The Invisibles23 Workshop will take place in Göttingen, Germany from August 28th to September 1st, 2023. It follows the Invisibles23 School in Bad Honnef.
The Invisibles23 Workshop is jointly organized by the Horizon 2020 Marie Curie ITN network HIDDeN, which continues the series of “Invisibles” events started in 2012 (Horizon 2020 Marie Curie ITN network Invisibles, Horizon 2020 Marie Curie ITN network Elusives and the Horizon 2020 RISE network InvisiblesPlus).
Topics include:
The Invisibles23 Workshop is organized in the context of the Horizon 2020 funded projects HIDDeN and Asymmetry.
HIDDeN is a European ITN project (H2020-MSCA-ITN-2019//860881-HIDDeN) focused on revealing the (a)symmetries we have yet to discover, hence hidden (a)symmetries, and the particles on which they act, in particular the invisible sector, made of neutrinos, dark matter and other elusive particles. It has received funding from the European Union’s Horizon 2020 research and innovation programme under the Marie Skłodowska-Curie grant agreement No 860881-HIDDeN”.
ASYMMETRY is a European Staff exchange program (HE-MSCA-SE-2022//101086085) investigating the essential asymmetries of Nature and CP violation in particle physics and cosmology. It has received funding from the European Union’s Horizon Europe programme under the Marie Skłodowska-Curie Actions Staff Exchanges (SE) grant agreement No 101086085-ASYMMETRY”.
Management Team: Rebeca Bello, Katrin Glormann
Email: invisibles23@uni-goettingen.de
Phone: +49 551 39 27889
This project has received funding /support from the European Union's Horizon 2020 research and innovation programme under the Marie Skłodowska -Curie grant agreement No 860881-HIDDeN
This project has received funding from the European Union’s Horizon Europe programme under the Marie Skłodowska-Curie Actions Staff Exchanges (SE) grant agreement No 101086085-ASYMMETRY”.
We revisit the left-right symmetric model and explore the hybrid regime where type-I and type-II seesaw mechanisms are equally responsible for the light neutrino masses. Barring only very specific choices of parameters we expect sizable lepton flavor violation and electron dipole moment in this region. We use results from recent neutrino oscillation fits, bounds on neutrinoless double beta decay, $\mu \to e \gamma$, $\mu \to 3e$, $\mu \to e$ conversion in nuclei, the muon anomalous magnetic moment, the electron electric dipole moment and cosmology to determine the viability of this region. We derive stringent limits on the heavy neutrino masses and mixing angles as well explore the implications for the new gauge boson mass.
Global analyses of different dark matter searches are necessary to determine the status of dark matter models. Highly accurate antiproton measurements from AMS-02 would add valuable information to such global analyses. I will present an analysis pipeline for fast and accurate antiproton likelihoods in global scans. The pipeline consists of a neural network emulator for antiproton flux simulations, and a likelihood calculator for accurate treatment of correlations and marginalization of propagation uncertainties. I will conclude with the status of scalar singlet dark matter considering new direct detection and LHC likelihoods in addition to the antiproton likelihood.
Recently, the ANITA collaboration announced the detection of new, unsettling Ultra-High-Energy (UHE) events. Understanding their origin is pressing to ensure success of the incoming UHE neutrino program.
In this talk, I will discuss the ANITA-IV events in contrast with the lack of observations in the IceCube Neutrino Observatory. I will introduce a general framework to study the compatibility between these two observatories both in the SM and Beyond Standard Model (BSM) scenarios.
Finally, I will discuss the constraints on BSM and highlight the importance of simultaneous observations by high-energy optical neutrino telescopes and new, UHE detectors to uncover cosmogenic neutrinos or discover new physics.
The existence of Dark Matter is one of the most important indications of physics beyond the Standard Model of particle physics. A promising class of Dark Matter candidate is represented by new massively interactive particles.
Direct Detection experiments can potentially find some of these candidates due the possible interactions of Dark Matter with Standard Model, in our case these possible interactions arise at first order radiative corrections.
