We examine the signals produced by dark-matter interactions with electrons, which play a crucial role in direct detection experiments employing heavy target materials, particularly in many well-motivated sub-GeV dark-matter scenarios. When the momentum transfer to target electrons is comparable to or exceeds their binding energy, atomic effects related to electron ionization become essential for accurately determining signal rates—especially in the case of fast-moving dark matter. In this paper, we revisit and extend the atomic ionization formalism, systematically comparing different approaches used to formulate the ionization form factor and identifying their respective domains of validity. As practical applications, we explore detection prospects in xenon target experiments. To illustrate our findings, we consider a specific scenario involving boosted dark matter, which often leads to high-momentum electron recoils. Our analysis demonstrates that the choice of formalism can significantly influence the interpretation of experimental data, depending on the regions of parameter space.

Saudi Arabia

Haider Alhazmi

United States

Doojin Kim

Kyoungchul Kong

Canada

Gopolang Mohlabeng

South Korea

Jong-Chul Park

Seodong Shin

Direct detection of fast-moving low-mass dark matter

Dark matter (DM) could self-annihilate into neutrinos in dense regions of the Universe. We consider the resulting flux of neutrinos from the Milky Way DM halo and derive exclusion limits on the annihilation cross section using XENONnT electron recoil data. Assuming a <math xmlns="http://www.w3.org/1998/Math/MathML" display="inline"><mi>J</mi></math> factor independent of the annihilation cross section, we find leading limits for DM masses below <math xmlns="http://www.w3.org/1998/Math/MathML" display="inline"><mi mathvariant="script">O</mi><mo stretchy="false">(</mo><mi>MeV</mi><mo stretchy="false">)</mo></math>. Self-annihilating DM affects the DM halo via dissolution, introducing a cross-section dependency on the halo profile and thus the <math xmlns="http://www.w3.org/1998/Math/MathML" display="inline"><mi>J</mi></math> factor. We discuss such a situation in more detail, finding that the signal rate is below the experimental sensitivity of XENONnT, leaving the annihilation cross section unconstrained.

Germany

Boris Betancourt Kamenetskaia

Merlin Reichard

India

Gaurav Tomar

Investigating sub-MeV dark matter annihilation to neutrinos using direct detection experiments

We propose a new dark-matter detection strategy that will potentially enable the search for super-light dark matter <math xmlns="http://www.w3.org/1998/Math/MathML" display="inline"><mrow><msub><mrow><mi>m</mi></mrow><mrow><mi>χ</mi></mrow></msub><mo>≃</mo><mn>0.1</mn><mtext> </mtext><mtext> </mtext><mi>keV</mi></mrow></math>, improving the minimum detectable mass by more than 3 orders of magnitude compared to ongoing experiments. This can be achieved by intimately integrating the target material, specifically the <math xmlns="http://www.w3.org/1998/Math/MathML" display="inline"><mi>π</mi></math>-bond electrons in graphene, into a Josephson junction to create a highly sensitive detector capable of detecting energy deposits from dark matter as small as <math xmlns="http://www.w3.org/1998/Math/MathML" display="inline"><mrow><mo>∼</mo><mn>0.1</mn><mtext> </mtext><mtext> </mtext><mi>meV</mi></mrow></math>. We investigate detection prospects of pg-, ng-, and <math xmlns="http://www.w3.org/1998/Math/MathML" display="inline"><mrow><mi mathvariant="normal">μ</mi><mi mathvariant="normal">g</mi><mtext>−</mtext><mi>scale</mi></mrow></math> detectors by calculating the scattering rate between dark matter and free electrons confined in two-dimensional graphene, including Pauli-blocking factors and in-medium screening effects. We find that the proposed detector is expected to not only serve as a complementary probe of superlight dark matter but also achieve higher experimental sensitivities than other proposed experiments, assuming zero readout noise, thanks to the extremely low threshold energy of our graphene Josephson junction sensor.

Gil-Ho Lee

Kin Chung Fong

Graphene-based super-light invisible matter particle search

We consider D-branes in the Dabholkar-Park (DP) background, a 9d orientifold theory obtained by gauging symmetry in the type IIB string theory compactified on a circle. Using anomalies in the world-sheet theory, we provide physical insights into the classification of stable D-branes by relative KR-theory. The nature, such as stability, of D-branes wrapping along the compactified circle can be extracted from information about 1d Majorana fermions on the boundary of the world-sheet. These Majorana fermions need to be introduced to consistently perform the GSO projection and the orientifold. We also construct D-brane states in the DP background. The spectrum of D-branes characterized by the relative KR-theory is correctly reproduced from the D-brane states.

Japan

Hiroki Wada

Satoshi Yamaguchi

Anomalies and D-branes in the Dabholkar-Park background

Abstract We explore extensive N-body simulations with two-component cold dark matter candidates. We delve into the temperature evolution, power spectrum, density perturbation, and maximum circular velocity functions. We find that the substantial mass difference between the two candidates and the annihilation of the heavier components to the lighter ones effectively endow the latter with warm dark matter-like behavior, taking advantage of all distinct features that warm dark matter candidates offer, without observational bounds on the warm dark matter mass. Moreover, we demonstrate that the two-component dark matter model aligns well with observational data, providing valuable insights into where and how to search for the elusive dark matter candidates in terrestrial experiments.

