Astrophysical probes of dark sectors using radiowave observations

29 Sept 2025, 09:00 → 3 Oct 2025, 16:00 Europe/London

This is the 1st UNDARK workshop, to be held in the  Instituto de Astrofísica de Canarias (IAC) during 29 September - 3 October 2025. This workshop will focus on astrophysical probes of fundamental questions related to the dark universe, with a specific emphasis on radio wave observations, as well as their possible connections with gravitational wave detection. The meeting is organized in the context of the UNDARK project and it aligns with the observational and instrumental expertise of the IAC in microwave astronomy, including experiments such as QUIJOTE, TMS, LSPE-STRIP, and GroundBIRD.   

Main website: https://meetings.iac.es/astrodarkradio/

UNDARK is funded through the  Widening participation and spreading excellence  programme (project number 101159929), which is part of the  European Research Area  (ERA) Policy Agenda and aims to harmonise research and innovation (R&I) capacities among all EU countries.

Funded by the European Union. Views and opinions expressed are however those of the author(s) only and do not necessarily reflect those of the European Union or European Research Executive Agency (REA). Neither the European Union nor the granting authority can be held responsible for them.

 

 

Monday 29 September

09:00 → 09:15 Registration

09:15 → 09:45 Welcome

09:45 → 10:15 Impact of satellite constellations in current and future radio wave observations

Speaker: Dr Federico Di Vruno (SKAO)

Dark and Quiet Skies -UNDARK.pptx

10:15 → 10:45 Dark Matter searches with LOFAR

The Low Frequency Array (LOFAR), a pan-European radio interferometer for the lowest radio frequencies, is currently undergoing an upgrade to enhance its simultaneous bandwidth and sensitivity. Commissioning observations with LOFAR2.0 will start in 2026. Already in its first phase, LOFAR was searching for WIMP dark matter and obtained competitive limits. For LOFAR2.0 we envision a dedicated search programme that targets dark matter candidates across many orders of magnitude in mass, ranging from ultra-light axion-like particles to QCD axions, weakly interacting massive particles, and primordial black holes. Combining state of the art imaging, spectroscopic, and spectro-polarimetric, as well as time domain observations will eventually allow us to probe the huge world of dark matter candidates. In this presentation I will give an overview on what was achieved with LOFAR so far, what could be done, and what are the observational and data analysis challenges ahead.

Speaker: Dominik Schwarz (Universität Bielefeld)

UNDARK_Schwarz.pdf

10:45 → 11:00 Searching for blue in the dark

Measurements of 21-cm intensity mapping in the dark ages promise to access very small scales that have yet to be probed, extending beyond the reach of CMB and galaxy surveys. In this talk, I will show how small-scale power-law enhancements--or blue tilts---of the primordial power spectrum affect the 21-cm power spectrum. Considering generic enhancements due to curvature modes, isocurvature modes and runnings of the spectral tilt, I will present forecasts for both Earth and lunar-based instruments of varying sizes.

Speaker: Mrs Jessie de Kruijf (University of Padova)

talk_Jessie_de_Kruijf.pdf

11:00 → 11:30 Coffee Break

11:30 → 12:00 Probing the dark sector with pulsars

Pulsars, which are very rapidly spinning neutron stars, can be instrumental in solving the puzzle, which has perplexed the minds of the scientific community for almost a century – dark matter (DM). In the talk I will mainly focus on the light DM candidates that can be searched for in pulsar observables. The ultralight scalar field DM (also known as "fuzzy" DM), consisting of bosons with extremely low masses of m ∼ $10^{−22}$ eV, solves some of the problems of the conventional cold DM hypothesis. It was shown by Khmelnitsky and Rubakov (2014) that such DM in the Milky Way induces oscillating gravitational potentials, leaving characteristic imprints in the time of arrivals of radio pulses from pulsars. In addition (Ivanov et al 2019, Castillo et al. 2022), the coupling of axion-like particles to photons alters the polarization properties of light, i.e. the plane of polarization of linearly polarized beam propagating through the axion field starts to oscillate with typical frequencies of $10^{-8}$ – $10^{-5}$ Hz. Searches for these two effects were performed in the data of the European Pulsar Timing Array (EPTA), and stringent constraints on the DM density and coupling constant between photons and axion-like particles have been set. In addition, traces of QCD axions with masses of around ~ $\mu$eV can be searched for with the spectroscopic observations of pulsars. We discuss the systematics and artifacts in pulsar data that can mimic the signal of interest and possible methods to avoid the existing biases.

