We present a new dark matter candidate, the inelastically decoupling relic (iELDER), which is a cold thermal relic whose abundance is determined by the freeze out of its inelastic scattering off of bath particles in the presence of <math xmlns="http://www.w3.org/1998/Math/MathML" display="inline"><mn>3</mn><mo stretchy="false">→</mo><mn>2</mn></math> self-annihilations. The dark matter is predicted to be light, in the <math xmlns="http://www.w3.org/1998/Math/MathML" display="inline"><mi mathvariant="script">O</mi><mo stretchy="false">(</mo><mi>MeV</mi><mo>−</mo><mi>GeV</mi><mo stretchy="false">)</mo></math> range, with significant self-annihilations and very weak inelastic couplings to ordinary matter. We demonstrate iELDER dark matter using a <math xmlns="http://www.w3.org/1998/Math/MathML" display="inline"><msub><mi>Z</mi><mn>3</mn></msub></math>-symmetric toy model as well as quantum chromodynamics (QCD)-like pion theories—the latter showing promising prospects for detection and providing a new benchmark for future searches.

Israel

Ronny Frumkin

United States

Yonit Hochberg

Eric Kuflik

Binyamin Vilk

Inelastically decoupling dark matter

In a seminal paper now a decade old, it was shown that dark-matter detectors geared at probing interactions with nucleons could also be used to probe dark-matter interactions with electrons. In this Letter, we show that new detector concepts designed to probe dark-matter–electron interactions at low masses can similarly be used to probe new parameter space for dark-matter–nucleon interactions. We demonstrate the power of this approach by using existing data from superconducting detectors to place new limits on the interactions of nuclei with MeV-scale dark matter. Further, we show that advances in detector technology that have been anticipated for electronic interactions will automatically extend sensitivity deep into uncharted territory for nuclear interactions. This doubles the effective science output of future low-threshold experiments.

Sinéad M. Griffin

Guy Daniel Hadas

United Kingdom

Katherine Inzani

Benjamin V. Lehmann

Dark-Matter–Electron Detectors for Dark-Matter–Nucleon Interactions

We present the first results from the Quantum Resolution-Optimized Cryogenic Observatory for Dark matter Incident at Low Energy (QROCODILE). The QROCODILE experiment uses a microwire-based superconducting nanowire single-photon detector (SNSPD) as a target and sensor for dark matter scattering and absorption, and is sensitive to energy deposits as low as 0.11 eV. We introduce the experimental configuration and report new world-leading constraints on the interactions of sub-MeV dark matter particles with masses as low as 30 keV. The thin-layer geometry of the system provides anisotropy in the interaction rate, enabling directional sensitivity. In addition, we leverage the coupling between phonons and quasiparticles in the detector to simultaneously constrain interactions with both electrons and nucleons. We discuss the potential for improvements to both the energy threshold and effective volume of the experiment in the coming years.

Switzerland

Laura Baudis

Alexander Bismark

Noah Brugger

Chiara Capelli

Ilya Charaev

Jose Cuenca García

Germany

Judith K. Hohmann

Alexander Kavner

Christian Koos

Artem Kuzmin

Severin Nägeli

Titus Neupert

Bjoern Penning

Diego Ramírez García

Andreas Schilling

First Sub-MeV Dark Matter Search with the QROCODILE Experiment Using Superconducting Nanowire Single-Photon Detectors

Inverse decays are an interesting avenue for producing dark matter in the early Universe. We study in detail various phases of dark matter parameter space where inverse decays control its abundance, expanding on our work of inverse decay (INDY) dark matter and going beyond. The role of initial conditions and the impact of departure from kinetic equilibrium are investigated as well. We show how these inverse decay phases can arise in theories of a kinetically mixed dark photon and dark Higgs, with promising prospects for detection at upcoming experiments.

Japan

Hitoshi Murayama

Phases of dark matter from inverse decays

Low-energy Compton scattering is an important background for sub-GeV dark matter direct-detection and other experiments. Current Compton scattering calculations typically rely on assumptions that are not valid in the low-energy region of interest, beneath <math><mrow><mo>∼</mo><mn>50</mn><mtext> </mtext><mtext> </mtext><mi>eV</mi></mrow></math>. Here we relate the low-energy Compton scattering differential cross section to the dielectric response of the material. Our new approach can be used for a wide range of materials and includes all-electron, band-structure, and collective effects, which can be particularly relevant at low energies. We demonstrate the strength of our approach in several solid-state systems, in particular, Si, Ge, GaAs, and SiC, which are relevant for current and proposed experiments searching for dark matter, neutrinos, and millicharged particles.

Rouven Essig

Slovenia

Yutaro Shoji

Aman Singal

Gregory Suczewski

Low-energy Compton scattering in materials

Axionlike-particles are a well-motivated extension of the Standard Model that can mediate interactions between the dark matter and ordinary matter. Here we consider an axion portal between the two sectors, where the axion couples to dark matter and to QCD gluons. We establish the relevant processes of interest across the scales of dark matter and axion masses and couplings, identify the distinct mechanisms that control the dark matter relic abundance in each case, and extract the resulting experimental signatures of the gluonic axion portal to dark matter.

Patrick J. Fitzpatrick

Rotem Ovadia

Yotam Soreq

Dark matter through the axion-gluon portal

Direct detection for sub-GeV dark matter is developing rapidly, with many novel experimental ideas and theoretical methods emerging. In this work, we extend the dielectric formalism for dark matter scattering to incorporate anisotropic material responses, enabling directionally sensitive experiments with a broad class of target materials. Using a simple model of an anisotropic electron gas, we demonstrate the importance of many-body effects such as the plasmon and show that, even when the dark matter kinetic energies are much smaller than the plasmon energy, the tail of an anisotropic plasmon can still produce a sizable daily modulation. We highlight the relevant experimental techniques required to establish the target response as well as the challenges in extracting a response function which is truly free of modeling uncertainties.

Christian Boyd

Yonatan Kahn

Eric David Kramer

Noah Kurinsky

To Chin Yu

Directional detection of dark matter with anisotropic response functions

Superconducting detectors have been proposed as outstanding targets for the direct detection of light dark matter scattering at masses as low as a keV. We study the prospects for directional detection of dark matter in isotropic superconducting targets from the angular distribution of excitations produced in the material. We find that dark matter scattering produces initial excitations with an anisotropic distribution, and further show that this directional information can be preserved as the initial excitations relax. Our results demonstrate that directional detection is possible for a wide range of dark matter masses, and they pave the way for light dark matter discovery with bulk superconducting targets.

Directional detection of light dark matter in superconductors

We propose a new thermal dark matter candidate whose abundance is determined by the freeze-out of inverse decays. The relic abundance depends parametrically only on a decay width, while matching the observed value requires that the coupling determining the width—and the width itself—should be exponentially small. The dark matter is therefore very weakly coupled to the standard model, evading conventional searches. This inverse decay dark matter can be discovered by searching for the long-lived particle that decays into the dark matter at future planned experiments.

Thermal Dark Matter from Freeze-Out of Inverse Decays

Superconducting nanowires, a mature technology originally developed for quantum sensing, can be used as a target and sensor with which to search for dark matter interactions with electrons. Here we report on a 180-hour measurement of a tungsten silicide superconducting nanowire device with a mass of 4.3 nanograms. We use this to place new constraints on dark matter–electron interactions, including the strongest terrestrial constraints to date on sub-MeV (sub-eV) dark matter that interacts with electrons via scattering (absorption) processes.