On this talk we will introduce the models considered, the calculation of the radiative correction and finally the possible phenomenology of these different candidates to Dark Matter in the context of Direct Detection
We present a FIMP dark matter (DM) candidate. FIMP dark matter is produced via the freeze-in mechanism that generally implies tiny coupling between the DM and the standard model particles, making DM direct detection and collider searches almost hopeless. This is not the case for DM at low reheating temperatures, where direct detection bounds play a fundamental role in constraining the parameter space. We show the viability of the model and discuss the details of the production mechanism and future experiments that can test it.
We perform a Bayesian search in the latest Pulsar Timing Array (PTA) datasets for a stochastic gravitational wave (GW) background sourced by curvature perturbations at scales around k=1e6 Mpc-1. These re-enter the Hubble horizon at temperatures around and below the QCD crossover phase transition in the early Universe. We include a stochastic background of astrophysical origin in our search and properly account for constraints on the curvature power spectrum from the overproduction of primordial black holes (PBHs). We find that the International PTA Data Release 2 significantly favors the astrophysical model for its reported common-spectrum process, over the curvature-induced background. On the other hand, the two interpretations fit the NANOgrav 12.5 years dataset equally well. We then set new upper limits on the amplitude of the curvature power spectrum at small scales. These are independent from, and competitive with, indirect astrophysical bounds from the abundance of PBH dark matter. Upcoming PTA data releases will provide the strongest probe of the curvature power spectrum around the QCD epoch.
Axion-like particles (ALPs) and heavy neutral leptons (HNLs) are both well-motivated extensions of the Standard Model. Their interaction offers an exquisite opportunity to unveil the nature of HNLs, even if they had tiny Seesaw-like mixing angles, which would make them almost impossible to test otherwise at collider. In this work, we point out a particularly clean process, the JALZ, which offers such a unique opportunity. We estimate its current and future sensitivity at the LHC.
In this work, we explore the thermal production mechanism Freeze-In and its applicability on the dark phases of the Next-to-2-Higgs-Doublet model (N2HDM). We study the phenomenological consequences on the two phases, namely the Full Dark Phase (FDP) and the Dark Singlet phase (DSP). In the FDP, we obtain two DM candidates, which both contribute to the observed DM relic density. However, one DM candidate undergoes the Freeze-Out process, while the other undergoes the Freeze-In process. In the DSP, one DM candidate exists and undergoes the Freeze-In process. After applying all relevant experimental and theoretical constraints, we explore the viable parameter regions in both phases.
I will discuss a tri-hypercharge extension of the Standard Model (SM) in which a separate gauged weak hypercharge is associated with each fermion family, avoiding the family repetition of the SM. Yukawa couplings for first and second family fermions arise at the non-renormalisable level, explaining the mass hierarchies observed for charged fermions along with the smallness of CKM mixing. I will show that the implementation of a seesaw type I mechanism naturally leads to a low scale seesaw, where the right-handed neutrinos may be as light as the TeV scale. Finally, the model predicts Z' bosons that could be as light as a few TeV, with implications for flavour-violating observables, LHC physics and electroweak precision observables.
In this work we study the present and future sensitivities of the rare meson decay facilities KOTO, LHCb and Belle II to a light dark sector of the minimal dark abelian gauge symmetry where a dark Higgs S and a dark photon ZD have masses ≲10 GeV. We have explored the interesting scenario where S can only decay to a pair of ZD's and so contribute to visible or invisible signatures, depending on the life-time of the latter. Our computations show that these accelerator experiments can access the dark Higgs (mass and scalar mixing) and the dark photon (mass and kinetic mixing) parameters in a complementary way. We have also discussed how the CMS measurement of the SM Higgs total decay width and their limit on the Higgs invisible branching ratio can be used to extend the experimental reach to dark photon masses up to ∼10 GeV, providing at the same time sensitivity to the gauge coupling associated with the broken dark abelian symmetry.
We explore the scenario of Pseudo-Dirac neutrinos, where the mass degeneracy of Dirac neutrinos is lifted due to a soft breaking of the lepton number, resulting in 3 pairs of mass states which are maximally mixed.