Speaker: Nataliya Porayko (University of Milano Bicocca)

Undark Porayko

Undark Porayko

12:00 → 12:30 Probing WISPs with neutron stars

Stars and galaxies offer powerful laboratories in which to probe fundamental physics. We will examine axion dark matter detection via resonant conversion in neutron star magnetospheres as well as discussing stellar superradiance for various light fields. Finally, time permitting, we will explore constrains on high frequency gravitational waves above 10kHz from stellar and galactic magnetic fields.

Speaker: Dr Jamie McDonald (University of Manchester)

Tenerife_2025 2.pdf

Tenerife_2025 2.pptx

12:30 → 14:15 Lunch

14:15 → 14:45 Radio signals from solar conversion of axion and dark photon dark matter

Axions and dark photons are some of the best-motivated light dark matter candidates. In a plasma, they can undergo resonant conversion into photons, resulting in nearly monochromatic signals. In the case of the Sun, this conversion can occur in the solar atmosphere, generating a distinct signal in the radio frequency band. We focus on this solar-induced radio signal and discuss the constraints derived from current observations, as well as the sensitivity reach of upcoming experiments such as the Square Kilometre Array (SKA).

Speaker: Dr Marco Taoso (Istituto Nazionale di Fisica Nucleare, Torino, Italy)

MTaoso_Undark.pdf

14:45 → 15:15 Searching for axion decay in the radio band

Axions and axion-like particles couple to photons through a distinctive two-photon vertex, that allows them to decay into two photons. In this talk, I will show how we can search for axion dark matter by looking for excess radiation resulting from axion decay within a narrow frequency band centered around half the unknown axion mass. At radio frequencies, the decay rate is enhanced by the presence of a photon background, producing to three characteristic signatures: one collinear emission and two echos.

Speaker: Elisa Todarello (U, Nottingham)

talk_Todarello_undark.pdf

15:15 → 15:45 Molecular clouds as laboratories of new physics

The lines of vibrational transitions from different ionized molecules in dense molecular clouds provide a diagnostic of the ionization rate within cloud. The ionization of such molecular clouds is expected to be predominantly driven by low-energy cosmic rays, which are believed to trigger chemical complexity in gas systems and play a key role in regulating star formation. However, additional sources of ionizing particles — such as UV/X-ray radiation, or electrons and positrons from light dark matter — can significantly modify the ionization and thermal balance of these environments. In this talk, we explore how such non-standard injections can affect molecular clouds, discuss optimal targets and demonstrate that astrochemical observations of ionized species offer a novel probe for different scenarios of new physics.

Speaker: Pedro De la Torre Luque (Institute of theoretical physics (IFT-UAM))

UNDARK_Ioniz.pdf

15:45 → 16:15 Coffee break

20:00 → 21:30 Cocktail

At Gulagú
https://gulagu.es/

Tuesday 30 September

09:15 → 09:45 A brief review of Fast Radio Burst

Fast Radio Burst (FRB) is a recently identified phenomenon involving bright bursts in radio waves that have travelled from extragalactic distances. In the last few years, the FRB field has made tremendous progress. The total number of published FRBs has exceeded 800, of which at least 100 have been localized to a host galaxy, with examples from both younger and older stellar populations. Several dozen FRBs have been seen to repeatedly burst, and chromatic periodic activity cycles have been identified in a few sources. FRBs have been detected by tens of radio telescopes, where emission has been seen from as low as 110MHz to as high as 8GHz. While the nature of FRBs is still an open question, interesting constraints are emerging from these observational clues. In this talk, I will review the major FRB results and discuss how we might use FRB as a cosmological probe.

