Dark Matter and Stars: Multi-Messenger Probes of Dark Matter and Modified Gravity

Jul 13, 2026, 8:00 AM → Jul 15, 2026, 6:00 PM Europe/London

Theatre 4A (University of Southampton)

The International Conference "Dark Matter and Stars: Multi-Messenger Probes of Dark Matter and Modified Gravity" aims to bring together scientists working across the different research fields of astrophysics, cosmology, and modified gravity. We want to look at the dark matter problem from different perspectives, considering it to be of particle nature, as well as modification of gravity. This meeting is intended to initiate cross-field discussions of dark matter searches, their current status, and future prospects.

CONFERENCE TOPICS

• Dark matter in compact stars (neutron stars, white dwarfs, exotic stars)
• Multi-messenger and gravitational wave probes of dark matter
• Supernovae simulations with dark matter
• Stars, Sun-like stars
• Exoplanets and brown dwarfs
• Cosmology
• Primordial black holes
• Modified gravity
• Models of dark matter
• Direct detection of dark matter

In the framework of the conference, we will host a special session dedicated to gravitational wave probes of dark matter, with particular emphasis on current and next-generation gravitational wave detectors.

We seek to encourage dialogue between different research groups to enhance collaboration and help to improve our understanding of dark matter. The conference is also planned to introduce the dark matter research field to encourage attendance by young scientists including Ph.D. students.

The meeting will be held at the University of Southampton, Southampton, United Kingdom. Registration opens at 8:15 am on Monday in the Mathematical Sciences Student Centre, Building 56, Southampton SO17 1BJ (map link).

The conference venue is in Room 4A, Building 54, 58 Salisbury Rd, Southampton SO17 1BJ (map link).

 

INVITED SPEAKERS

David Cerdeño (Inst. for Theor. Phys., IFT-UAM/CSIC)

Katy Clough (Queen Mary U.)

Djuna Croon (Durham U.)

Malcolm Fairbairn (King's Coll. London)

Chris Kouvaris (National Tech. U. Athens)

Sumit Kumar (Utrecht U.)

Ken Mimasu (Southampton U.)

Lina Necib (MIT) 

Ángeles Pérez García (Salamanca U.)

Justin I. Read (Surrey U.)

Bangalore Sathyaprakash (Penn State U.)

Joseph Silk (Johns Hopkins U. / Oxford U. / Paris Inst. Astrophys.)

Aaron Vincent (Queen's U.)

Miguel Zumalacárregui (Albert Einstein Inst., Potsdam)

 

ORGANISING COMMITTEE

Violetta Sagun - Chair (Southampton U.)
Nils Andersson (Southampton U.)
Afonso Robalo Ávila (Coimbra U./ Southampton U./Strasbourg U.)
Ian Jones (Southampton U.)
Ilídio Lopes (IST, Lisbon U.)
Miquel Miravet-Tenés (Southampton U.)
Tracy Storey (Southampton U.)

 

SCIENTIFIC ADVISORY COMMITTEE

Joseph Bramante (Queen's U.)
Nicholas Evans (Southampton U.)
Ilídio Lopes (IST, Lisbon U.)
Violetta Sagun (Southampton U.)
Joseph Silk (Johns Hopkins U. / Oxford U. / Paris, Inst. Astrophys.)
Aaron Vincent (Queen's U.)

 

We gratefully acknowledge the support of the Southampton Theory Astrophysics and Gravity (STAG) Research Centre, London Mathematical Society, and Nuclear Physics European Collaboration Committee (NuPECC) for this conference.

 

WARNING: Please ignore any spam emails targeting participants of the Dark Matter and Stars conference. Do not reply to these messages or click on any links they may contain. All official correspondence will be conducted exclusively through the conference email address.

ICDMS 2026_Joining Instructions_final.pdf

ICDMS2026 poster.pdf

Public Lecture of Joseph Silk poster.pdf

Mon, July 13

8:00 AM → 8:45 AM Registration

8:45 AM → 9:00 AM Conference opening

9:00 AM → 10:00 AM Invited talks

9:00 AM Indirect detection of dark matter

Speaker: Prof. Joseph Silk (Johns Hopkins U. / Oxford U. / Paris Inst. Astrophys)

9:30 AM Gravitational probes of dark matter

Dark matter (DM) makes up most of the mass of the Universe but remains mysterious. I discuss recent progress in constraining its properties through its gravitational influence. I show that the latest constraints from dwarf galaxies, galaxy clusters and the cosmic microwave background rule out weak-field alternative gravity explanations for DM, favouring a new, cold, collisionless, particle (CDM). However, CDM has, for a long time, faced a range of "small scale tensions", including the "cusp-core", "missing satellites" and "satellite planes" problems. I show that all of these are likely solved by "baryonic effects" during galaxy formation. I present observational evidence that the cusp-core problem owes to baryonic feedback "heating up" DM, while "missing satellites" is solved by an improved empirical mapping of starlight to DM, combined with satellite destruction by the Milky Way's stellar disc. Finally, I present new high resolution numerical simulations of MW-mass galaxies in which long-lived satellite planes naturally emerge. I conclude with a discussion of the latest constraints on self-interacting, wave-like and warm dark matter models.

Speaker: Justin Read (Surrey University)

10:00 AM → 10:30 AM Coffee break

10:30 AM → 11:00 AM Invited talks

10:30 AM Theory and Machine Learning for Indirect Detection of Dark Matter

In this talk, I will explore the interfacing of simulations, observations, and machine learning techniques to constrain the distribution of Dark Matter for indirect detection. I will focus on the Galactic Center and dwarf galaxies as laboratories for Dark Matter detection. For the Galactic Center, I will show how we can combine the theoretical understanding of adiabatic contraction with bursty feedback to predict the Dark Matter density profile in the inner Milky Way, and the resulting range of indirect-detection signals from the Galactic Center. For dwarf galaxies, I will present GraphNPE, a novel Graph Neural Network methodology that facilitates the accurate extraction of Dark Matter density profiles, validated against realistic FIRE-2 simulations and applied to two dwarf galaxies, Boötes I and Draco. I will conclude by arguing that the Milky Way and galactic dynamics more broadly offer a complementary probe of Dark Matter, showing direct examples of how stellar dynamics can be integrated with our understanding of Dark Matter in the Galaxy and its connection to detection experiments.

Speaker: Lina Necib (MIT)

11:00 AM → 12:00 PM Contributed talks

11:00 AM Heavy dark matter in rapidly evolving massive stars

Dark matter (DM) constitutes most of the matter content of the Universe, yet its particle nature remains unknown. While laboratory searches and cosmological probes have placed strong constraints on many candidate models, astrophysical environments provide a complementary avenue to test DM interactions under extreme conditions. Stars are particularly promising laboratories: as they move through their host halos, DM particles may scatter with stellar constituents, lose energy, and become gravitationally captured. Once accumulated, DM can alter stellar evolution through annihilation heating, enhanced luminosity, or—in the case of heavy non-annihilating DM—through self-gravitation and eventual collapse. Understanding capture in realistic stellar environments is therefore essential for connecting stellar observations to particle DM physics.

In this talk, I will discuss the capture of heavy DM in rapidly evolving massive stars, with emphasis on the first stellar populations and their later metal-enriched descendants. Using stellar evolution simulations from the zero-age main sequence to advanced burning stages, we show that DM capture depends sensitively on the changing internal structure and composition of the star. During the early hydrogen- and helium-dominated phases, capture is largely controlled by scattering on light nuclei. As nuclear burning proceeds, metal production generates a dense core surrounded by a lighter envelope, substantially enhancing the capture of ultra-heavy DM and requiring a multi-component treatment with several nuclear targets.