Using prospects on the measurement of $pp$ and $^7$Be solar neutrinos in JUNO, we will demonstrate the capability of the experiment to explore the parameter space of including one of these extra finely split mass states, as well as the bounds it will be able to set on the full pseudo-Dirac scenario. We will show that JUNO will be able to put a 3$\sigma$ limit on the mass splitting being $\delta m^2$ $\lt$ 1.19 $\times$ 10$^{−13}$ eV$^2$ for a full Pseudo-Dirac scenario with identical mass splittings.
Axions and axion-like particles (ALPs) are well motivated new physics candidates that couple to the Standard Model fields via classically shift-invariant dimension-5 operators. In this talk I will show how one-loop diagrams with virtual ALP exchange generate dimension-6 SMEFT operators via renormalization group evolution, independently of the mass of the ALP. I will then present indirect bounds on the ALP couplings obtained in a global analysis from experimental constraints on SMEFT Wilson coefficients.
We study the cosmology of an internally thermalized dark matter (DM), which is either coupled only gravitationally with the standard model (SM) sector, or may have a very feeble non-gravitational interaction that does not thermalize the two sectors. In the former scenario, the DM may undergo number-changing self-scatterings in the early Universe, eventually freezing out to the observed DM abundance. If these reactions, such as a 3$\rightarrow$2 process, take place when the DM is non-relativistic, DM cannibalizes itself to cool much slower than standard non-relativistic matter during the cannibal phase. We find that depending upon the DM self-couplings, a scalar cannibal DM with mass in the range of around 80 eV to 700 TeV can make up the observed DM density and satisfy all the constraints, when the initial DM temperature ($T_{\rm DM}$) is lower than the SM one ($T_{\rm SM}$), with $T_{\rm SM}/9100 < T_{\rm DM} < \,T_{\rm SM}/1.1$. In the latter scenario, we further investigate the origin of the initial DM energy density in the Universe at the post-inflationary reheating epoch, and determine to what extent inflaton-mediated DM-SM scattering reactions can modify the temperature of the DM, thereby changing the initial conditions of DM temperature evolution during its non-relativistic phase. In each scenario, we evaluate the cosmological constraints from the cosmic-microwave background power spectrum, the big-bang nucleosynthesis limits on the relativistic degrees of freedom, the Lyman-$\alpha$ limits on the DM free-streaming length, and the Bullet Cluster constraints on DM elastic self-scatterings.
Flavour violation in axion models can be generated by choosing flavour non-universal Peccei-Quinn(PQ) charges. Such an axion is easily implemented in a UV completion with a DFSZ model: containing two Higgs doublets (PQ-2HDM) and the PQ scalar, decoupled at low energies. This charge arrangement also produces flavour violation at tree level in the PQ-2HDM, which we will show it is directly correlated to the flavour violation of the axion. This general relation allows us to link flavour violating observables across the scales of the axion and the 2HDM, in such a way that information of one sector is directly related with the other. We will show in two examples how this can be done using flavour violating observables in the quark and lepton sector, finding an important interplay between astrophysical and LHC searches.
While we enter the precision era of neutrino mixing parameters, there is still one long-standing tension: the solar mass square difference measured by different experiments. The reactor antineutrino experiment KamLAND finds a best fit larger than the one obtained with solar neutrino data. The current tension ($\sim 1.5 \sigma$) is not large enough to consider the measurements incompatible, but future data may help either to close or to stand out this issue. Here, we discuss how a future supernova burst in our galaxy could be used to determine the solar neutrino mass splitting at the Hyper-Kamiokande detector, and discuss how this could contribute to the current situation. We study Earth matter effects for different sets of neutrino spectra and study the impact of the supernova position. Although the final capabilities depend on the details of the supernova neutrino spectra arriving at Earth and the final trajectory through the Earth, for some models and directions, error bands comparable to those obtained with KamLAND data could be attained. If supernova neutrino data prefers the solar data best fit, the tension with KamLAND data could grow up to $\gtrsim 5 \sigma$ level.
Dark sectors with a QCD-like structure and composite particles can provide a viable dark matter candidate along with unexplored discovery potential at particle collider experiments. As the community is working towards benchmarks to motivate dedicated searches, there is still a lot of work to do in improving our understanding of such strongly-interacting dark sectors. In this talk, I will give a brief overview of the strongly-interacting dark sector landscape and discuss relevant constraints from cosmology and collider experiments.
