arXiv subjects

Jayden L. Newstead

Publications and source records attributed to Jayden L. Newstead.

At least 19 recordsLinked to original sources

arXiv2026

Spin-independent scattering of pseudoscalar-mediated dark matter

Dark matter with pseudoscalar couplings provides a well-motivated scenario in which direct-detection signals are suppressed at tree level, since the scattering off nuclei is both spin-dependent and momentum suppressed. While spin-independent scattering is absent at tree level, it arises at one loop and can provide the leading direct-detection signal. We revisit this scenario in a general sub-electroweak effective field theory with a light pseudoscalar mediator, including interactions through to mass-dimension-six. We compute the matching onto the quark and gluon operators relevant for direct detection to determine whether this scenario could be detectable at future experiments, while also requiring consistency with the observed dark matter relic-abundance and indirect-detection limits. We find that while models with a pseudoscalar mediator can generate spin-independent cross sections above the neutrino floor, this generally requires additional new physics below the TeV scale.

hep-ph↗

arXiv2026

Exothermic and Endothermic Inelastic Dark Matter Interpretations at LZ: Sideband Constraints and Future Prospects

The LZ experiment has extended its nuclear-recoil search to 270 keV and reports a single nuclear-recoil-like event, LZ230616, at $\sim250$ keV, in a region with negligible expected background. We show that exothermic inelastic dark matter, in which the ambient dark state down-scatters and releases its mass splitting $|δ|$ as recoil energy, can naturally produce a recoil peak at this energy while remaining consistent with the null result at lower energies. Our simple fit leaves the mass unconstrained, because a heavy candidate can hide its peak above the LZ region-of-interest. However, we show that the empty high-energy sideband, which LZ uses for background validation, disfavors broadly peaked spectra. For an exothermic explanation, the sharper peaks produced by lighter dark matter with larger mass splittings are therefore preferred. Realizing this scenario requires cosmologically stable states and a leptophobic mediator. Normalizing to the one observed event, we predict $\simeq4.5$ signal events in LZ's projected 1000 live-day exposure, and show that existing XENONnT and PandaX-4T data could already test the interpretation in an extended analysis window.

hep-ph↗

arXiv2026

Dark matter energy exchange in stars orbiting supermassive black holes

Stars on tight orbits around the supermassive black hole at the Galactic Center pass through regions where the dark matter~(DM) density may be strongly enhanced. We compute the orbit-averaged DM-induced energy exchange for S4714 as an example. It is a star on an exceptionally close and relativistic orbit around Sagittarius~A*. For a spiked dark matter profile, the exchange reaches the stellar luminosity at $σ_{χp} \sim 10^{-36}~\mathrm{cm}^2$ for MeV-GeV masses and $σ_{χe} \sim 5\times10^{-38}~\mathrm{cm}^2$ for sub-MeV masses, opening a new annihilation-free route toward dark-star phases. These cross sections lie within the range predicted by freeze-in scenarios and are consistent with cosmic-ray--boosted and solar-reflection dark matter constraints.

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arXiv2026

Dark Matter Induced Nucleon Decay Through the Neutron Portal

The neutron portal operator provides a theoretically motivated connection between the visible and dark sectors and features in several well-studied asymmetric dark matter models. This operator leads to dark matter induced nucleon decays that mimic the experimental signature of "ordinary" nucleon decays. In this work, we reinterpret Super-Kamiokande nucleon decay searches for $n \rightarrow π^0 ν$ and $p \rightarrow π^+ ν$ to constrain dark matter induced nucleon decays. For GeV-scale dark matter, we obtain lower bounds of $\mathcal{O}(1~\rm{TeV})$ on the scale of the effective neutron portal operator. We also discuss the prospects for future searches at Hyper-Kamiokande and highlight the importance of a dedicated experimental analysis with reduced systematic uncertainties.