Jeong Han Kim

Se Hwan Lim

Warm Surprises from Cold Duets: -Body Simulations with Two-Component Dark Matter

We propose a new approach to search for light dark matter (DM), with keV–GeV mass, via inelastic nucleus scattering at large-volume neutrino detectors such as Borexino, DUNE, Super-K, Hyper-K, and JUNO. The approach uses inelastic nuclear scattering of cosmic-ray boosted DM, enabling a low-background search for DM in these experiments. Large neutrino detectors, with higher thresholds than dark matter detectors, can be used, since the nuclear deexcitation lines are <math><mrow><mi>O</mi><mo>(</mo><mn>10</mn><mo>)</mo><mtext> </mtext><mtext> </mtext><mi>MeV</mi></mrow></math>. Using a hadrophilic dark-gauge-boson-portal model as a benchmark, we show that the nuclear inelastic channels generally provide better sensitivity than the elastic scattering for a large region of light DM parameter space.

Bhaskar Dutta

Wei-Chih Huang

Australia

Jayden L. Newstead

Iman Shaukat Ali

Prospects for Light Dark Matter Searches at Large-Volume Neutrino Detectors

We propose a novel experimental scheme, called DAMSA (Dump-produced Aboriginal Matter Searches at an Accelerator), for searching for dark-sector particles, using rare nuclear isotope accelerator facilities that provide high-flux proton beams to produce a large number of rare nuclear isotopes. The high-intensity nature of their beams enables the investigation of dark-sector particles, including axionlike particles (ALPs) and dark photons. By contrast, their typical beam energies are not large enough to produce the backgrounds such as neutrinos resulting from secondary charged particles. The detector of DAMSA is then placed immediate downstream of the proton beam dump to maximize the prompt decay signals of dark-sector particles, which are often challenging to probe in other beam-dump-type experiments featuring a longer baseline, at the expense of an enormous amount of the beam-related neutron background. We demonstrate that beam-related neutrons can be significantly suppressed if the signal accompanies multiple, correlated visible particles in the final state. We show that the close proximity of the detector to the ALP production dump makes it possible to probe a high-mass region of ALP parameter space that the existing experiments have never explored.

Wooyoung Jang

Youngjoon Kwon

Min Sang Ryu

Richard G. Van de Water

Un-Ki Yang

Jaehoon Yu

Search prospects for axionlike particles at rare nuclear isotope accelerator facilities

Abstract We apply the festina lente (FL) bound on a hidden sector with U(1) gauge symmetries. Since the FL bound puts a lower bound on masses of particles charged under the U(1) gauge symmetries, it is possible to constrain the hidden sector even with a tiny coupling to the Standard Model. In particular, we focus on the phenomenological implications of the FL bound on milli-charged particles, which naturally arise when kinetic mixing between the photon and the hidden photon is allowed. It turns out that the milli-charged particle with the mass M ≲ 5 meV is prohibited by the FL bound in the case of a single hidden U(1), insensitively of the value of small kinetic mixing. This bound is crucial when bosonic dark matter is taken into consideration in this framework: the fuzzy bosonic dark matter models requesting minuscule masses are ruled out by the FL bound if the longevity of dark matter is protected by the hidden gauge symmetry.

Kayoung Ban

Dhong Yeon Cheong

Hiroshi Okada

Hajime Otsuka

Seong Chan Park

Phenomenological implications on a hidden sector from the festina lente bound

The sensitivity to dark matter signals at neutrino experiments is fundamentally challenged by the neutrino rates, as they leave similar signatures in their detectors. As a way to improve the signal sensitivity, we investigate a dark matter search strategy which utilizes the timing and energy spectra to discriminate dark matter from neutrino signals at low-energy, pulsed-beam neutrino experiments. This strategy was proposed in our companion paper Phys. Rev. Lett. 124 (2020) 121802 [1], which we apply to potential searches at COHERENT, JSNS2, and CCM. These experiments are not only sources of neutrinos but also high intensity sources of photons. The dark matter candidate of interest comes from the relatively prompt decay of a dark sector gauge boson which may replace a Standard-Model photon, so the delayed neutrino events can be suppressed by keeping prompt events only. Furthermore, prompt neutrino events can be rejected by a cut in recoil energy spectra, as their incoming energy is relatively small and bounded from above while dark matter may deposit a sizable energy beyond it. We apply the search strategy of imposing a combination of energy and timing cuts to the existing CsI and LAr data of the COHERENT experiment as concrete examples, and report a mild excess beyond known backgrounds. We then investigate the expected sensitivity reaches to dark matter signals in our benchmark experiments.

Shu Liao

Louis Strigari

Adrian Thompson

Searching for dark matter signals in timing spectra at neutrino experiments

The dark matter interpretation for a recent observation of excessive electron recoil events at the XENON1T detector seems challenging because its velocity is not large enough to give rise to recoiling electrons of <math> <mi>O</mi> <mfenced> <mi>keV</mi> </mfenced> </math> $$ \mathcal{O}\left(\mathrm{keV}\right) $$ . Fast-moving or boosted dark matter scenarios are receiving attention as a remedy for this issue, rendering the dark matter interpretation a possibility to explain the anomaly. We investigate various scenarios where such dark matter of spin 0 and 1/2 interacts with electrons via an exchange of vector, axial-vector, pseudo-scalar, or scalar mediators. We find parameter values not only to reproduce the excess but to be consistent with existing bounds. Our study suggests that the scales of mass and coupling parameters preferred by the excess can be mostly affected by the type of mediator, and that significantly boosted dark matter can explain the excess depending on the mediator type and its mass choice. The method proposed in this work is general, and hence readily applicable to the interpretation of observed data in the dark matter direct detection experiment.

Implications of the XENON1T excess on the dark matter interpretation