I will also highlight recent advances in the theory of heavy-DM capture in compact stars, where multiple scatterings, realistic trajectories, nuclear form factors, and in-medium thermalization effects become crucial. These developments clarify how efficiently heavy DM can be trapped and transported to stellar centers, and how rapidly it can thermalize after capture.

Our results indicate that, for viable regions of parameter space beyond current direct-detection bounds, heavy annihilating DM may reach capture–annihilation equilibrium within the short lifetime of a massive star. For non-annihilating DM, the accumulated population can become self-gravitating and potentially collapse into a black hole capable of consuming the host star from within. These findings demonstrate that accurate stellar modeling, combined with improved capture formalisms, opens a powerful new window on heavy DM through massive stars and stellar remnants.

Speaker: Giorgio Busoni (Adelaide University)

11:15 AM Dark photons from red dwarfs

Light dark photons can be produced in stellar systems and thus contribute to the stellar cooling rate. The additional cooling changes the evolution of the star and has an impact on various observables properties such as radius, photon luminosity or the emitted neutrino fluxes. This has been exploited before to derive limits based on observations of the Sun and horizontal branch stars. Given the wealth of astrophysical data collected in the last decade and the improvements in modeling stellar evolution it is an interesting question to investigate whether other stellar systems offer a complementary avenue towards testing dark photons.
Here, we study the effect on an alternative class of stars. We focus on the impact of dark photon induced cooling on red dwarfs, i.e. the lowest mass stars on the Hydrogen main sequence. Running simulations of the evolution of red dwarfs with dark photon cooling we determine the impact on observable global properties of these stars. We find that the red dwarf mass-radius relation provides a powerful probe of additional cooling. Combining our simulations with precise determination of mass and radius derived from observations of eclipsing binaries that have recently become available, we derive competitive limits from this alternative observable.

Speaker: Stefan Vogl (University of Freiburg)

Vogl_Southampton.pdf

11:30 AM Looking for lights from the darkness: MeV-scale solar ALP signals

MeV-scale axion-like particles (ALPs) can be produced abundantly in the Sun. The photons from ALP decay could deviate significantly from the original ALP direction, or even from roughly the opposite direction of the Sun. The nontrivial angular and spectral distributions enable us new methods to detect the lights from the darkness. We consider the space detection and terrestrial experiments at the South Pole. It is found that there is a critical height for the terrestrial searches, below which there is no flux at all for some regions of the parameter space. In the next-generation experiments, we can explore the coupling of ALP to photons up to $10^{−12}$ GeV$^{−1}$, surpassing the current supernova limits.

Speaker: Yongchao Zhang

11:45 AM DarkMatterLive: A Live Framework for Unifying Constraints on Dark Matter and Dark Sector Physics

Dark matter searches now span a wide range of experimental and observational programmes, from collider and fixed-target experiments to direct detection, indirect searches, and cosmological probes. Yet the resulting constraints are often presented in different variables, conventions, and model assumptions, making it difficult to compare them consistently or to build coherent global pictures of viable dark matter and dark sector parameter space. This challenge is especially relevant in cross-field settings, where particle-physics limits, cosmological bounds, and astrophysical constraints must be interpreted side by side.

DarkMatterLive is a collaborative platform designed to address this problem by building and sharing interactive visualisations of dark matter and dark sector constraints in a common, model-aware framework. Based on published experimental and observational results, it brings together limits that are otherwise difficult to compare and, where possible, recasts them into standard variables following widely used benchmark conventions. In this way, the platform helps connect results across particle physics, cosmology, and astrophysics while preserving clear links to the original sources, assumptions, and caveats.

A representative use case is dark photon, where limits on kinetic mixing can be mapped into alternative parameter spaces and compared with complementary constraints from other probes. Hosted on CERN PaaS cloud infrastructure, DarkMatterLive is publicly available through https://darkmatter.web.cern.ch/ web interface, with benchmark plots online and a citable release archived as 10.5281/zenodo.18135859. The framework also interfaces naturally with community resources such as the HEPData portal, helping organise new inputs within a transparent review workflow.

To support broad community use, DarkMatterLive provides a data-ingestion workflow based on CSV curve data and JSON metadata. New results and key reinterpretation and renormalisation factors are documented and peer-reviewed through GitHub pull requests or CERN GitLab merge requests before inclusion. Additional AI-MCP-based ingestion modules are being integrated into the platform workflows. DarkMatterLive is intended as an open tool for connecting particle, astrophysical, and cosmological perspectives on dark matter and dark sector physics, and for enabling more reproducible construction of global constraints across communities.

Speaker: Dr Brij Kishor Jashal (Rutherford Appleton Laboratory)

12:00 PM → 2:00 PM Lunch

2:00 PM → 3:00 PM Invited talks

2:00 PM Gravitational lensing of waves: a new window into astrophysics, dark matter & gravity

Just like light, gravitational waves (GWs) are gravitationally lensed by massive objects in the Universe. Moreover, their low frequency, phase coherence, and lack of absorption make GWs complementary to lensed electromagnetic sources. In addition to gravitational magnification and the formation of multiple images, lensed GWs exhibit genuine wave-propagation effects such as diffraction, i.e., the bending of the signal’s wavefront. Lensing diffraction imprints a frequency-dependent modulation on the signal, encoding information about the lens mass and its distribution. I will describe the rich phenomenology of lensing diffraction as a means to discover high-redshift, magnified binary mergers and to probe small-scale structures, including dark matter. In theories beyond GR, novel propagation effects such as birefringence and dispersion—polarization- and frequency-dependent phase shifts—provide new tests of cosmological gravity and dynamical dark energy. In addition to recent theoretical developments, I will present the latest analysis of GW231123, the first candidate for a diffracted and magnified compact binary coalescence.

Speaker: Dr Miguel Zumalacarregui (Max Planck Institute for Gravitational Physics - Albert Einstein Institute)

2:30 PM Gravitational Waves as Tracers of Large Scale Structures: Opportunities for Multi-Messenger Cosmology

The large-scale structure (LSS) of the Universe has traditionally been mapped through galaxy surveys. The third generation (3G) of gravitational wave (GW) detectors, such as the Einstein Telescope and Cosmic Explorer, will provide an independent probe for LSS using compact binary mergers as tracers of the underlying matter distribution in the Universe. In the 3G era, we will be able to measure the LSS properties, such as clustering bias and the baryon acoustic oscillations feature, solely from GW localization observations. These measurements could shed light on the astrophysical origins of the compact binaries by observing the redshift evolution of their clustering properties. In combination with cosmological surveys such as the Square Kilometer Array, Euclid, and the Vera C. Rubin Observatory, the 3G detector network will be able to constrain cosmological parameters and the structure formation history of the Universe. This talk will review strategies for probing multi messenger LSS observations, highlight the scientific opportunities, and discuss the challenges that must be addressed to realize their full potential.

Speaker: Sumit Kumar (Utrecht University)

3:00 PM → 3:30 PM Coffee break

3:30 PM → 5:00 PM Contributed talks

3:30 PM Dark matter and Fermi balls

It has long been known that if the dark sector includes an attractive Yukawa force, dark halos can readily form, well before matter-radiation equality. However, the same scalar field which mediates the Yukawa force also allows these structures to radiatively cool, causing them to further collapse. I will discuss the evolution of these dark halos as they cool into Fermi balls and even primordial black holes, touching on the potentially rich phenomenology of these compact dark structures.

