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Phenomenology of Dark Matter in Neutron Stars and compact objects

• Giorgio Busoni (Adelaide University)

It is well-established that Dark Matter can be captured and accumulate in celestial objects. While this phenomenon has been extensively studied for the Sun and Earth, recent interest has shifted towards compact objects such as White Dwarfs and Neutron Stars. In this talk, I will make a review of the most recent studies on limits and constraints on Dark Matter arising from their interaction with compact objects like Neutron Stars and White Dwarfs. I will review the most recent and up-to-date formalism to compute the Dark Matter interaction and Capture Rates in such objects, outlining the important differences with the formalism used and the effects considered compared to non-compact objects. I will then move to discuss two recent results related to these objects. For Neutron Stars, we consider Dark Matter candidates that are capable of annihilation. The capture of Dark Matter and its subsequent annihilation can lead to the heating of old, isolated Neutron Stars. For kinetic heating to occur, the captured Dark Matter must undergo sufficient scattering to transfer its kinetic energy to the star. Our findings show that this energy transfer typically happens rapidly, and that capture-annihilation equilibrium — and hence maximal annihilation heating — can be reached without the complete thermalization of the captured Dark Matter. For White Dwarfs, we explore a scenario where the Dark Matter is very heavy and cannot annihilate. In the heavy Dark Matter regime, multiple collisions are required for the Dark Matter to become gravitationally bound. We present an improved approach to calculate the scattering rates for these collisions, particularly when the Dark Matter interacts with the ion constituents of a White Dwarf.

How I learned to worry about the white dwarf bomb

• Melissa Diamond

Dark matter can trigger runaway fusion in white dwarfs leading to Type IA supernovae. In this talk I will explore how this has been used to place constraints on different dark matter models. I will show how uncertainty in the composition of white dwarfs can weaken these constraints by several orders of magnitude

The neutron lifetime anomaly, dark baryons, and their impact on neutron star mergers

• Steven Harris (Indiana University)

One motivation for the existence of a dark sector is the neutron lifetime anomaly, where two different measurements of the neutron lifetime give different results. This discrepancy can be resolved if the neutron is allowed to decay to a dark baryon and a light scalar. If these particles exist, they could modify the equation of state of dense matter and affect the beta equilibration of neutron stars. I will discuss the bulk viscosity of dense matter containing a population of dark baryons and its possible impacts on neutron star merger dynamics.

The Impact of Dark Matter on the Dynamics of Binary Neutron Star Mergers

• Violetta Sagun (University of Southampton)

Binary neutron star mergers provide insights into strong-field gravity and the properties of ultra-dense nuclear matter. These events offer the potential to search for signatures of physics beyond the standard model, including dark matter. We present the first numerical-relativity simulations of binary neutron star mergers admixed with dark matter, based on constraint-solved initial data. Modeling dark matter as a non-interacting fermionic gas, we investigate the impact of varying dark matter fractions and particle masses on the merger dynamics, ejecta mass, post-merger remnant properties, and the emitted gravitational waves. Our simulations suggest that the dark matter morphology - a dense core or a diluted halo - may alter the merger outcome. Scenarios with a dark matter core tend to exhibit a higher probability of prompt collapse, while those with a dark matter halo develop a common envelope, embedding the whole binary. Furthermore, gravitational wave signals from mergers with dark matter halo configurations exhibit significant deviations from standard models when the tidal deformability is calculated in a two-fluid framework, neglecting the dilute and extended nature of the halo. This highlights the need for refined models in calculating the tidal deformability when considering mergers with extended dark matter structures. These initial results provide a basis for further exploration of dark matter's role in binary neutron star mergers and their associated gravitational wave emission and can serve as a benchmark for future observations from advanced detectors and multi-messenger astrophysics.

