Illuminating Dark Matter (2025)

Masha Baryakhtar
University of Washington

Order and Disorder: Dielectrics for Wave Dark Matter Detection

Theories that seek to explain the outstanding puzzles of the Standard Model of particle physics often predict ultralight, feebly-interacting particles. These ultralight particles—scalars, axions, and dark photons—are often produced in the early universe. I will focus on my experimental proposals based on dielectric metamaterials, in which axion and dark photon dark matter can efficiently convert to detectable single photons. While an ordered stack provides the deepest dark matter reach, embracing the randomness of a disordered powder allows for a robust, broadband search.
 

Brian Batell
University of Pittsburgh

Cosmic Stability of Dark Matter from Pauli Blocking

I will discuss a novel sub-eV scalar dark matter (DM) candidate whose stability is due to the Pauli exclusion of its fermionic decay products. The stability of the DM condensate against decays, scatterings, and parametric resonance will be examined. Scattering can populate an interacting thermal dark sector component to energies far above the DM mass which can be probed through precision cosmology. If the lightest neutrino stabilizes the DM, the cosmic neutrino background (CnuB) can be significantly altered from the standard cosmology and thus be probed in the future by CnuB detection experiments.
 

Asher Berlin
Fermilab

Cavendish Tests of Millicharged Particles

A terrestrial population of millicharged particles that interact significantly with normal matter can arise if, e.g., they make up a dark matter subcomponent or if they are light enough to be produced in cosmic ray air showers. Such particles may have evaded detection to date if, through repeated scatters, they rapidly thermalize down to terrestrial temperatures, well below the thresholds of most existing dark matter detectors. I will discuss how reinterpretations of Cavendish tests of Coulomb’s Law, first performed in the late 18th century, provide some of the strongest bounds on this largely unexplored parameter space. I will also propose a simple modification to explore an even larger region of new parameter space, with sensitivity to the irreducible millicharge density generated from cosmic rays.
 

Joe Bramante
Queen’s University

Prospects for Neutron Stars as Dark Matter Detectors

I will review work over the past decade on the possibility that thermal measurements of neutron stars could serve as an incisive, next generation search for dark matter interactions.
 

Miriam Diamond
University of Toronto

Searches for Long-Lived Particles with MATHUSLA

Long-Lived Particles (LLPs) beyond the Standard Model emerge in numerous theoretical frameworks that address key open questions in physics — including dark matter, as well as the hierarchy problem, neutrino masses, and the baryon asymmetry of the universe. The LHC may be producing a significant number of neutral LLPs with masses above a GeV, yet these elusive particles could be escaping detection by the main LHC experiments. To bridge this gap, we have recently produced a Conceptual Design Report for the MATHUSLA detector (MAssive Timing Hodoscope for Ultra-Stable neutraLpArticles), a dedicated surface-based experiment positioned above CMS designed to operate during the High-Luminosity LHC era. MATHUSLA consists of multiple layers of plastic scintillators with wavelength-shifting fibers coupled to silicon photomultipliers, surrounding a large, air-filled decay volume. In this talk, we will present the 40-square-meter MATHUSLA design, optimized for low construction cost while maintaining world-leading sensitivity to LLPs. Additionally, we will discuss our detailed Monte Carlo studies of rare Standard Model background processes in MATHUSLA, and show results from “demonstrator modules” that have been constructed at the University of Victoria and the University of Toronto.
 

Juan Estrada
Fermilab

Dark Matter with Low Threshold Sensors Underground, in Beams and in Telescopes

I will discuss current ideas and plans for exploring the dark sector using skipper- CCDs and other low-threshold silicon imagers in underground experiments, particle beams, and telescopes. There will be a special focus on developments centered at Fermilab, including opportunities for utilizing the future beam facilities at the lab.
 

Glennys Farrar
New York University

The Origin of Ultrahigh Energy Cosmic Rays

Glennys Farrar will give a succinct overview of what is known and what remains uncertain about the spectrum, composition and arrival directions of ultrahigh-energy cosmic rays detected on Earth. Two features of the data compellingly single out binary neutron star mergers as the source of UCRs. A simple analysis of how UCRs are accelerated, initialized to the magnetic fields produced in the merger, predicts a spectrum in quantitative agreement with observation. Smoking-gun predictions of the scenario are 1) coincidences between EHE neutrinos and the gravitational wave produced by the BNS merger and 2) the highest energy UCRs are more massive than iron, having originated as r-process elements.
 

Stefania Gori
University of Califonia, Santa Cruz
Axion Mediated Dark Matter: from Models to Experimental Tests
The direct detection of sub-GeV dark matter (DM) remains a significant challenge due to the low recoil energies involved. In this talk, we focus on the scattering rate of sub-GeV DM particles interacting via spin-dependent couplings with nucleons, in solid-state targets. For DM masses below 100 MeV, the dominant scattering process involves incoherent multiphonon production, which offers a promising avenue to extend sensitivity to this low-mass regime. We evaluate the potential of upcoming experiments to detect such interactions and compare their sensitivity to existing constraints, including those from stellar cooling limits, beam dump experiments, and meson factory searches that probe the mediating particle. Incorporating these bounds, we estimate that future detectors could observe a few scattering events per kilogram per year of exposure.
 