Speaker: Dr Cherry NG-GUIHENEUF (LPC2E/CNRS)

UNDARK2025_FRB_Cherry.pdf

09:45 → 10:15 Radio Pulsars, Transients, and the Evolving Neutron Star Landscape

Neutron stars are among the most extreme and diverse objects in the universe, offering rich insight into stellar evolution, binary formation, extreme gravity, magnetosphere and emission physics. This talk provides an overview of their observational manifestations across the electromagnetic spectrum, with a focus on radio pulsars and their role in shaping our understanding of the broader neutron star population. I will also discuss Fast Radio Bursts, highlighting what we know about their possible connection to neutron stars, and how search techniques have advanced both fields. Large-scale radio surveys have significantly expanded our view of the so-called "neutron star zoo," revealing new sub-classes and population trends. Finally, I will discuss how current and upcoming radio facilities are poised to drive the next wave of discoveries in neutron star science.

Speaker: Dr Emilie Parent (ICE)

UNDARK 2025 - IAC - Emilie Parent v2.pdf

10:15 → 10:45 Radio Searches for Axions Near Neutron Stars

Radio observations of compact objects (e.g., neutron stars and black holes) offer a powerful window into ultralight dark matter candidates like axions and dark photons. In particular, axions in the radio frequency range can be produced and converted into observable radio signals in the extreme conditions surrounding neutron stars. I will present an update on recent advances in axion searches using radio data from neutron stars and highlight some emerging ideas.

Speaker: Anirudh Prabhu (Princeton University)

UNDARK_prabhu.pdf

10:45 → 11:00 ALP Distribution in Magnetically Deformed Neutron Stars

We investigate the distribution of an interacting axion-like massive field within a magnetized Neutron Star. We consider the effect of an intense axially symmetric stellar magnetic field B(θ, ϕ) including density dependence adding another much weaker but non-vanishing electric field. We particularize the latter for the case when a finite chiral charge density is present.The axion field is thus coupled to a generic function Q(F0, G0) depending on Lorentz invariants F0, G0 which can be constructed from these electromagnetic fields. From this, the static axion field equations are solved as function of stellar radius and angular direction, a(r, θ, ϕ), using a prescribed linear form for Q. In addition, we use a semi-analytical approach to calculate the stellar structure in this hybrid system where pressure components are treated under a perturbative scheme, provided induced deformations with respect to spherical symmetry are tiny. Our results show that the axion couplings to magnetic and electric fields along with its mass critically determines the axion distribution. We discuss excluded parameter regions provided axion oscillation probability into photons in external layers may result in enhanced temperatures with respect to standard emission models. We perform a critical discussion on the constraints this poses in the current status of the axion parameter space.

Speaker: Duvier Fontanella (U. Salamanca)

Undark_D_Suarez-Fontanella.pdf

11:00 → 11:30 Coffee Break

11:30 → 12:00 The Next Generation Event Horizon Telescope

Building on the previous successes of the Event Horizon Telescope (EHT), the proposed next-generation enhancements (ngEHT) aim to produce the first detailed movies of black holes. This initiative significantly advances from the static images previously captured by employing small-diameter dishes and advanced instrumentation across new global sites, thereby increasing resolution, sensitivity, and temporal coverage. The upgrade enables time-resolved imaging to study the dynamics of luminous matter as it approaches the event horizon, providing unprecedented insights into the processes of energy extraction and jet formation in black holes. By operating across three simultaneous observing bands, the ngEHT extends tests of General Relativity with precise measurements of matter and light orbits around black holes. Additionally, it will enhance our understanding of black hole demographics and constrain black hole spin through detailed polarization studies.

Speaker: Dr Jose Luis Gómez (IAA)

ngEHT Undark IAC.key

ngEHT Undark IAC.pdf

12:00 → 12:30 Towards the measurement of spectral distortions from space

Abstract: Since COBE/FIRAS results the CMB spectrum is known to be a quasi-perfect blackbody. However, both standard and non-standard physics processes inevitably lead to spectral distortions which provide a unique opportunity to reveal a novel tracer of the early Universe, particle physics and structure formation and to probe otherwise inaccessible features. I will present some of the ongoing efforts with BISOU and FOSSIL to design and fly a future satellite in order to achieve the unprecedented leap forward in sensitivity that will allow us to detect these spectral distortions and to probe the thermal history of the Universe over time, providing us with both guaranteed science results and a rich discovery potential for new physics.