Neutron Stars with Dark Matter Halos

• Shafayat Shawqi (University of Alberta)

The high densities of neutron stars (NSs) could provide astrophysical locations for dark matter (DM) to accumulate. Depending on the DM model, these DM admixed NSs (DANSs) could have significantly different properties than pure baryonic NSs, accessible through X-ray observations of rotation-powered pulsars. We adopt the two-fluid formalism in general relativity to numerically simulate stable configurations of DANSs, assuming a fermionic equation of state (EOS) for the DM with repulsive self-interaction. The distribution of DM in the DANS as a halo affects the path of X-rays emitted from hot spots on the visible baryonic surface causing notable changes in the pulse profile observed by telescopes such as NICER, compared to pure baryonic NSs. We explore how various DM models affect the DM mass distribution, leading to different types of dark halos. We quantify the deviation in observed X-ray flux from stars with each of these halos. We identify the pitfalls in interpreting mass and radius measurements of NSs inferred from electromagnetic radiation and constraining the baryonic matter EOS, if these dark halos exist.

Can local compact stars constrain Dark Matter interactions?

• Sandra Robles (Fermilab)

Exotic Low-Mass Black Holes: Fantastic Beasts and How to Find Them

• Basudeb Dasgupta

Black holes are products of standard stellar evolution, that can be no lighter than about 2.5 times the mass of our Sun. Some dark matter theories predict the possibility of exotic low-mass black holes, formed by the dark-matter-induced collapse of neutron stars. These exotic objects, unfortunately, are very similar to neutron stars in most respects and it is hard to distinguish the two. We show how low-mass black holes may be distinguished from neutron stars.

Echoes of Axion Dark Matter and Axion Stars

• Yitian Sun

Axion echoes occur when axions undergo stimulated decay due to background radio fluxes, producing decay photons traveling in nearly the opposite direction of the stimulating rays. In our galaxy, bright radio sources such as supernova remnants and synchrotron radiation can induce echoes from diffuse axion dark matter, which enables various types of radio telescopes to search in competitive axion parameter space by looking for the echo image of both point-like and extended sources. In this talk, I will explain the geometry of axion echoes and the observation strategies we employ to probe axion dark matter. I will also discuss recent work on observing echoes of solar radio emissions from axion stars.

Boosted dark matter driven by cosmic rays and diffuse supernova neutrinos

• Tushar Gupta

Direct detection of light dark matter can be significantly enhanced by upscattering of dark matter with energetic particles in the cosmic ambient. This boosted dark matter flux can reach kinetic energies up to tens of MeV, while the typical kinetic energies of GeV mass dark matter particles in the Milky Way halo are of the order of keV. Dark matter boosted by energetic diffuse supernova background neutrinos can be detected only through nuclear or electron scattering in ground-based detectors requiring a nonzero interaction of dark matter with nucleon or electron, in addition to its interaction with neutrino. However, in the presence of dark matter-nucleon (electron) interaction, the scattering of dark matter with cosmic rays is unavoidable. Thus, we consider boosted dark matter resulting from diffuse supernova neutrinos as well as cosmic protons (electrons) considering both energy-dependent and energy-independent scattering cross sections between dark matter and standard model particles. We explore this scenario in dark matter detectors such as XENONnT and neutrino detectors like Super-Kamiokande.

Modified Axion and Dark Photon Emission from Magnetic Dispersion

• Nirmalya Brahma (McGill University)

Some of the strongest constraints on axions and dark photons (DPs) come from their emission in astrophysical plasmas. However, many of these studies assume isotropic plasma conditions, which are rarely realized in realistic environments due to the ubiquitous presence of magnetic fields. In magnetized plasmas, the standard transverse and longitudinal photon polarization modes become mixed, leading to new propagation eigenmodes. In this talk, I will present a general formalism to determine these modified normal modes and their couplings to axions and DPs in anisotropic magnetized media. Using magnetic white dwarfs (MWDs) as a case study, I will demonstrate how magnetic dispersion modifies the resonance structure and leads to strongly directional emission, extending or reshaping the regions where resonant production can occur inside the star.