Hot white dwarfs lose energy mainly by emitting neutrinos through plasmon decay from the inner part of the star. Dark sectors, which are being studied to explain a broad collection of anomalies and unknown physics, do have an impact in the energy lost by this mechanism. I will focus on a Three Portal model that connects dark sectors to the Standard Model through a dark scalar (Higgs), a dark photon and dark neutrino states. The aim is to study the impact of the dark photon and dark neutrino states in the cooling mechanism of a white dwarf.
In this talk we will explore how extensions of the Standard Model (SM) scalar sector featured in radiative neutrino mass models can generically accommodate U(1)_Y gauge symmetry breaking in the early Universe. Using the Zee-Babu neutrino mass generation model as a template, we investigate the rich phenomenology that arises when accounting for such high-temperature hypercharge symmetry non-restoration in addition to electroweak (EW) symmetry breaking of the standard thermal history. Our focus lies on the baryon asymmetry generating mechanisms which emerge according to subtleties in these thermal histories. Generally, we find that such settings give rise to phase structures which permit strong first order EW phase transitions as needed for EW baryogenesis whilst comfortably allowing for evasion of present experimental constraints on the lepton and scalar sectors. Furthermore, we discuss a novel leptogenesis mechanism which crucially relies on the high-temperature U(1)_Y breaking phase and the exotic phenomenology of charge-breaking SM lepton masses therein.
We consider a minimal SO(10) Grand Unified Theory (GUT) model that can reproduce the observed fermionic masses and mixing parameters of the Standard Model. We calculate the scales of spontaneous symmetry breaking from the GUT to the Standard Model gauge group using two-loop renormalisation group equations. This procedure determines the proton decay rate and the scale of U(1)B−L breaking, which generates cosmic strings and the right-handed neutrino mass scales. Consequently, the regions of parameter space where thermal leptogenesis is viable are identified and correlated with the fermion masses and mixing, the neutrinoless double beta decay rate, the proton decay rate, and the gravitational wave signal resulting from the network of cosmic strings. We demonstrate that this framework, which can explain the Standard Model fermion masses and mixing and the observed baryon asymmetry, will be highly constrained by the next generation of gravitational wave detectors and neutrino oscillation experiments which will also constrain the proton lifetime.
The singlet scalar Higgs portal model provides one of the simplest explanations of dark matter in our Universe.
Its Higgs resonant region, $m_\text{DM}\approx m_h/2$, has gained particular attention, being able to reconcile the tension between the relic density measurement and direct detection constraints.
Interestingly, this region is also preferred as an explanation of the Fermi-LAT $\gamma$-ray Galactic center excess.
We perform a detailed study of this model using $\gamma$-ray data from the Galactic center and from dwarf spheroidal galaxies and combine them with cosmic-ray antiproton data from the AMS-02 experiment that shows a compatible excess.
In the calculation of the relic density, we take into account effects of early kinetic decoupling relevant for resonant annihilation.
The model provides excellent fits to the astrophysical data either in the case the dark matter candidate constitutes all or a subdominant fraction of the observed relic density.
We show projections for future direct detection and collider experiments to probe these scenarios.
Axion-like-particles (ALPs) are among the most well motivated extensions of the Standard Model. In many scenarios, they are understood as the (pseudo) Nambu-Goldstone bosons of sponteneously broken U(1) symmetries and are thus (approximately) invariant under shift-symmetry. In this talk we investigate the origin of the shift-symmetry by directly studying the physical properties of amplitudes involving ALPs and matter particles. To do this, we use on-shell methods, that allows us to write the amplitudes without the need of fields and Lagrangians. With these methods we can characterise all shift-symmetric interactions of ALPs and easily construct a non-redundant basis for higher-order amplitudes. We show how such higher-order interactions can be relevant and even surpass the effects of dimension 5 operators at future lepton colliders.