Speaker: Dr Nabila Aghanim (Orsay, IAS)

UNDARK-Sep2025.pdf

12:30 → 12:45 Jupiter Metallic Hydrogen as Dark Matter Refrigerator: Probing sub-GeV Dark Matter-Electron Theory target with the Jovian Airglow

Jupiter has long been considered a pre-eminent target for dark matter searches, due to its proximity, mass, and low astrophysical backgrounds. However, low-mass dark matter (typically lighter than 400 MeV) is expected to efficiently evaporate from the Jovian core via interactions with standard model particles. We show that in the case of leptophilic dark matter, these evaporation limits are eliminated due to the fact that electrons throughout most of Jupiter are found in a metallic state where the electrons completely fill the Fermi-Dirac particle distribution and thus cannot donate energy to evaporate the dark matter particle. Applying this effect to previous studies of dark matter-induced airglows on the Jovian surface, we show stretch dark matter limits down to the MeV-regime, hitting the theoretically motivated targets for Mev-scale leptophilic dark matter.

Speaker: Thong Nguyen (Stockholm University)

Thong_1stUNDARK.pdf

12:45 → 14:15 Lunch

14:15 → 14:45 Superradiance bounds on axions

Speaker: Samuel Witte (U. Oxford)

Tenerife_2025_pdf.pdf

14:45 → 15:15 Reassessing graviton detectability in light of high-frequency gravitational wave searches

The graviton is the long-postulated quantum counterpart of gravitational waves. It has been conjectured, based on arguments most often attributed to Freeman Dyson, that the graviton, provided it exists, could be fundamentally undetectable, and that the Universe may therefore forever hide it from us. In this talk, we’ll revisit these postulates in light of recent developments, examining the physical assumptions on which the Dyson argument rests, and exploring possible avenues for reassessing the question of graviton detectability amid the growing landscape of high-frequency gravitational wave searches.

Speaker: Dr Javier De Miguel (IAC)

jdemiguel_Undark_20250930.pdf

15:15 → 15:45 Radiotelescopes as probes of high-frequency GWs

This talk will explore the conversion of gravitational waves into photons in the presence of cosmic magnetic fields, a process that offers a novel window into the gravitational universe at radio frequencies. Such conversions naturally lead to distortions in the cosmic microwave background, which can serve as an indirect probe of gravitational waves from early universe, particularly before the epoch of reionization. I will discuss how this mechanism provides a unique approach to constraining gravitational waves in the megahertz to gigahertz frequency range—well beyond the reach of current direct detection methods.

Speaker: Dr Camilo Alfredo García-Cely (IFIC)

GarciaCelyTenerife.pdf

15:45 → 16:15 Coffee Break

18:30 → 19:30 Outreach talk (in Spanish): El fondo cósmico de microondas: desvelando el origen del Universo.

Convener: Jose Alberto Rubiño

Wednesday 1 October

09:00 → 17:00 Full day excursion to the Teide National Park

Meeting point: Bus stop behind Nivaria Hotel at 9:00
https://maps.app.goo.gl/K9T7DFg8xVPRnise6

Thursday 2 October

09:15 → 09:45 The Radio Synchrotron Background – Status and Prospects

The background brightness level of diffuse radio emission on the sky and its level of anisotropy are seemingly significantly higher than those which can result from known classes of astrophysical radio sources. In contrast to the more well-known photon backgrounds at microwave, infrared, optical/UV, X-ray, and gamma-ray wavelengths, where the levels of brightness and anisotropy at least roughly match those expected from known cosmological and astrophysical sources, the "radio synchrotron background" at radio wavelengths provides clear motivation for considering new sources and new particle-based emission mechanisms, including those from the dark sector. This talk will summarize the current understanding of the radio synchrotron background and some of the proposed particle-based emission mechanisms.

Speaker: Prof. Jack Singal (University of Richmond)

UNDARK - Singal - Radio Background.pptx

09:45 → 10:15 The Tenerife Microwave Spectrometer (TMS): absolute spectral measurements in the 10–20GHz range

The Tenerife Microwave Spectrometer (TMS) is a new absolute spectrometer operating in the 10–20 GHz range, to be installed at the Teide Observatory (Tenerife, Spain), next to the QUIJOTE (Q-U-I JOint TEnerife) experiment. Its main scientific goal is to accurately measure absolute spectral distortions of the sky spectrum in this frequency range, with particular emphasis on characterizing the absolute synchrotron monopole from our Galaxy and detecting possible deviations of the CMB spectrum from a pure blackbody law. TMS will also provide absolute calibration for the QUIJOTE experiment. In the first part of the talk, we will review the status and scientific objectives of TMS, focusing on the characterization of the radio synchrotron background and its potential connections to fundamental physics. In the second part, we will present specific developments for TMS, including some aspects of the instrument's thermal model and a detailed characterization of the radiometric chain, aimed at predicting the systematic effects that may impact the final measurements.