Speaker: Zachary Picker

3:45 PM Macroscopic dark matter in the era of Roman

Primordial black holes (PBHs) are a well-motivated candidate for dark matter that may constitute a sub-fraction of the dark sector in the Earth-mass range. The strongest observational probe of this population is through gravitational microlensing, an effect in which the bending of light by a massive object results in the apparent transient magnification of a distant source. While ground-based observatories have produced tantalizing hints of a PBH population in this mass range, our understanding of this potential signal will be transformed with the launch of the Roman Space Telescope in August 2026, whose Galactic Bulge Time Domain Survey will usher in a new era of discovery in this field. In this talk, I will discuss how by leveraging the high-statistics observations that Roman will make, we will be able to discern multiple subpopulations of non-luminous lenses and provide a new window into the existence of macroscopic dark matter.

Speaker: William DeRocco (University of Maryland, College Park)

4:00 PM Probing high-frequency gravitational waves from PBH dark matter

Light primordial black holes (PBHs) are viable candidates for dark matter. If they constitute a sizable fraction of dark matter, PBH mergers can occur frequently in the Milky Way Galaxy. The merger remnants are Kerr black holes and hence possess spin. In the presence of a light bosonic field with a Compton wavelength comparable to the black-hole radius, superradiant boson clouds can form around the remnants. These clouds can emit nearly monochromatic high-frequency gravitational waves. In this work, we investigate the possibility of probing such gravitational waves with telescopes through photons converted from gravitational waves in the magnetic fields of the Milky Way.

Speakers: Asuka Ito (Kobe University), Kazunori Kohri

4:15 PM Tidal Love Numbers of Black Holes Dressed by Dark Matter

Tidal Love numbers (TLNs) encode the deformability of compact objects under external tidal fields and leave observable imprints in gravitational wave signals. While black hole TLNs vanish in vacuum general relativity, the presence of surrounding matter can alter this picture. This talk presents a study of the axial (magnetic) TLNs of a Schwarzschild black hole embedded in a spherically symmetric dark matter distribution, modeled as an anisotropic fluid with three astrophysically motivated density profiles: Einasto, Hernquist, and NFW. Analytic closed-form expressions are derived via a small-compactness expansion and benchmarked against direct numerical integration of the perturbation equations. A key finding is that profiles without compact support generically produce logarithmic terms in the asymptotic expansion of the perturbation variable, obstructing the standard tidal matching procedure and pointing to the subtleties of defining tidal observables for black holes dressed by matter. The broader implications for gravitational wave detectability with next-generation detectors are discussed, highlighting dark matter environments around compact objects as a promising multi-messenger target.

Speaker: Simone D'Onofrio (ICE - CSIC)

4:30 PM Unveiling Flat Galaxy Rotation Curves out to 1 Mpc in a Simulated ΛCDM Universe

Recent weak-lensing measurements reported that circular velocity curves of galaxies remain flat out to ~1 Mpc, potentially posing a tension with the standard ΛCDM model. In this work, we investigate the origin of these extended flat rotation curves using the IllustrisTNG cosmological simulation. We select isolated galaxies from the simulation and construct circular velocity profiles in three distinctive ways: (1) directly from the enclosed mass of particles gravitationally bound to the host galaxy, (2) from the enclosed mass of all particles within a large aperture, and (3) from the excess surface density profile measured in the simulation, which is designed to most closely mirror what is measured in weak-lensing observations. We find that ΛCDM can naturally produce flat rotation curves out to the virial radius and, in most mass bins, nearly flat profiles out to 1 Mpc when the contribution from surrounding matter is included. This indicates that the extended flatness inferred from weak-lensing can be explained largely by environmental mass contributions, rather than by a failure of ΛCDM itself. The most notable residual discrepancy arises in the lowest-mass bin, where the simulated profile declines beyond the virial radius while the observed profile remains flat to 1 Mpc. We further find that, in this mass regime, galaxies residing in more massive and lower-concentration halos tend to exhibit flatter outer rotation curves.

Speaker: Daeun Jeong (Seoul National University)

4:45 PM The degeneracies and successes of MOND and DARK MATTER in reproducing galaxy rotation curves and scaling relations

High-resolution kinematic measurements of disc galaxies continue to exhibit a persistent mismatch between the observed rotation curves and the distribution of visible components, reinforcing either the necessity for a "dark" matter component or a departure from standard gravitational dynamics in the low-acceleration regime. We present the modelled rotation curves of 115 disc-dominated late-type spiral galaxies from the SPARC database, using a suite of models including Cold Dark Matter (CDM) models with and without baryonic feedback, Warm DM, Fuzzy DM, and Modified Newtonian Dynamics (MOND) in order to assess their relative performance and highlight any degeneracies. We find that no model can be safely excluded by current data, although we find a mild evidence for a preference for CDM models with baryonic feedback. However, when including the weak lensing data of the mean galaxy rotation curves of low-mass galaxies out to ∼ 1 Mpc, we find a nearly perfect degeneracy between MOND and DM models, at least up to the virial radius. We further test all the models against the global scaling relations of galaxy luminosity versus halo mass and circular velocity, as inferred from abundance matching, or the radial acceleration relation, finding that all models again predict very similar trends, with exceptionally narrow scatter around the luminosity-circular velocity relation. The increased scatter observed around the luminosity-halo mass relation exhibited by some of the models can be largely attributed to the limited radial extent of certain rotation curves, particularly in cases where the data do not probe sufficiently near the maximum circular velocity. We confirm a degeneracy between MOND and CDM also in the outputs of the TNG50 hydrodynamic simulation which predicts that, despite differences in internal structure, a traditional CDM model inclusive of baryonic feedback is consistent with all rotation curves up to the virial radius as inferred from weak lensing analysis. Finally, we will show preliminary results on the comparison between some z~1-2 galaxies with detailed rotation curve measurements and the predictions from our best MOND and CDM with baryonic feedback models against, to test their performance in a very different regime.

Speaker: Amy Smith (University of Southampton)

3:30 PM → 5:00 PM Contributed talks 2

3:30 PM SN1987A constraints on Hadronically Interacting Sub-GeV Dark Matter

We derive conservative upper limits on the dark-matter–nucleon scattering cross-section for sub-GeV mass dark matter using low-energy chiral effective field theory, independent of UV details. The leading-order hadronic couplings are most severely constrained by the supernova cooling argument via processes such as nucleon bremsstrahlung and pion–DM conversion. We rule out both spin-independent and spin-dependent cross-sections ≳ 10^(−50)cm² for DM masses in the keV–a few hundred MeV range—several orders of magnitude stronger than existing cosmological and meson decay constraints, with significant implications for future low-mass direct detection experiments.

Speaker: Zun Wang (Southeast University)

3:45 PM Orbit-Corrected Multi-Scatter Dark Matter Capture in Diverse Stellar Environments

We present a comprehensive comparison of three WIMP dark matter capture rate formalisms applied to four distinct stellar environments, representative of different mass classes and evolutionary stages. For each stellar model, we compute the capture rate using a single-scatter approximation, a multi-scatter chord based method, and a new orbit-corrected variant that accounts for gravitational deflection of dark matter trajectories. We explore a parameter grid spanning spin-independent cross-sections of $10^{-44}$ to $10^{-35}$ cm$^2$ and WIMP masses in the range $5$ to $500$ GeV, assuming local (solar system) dark matter properties. We identify the regimes where orbit corrections produce significant departures from the chord-based method, quantify the breakdown of the single-scatter limit, and characterise the approach to the geometric capture ceiling across all stellar types.

