, and conclude with a look at the next generation facilities such as CTA and SWGO.

Speaker: Dr Gavin Rowell

gpr-Gamma.pdf

113 Improving Theoretical Predictions for Gamma-Ray Signals from Heavy WIMPs

Speaker: Tracy Slatyer

Slatyer_DSU_22_PDF.pdf

10:30 Coffee break

Plenary

Livestream link: https://tinyurl.com/DSU2022plenary

Convener: Sven Heinemeyer (CSIC (Madrid, ES))

114 The Universe as a Lab for New Physics Across Cosmic Times

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Speaker: Prof. Cora Dvorkin

115 Dark matter with GAMBIT

I give an update on results for dark matter obtained using GAMBIT, the Global And Modular BSM Inference Tool. After briefly describing the main features of the GAMBIT code, I highlight why GAMBIT is a promising framework to isolate sign of physics beyond the standard models (BSM) of particle physics and cosmology. Then I show the latest GAMBIT results for various models containing a dark matter candidate.

Speaker: Csaba Balazs

GAMBIT update 2.pdf

116 Has the CMSSM survived Planck, the LHC, Direct and Indirect Detection experiments?

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Speaker: Keith A. Olive (University of Minnesota (US))

DSU2023.pdf

DSU22.pdf