Speakers: Jose Alberto Rubiño, Ms Ángela Arriero (IAC)

TMS-UNDARK-Sept2025_2.pdf

10:15 → 10:45 Testing the instability of the cosmic nu background

I will discuss how new cosmological observations are able to test the instability of the neutrino background in new regions of the parameter space, in particular longer lifetimes. Specifically, I will consider three phenomenological tools: the cosmological upper bound on neutrino masses, 21cm cosmology and excess radio background. In the latter case I will present new results on how the ARCADE 2 data can be explained by decaying relic neutrinos, including a model that can realise this solution in agreement with all other constraints. I will point out the importance of coming TMS measurements to test such a solution likely in a unambiguous way.

Speaker: Pasquale Di Bari (U. Southampton)

PDB4UNDARK.pdf

10:45 → 11:00 Search for dark sectors using radio galaxies through cosmic birefringence

Several papers have recently reported 'cosmic birefringence', the rotation of polarization planes of photons, from Cosmic Microwave Background (CMB) polarization (e.g. Minami & Komatsu, 2020). Since this phenomenon violates parity symmetry, this signal, if confirmed, strongly suggests new physics beyond the standard framework of physics. Axion-like particles (ALP) is a plausible candidate of the origin of cosmic birefringence and can also behave as dark sectors (e.g. Fujita et al. 2021). However, recent observations of cosmic birefringence using CMB alone still have a concern of systematical errors and a difficulty of tomographic measurements. In this talk, I propose a method for independent tests for cosmic birefringence (Naokawa, 2025) using radio galaxies inspired by pioneering works in the 1990 (e.g. Carroll et al., 1990). With an ongoing and forthcoming radio surveys such as SKA, we might be able to confirm the reported signal not relying on CMB.

Speaker: Mr Fumihiro Naokawa (University of Tokyo)

251002_UNDARK.pdf

11:00 → 11:30 Coffee break

11:30 → 12:00 Radio signatures of fundamental physics

Speaker: Dr Bryce Cyr (MIT)

UNDARKFundament_Cyr.pdf

12:00 → 12:30 Status of the LiteBIRD mission to explore cosmic inflation

LiteBIRD is a next-generation cosmic microwave background (CMB) probe currently under development by an international team led by JAXA. The probe is scheduled for launch in the mid-2030s and will be positioned at the Sun-Earth L2 point, and conduct a three-year all-sky survey observation at frequencies ranging from 34 GHz to 448 GHz. The observational results from LiteBIRD will provide the most sensitive all-sky polarization maps in these frequency bands, with the primary objective of measuring the tensor-to-scalar ratio “r” with unprecedented sensitivity. This will allow LiteBIRD to probe and rule out well-motivated inflationary models. At this conference, we will report on the latest progress of LiteBIRD.

Speaker: Prof. Ken Ebisawa (JAXA/ISAS)

20251002TenerifeV3.pdf

20251002TenerifeV3.pptx

12:30 → 12:45 The GroundBIRD experiment: status and perspectives

The GroundBIRD telescope is a cosmic microwave background (CMB) experiment located at the Teide Observatory in Tenerife (~2400 m asl), Spain. It is designed to observe the intensity and polarization anisotropy of the CMB at large angular scales (ℓ>6, up to ℓ~300), with the main scientific objective of accurately measuring the optical depth (τ) to the Universe’s reionization epoch. While small-scale CMB observations are sensitive to the sum of neutrino masses (Σmν), this measurement is degenerate with τ, which characterizes the damping of CMB anisotropies caused by scattering off free electrons along the line of sight. Consequently, uncertainties in τ directly influence the precision of Σmν constraints. Therefore, a precise measurement of τ is crucial for effectively limiting the total neutrino mass. The experiment aims to measure CMB polarization using a rapidly rotating telescope (up to 20 rpm) fixed at 70-deg elevation, enabling it to cover ~40% of the sky daily from the Northern Hemisphere. It employs 161 lenslet-coupled kinetic inductance detectors (KIDs) - 138 at 145 GHz for CMB peak detection, 23 at 220 GHz for dust mitigation - installed on a ~250 mK cryogenic stage. While laboratory tests confirmed stable detector performance, on-site observations indicated responsivity variations due to atmospheric radiation (PWV ~0.4 mm/hour) and focal plane temperature drifts (~2 mK/hour). This work examines how these environmental factors affect KID responsivity, using PWV-based modeling and comparisons with observational data. Finally, we present the current status and perspectives of the GroundBIRD experiment.