Thermal effects on dark matter particle production

• Hugo Schérer (McGill University)

Particles properties in an ambient medium are very different from those in vacuum. Their masses and lifetimes change, and new processes even become possible. For example, in the Standard Model, photons in a plasma (plasmons) acquire an effective mass and can decay into neutrinos, a process forbidden in vacuum. These kinds of thermal effects are especially relevant for dark matter phenomenology, since dark matter production always happens inside a medium of particles, or even from this medium. Examples of these environments include the inside of stars. Yet, many calculations of dark matter production still rely on a vacuum-based treatment, and miss key in-medium effects. In this talk, I will present a systematic formalism to quantify the thermal corrections to particle dynamics. Using this approach, I will demonstrate how qualitatively new amplitudes that have no vacuum analog arise in a medium, and how such amplitudes can impact dark matter production. I will show how these effects can alter dark matter predictions, and why they are essential for accurate dark matter phenomenology.

Dark neutron star formation in a heavy mirror dark sector

• Jacob Litterer (University of Porto)

I will discuss dark matter neutron stars in a class of models where the dark sector is a copy of the Minimal Supersymmetric Standard Model, but with the important difference that the dark supersymmetry-breaking scale is much higher than in the visible sector. This scenario allows the dark quark mass hierarchy to be different from the visible sector, resulting in a stable dark neutron which can play the role of cold dark matter on large scales at late times, while dark dissipative cooling allows additional early collapse of overdensities on small scales. At late times these become either small black holes or dark neutron stars. There are possibilities for detection of a visible luminosity due to kinetic mixing between the dark and visible photons, in addition to gravitational microlensing.

Immortal Stars at the Galactic Center

• Isabelle John

Dark matter can be captured in stars and annihilate, providing the star with a new energy source in addition to nuclear fusion. This significantly changes stellar evolution at the Galactic Center, where the dark matter density is extremely high. As dark matter burning replaces nuclear fusion partially or completely, stars become longer-lived, as they use up hydrogen more conservatively, or even become immortal, as dark matter is re-supplied continuously. We show that this results in several prominent features that distinguish stellar populations in dark matter dense environments from populations without dark matter. This may offer an explanation for the unusual age and mass distribution of stars at the Galactic Center. In some scenarios, the dark matter annihilation power can become so intense to disrupt star formation entirely, allowing us to derive constraints on dark matter-nucleon cross sections and density profiles based on stellar observations close to the Galactic Center.

Milky Way White Dwarfs as Sub-GeV to Multi-TeV Dark Matter Detectors

• Lillian Santos-Olmsted

We show that Milky Way white dwarfs are excellent targets for dark matter (DM) detection. Using Fermi and H.E.S.S. Galactic center gamma-ray data, we investigate sensitivity to DM annihilating within white dwarfs into long-lived or boosted mediators and producing detectable gamma rays. Depending on the Galactic DM distribution, we set new constraints on the spin-independent scattering cross section down to 10^-45 − 10^-41 cm2 in the sub-GeV DM mass range, which is multiple orders of magnitude stronger than existing limits. For a generalized NFW DM profile, we find that our white dwarf constraints exceed spin-independent direct detection limits across most of the sub-GeV to multi-TeV DM mass range, achieving sensitivities as low as about 10^-46 cm2. In addition, we improve earlier versions of the DM capture calculation in white dwarfs, by including the low-temperature distribution of nuclei when the white dwarf approaches crystallization. This yields smaller capture rates than previously calculated by a factor of a few up to two orders of magnitude, depending on white dwarf size and the astrophysical system.

Probing Dark Matter in Red Giants

• Seokhoon Yun (IBS-CTPU)

Red giants (RGs) offer a relevant astrophysical laboratory to explore the interaction between dark matter (DM) and ordinary matter. Once captured, DM particles accumulate and thermalize near the center of the helium-rich core. As their number increases, the DM population can become self-gravitating and undergo gravitational collapse. This process leads to a localized release of energy through interactions with the helium-rich environment, potentially inducing premature helium ignition via the triple-alpha process. In this talk, I will discuss the heating mechanism driven by collapsing DM and the conditions under which it leads to runaway helium ignition. By estimating the critical DM mass required for this transition, we derive constraints on DM properties based on the observational fact that RGs do not ignite helium too early. Remarkably, this allows RGs to probe DM masses around $10^{12}$–$10^{13}\,\mathrm{GeV}$, with sensitivity comparable to or exceeding that of current direct detection experiments.