I will review different ideas to probe leptogenesis with gravitational waves caused by first-order phase transitions or cosmic strings. In particular, I will focus on local cosmic strings produced after the breaking of a U(1)_(B-L) gauge symmetry that gives masses to right-handed neutrinos. Cosmic strings are expected to produce a stochastic gravitational background that could be probed experimentally in the very near future by e.g. LISA. In our work, we investigate what impact an observation of stochastic gravitational waves originating from U(1)_B-L cosmic strings could have on our understanding of mechanisms that are relevant for leptogenesis. In particular, we scrutinize whether particle production from local cosmic strings in the early universe could have affected leptogenesis via non-thermal production of right-handed neutrinos.
Dark matter direct (and indirect) detection experiments usually can only determine a specific combination of a power of the coupling and the dark matter density. This is also true for axion haloscopes which are sensitive to the product $g^{2}_{a\gamma\gamma}\rho_{\rm DM}$, the combination of axion-photon coupling squared and the dark matter density.
In this note we show, that in the lucky case when we intersect with a so-called axion minicluster of a suitable size, we can utilize the spectral information available in haloscopes to determine the gravitational potential of the minicluster. We can then use this to measure separately the coupling and the density of the minicluster.
We investigate different classes of models, in which the dark matter candidate arises
as a hadronic state of dark constituent quarks, which are charged under both the new
confining dark gauge group and the standard model. Specifically, we focus on the case
of quarks in the fundamental representation of SU(N), which are heavier than the dark
QCD confinement scale. Recent literature has demonstrated that this class of models
can lead to a first order phase transition of the dark sector, which effectively results in
a significant depletion of the dark matter relic abundance, due to a second annihilation
stage after the usual freeze-out. In this study, we assess the distinctive thermal history
associated with these type of models and perform a comprehensive study of the relevant
parameter space - spanned by the dark QCD scale and the dark matter mass - beyond
what was considered so far. We combine the experimental bounds from direct and
indirect searches as well as specific collider signals and confront it with the predicted relic abundance to constrain the viable parameter space for these models.
We present an updated and improved global fit analysis of current flavor and electroweak precision observables to derive bounds on the mixing of heavy neutrinos.
This new analysis is motivated by new and updated experimental results on key observables such as $V_{ud}$, the invisible decay width of the $Z$ boson and the $W$ boson mass. It also improves upon previous studies by considering the full correlations among the different observables and explicitly calibrating the test statistics, which may present significant deviations from a $\chi^2$ distribution.
The results are provided for three different models: the minimal scenario with only 2 neutrinos, the next to minimal one with 3 neutrinos, and the most general one with an arbitrary number of heavy neutrinos that we parametrize via a generic deviation from a unitary lepton mixing matrix.
We derive new constraints on effective four-fermion neutrino non-standard interactions with both quarks and electrons. This is done through the global analysis of neutrino oscillation data and measurements of coherent elastic neutrino-nucleus scattering (CEvNS) obtained with different nuclei. In doing so, we include not only the effects of new physics on neutrino propagation but also on the detection cross section in neutrino experiments which are sensitive to the new physics. We consider both vector and axial-vector neutral-current neutrino interactions and, for each case, we include simultaneously all allowed effective operators in flavour space. To this end, we use the most general parametrization for their Wilson coefficients under the assumption that their neutrino flavour structure is independent of the charged fermion participating in the interaction. The status of the LMA-D solution is assessed for the first time in the case of new interactions taking place simultaneously with up quarks, down quarks, and electrons. One of the main results of our work are the presently allowed regions for the effective combinations of non-standard neutrino couplings, relevant for long-baseline and atmospheric neutrino oscillation experiments.
We investigate the model "CP in the Dark" with a the scalar sector consisting of two doublet and one singlet scalar fields. The imposed specific discrete symmetry leads to a SM-like phenomenology with a hidden scalar sector. In a specific limit of the model parameters we were able to show that the model provides three DM candidates. Two of which contribute to the total relic density via the freeze-out mechanism and one via the freeze-in mechanism. This allows us to obtain the full observed relic density of the universe while simultaneously fulfilling all the relevant experimental and theoretical constraints.
Nuclear matrix elements (NME) are a crucial input for the interpretation of neutrinoless double beta decay data. A representative set of recent NME calculations from different methods is taken, and a combined analysis of the available data performed in order to investigate the impact on the current and future sensitivities on the effective Majorana mass $m_{\beta\beta}$. A crucial role is played by the recently discovered short-range contribution to the NME, induced by light Majorana neutrino masses. Depending on the NME model and the relative sign of the long- and short-range contributions, the current $3\sigma$ bounds change, and the sensitivity of next-generation experiments can be either pushed beyond the inverted mass ordering region or never reach this one.