Speaker: Dr Alessandro Fasano (IAC)

2025_10_02_GB_fasano.pdf

12:45 → 14:15 Lunch

14:15 → 14:45 On the extra-galactic signal present in QUIJOTE intensity maps

We combine the different frequency intensity maps built by the QUIJOTE collaboration in an attempt to isolate the Galactic dominant emission and constrain the extragalactic signal. For this purpose we apply a novel technique that identifies, region by region, the frequency scaling of the dominant emission and corrects for it, leaving a map of weak signals, subtraction residuals, and instrumental noise. When applying this approach on the 11 and 13 GHz QUIJOTE data and cross-correlating the resulting maps with extra-galactic surveys, we find evidence (at the 2-3 $\sigma$ level) of common signal with the NVSS radio survey, the WISE galaxy survey, and the Planck lensing convergence map. We apply exactly the same algorithm on WMAP 23 and 33 GHz intensity maps, finding extremely similar results. A detailed analysis of this cross-correlation hints a bright, radio source populated at z~3.5, presumably composed by Active Galactic Nucleii (AGN), whose contribution to the ARCADE excess at ~3-5 GHz is significant, although it depends on the effective bias of the radio-population, and its effective radio spectral index. Last, but not least, using QUIJOTE 11 and 13 GHz maps we set the first constraints on the CO J 1->0 emission during the end of Reionization (z~8), discarding correlated CO intensities at the level of 10^3 bias_{CO} \muK.

Speaker: Dr Carlos Hernández-Monteagudo (IAC)

QUIJOTE_Iextra_CHM.pdf

14:45 → 15:15 Dark Matter signatures in the radio domain

Speaker: Elena Pinetti (CCA - Flatiron Institute)

15:15 → 15:45 Searching for Dark Matter with MISTRAL at the SRT

MISTRAL (Millimeter Sardinia Telescope Receiver based on Array of Lumped-element KIDs) is a state-of-the-art camera equipped with 415 Kinetic Inductance Detectors (KIDs), operating at the focal plane of the 64-meter Sardinia Radio Telescope (SRT). Designed for observations in the millimeter band, MISTRAL observes the sky at a central frequency of 90 GHz (3.3 mm wavelength), achieving an angular resolution of 12 arcseconds across a 4 arcminute field of view. The instrument’s high sensitivity enables detailed studies of the inverse Compton scattering of Cosmic Microwave Background (CMB) photons by hot electrons residing in the intracluster medium (ICM) of galaxy clusters (the Sunyaev-Zel’dovich effect) and their surrounding environments. This capability allows MISTRAL to probe the thermal and dynamical properties of both relaxed and merging (unrelaxed) galaxy clusters, providing insights into their formation and evolution. Additionally, MISTRAL’s fine angular resolution makes it a powerful tool for mapping the distribution of baryonic matter in the Universe, including the elusive baryonic dark matter that may reside in the filamentary structures of the cosmic web—the large-scale network of gas and dark matter connecting galaxy clusters. By detecting these faint signals, MISTRAL contributes to our understanding of missing baryons, a key unresolved question in modern astrophysics.

Speaker: Dr Elia Battistelli (Sapienza University of Rome)

Tenerife_2025.pdf

Tenerife_2025.pptx

15:45 → 16:15 Coffee Break

19:30 → 22:30 Conference dinner

At Meson el Drago
https://www.dragogamonal.com/
Meeting point: Bus stop behind Nivaria Hotel at 19:30
https://maps.app.goo.gl/K9T7DFg8xVPRnise6

Friday 3 October

09:15 → 09:45 Cosmology with SKAO

I will review the updated science cases from the SKA Cosmology science working group.