Speaker: Diogo Capelo

4:00 PM Testing bosonic dark matter through white dwarf mass measurements

We investigate a potential origin of the persistent discrepancies between white-dwarf mass estimates derived from electromagnetic techniques and those inferred from gravitational-redshift measurements, which can differ by $\sim5$–$15%$ across independent datasets. While part of this tension may arise from thermal effects, atmospheric modelling, or observational uncertainties, a subset of measurements remains difficult to reconcile within standard frameworks. We propose an alternative scenario in which a gravitationally bound, electromagnetically invisible bosonic scalar field contributes to the stellar mass budget. Within this framework, we construct stationary mixed configurations describing composite white dwarf–boson-star systems formed by ordinary degenerate matter coupled only gravitationally to a scalar dark-matter component. By exploring families of equilibrium solutions, we show that a dark-matter fraction $f_{\rm DM}\sim5$–$15%$ can naturally reproduce the observed redshift excess without conflicting with current observational constraints. Our results provide a physically motivated interpretation of the inferred mass bias, suggest potential observational signatures, and enable preliminary constraints on the compactness and particle-mass scale of the ultralight bosonic field. Combining the theoretical modelling with Bayesian model selection, we outline prospective bounds on the properties of the underlying dark-matter candidate.

Speaker: Jorge Castelo Mourelle (Universidad Nacional Autónoma de México- Institute of Nuclear Sciences (ICN))

4:15 PM Dark Compact Object Mimics

Gravitational wave measurements of tidal deformability during binary inspiral are sensitive to a combination of the tidal Love number and compactness, leaving the radius of a compact object free to be unconstrained in the absence of electromagnetic information. This degeneracy means that a dark compact object with an appropriately tuned equation of state can mimic a neutron star across all current observational diagnostics. We construct and analyse exotic compact objects composed entirely of self-interacting asymmetric fermionic dark matter with a repulsive Yukawa interaction, treating 1 GeV and 10 GeV dark matter candidates and employing the Hartle-Thorne formalism to second order to capture rotational behaviour. Comparing tidal and rotational observables against the SLy4 neutron star baseline, we characterise the extent of this mimicry and its limitations. While the EOS-independent universal relations that underpin standard neutron star inference remain approximately satisfied within single-fluid dark matter models, tidal and rotational properties may reveal distinguishable signatures accessible to next-generation detectors. We discuss the implications for gravitational wave data analysis and the prospects for using binary merger observations as a dark matter probe.

Speaker: Zakary Fuaad Buras-Stubbs

4:30 PM Dark matter mounds from the collapse of supermassive stars: a general-relativistic analysis

Recent work has highlighted the importance of a fully relativistic treatment of the dephasing of gravitational waves induced by dark-matter overdensities in extreme mass-ratio inspirals (EMRIs). We developed a fully general-relativistic formalism for the more realistic scenario in which a supermassive stellar progenitor collapses to a black hole and produces a shallower dark matter overdensity, or “mound”. We follow self-consistently the evolution of the supermassive star, its collapse, and the subsequent growth of the resulting black hole, together with the collisionless dark matter orbits. We find that in the regime where the collapse becomes non-adiabatic, the dark matter distribution unction is significantly reshaped, with a clear depletion in the low-binding-energy region of phase space. Our results provide a more realistic prediction for the dark matter phase-space distribution around supermassive black holes, which is an essential step in using future EMRI observations to extract information about their formation history and the nature of dark matter.

Speaker: Roberto Caiozzo (SISSA)

4:45 PM Supermassive BHs seeds from direct collapse of CDM-curvature peaks in ΛCDM

In the first part of this talk I will present results from numerical relativity simulations of a toy-model cosmic web of over-densities, voids and filaments with the Einstein Toolkit, evolving from standard growing-mode perturbative CDM initial conditions in the matter era, at z ~ 300. I will show how the first collapse of peaks of over-densities is very well predicted by the simple "top hat” model (AKA Oppenheimer-Sneyer collapse). Although this simple cosmic web structure doesn’t assume any symmetries, the collapse of peaks is quasi-spherical, which naturally leads to the conjecture that a horizon can form very early. In the second part I will briefly present current numerical relativity efforts to identify a horizon enclosing these CDM peaks, as well as analytic results from Galoppo, Bruni and Harada 2605.30145 (based on exact solutions of Einstein equations) showing that supermassive black hole seeds can form from the direct collapse of the peaks of overdensities in the CDM distribution, with masses M ~ 10^3-10^6 at z ~ 10, or even earlier.

Speaker: Marco Bruni (University of Portsmouth)

5:00 PM → 6:15 PM Poster session & welcome reception

6:30 PM → 7:50 PM Public lecture of Prof. Joseph Silk 'Telescopes on the Moon'

Tue, July 14

9:00 AM → 10:00 AM Invited talks

9:00 AM Constraining Dark Matter with Gravitational-Wave Observations of Binary Neutron Stars

Certain asymmetric dark matter candidates can accumulate in neutron star cores and trigger their collapse into low-mass black holes. If this process occurs in compact binaries, the Universe may contain distinct populations of binary neutron stars and low-mass binary black holes. Gravitational-wave observations can distinguish these populations through their tidal deformabilities, which vanish for black holes but are nonzero for neutron stars. In this talk, I will show how current and next-generation gravitational-wave detector networks, including Cosmic Explorer and the Einstein Telescope, can measure the relative abundances of these populations to infer the timescale for dark-matter-induced neutron star implosions. These measurements can in turn constrain the particle properties of dark matter, providing a novel connection between gravitational-wave astronomy and fundamental physics.

Speaker: Bangalore Sathyaprakash (The Pennsylvania State University)

9:30 AM Dark matter in the strong field regime

Light scalar particles arise naturally in many extensions of the standard model and are compelling dark-matter candidates. Gravitational interactions near black holes can trigger the growth of dense scalar configurations that, if sustained during inspiral, alter binary dynamics and imprint signatures on gravitational-wave signals.  I will describe how numerical relativity simulations can support modelling of such environments, and our recent results applying them to gravitational wave data.

Speaker: Katy Clough

10:00 AM → 10:30 AM Coffee break

10:30 AM → 11:30 AM Invited talks

10:30 AM Searching for Dark Matter in the Shadow of Stellar Uncertainty

Gravitational wave observations have opened a direct route to studying black hole (BH) populations. In principle, primordial and astrophysical BHs may be distinguishable through their mass, spin, redshift, and merger-rate distributions. At the same time, the observed BH population provides a new probe of nuclear and particle physics in stellar cores. A major obstacle is that the late evolution of heavy stars remains insufficiently understood, especially near and above the predicted BH mass gap. I will discuss stellar evolution simulations of very massive BH progenitors, focusing on how predicted remnant masses and spins depend on uncertain assumptions. I will also discuss some recent observations which have challenged our understanding of how the most massive BHs form.

Speaker: Dr Djuna Croon (IPPP Durham)

11:00 AM Black Holes, Gravitational Waves, the First Stars and Dark Matter

I will discuss how understanding the Nanograv observations has led us to focus on the growth of supermassive black holes in the early Universe, and how understanding how this has taken place, together with observations from JWST, have led us to new constraints on the nature of dark matter.