Impact of Different Prescriptions of Dark Matter Transport on Stellar Evolution

• Diogo Manuel Ribeiro dos Santos Ferreira Capelo

This work presents preliminary findings from an ongoing investigation into the evolutionary ramifications of diverse Dark Matter (DM) transport mechanisms within stellar interiors. Particular emphasis is placed on the transport prescription proposed by Banks et al. (2022, 2024), derived from realistic simulations of the Boltzmann collision equation. This methodology has been integrated into a bespoke computational framework that self-consistently models DM accretion and its resultant stellar impacts in conjunction with the MESA stellar evolution code. Comparative simulations, tracking stellar evolution up to the Tip of the Red Giant Branch (TRGB), are utilized to elucidate and quantify the differential effects of various DM transport models on stellar evolutionary pathways.

Dark Stars, a possible solution to two recent astronomical puzzles

• Cosmin Ilie (Colgate University)

Launched at the end of 2021, the James Webb Space Telescope (JWST) has already begun to revolutionize our view of the cosmic dawn era. Specifically, it discovered an unexpectedly large number of extremely bright objects in the sky from the early Universe, whose light was emitted more than thirteen billion years ago. If these objects are interpreted as some of the first galaxies ever assembled, their discovery would be in stark contrast with the expectation set by numerical simulations, which predicted such bright galaxies to have formed significantly later. For this reason, those JWST objects are sometimes mistakenly called "cosmology breakers." In fact, in view of HST data, which highly disfavors a cosmological solution to this problem, it would be more appropriate to call them "astrophysics benders." Taken at face value, the JWST data implies that the first galaxies were incredibly efficient in converting of gas to stars. In addition, a combination of IR and X-ray data data further strengthen another problem in astrophysics: the origin of the supermassive black holes that power the large number of very bright quasars observed when the Universe was younger than 900 Myrs. Combined, those two problems indicate that the current understanding of the formation of the first stars and galaxies is, at best, incomplete. This "understanding" is largely based on theoretical and numerical models that ignore the role Dark Matter can play on the formation of the first stars. However, in 2008 Spolyar, Freese, and Gondolo [Phys. Rev. Lett. 100, 051101] have shown that the heat due to the annihilation of Weakly Interactive Massive Particles (WIMPs) at the center of high redshift Dark Matter halos can halt the collapse of zero metallicity protostellar gas clouds. In other words, a new kind of star can form, powered exclusively by Dark Matter annihilations. In view of their power source, those objects are called Dark Stars, although, they can be as bright as a galaxy and grow as massive as a million Suns. In this talk I will review the theoretical and observational status of Dark Stars and show how they can be natural solutions to both of the puzzles described above. Specifically, I will demonstrate how Dark Stars can provide natural massive Black Hole seeds needed to explain the most distant quasars ever observed, such as UHZ1. I will also discuss the three Supermassive Dark Star candidates already identified with JWST (JADES-GS-z-13, JADES-GS-z12, and JADES-GS-z-11) [Ilie et al. PNAS 120 (30)]. Moreover, I will present updated results in view of recently available NIRSpec data. For instance, we find that the most distant object ever observed JADES-GS-z14-0 could be a Supermassive Dark Star that powers an ionization bound nebula. Lastly, I end with an analysis of the prospects for spectroscopic confirmation of Dark Stars. The unambiguous detection of any such object, via any of its spectroscopic smoking gun signatures (such as the HeII1640 absorption, of which hints exist in the JADES-GS-z14-0 NIRSpec spectra) would imply the first non-gravitational confirmation of the existence of Dark Matter.

Probing dark matter annihilation through planetary airglow and internal heat flow

• Marianne Moore (MIT)

The annihilation of accumulated dark matter within planetary bodies could lead to observable signatures in the form of anomalous UV airglow and excess internal heat flow. We use existing UV and IR spectral data obtained by spaceprobe flybys of Solar System planets to constrain such effects. We consider dark matter annihilating through both short- and long-lived mediators and account for the spatial distribution of dark matter within planetary interiors. Our results highlight planetary spectroscopy as a complementary approach for probing dark matter properties.