Speaker: Dr Anna Bonaldi (SKAO)

UNDARK_Bonaldi.pdf

UNDARK_Bonaldi.pptx

09:45 → 10:15 Non cold DM imprint on 21cm Cosmology

In my talk I will describe the imprint of Non cold dark matter scenarios on the redshifted 21cm signal arising from cosmic dawn and epoch of reionization. I will in particular focus on the 21cm power spectrum characterizing the variance in perturbations of the early universe intergalactic medium and prospects of sensitivity by radio telescope arrays such as HERA. The Non-cold dark matter properties will be defined by the DM free-streaming properties, as in the case of the vanilla thermal warm dark matter, or collisional damping, as in the case of dark matter interacting with neutrinos. I will in particular clarify under which conditions 21cm Cosmology might improve on existing non-cold dark matter probes and if it might be able to distinguish between different type of non-cold candidates.

Speaker: Laura LOPEZ HONOREZ (Universite Libre de Bruxelles)

25-UNDARK-Workshop-LLH.pdf

10:15 → 10:45 Not-quite-primordial black holes

In this talk, I will discuss a new mechanism for the formation of seeds of supermassive black holes at early cosmic epochs. Enhanced density fluctuations with amplitudes that are not large enough to form primordial black holes post-inflation can still lead to collapsed dark matter halos at very early times. For halos forming prior to 1+z ~ 200, the Cosmic Microwave Background (CMB) is energetic enough to suppress the formation of molecular hydrogen, hence preventing cooling and fragmentation, as a consequence of which baryons falling into the potential well of the halo may undergo “direct collapse" into a black hole. I will show using a few illustrative models how this mechanism may account for the abundance of high-redshift black holes inferred from observations by the James Webb Space Telescope while remaining consistent with current limits from CMB spectral distortions. Limits on the primordial power spectrum are also derived by requiring that the universe not reionize too early.

Speaker: Dr Wenzer Qin (NYU)

2025-09-30 UNDARK.pdf

2025-09-30 UNDARK.pptx

10:45 → 11:00 Are low-frequency radio telescopes sensitive to light dark matter?

Speaker: Mr Ruben Zatini (Instituto de Astrofísica de Canarias)

Presentation_UNDARK_WS1.pdf

11:00 → 11:30 Coffee Break

11:30 → 12:00 ALMA and its role in the search of dark matter

The Atacama Large Millimeter/submillimeter Array (ALMA) has emerged as a powerful instrument in the search for dark matter, offering unique insights through gravitational lensing and searches for exotic dark matter candidates such as axions, among other things. In this presentation, I will review recent advances and ongoing challenges in the use of ALMA for dark matter studies. I will discuss the status and prospects of such searches also in view of ALMA’s ongoing Wideband Sensitivity Upgrade, alongside complementary approaches using future radio facilities such as the Atacama Large Aperture Submillimeter Telescope (AtLAST).

Speaker: Dr Evanthia Hatziminaoglou (ESO)

UndarkTenerife031025.pdf

UndarkTenerife031025.pptx

12:00 → 12:30 SMILE (Search for MIli-LEnses) to unravel the dark

Several methods are employed in projects seeking to understand the elusive nature of dark matter (DM). The approach used by the Search for MIlli-LEnses (SMILE) — https://smilescience.info/ —project makes use of strong gravitational lens systems in the milliarcsecond regime, where the lens is a compact object with mass between ~ 10^6 and 10^9 solar masses. This mass range is crucial for the widely accepted ΛCDM cosmological model, which predicts the existence of many more DM sub-galactic halos ( < 10^11 solar masses) than the currently observed number. To explore such small angular scales, high-resolution radio VLBI data are used. Searching for milli-lenses in a catalog of ~ 5000 radio loud active galaxies will allow us to detect lenses in this mass range, or, failing that, to tighten significantly our constraints on the number of sub-galactic halos and consequently discard some viable DM models.

Speaker: Dr Carolina Casadio (Institute of Astrophysics - FORTH)

Casadio_UNDARK_2025.pdf

12:30 → 12:35 Farewell

1stUNDARKwrkshp 2.pdf

12:35 → 14:20 Lunch