Speaker: Prof. Malcolm Fairbairn (Physics, King's College London)

11:30 AM → 11:45 AM Contributed talks

11:30 AM Microlensing of continuous gravitational waves as probes of dark matter

Microlensing surveys targeting the stellar fields of the Magellanic Clouds, the Galactic Bulge, and M31 have long constrained the abundance of Massive Compact Halo Objects (MACHOs) and galactic halo structure. Just as electromagnetic radiation is gravitationally lensed, so too are gravitational waves (GWs) producing repeated or chromatically distorted signals. For short-lived transient sources such as compact binary mergers, the relative motion between source, lens, and detector can safely be ignored.

Continuous gravitational waves (CGWs) are undetected signals, sustaining over timescales comparable to or exceeding full observing runs. Candidate sources include rotating asymmetric neutron stars, inspiralling compact binaries, and ultralight boson clouds around black holes. For CGWs, source-lens-detector motion can no longer be neglected and lensing results in time-varying amplitude magnification and SNR modulation, producing a GW analogue of the optical Paczyński curve.

In this work, we model the lensing signatures of CGWs across a range of dark matter profiles, including bare and dressed primordial black holes and self-interacting dark matter. We show that these signatures not only boost detectability through amplitude magnification, but also carry distinguishable imprints of the underlying dark matter distribution opening new observational avenues for discriminating between warm and cold dark matter scenarios.

Speaker: Dr Sreekanth Harikumar (Nicolaus Copernicus Astronomical Center, Warsaw)

11:45 AM → 12:00 PM Conference photo

12:00 PM → 2:00 PM Lunch

2:00 PM → 3:00 PM Discussion session: GW probes of DM

3:00 PM → 3:30 PM Coffee break

3:30 PM → 4:00 PM Invited talks

3:30 PM Dark matter in main sequence stars and beyond

The Sun and other nearby stars can act as powerful probes of particle dark matter, thanks to precision observations. However, because the effect of dark matter is small, we must be certain that our modelling of the effect of dark matter and the stellar response is correct. I will discuss recent developments on modelling the subtle effects of dark matter, with some focus on helio- and asteroseismology.

Speaker: Aaron Vincent (Queen's University)

5:00 PM → 7:00 PM Secrets of the Titanic — A Walking Tour

7:00 PM → 10:00 PM Conference dinner

Wed, July 15

9:00 AM → 10:00 AM Invited talks

9:00 AM Multimessenger probes of Dark matter in Neutron Stars

Neutron stars provide unique laboratories for probing fundamental physics under extreme conditions of density, gravity, and magnetic field strength. In this talk, I will review several intriguing aspects of axions, ALPs and other well-motivated dark matter candidates in the ultradense and strongly magnetized interiors and magnetosphere of neutron stars. As complementary indirect probes of the dark sector, neutron stars offer the possibility of testing the coupling of dark particles to intense electromagnetic fields, as well as their potential impact on the generation and damping of gravitational-wave signals. I will discuss observational windows in which correlated electromagnetic and gravitational-wave signatures may arise, particularly in compact binary coalescences. I will also comment on possible modifications of neutron-star properties induced by dark matter, should it be sufficiently abundant in these environments.

Speaker: MARÍA ÁNGELES PÉREZ GARCÍA (University of Salamanca)

9:30 AM Compact Stars as Portals to Extra-Dimensional Dark Matter

Dark matter that propagates in extra dimensions can substantially soften the equation of state and lead to collapse of dark matter inside neutron stars, eventually destroying the host star. Based on that scenario constraints can be drawn on extra-dimensional dark matter.

Speaker: Chris Kouvaris (National Tech. U. Athens)

10:00 AM → 10:30 AM Coffee break

10:30 AM → 12:00 PM Contributed talks

10:30 AM Probing neutrinophilic scalars in muon and double beta decay

Self-interacting neutrinos are well-motivated particles in order to solve problems such as Hubble tension in cosmology. Neutrino-philic scalars, such as flavons and Majorons, can be solutions to BSM puzzles, such as lepton number and lepton flavour violations. New muon decay channels (e.g. µ → eϕ, µ → eϕϕ) will be introduced by neurtino-scalar couplings and µ → eνν will have additional contribution from scalar one-loop effect. Scalar-facilitated neutrino self-interaction can also contribute to two-neutrino double beta decay, the shape of the two-electron spectrum in double beta decay experiments can therefore be modified. The interference between SM and scalar facilitated diagrams will enhance the sensitivity to new physics when the final state particles are the same as SM process. These new channels and enhancements will lead to a wider neurtino-scalar coupling parameter space that can be tested in future experiments.

Speaker: Zhong Zhang

10:45 AM The Sound of the Universe: A Resonant Gravitational Instability Driven by Baryon-Dark Matter Relative Drift

The classical Jeans instability states that baryonic perturbations grow only above the Jeans scale, while cold dark matter is unstable on all scales. In this talk, I will show that the relative drift between baryons and dark matter after decoupling fundamentally alters this picture.
When the projected DM drift is subsonic, a new resonant gravitational instability – the Shalaby‑Broderick instability – drives exponentially growing sound waves in the baryons, with growth rates exceeding the intrinsic DM growth rate. In baryon‑dominated environments, the instability also opens a stable window between the Jeans scale and the resonant scale.
I will demonstrate that the associated timescales range from years to tens of millions of years across diverse astrophysical systems – planets, stars, molecular clouds, galaxies, and galaxy clusters – typically much shorter than their ages. On cosmological scales, the instability enhances baryon density perturbations for appropriately oriented modes while suppressing those aligned with the DM stream, leaving a distinct anisotropic imprint on the 21 cm signal and the distribution of early galaxies.
Crucially, this resonant mechanism provides a fundamentally new way to detect dark matter directly – not through particle‑particle collisions, but through the gravitational resonance between baryonic sound waves and Doppler‑shifted DM modes. This opens observational windows via seismic vibrations (Earth, Moon, ice sheets), galactic spiral structure, and pulsar timing arrays – turning the relative motion of dark matter from a nuisance into a powerful diagnostic tool.

Speaker: Dr Mohamad Shalaby (University of Waterloo)

11:00 AM 2D BAO vs 3D BAO: Hints for new physics?

As next-generation telescopes and observational surveys continue to expand the boundaries of our understanding, tensions and discrepancies between observational datasets are becoming increasingly prominent. In this work, we focus on one such discrepancy: the differences between 2D and 3D Baryon Acoustic Oscillation (BAO) measurements. Without extending beyond the standard $\Lambda$CDM framework, we systematically study and highlight this discrepancy in different parameter spaces. By analyzing BAO observational datasets from two distinct methodologies (2D and 3D) alongside the Pantheon Plus SNIa sample, we identify a significant systematic difference: 2D BAO measurements consistently yield higher values of $hr_d$ compared to both 3D BAO in SDSS and DESI analyses. While 2D BAO measurements appear to bridge the Hubble tension by simultaneously accommodating both a higher $H_0$ value (aligning with SH0ES) and a larger sound horizon $r_d$ (matching Planck), this apparent reconciliation comes at the cost of introducing tension with the well-constrained Planck measurement of $\Omega_{m0}h^2$ . This behavior arises because of systematically higher values of the product $H_0$ observed in 2D BAO analysis compared to 3D analyses. Therefore, given these systematic differences, we advocate for careful consideration when using 2D BAO measurements to address the Hubble tension, suggesting that understanding the origin of this 2D-3D discrepancy should be a priority for future investigations.