The Sun, White Dwarfs and Black Holes as WIMP detectors

• Stefano Scopel (Sogang University)

The WIMP indirect detection signal is enhanced by the square of the WIMP density, and celestial bodies can catalyze WIMP annihilation by accumulating WIMPs with their gravitational potential. In particular, WIMP annihilation can induce a GeV neutrino signal from the Sun, the increase of the total luminosity of White Dwarfs in nearby Globular Clusters, or a sizeable radio emission from the Dark Matter cusp in the Black Hole of low--mass X--ray binaries. I will discuss how such signals can be complementary to direct detection to probe the WIMP thermal decoupling scenario and, in particular, they allow to obtain bounds that do not depend on the WIMP velocity distribution.

Probing a local dark matter halo with neutrino oscillations

• Andrey Shkerin

Dark matter particles can form halos gravitationally bound to massive astrophysical objects. The Earth could have such a halo where depending on the particle mass, the halo either extends beyond the surface or is confined to the Earth's interior. We consider the possibility that if dark matter particles are coupled to neutrinos, then neutrino oscillations can be used to probe the Earth's dark matter halo. In particular, atmospheric neutrinos traversing the Earth can be sensitive to a small size, interior halo, inaccessible by other means. Depending on the halo mass and neutrino energy, constraints on the dark matter-neutrino couplings are obtained from the halo corrections to the neutrino oscillations.

Illuminating Very Heavy Dark Matter in the Earth with Tau Neutrinos

• Qinrui Liu (Queen's University)

Dark matter accumulates inside Earth as the planet plows through the dark matter halo in the Milky Way. Possible annihilation of dark matter to Standard Model particles can be probed in indirect dark matter searches. Among the messengers, neutrinos are uniquely ideal as they can escape dense regions. Neutrino telescopes offer opportunities to search for dark matter signals from the Earth. Such studies have been restricted to dark matter masses below PeV as the Earth becomes opaque to very-high-energy neutrinos. However, the tau regeneration effect enables very-high-energy tau neutrinos to traverse the Earth and regenerate at lower energies, resulting in a detectable signal. In this talk, I will discuss utilizing neutrino telescopes operating at TeV-PeV energies to probe very heavy dark matter and present upper limits on the spin-independent dark matter–nucleon cross section derived from IceCube public data.

Reconstructing PTA measurements via early seeding of supermassive black holes

• Sohan Ghodla (Colgate University)

Recent observations of high redshift supermassive black holes (SMBHs) challenge their conventional formation pathways. Studies further suggest that SMBH binaries with total masses $\gtrsim 10^9 M_\odot$ could be the primary sources of the nanohertz gravitational-wave background detected by Pulsar Timing Arrays (PTAs). Owing to their extreme masses, these binaries are likelier to have assembled earlier than their lower-mass counterparts and may descend from the first SMBHs revealed by the James Webb Space Telescope. In this work, we explore a scenario in which a fraction of present-day SMBHs were seeded by the collapse of supermassive dark (matter powered) stars (SMDs) at redshifts $z\approx10$–30. We demonstrate that SMD-seeded SMBHs, with comoving seed number density of $\mathcal{O}(10^{-3}) \, {\rm Mpc}^{-3}$, can be the dominant contributor to the PTA signal, with $m > 10^9$ binaries acquiring a peak merger rate at $z< 1$. By contrast, we show that SMBHs seeded via the popular direct-collapse channel contribute only sub-dominantly.

Picolensing as a probe of compact dark matter

• Sergey Sibiryakov (McMaster U. & Perimeter Inst.)