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arXiv2026

Discriminating Dark Matter Origins with Directional Detection

Scenarios where dark matter is boosted to relativistic velocities provide a promising probe of sub-GeV dark matter. Cosmic-ray upscattered and supernova-produced dark matter generate relativistic fluxes peaked toward the Galactic Centre, an anisotropy that offers a strong directional signature and is not mimicked by any terrestrial or cosmic background. We determine how many directional recoil events are required in a gas time-projection chamber to distinguish various scenarios for the origin of dark matter particles arriving in the solar system, which are otherwise indistinguishable without directionality. We find that standard halo dark matter particles can be distinguished from boosted populations with as few as $\mathcal{O}(20)$ events under reasonable track reconstruction performance and background conditions.

hep-ph↗

arXiv2026

Directional recoil detection for CEvNS measurements with light nuclei at the Spallation Neutron Source

The coherent elastic scattering of neutrinos on nuclei, also known as CEvNS, has been studied for several years by the COHERENT program of experiments using neutrinos from stopped-pion decays produced at the Spallation Neutron Source (SNS). We propose a new approach for CEvNS measurements at the SNS that aims to complement the COHERENT experiments in two main ways: by reconstructing the angular distribution of CEvNS-induced recoils, and by measuring CEvNS on much lighter target nuclei such as helium, carbon, and fluorine. The proposed detector would employ a gaseous time-projection chamber with a highly segmented charge readout to enable the spatial reconstruction of $\sim$10-500 keV ionisation tracks created by CEvNS-induced recoils. This would enable the simultaneous measurement of the CEvNS recoil energy and scattering angle, thereby allowing event-by-event reconstruction of the neutrino energy. We estimate that a 60:40 He:CF$_4$ gas mixture at atmospheric pressure offers a good trade-off between total target mass and good directionality and could deliver a detection of the angular distribution of CEvNS, even under pessimistic background conditions. We project the sensitivity of 1 and 10 m$^3$-scale detectors in the context of several physics cases, including: the measurement of the Standard Model CEvNS cross section, reconstruction of the flavour-dependent neutrino fluxes, observing the neutrino-induced Migdal effect, constraints on beyond-Standard Model neutrino interactions, and probing 10-eV-scale sterile neutrinos.

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arXiv2025

Nuclear and electron scattering by neutrinos and dark matter in condensed systems

Low-threshold dark matter detectors, in particular cryogenic detectors based on dielectric materials, are among the best tools for probing sub-GeV dark matter masses. In the coming years detectors of this type will become sensitive to solar neutrino scattering. Previous work has shown that, for dark matter scattering at very low recoil energies, one must include collective excitations of the electrons in the solid. In this work, we have computed the collective excitations due to neutrino scattering on electrons and nuclei. We find the full electron-scattering response at leading order is captured by 5 structure factors and identify the leading component with the electron energy-loss function. Then, using silicon and germanium detectors as an example, we perform a dark matter sensitivity study and compute their respective neutrino floors. Lastly, we show that these detectors are sensitive to unexplored scenarios of beyond-Standard Model neutrino physics, within the exposure required to reach the neutrino floor.

hep-ph↗

arXiv2025

Measuring the Cosmic Ray Spectrum with Next Generation Neutrino Detectors

We investigate the capabilities of upcoming kiloton-scale neutrino detectors, such as Hyper-Kamiokande, in determining the primary cosmic ray spectrum. These detectors provide full-sky coverage and long-term monitoring, unlike traditional satellite and balloon experiments that measure cosmic ray flux at specific altitudes and locations. By analyzing the atmospheric neutrino flux generated by cosmic ray interactions, we demonstrate that future detectors can differentiate between various cosmic ray models with high statistical significance, even when accounting for uncertainties in neutrino cross sections and hadronic interactions. We introduce a technique for reconstructing the primary cosmic ray spectrum using neutrino measurements, which reduces the flux uncertainty from approximately 20\% to about 7\%. We then show that Hyper-K has the potential to increase sensitivity to neutrino oscillation parameters, such as $\sin^2θ_{23}$, by a factor of 2. Our results highlight the complementary role of neutrino detectors in cosmic ray physics and their critical importance for precision measurements in particle astrophysics.

hep-ph↗

arXiv2025

Detailed nuclear structure calculations for coherent elastic neutrino-nucleus scattering

Any discovery of `new physics' in the neutrino sector first requires a precise prediction of the expected Standard Model cross section. Currently, Coherent Elastic neutrino-Nucleus Scattering (CEvNS) experiments are statistics limited. However, as new and future experiments scale up, it will be necessary to improve the theoretical predictions. Here we review the calculation of the CEvNS cross section in a consistent theory of hadronic currents and compute the relevant nuclear form factors using the nuclear shell model. The uncertainty on the form factors is explored by repeating the calculation for various shell model interactions and with Skyme-Hartree-Fock evaluations of the Weak-charge radii. We then refine the Standard Model predictions for the recent experimental results of the COHERENT experiment. We find that our cross sections are in good agreement with previous predictions, but with significantly smaller uncertainties - by up to a factor of 10. Near-future CEvNS experiments will meaningfully benefit from improved predictions through an increased sensitivity to new-physics signals.