Furthermore, perspectives on the possibility to distinguish between different NME calculations by assuming a positive signal and by combining measurements from different isotopes is presented.
The fundamental nature of neutrinos, whether they are Dirac or Majorana fermions, is still unknown and has been an open question for long time. If we consider neutrinos to be Majorana type, then the two flavour neutrino mixing matrix contains a Majorana phase. However, this phase doesn't appear in neutrino oscillation probabilities for vacuum as well as for matter modified oscillations. This leads us to the questions, "what are the conditions under which the Majorana phase appears in the oscillation probabilities ?". We find that the Majorana phase remains in the oscillation probabilities if the neutrino decay eigenstates are not the same as the mass eigenstates. In such a condition we find the possibilities of two kinds of CP-violation in our work: one due to the Majorana phase and the other due to the off-diagonal parameter of the neutrino decay matrix. We point out an another interesting result that the CP-violating terms in the oscillation probabilities are sensitive to neutrino mass ordering.
We investigate the experimental signal of the cosmic axion spin precession experiment (CASPEr) with respect to its power spectrum. Here, special attention is given to the velocity spectrum of the stochastic axion field and its influence on the experimental signal. This investigation aims to ascertain if the dark matter (DM) velocity spectrum is measurable using the CASPEr experiment. The stochastic axion field in this discussion is modeled using the standard halo model of the dark matter velocity distribution. Its influence on the experimental power spectrum is analyzed both analytically and numerically. We use the results of our analysis to show that although non-linearities are present in the dynamics of the experiment, we can reconstruct the axion DM velocity spectrum by solving a linear inverse problem. This is made possible by the scale structure of the experiment, which enables us to linearize the time evolution of the system's dynamics.
This is demonstrated by successfully reconstructing the velocity spectrum from numerically generated power spectra in different cases.
We present a comprehensive discussion of the Stodolsky effect for dark matter (DM), and discuss two techniques to measure the effect and constrain the DM parameter space. The Stodolsky effect is the spin-dependent shift in the energy of a Standard Model (SM) fermion sitting in a bath of neutrinos. This effect, which scales linearly in the effective coupling, manifests as a small torque on the SM fermion spin and has historically been proposed as a method of detecting the cosmic neutrino background. We generalise this effect to DM, and give expressions for the induced energy shifts for DM candidates from spin-0 to spin-3/2, considering all effective operators up to mass dimension-6. In all cases, the effect scales inversely with the DM mass, but requires an asymmetric background. We show that a torsion balance experiment is sensitive to energy shifts of ΔE≳10^−28 eV, whilst a more intricate setup using a SQUID magnetometer is sensitive to shifts of ΔE≳10^−32eV. Finally, we compute the energy shifts for a model of scalar DM, and demonstrate that the Stodolsky effect can be used to constrain regions of parameter space that are not presently excluded.
The lack of information before Big Bang Neucleosynthesis (BBN) allow us to assume the presence of a new species $\phi$ whose energy density redshifts as $a^{-(4+n)}$ where $n>0$ and $a$ is the scale factor. In this non-standard cosmological setup, we have considered $U(1)_{L_\mu-L_\tau}\otimes U(1)_X$ gauge extension of the Standard Model (SM) and studied different phases of the cosmological evolution of a thermally decoupled dark sector such as leak-in, freeze-in, reannihilation, and late-time annihilation. This non-standard cosmological setup facilitates a larger portal coupling $(\epsilon)$ between the dark and the visible sectors even when the two sectors are not in thermal equilibrium. The dark sector couples with the $\mu$ and $\tau$ flavored leptons of the SM due to the tree level kinetic mixing between $U(1)_X$ and $U(1)_{L_\mu-L_\tau}$ gauge bosons. We show that in our scenario it is possible to reconcile the dark matter relic density and muon $(g-2)$ anomaly. In particular, we show that for $3\times 10^{-4}<\epsilon<10^{-3}$, $30{\rm MeV}