The gravitational lensing parallax of gamma-ray bursts (GRB), also known as picolensing, is a promising probe of compact dark matter, such as primordial black holes (PBH). A future space mission consisting of two X-ray/gamma-ray detectors in the Swift/BAT class can probe PBHs in the asteroid-mass window — a range of masses that has been notoriously hard to constrain by any other means. I will discuss the robustness of the projected reach of such mission with respect to the astrophysical uncertainties, most important being the uncertainty in observed GRB angular sizes. I will show that a setup with the separation between the two detectors on the order of the Earth–L2 distance makes such a mission robust. Baselines on the order of an astronomical unit further extend the reach to higher masses with the sensitivity competitive or exceeding the existing microlensing constraints. Implications of these results to other types of compact dark matter will be briefly discussed.

Mapping out the Dark Matter in the Milky Way with Stars

• Lina Necib (MIT)

In this talk, I will explore the interfacing of simulations, observations, and machine learning techniques to construct a detailed map of Dark Matter in the Milky Way, focusing on the Galactic Center/Halo and dwarf galaxies. For the Galactic Halo, I will present a recent work that reveals a decline in the stellar circular velocity, inducing tensions with established estimates of the Milky Way's mass and Dark Matter content. I will discuss how the underestimated systematic errors in such a common methodology necessitates a revised approach that combines theory, observations, and machine learning. In dwarf galaxies, I will present a novel Graph Neural Network methodology that facilitates the accurate extraction of Dark Matter density profiles, validated against realistic simulations. I will conclude with a discussion on the future trajectory of astroparticle physics, emphasizing the need for the integration of astrophysical probes, particularly those of stellar dynamics, with our understanding of Dark Matter in the Galaxy and its connection with Dark Matter detection experiments.

Testing the Robustness of Via Machinae Stellar Stream Candidates

• Rafael Porto

We build upon the results of the Via Machinae algorithm for stellar stream-finding in *Gaia* data, employing new tests to identify the stream candidates most likely to represent real stellar streams. We measure the consistency with which candidates are discovered across multiple retrainings of the Via Machinae neural density estimators, and we find that classifying candidates based on this metric reduces the expected rate of false positive discoveries by a factor of roughly 2 while increasing the number of stream candidates classified as real by more than 20%. As an independent test, we apply an automated orbit-fitting algorithm to determine whether each candidate lies along a physical orbit integrated in a model of the Milky Way gravitational potential. We present a list of candidates that pass both these tests and merit follow-up observations, some of which are to our knowledge previously unknown.

Angular-Velocity Offsets in Galactic Rotation Curves: A New Clue to Dark Matter-Baryonic Coupling

• Tomer Zimmerman (Ariel University)

Understanding the distribution of dark-matter halos in galaxies is crucial for testing ΛCDM and alternative theories of gravity. In this talk I will present a phenomenological pattern, found in the rotational data of disk galaxies, which may point to an underlying property of dark-halo distributions. The pattern is revealed by re-expressing rotation curves in terms of angular velocities. We find that in a large sample of 143 high-quality rotation curves, the difference between observed and baryon-predicted angular velocities is well-described by a constant shift. This constant angular-velocity offset provides a surprisingly effective fit, outperforming traditional dark-halo models. Incorporating this constant-offset feature into the dynamical equations yields a single-parameter dark-halo profile explicitly and intrinsically linked to the baryonic distribution. This result suggests a deeper coupling between baryonic and dark matter components, offering a new empirical avenue to explore the nature of dark matter. Our findings may point toward a universal regularity in disk galaxies' rotation, with implications for both dark matter phenomenology and alternative theories of gravity.

Lyman-alpha Constraints on Atomic Dark Matter from N-body Simulations

• Linda Yuan

Atomic dark matter (ADM) models, with a minimal content of a dark proton, dark electron, and a massless dark photon, are motivated by theories such as Mirror Twin Higgs. ADM models might address the seeming tension between cold dark matter (CDM) and observations at small scales: excessive number of dwarf galaxies in the Milky Way, and the cuspiness of galactic cores. ADM has been shown to suppress matter perturbations on small scales. N-body simulations with percent ADM subcomponent predict interesting sub-galactic structures. We use similar N-body simulations and Lyman-alpha forest data, which is sensitive to small-scale ADM effects, to produce robust constraints on ADM parameter space. We use machine learning methods to optimize computational efficiency when scanning over the parameter space.