Craig Group
University of Virginia

The Status of LDMX and Related Opportunities

The Light Dark Matter eXperiment (LDMX) is a proposed electron-beam fixed-target experiment that would take place at SLAC and run parasitically with unused electrons from the LCLS-II electron gun. The small-scale experiment promises unprecedented sensitivity to the dark sector in the 1-100 MeV mass scale. Physics opportunities and the status of the planning effort for LDMX will be covered. Other opportunities, related to the beam upgrade at Fermilab, will also be mentioned.
 

Anson Hook
University of Maryland

Predicting the Dark Matter–Baryon Abundance Ratio

We discuss relaxation solutions to the dark matter–baryon coincidence problem in the context of QCD axion dark matter. In relaxation solutions, a moduli dynamically adjusts the mass of dark matter and baryons until their energy densities are O(1) the same. Because the QCD axion is heavily connected to QCD, scanning the QCD axion mass inherently also scans the proton mass. In the context of relaxation solutions, this implies that the ratio of dark matter to baryon abundances (ΩDM/ΩB) is a ratio of beta functions, showing that these models can only accommodate discrete values of ΩDM/ΩB, thereby “predicting” the ratio of the dark matter to baryon abundances.

The original composite axion model has only a single integer degree of freedom N, the size of the gauge group, and we show that when N = 8, the observed value of ΩDM/ΩB = 5.36 is reproduced to within its percent level error bars. Novel tests of this model include more precise measurements of ΩDM/ΩB, a better lattice determination of the dependence of the proton mass on the high-energy QCD gauge coupling, as well as more traditional tests such as fifth force experiments.
 

Felix Kling
DESY

From FASER to the FPF: Looking Forward for Illuminate Dark Matter at the LHC

Physics searches and measurements at high-energy collider experiments traditionally focus on the high-pT region. However, for light and weakly-coupled particles, this emphasis may be misguided, as light particles tend to be highly collimated around the beam line, allowing sensitive searches with small detectors. The FASER experiment was specifically designed to capitalize on this opportunity, expanding the LHC’s physics potential by searching for feebly interacting particles and studying neutrino interactions at TeV energies. The proposed Forward Physics Facility aims to extend this program in the HL-LHC era. In this talk, I will provide an overview over this emerging forward physics program and its potential to offer unique insights for dark sector searches and neutrino measurements.
 

Zhen Liu
University of Minnesota

Beam/Power Sourced Millicharged Particles and Dark Photons

In this talk, I will first present recent progress in using Beam to source millicharged particles, as well as new search constraints and projections from various technologies, ranging from Liquid Argon to Skipper CCD. In the second part, I will present recent developments in a light-shining-through-wall experiment with high- quality superconducting RF cavities, known as Dark SRF.
 

Maxim Pospelov
University of Minnesota

Neutron Stars as Probes of Dark Sector

Neutron stars are born in the violent supernova explosions, when the temperatures reach tens of MeV, replicating in some aspects the environment of the very early Universe. We investigate the faith of MeV dark matter particles in the freeze-in regime that get produced and gravitationally trapped in the newly born neutron stars. We show that the late time annihilation of dark matter back to the Standard Model states will lead to an additional source of heat generation that may be incompatible with observation of stars’ surface temperatures. This sets nontrivial constraints on the space of dark matter models.
 

Subir Sarkar
Oxford University

A Challenge to the Standard Cosmological Model

In the ΛCDM cosmological model, the Universe is assumed to be isotropic and homogeneous when averaged on large scales. That the Cosmic Microwave Background has a dipole anisotropy is interpreted as due to our peculiar (non- Hubble) motion because of local inhomogeneity. There must then be a corresponding dipole in the sky distribution of sources at high redshift. Using catalogues of radio sources and quasars, we find that this expectation is rejected at

>5σ, i.e., the distribution of distant matter is not isotropic in the ‘CMB frame.’ This calls into question the standard practice of boosting to this frame to analyse cosmological data, in particular to infer acceleration of the Hubble expansion rate using Type Ia supernovae, which is then interpreted as due to a cosmological constant Λ. We find that the inferred acceleration is in fact anisotropic (in the direction of the CMB hotspot) and likely a general relativistic effect because of our being embedded in a coherent bulk flow — rather than due to dark energy.
 

Kate Scholberg
Duke University

Dark Matter Searches at Spallation Sources

I’ll describe experimental searches for dark matter at spallation sources. I’ll review current results and discuss prospects for the future.
 

Brian Shuve
Harvey Mudd College

Baryogenesis from Dark Matter Freeze In

Models of freeze in feature a departure from equilibrium over an extended period of the early universe’s history, and they can naturally give rise to the observed matter- antimatter asymmetry. I will present recent developments in freeze-in baryogenesis, including a novel, testable mechanism for the simultaneous production of dark matter and baryogenesis via dark matter oscillations. I will highlight the connections between the early universe dynamics and phenomenology, including tests at colliders, and in cosmological and astrophysical observables.
 

Yotam Soreq
Israel Institute of Technology

The Interplay Between Precision and Intensity for BSM Searches

In this talk, we will discuss novel methods to hunt for new physics beyond the standard model at different energy and length scales, from atomic physics to future colliders.
 

Haibo Yu
UC Riverside

Astrophysical Signatures of Gravothermal Collapse in Dark Matter Halos

Haibo Yu will present recent high-resolution N-body simulations of self-interacting dark matter and examine their implications across a wide range of astrophysical observations. Yu will highlight novel signatures associated with gravothermal collapse in dark matter halos. Yu will explore the prospects for detecting these signatures through observations of strong gravitational lensing systems, stellar streams, and supermassive black holes. These studies open new avenues for probing the fundamental nature of dark matter.