Speaker: Ruchika Ruchika (Salamanca University)

11:15 AM Mechanism of kinetic equilibrium between SIMP and radiation

Strongly Interacting Massive Particles (SIMPs) provide an intriguing alternative to conventional collisionless dark matter (CDM) scenarios, particularly in light of tensions between CDM predictions and observations on small astrophysical scales. In SIMP models, the observed dark matter relic abundance is generated through self-annihilation processes such as $3 \to 2$ or $4 \to 2$, involving only dark sector particles. However, these processes can overheat the dark sector and potentially jeopardize structure formation. This issue can be resolved if the DM particles are in kinetic equilibrium with lighter particles, which redshifts similar to radiation during DM freezeout, either in the SM or the dark sector. In conventional SIMP models, the interactions responsible for kinetic equilibrium are often related by crossing symmetry to pair-annihilation processes, inevitably inducing sizable dark matter annihilation into radiation. This leads to strong constraints on the allowed parameter space. In this talk, I will introduce a novel mechanism in which dark matter–radiation scattering and annihilation are governed by different combinations of parameters. I will show that it can be naturally realized in new physics models, and then discuss their potential detections.

Speaker: AJAY Kaladharan

11:30 AM Primordial Gravitational Waves as Complementary Probe of Dark Matter Indirect Detection & Axion

We propose a novel cosmological probe of dark matter (DM) and QCD Axions through inflationary primordial gravitational wave (GW) measurements highlighting its complementarity with traditional indirect detection. In scenarios like early matter domination (EMD), the thermal DM relic is diluted and then replenished via non-thermal production, leaving characteristic imprints on the primordial GW spectrum, inducing frequency-dependent suppressions in the GW amplitudes.

Speaker: Anish Ghoshal (University of Sussex)

11:45 AM Gravitational wave production during reheating: From the inflaton to primordial black holes

We calculate the gravitational waves (GWs) produced by primordial black holes (PBHs) in the presence of the inflaton condensate in the early Universe. Combining the GW production from the evaporation process, the gravitational scattering of the inflaton itself, and the density fluctuations due to the inhomogeneous distribution of PBHs, we propose for the first time a complete coherent analysis of the spectrum, revealing three peaks, one for each source. Three frequency ranges (∼
kHz, GHz, and PHz, respectively) are expected, each giving rise to a similar GW peak amplitude Ω_GW. We also compare our predictions with current and future GWs detection experiments.

Speaker: Dr Rishav Roshan (University of Southampton)

10:30 AM → 12:00 PM Contributed talks 2

10:30 AM Generating ultra-compact hybrid stars with bosonic dark matter

We investigate the impact of a stiff dark matter equation of state (EoS) on the structure and stability of neutron stars. For dark matter, we use bosonic, self-interacting scalar fields that generate ultra-compact boson stars with compactness exceeding 1/3. Varying the dark matter particle mass and stiffness shifts stellar configurations across distinct regions of the mass–radius diagram, including regimes inaccessible to normal hadronic matter. We further examine the impact of a phase transition to quark matter and identify features that distinguish these hybrid configurations from stars without a quark core. In both scenarios, stability is assessed within a two-fluid framework by analyzing the onset of unstable radial modes.

Speaker: Dr. ISHFAQ AHMAD RATHER (Institute for Theoretical Physics, Goethe University, 60438 Frankfurt am Main, Germany)

10:45 AM Rotating Neutron Stars with Dark Matter Halos

If dark matter (DM) exists in halos around rotating neutron stars (NSs), it will be essential to understand the effects of rotation on the distribution of DM and baryonic matter (BM) in the stars to interpret observations. In this work, we construct rapidly rotating dark matter admixed neutron stars (DANS) with DM halos using the two-fluid approximation, where the BM and DM interact only through gravity. Our goal is to describe rapidly rotating millisecond-period DANS spun up by the accretion of BM from a zero angular momentum state. We extend the Rapidly Rotating Neutron Star (RNS) code to compute axisymmetric configurations in which the BM rotates rigidly while the DM remains torque-free and differentially rotates through the frame-dragging of spacetime. For the first time, we examine in detail local and global definitions of mass in general relativity for two-fluid systems, showing how their differences affect the interpretation of baryonic and dark component masses. We compute energy density and frame-dragging frequency profiles for DANS with three different characteristic DM halos. We demonstrate that rapid BM rotation reduces DM halo sizes if central energy densities are kept constant between non-rotating and rotating models. We also construct sequences of DANS to create mass and radius curves and compare rotating and non-rotating cases. We quantify deviations in the spacetime metric outside the baryonic surfaces of these sequences of stars caused by the DM halos. We hypothesize that the size of this quantity could indicate whether a DM halo will significantly impact X-ray pulse profile modeling. These results provide a framework for assessing the observational consequences of DM halos around rapidly rotating NSs.

Speaker: Shafayat Shawqi (University of Alberta)

11:00 AM Gravitational synchronization in bosonic dark matter admixed neutron stars

Neutron stars offer unique natural laboratories for probing the interaction between dark matter and baryonic matter. In this talk, I will present our recent work modeling dark matter as an ultralight bosonic field that accretes onto neutron stars, forming fermion-boson stars. I will discuss our numerical relativity simulations in spherical symmetry, through which we extract and analyze the radial oscillation mode spectra of these configurations.
A central result is the gravitational synchronization between the fermionic and bosonic components: regardless of the equation of state, our simulations consistently show that both components lock in phase, enriching the oscillation spectrum and giving rise to stable multi-state scalar configurations that reshape the hierarchy of neutron-star radial modes. I will further present a practical procedure to compute the new dominant neutron-star oscillation mode frequencies as a function of the bosonic mass, and close by discussing the broader implications of these findings for neutron-star physics and the prospects for gravitational-wave detection.

Speaker: Claudio Cesar Lazarte Melgar (Universitat de València)

11:15 AM Scalar-Field-Admixed Binary Neutron Star Merger Simulations

Binary neutron star mergers provide a laboratory for probing fundamental physics in strong-gravity regimes through gravitational-wave and electromagnetic signals. We use numerical-relativity simulations to study possible beyond-the-Standard-Model effects in these systems, focusing on a minimally coupled scalar field surrounding the binary, and lighter-than-QCD axions coupled to baryonic matter.
For the scalar field case, we examine whether the field remains bound during the late inspiral and merger, and whether it leaves observable imprints. We find that the scalar field can form a common cloud around the binary that persists through the merger. At sufficiently high densities, it produces measurable effects, including inspiral dephasing, a less compact post-merger remnant, and reduced dynamical ejecta. However, for astrophysically motivated densities, these signatures are small and likely difficult to detect with current or near-future gravitational-wave observatories.

Speaker: Rohan Srikanth

11:30 AM EMRIs as probes of dark matter and neutron star equation of state

Extreme mass-ratio inspirals (EMRIs) are expected to be among the most informative gravitational-wave sources for LISA, offering unprecedented access to the environments of supermassive black holes. In this talk, I will discuss how dense dark matter spikes surrounding these black holes can leave measurable imprints on EMRI signals through dynamical friction, potentially opening a new window onto both the distribution of dark matter in galactic nuclei and the nature of the inspiraling compact object. I will also address the astrophysical viability of such dark matter overdensities by examining their long-term evolution under perturbations from stars and compact objects. Together, these studies suggest that environmental effects may provide a powerful opportunity to extract new fundamental and astrophysical information from future LISA observations.