The SABRE South Experiment at the Stawell Underground Physics Laboratory

• Yi Yi Zhong

SABRE is an international collaboration that will operate similar particle de- tectors in the Northern (SABRE North) and Southern Hemispheres (SABRE South). This innovative approach distinguishes possible dark matter signals from seasonal backgrounds, a pioneering strategy only possible with a southern hemisphere experiment. SABRE South is located at the Stawell Underground Physics Laboratory (SUPL), in regional Victoria, Australia. SUPL is a newly built facility located 1024 m underground (∼2900 m water equivalent) within the Stawell Gold Mine and its construction has been com- pleted in 2023. SABRE South employs ultra-high purity NaI(Tl) crystals immersed in a Linear Alkyl Benzene (LAB) based liquid scintillator veto, enveloped by passive steel and polyethylene shielding alongside a plastic scintillator muon veto. Signifi- cant progress has been made in the procurement, testing, and preparation of equipment for installation of SABRE South. The SABRE South muon detector and the data acquisition systems are actively collecting data at SUPL and the SABRE South’s commissioning is planned to be completed by the end of 2025. This presentation will provide an update on the overall progress of the SABRE South construction, its anticipated performance, and its potential physics reach.

Enlightening the search for dark matter (and exotic physics) with atomic phenomena

• Benjamin Roberts

The mystery of dark matter is one of modern physics' biggest puzzles. Astrophysical evidence suggests that around 85% of the universe’s matter is "dark", yet we have never directly observed it, nor do we know its microscopic properties. Most dark matter experiments focus on WIMPs (weakly interacting massive particles), with masses ~ 10-1000 times that of a proton. As WIMP searches continue to yield no results, interest is growing in exploring a wider range of possibilities. With the possible dark matter mass range spanning an astounding 90 orders of magnitude, extending dark matter searches beyond the WIMP paradigm requires entirely new and sensitive experimental strategies. In this talk, I’ll discuss the compelling case for particle dark matter and explore some new approaches that leverage atomic phenomena to extend the dark matter search into lower mass ranges enlightening our search for dark matter, including taking advantage of the extraordinary precision of optical atomic clocks. - Phys. Rev. Lett **134**, 031001 (2025) - Phys. Rev. D **108**, 083030 (2023) - Nature Comms. **8**, 1195 (2017)

Cosmological gravitational particle production: Starobinsky vs Bogolyubov, uncertainties, and issues

• Duarte Da Silva Feiteira

Gravitational particle production provides an ever-present background in non-thermal dark matter studies. I discuss the correspondence between the Starobinsky and Bogolyubov approaches to the problem of inflationary particle production, and derive strong constraints on frameworks with scalar dark relics. (Based on D. Feiteira, O. Lebedev, arXiv:2503.14652)

Almost Minimal Dark Matter

• Spencer Griffith

Numerous models of particle dark matter have been proposed, many of which remain viable given current experimental and observational constraints. Minimal dark matter is an extremely attractive option since it envisions the addition of a single SU(2) multiplet to the standard model, rather than a complicated array of particles and interactions. However, experimental limits already rule out a subset of minimal dark matter possibilities and are approaching the predicted phase space of the remaining candidates. We consider extensions to the minimal dark matter paradigm, particularly a combination of two multiplets with a Higgs coupling, and the non-perturbative effects which may alleviate this experimental pressure.

Fitting the DESI BAO Data with Dark Energy Driven by the Cohen--Kaplan--Nelson Bound

• Patrick Adolf

Motivated by the work of Cohen, Kaplan and Nelson (CKN) in which the authors argue that gravity resticts the range of validity of a QFT, we consider a time-dependent dark energy density, scaling proportional to the squared Hubble parameter $H(z)$. These models are of particular interest in the light of the recent data release of the DESI collaboration, since the measurements show an increasing preference for time-depending dark energy models in comparison to the $\Lambda$CDM model. In our work, we compare the generalized CKN models to DESI BAO, supernova datasets and model-independent Hubble measurements and find a preference of up to $2.6\,\sigma$ over the $\Lambda$CDM model.

Closing