Speaker: Theo Karydas (GRAPPA, University of Amsterdam)

11:45 AM Dynamical friction on binary stars in the faintest dwarf galaxies

We study binary stars moving through a uniform dark matter background and experiencing dynamical friction. The centre-of-mass motion of the pairs is taken into account. We derive formulas and timescales for the secular evolution of the orbital parameters for both wide and close binaries. We apply these results to environments typical of dark matter dominated ultra-faint dwarf galaxies and show that some binaries undergo significant eccentricity oscillations, while their semi-major axes decrease more gradually. We consider a simple binary star population and find that dynamical friction, notably, can enhance the bias from unresolved binaries in velocity dispersion measurements. With future, more detailed theoretical studies and improving observational capabilities, binary stars may serve as a tool to probe the dark matter content of some of the faintest galaxies.

This talk is based on 2602.20245 (and partially on 2604.06304).

Speaker: Mr Nicolas Esser

12:00 PM → 2:00 PM Lunch

2:00 PM → 3:00 PM Invited talks

2:00 PM Dark matter searches at colliders

I will review the programme of Dark Matter searches at the LHC from EFT approaches to simplified models and beyond, discussing the complementarity with direct/indirect searches and the connection to searches for hidden sectors.

Speaker: Ken Mimasu (University of Southampton)

2:30 PM A diffuse flux of Galactic MeV ALPs

MeV scale axion-like particles can be produced with semi-relativistic velocities in Galactic supernovae, leading to a diffuse flux that can be detectable in neutrino water-Cherenkov detectors. This is possible through their absorption on free protons, ap→pγ, where the resulting photon has approximately the energy of the ALP. This new signature is complementary to the usual one from oxygen de-excitation, and can be exploited in various ways. Using SuperKamiokande data, new constraints on the ALP-proton coupling can be derived in regions that cooling bounds cannot probe. Also, this new signature, combined with the one expected at 7 MeV from oxygen de-excitation, could allow us to disentangle ALP-neutron and ALP-proton couplings in the case of a detection.

Speaker: David Cerdeño (Institute for Theoretical Physics (IFT-UAM/CSIC))

3:00 PM → 3:30 PM Coffee break

3:30 PM → 4:45 PM Contributed talks

3:30 PM Uncertainty Relation for Retarded Gravity

Gravity and electromagnetic interactions are the only fundamental physical interactions (outside the nuclear domain). In this work, we shall concentrate on Hamiltonians containing gravitational interaction, which according to general relativity must be retarded. In recent years, retarded gravity has explained many of the mysteries surrounding the “missing mass” related to galactic rotation curves, the Tully–Fisher relations, and gravitational lensing phenomena. Indeed, a recent paper analyzing 143 galaxies has demonstrated that retarded gravity will suffice to explain galaxies’ rotation curves without the need to postulate dark matter for multiple types of galaxies. Moreover, it also demystified the “missing mass” related to galactic clusters and elliptic galaxies in which excess matter was derived through the virial theorem. Here, we give a mathematical criterion that specifies the cases in which retardation is important for gravity (and when it is not). The criterion takes the form of an inequality.

Bibliography

Yahalom, A. Gravitational Hamiltonian Systems and the Retarded Gravity Inequality. Entropy 2024, 26, 986. https://doi.org/10.3390/e26110986

Speaker: Prof. Asher Yahalom (Ariel University)

Retarded Gravity 070726.pdf

Uncertainty Relation for Retarded Gravity 070726.pdf

Uncertainty Relation for Retarded Gravity 070726.pptx

3:45 PM Heavy Dark Baryons: Self-Interactions and the Dark Matter–Baryon Coincidence

We investigate minimal dark matter models based on a confining ($SU(N)$) dark sector, motivated by the central role of non-Abelian gauge forces in the Standard Model. After arguing that dark gluons alone cannot provide viable self-interacting dark matter capable of addressing small-scale structure tensions, we consider theories with dark quarks. Although light dark quarks can generate velocity-dependent self-interactions, they typically require additional structure. We focus instead on the heavy-quark regime, where dark matter forms automatically stable heavy baryons. Exploiting the separation between the compact baryon size and the confinement scale, we compute self-interacting cross sections and find behavior that differs from standard approximations. The parameter space favored by self-interactions points away from conventional freeze-out and towards GeV-scale dark matter, motivating an asymmetric origin and suggesting a possible link to the dark matter–baryon coincidence.

Speaker: Giovani Dalla Valle Garcia (The University of Melbourne)

4:00 PM Analytical sub-$poly\Lambda$CDM through cosmic observations

deviations in the dark energy sector. We systematically compare $\Lambda$CDM with phenomenological extensions inspired by Scalar–Vector–Tensor (SVT) modified gravity, collectively denoted as poly$\Lambda$CDM. These models introduce exotic components with constant equations of state, parametrised by their present‑day density parameters $\Omega_v$, $\Omega_x$, $\Omega_z$ and a fixed exponent $\alpha = 0.5$ for the SVT sector. We use Pantheon+SH0ES Type Ia supernovae (1701 objects), DESI early data release baryon acoustic oscillations (12 correlated measurements), and the Planck 2018 compressed likelihood for the CMB angular scale $\ell_a$. For the CMB we employ the exact sound horizon expression, relating $r_s(z_*)$ to the drag‑epoch scale $r_d$ via the integral correction, with baryon and photon densities scaled consistently with $H_0$. Model comparison uses the Akaike Information Criterion corrected for small samples (AICc). We study a subset of poly$\Lambda$CDM models. Single‑component extensions ($v\Lambda$CDM and $x\Lambda$CDM) yield $\Delta\mathrm{AICc} = 1.07$ and $0.90$ respectively, indicating statistical equivalence with $\Lambda$CDM. Two‑component models ($xz\Lambda$CDM and $vx\Lambda$CDM) are disfavoured ($\Delta\mathrm{AICc} = -1.13$ and $-0.11$). Constraints on exotic densities – e.g. $\Omega_v = 0.37 \pm 0.21$ from $v\Lambda$CDM – provide useful bounds on modified gravity effects across cosmic history. Although $\Lambda$CDM remains the most parsimonious description of current data, the extended models are not ruled out and serve as valuable phenomenological tools to test fundamental physics, particularly in quantifying deviations from a cosmological constant. Current, and upcoming surveys, with advanced data analysis, will sharpen these constraints. This work can be considered as an novel observational test a complementary to gravitational waves potentially testing novel cosmological theories that rise from advanced tensor theories (ATT), advanced manifold metric pairs (AMMP), functors of actions theories (FAT).

Speaker: Pierros Ntelis (Harbin Institute of Technology and Institute of Theoretical Physics at NUU)

4:15 PM Something intangible into something invisible: dark matter searches with neutrinos

As other Standard Model particles, neutrinos can be emitted in dark matter pair-annihilation or decay processes. However, unlike other messengers, neutrinos undergo neither deflection nor absorption over cosmic distances, making them an ideal probe for inspecting dark matter interactions in astrophysical sources, potentially yielding sizeable, high-energy fluxes. Besides, neutrinos can scan very luminous regions such as the Galactic Centre, where a major dark matter reservoir is expected, with a minimal nuisance from background. Neutrino telescopes also have a unique opportunity to look at the Sun, probing interactions of dark matter from the Galactic halo accumulating in its interior.
KM3NeT is a multi-purpose neutrino observatory composed of underwater Cherenkov arrays installed in the Mediterranean Sea. Given its latitude and its ability to measure up-going neutrinos that propagate through the Earth, KM3NeT has the Milky Way Centre in sight for about 70% of the time. Thanks to the optical properties of water KM3NeT has an excellent performance in the reconstruction of coordinates, energy and flavour of neutrino events. Its coverage spans an energy range from the GeV to tens of PeV, opening a broad window onto various dark matter candidate masses. KM3NeT has conducted indirect searches for neutrinos produced in pair annihilations of WIMPs (weakly interacting massive particles), characterising potential signatures from the Galactic Centre using an unbinned maximum likelihood algorithm. Similarly, KM3NeT constrains the WIMP-nucleon scattering cross section occurring in the Sun providing limits that complement the landscape of direct searches. Beyond standard WIMPs, neutrinos probe alternative scenarios, such as heavy dark matter in a secluded scenario, or light dark matter boosted or upscattered by cosmic rays. The decay of a heavy dark matter particle was tested as a possible source for the extreme energy of KM3-230213A, a recently observed neutrino event, still lacking a conclusive astrophysical origin. Utilizing a modular layout, KM3NeT is continuously expanding while actively recording data in its partial configurations. This work presents the latest results obtained from these recently installed configurations.

Speaker: Sara Rebecca Gozzini

4:30 PM The BULLKID-DM experiment: searching for light WIMPs using monolithic arrays of detectors

BULLKID-DM is a cryogenic experiment designed for the direct detection of WIMP-like dark matter particles with mass of 1 GeV or below. The detector will consist of a stack of 16 intrinsic silicon wafers, for a total mass of 800 g, carved into 2320 active dice each with a volume of 5.4×5.4×5 mm3. The silicon dice will be instrumented with multiplexed phonon-mediated Kinetic Inductance Detectors (KIDs), acting as particle absorbers with an individual energy threshold of 200 eV or better. This design results in a fully monolithic yet highly segmented structure, with volume fiducialization capabilities to improve background discrimination. The detector will be operated in a dry dilution refrigerator at the Gran Sasso underground laboratory (LNGS).

To minimize the environmental background, besides the use of radiopure materials, a comprehensive shield system will be implemented, consisting of a mixture of lead, copper and neutron moderator material (B4C) placed both inside and outside the cryostat. A cryogenic anti-coincidence veto system, using scintillating crystals with KIDs readout, is also designed to further suppress the external gamma backgrounds.

A 60 g demonstrator with 180 dice is being tested in a surface laboratory with a lead and copper radiation shield, and it is intended to be validated at LNGS by late 2026. The full experiment is expected to be commissioned in 2027. This presentation will show the milestones achieved so far and the future plans of BULLKID-DM.

Speaker: Matteo Cappelli (Sapienza Universita e INFN, Roma I (IT))

3:30 PM → 4:45 PM Contributed talks 2

3:30 PM High-accuracy binary modelling in scalar-tensor theories of gravity using the self-force approach

A key science target for the upcoming LISA mission is testing General Relativity and probing alternative theories of gravity through the observation of extreme-mass-ratio inspirals (EMRIs). Generating the requisite waveform templates for these systems using numerical relativity is computationally intractable due to the disparate length and time scales involved. Gravitational perturbation theory resolves this bottleneck: by leveraging the extreme mass ratio, we can accurately model the binary dynamics using the self-force approach. Currently, a massive effort is underway to develop high-accuracy self-force models in General Relativity, with a primary obstacle being the derivation and computation of second-order perturbative contributions. However, robustly testing our fundamental theory of gravity also requires rigorous models of EMRIs in modified gravity, allowing us to measure which frameworks best describe the LISA data. In this talk, I formulate the self-force method in general shift-symmetric scalar-tensor theories of gravity through second perturbative order. This work represents the first time the self-force method has been derived beyond linear order for a theory of gravity outside General Relativity. I will also outline progress in extending and implementing our model for future LISA data analysis in testing our theory of gravity.

Speaker: Andrew Spiers (University College Dublin)

3:45 PM Developing Numerical Techniques to Test Scalar–Tensor Theories of Gravity

In this talk, I will describe our recent work on developing a finite element method (FEM)-based code designed to solve the field equations arising in scalar–tensor theories of gravity. In particular, I will explain how our numerical code, SELCIE, can be used to simulate, design, and optimise laboratory, space, and astrophysical tests of gravity. I will present the most recent results on simulating dynamical and static systems, and how these results can be used to optimise ongoing and future tests of gravity. Finally, I will discuss how the outlined tools can be applied to a broader class of theories, e.g. scalar–tensor theories for dark matter.

Speaker: Dr Andrius Tamosiunas (University of Oslo)

4:00 PM Compact stars in $f(R,T,L_m)$ gravity

We investigate the relativistic structure of compact stars within the modified gravity framework $f(R,T,L_m)=R+\alpha T L_m$, which introduces a non-minimal coupling between matter and curvature. The modified Tolman-Oppenheimer-Volkoff equations are solved for neutron stars, quark stars and white dwarfs using realistic equations of state, considering two standard choices for the matter Lagrangian density, $L_m=p$ and $L_m=-\rho$. We show that the coupling parameter $\alpha$ significantly affects the mass-radius relations of such stellar systems. In particular, for white dwarfs, the gravity model allows stable super-Chandrasekhar configurations at high central densities, while for neutron stars it leads to noticeable deviations depending on the choice of $L_m$. The general relativity limit is recovered for $\alpha \to 0$. Furthermore, we confront our models with observational data, including neutron star measurements and white dwarf constraints, to place bounds on $\alpha$. These findings demonstrate that $f(R,T,L_m)$ gravity provides a viable and testable framework for describing the internal structure of compact stars beyond general relativity.

Speaker: Juan Zárate Pretel (Centro Brasileiro de Pesquisas Físicas)

Presentation_JuanZ.pdf

4:15 PM Quantum fields in boson star spacetime

Boson stars are appealing black hole mimickers and dark matter candidates. They have been extensively studied in classical gravity, but their quantum properties remain comparatively unexplored. We compute the quantum scalar fields and stress tensor in boson star spacetimes within the framework of semiclassical gravity. Divergences are regularized using Pauli-Villars fields, and accurate numerical results are obtained through spectral methods. Employing coherent states enables a direct comparison between the classical part of the stress tensor and the quantum fluctuation. Our results indicate that strong spacetime curvature is the primary source of large quantum effects. The renormalized quantum energy density is mostly positive but the radial pressure is negative, suggesting that classical boson star solutions require modification once quantum effects are included. Moreover, in regimes of large curvature, the quantum fluctuations can constitute a significant fraction of the total stress tensor. The methods developed can be generalized to other compact objects and used to study their response to quantum corrections.

Speaker: Qi-Xin Xie (University of Nottingham)

4:30 PM Quantum consistency meets number theory to predict dark matter spectra

Quantum consistency conditions impose powerful constraints on particle theories, but are typically treated as technical requirements in model building. Here we show that anomaly cancellation in a broad class of chiral sectors with light minicharged dark matter is exactly equivalent to the degree-3 Prouhet–Tarry–Escott problem in number theory. This correspondence yields a model-independent lower bound of four mass eigenstates and identifies a large class of minimal solutions with partner states of equal minicharge and nearby mass. These spectral features provide distinctive, testable signatures for laboratory, astrophysical and cosmological searches. By recasting quantum consistency as a number-theoretic classification problem, our results connect formal constraints to predictive structure in dark sectors, establishing a direct bridge between number theory and quantum physics.

This talk is based on expanded version of https://arxiv.org/abs/2603.12320 and follow-up works.

Speaker: Dr Yu-Dai Tsai (Fermilab)

4:45 PM → 5:00 PM Conference closing