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arXiv2024

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

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 O(10) MeV. 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.

hep-ph↗

arXiv2024

Enhancing DUNE's solar neutrino capabilities with neutral-current detection

We show that the Deep Underground Neutrino Experiment (DUNE) has the potential to make a precise measurement of the total active flux of 8B solar neutrinos via neutral-current (NC) interactions with argon. This would complement proposed precise measurements of solar-neutrino fluxes in DUNE via charged-current (CC) interactions with argon and mixed CC/NC interactions with electrons. Together, these would enable DUNE to make a SNO-like comparison of rates and thus to make the most precise measurements of $\sin^2θ_{12}$ and $Δm^2_{21}$ using solar neutrinos. Realizing this potential requires dedicated but realistic efforts to improve DUNE's low-energy capabilities and separately to reduce neutrino-argon cross section uncertainties. Comparison of mixing-parameter results obtained using solar neutrinos in DUNE and reactor antineutrinos in JUNO (Jiangmen Underground Neutrino Observatory) would allow unprecedented tests of new physics.

hep-ph↗

arXiv2024

Cosmic-ray dark matter confronted by constraints on new light mediators

The detectability of light dark matter in direct detection experiments is limited by the small kinetic energy of the recoiling targets. Thus, scenarios where dark matter is boosted to relativistic velocities provide a useful tactic to constrain sub-GeV dark matter particles. Of the possible dark matter boosting mechanisms, cosmic-ray upscattering is an appealing paradigm as it doesn't require any additional assumptions beyond dark matter coupling to nucleons or electrons. However, detectable signals are obtained only with relatively large cross sections which, in turn, can only be realized with large couplings, light mediators or composite dark matter. In this work we consider a general set of light mediators that couple dark matter to hadrons. Using data from Borexino, XENON1T, LZ and Super-K, we show that existing constraints on such mediators preclude appreciable cosmic-ray dark matter upscattering. This finding highlights the limited applicability of cosmic-ray upscattering constraints and suggests they only be used in model-dependent studies.

hep-ph↗

arXiv2024

Exploring light dark matter with the Migdal effect in hydrogen-doped liquid xenon

An ongoing challenge in dark matter direct detection is to improve the sensitivity to light dark matter in the MeV--GeV mass range. One proposal is to dope a liquid noble-element direct detection experiment with a lighter element such as hydrogen. This has the advantage of enabling larger recoil energies compared to scattering on a heavy target, while leveraging existing detector technologies. Direct detection experiments can also extend their reach to lower masses by exploiting the Migdal effect, where a nuclear recoil leads to electronic ionisation or excitation. In this work we combine these ideas to study the sensitivity of a hydrogen-doped LZ experiment (HydroX), and a future large-scale experiment such as XLZD. We find that HydroX could have sensitivity to dark matter masses as low as 5~MeV for both spin-independent and spin-dependent scattering, with XLZD extending that reach to lower cross sections. Notably, this technique substantially enhances the sensitivity of direct detection to spin-dependent proton scattering, well beyond the reach of any current experiments.

hep-ph↗

arXiv2023

Probing the dark sector with nuclear transition photons

Here we present world-leading sensitivity to light ($< 170$ MeV) dark matter (DM) using beam-dump experiments. Dark sector particles produced during pion decay at accelerator beam-dumps can be detected via scattering in neutrino detectors. The decay of nuclei excited by the inelastic scattering of DM is an unexploited channel which has significantly better sensitivity than similar searches using the elastic scattering channel. We show that this channel is a powerful probe of DM by demonstrating sensitivity to the thermal relic abundance benchmark in a scalar DM dark-photon portal model. This is achieved through the use of existing data, obtained by the KARMEN experiment over two decades ago, which allow us to set world-leading constraints on this model over a wide mass range. With experimental improvements planned for the future, this technique will be able to probe the thermal relic benchmark for fermionic DM across a wide mass range.

hep-ph↗

arXiv2022

Inelastic nuclear scattering from neutrinos and dark matter

Neutrinos with energy of order 10~MeV, such as from pion decay-at-rest sources, are an invaluable tool for studying low-energy neutrino interactions with nuclei -- previously enabling the first measurement of coherent elastic neutrino-nucleus scattering. Beyond elastic scattering, neutrinos and dark matter in this energy range also excite nuclei to its low-lying nuclear states, providing an additional physics channel. Here, we consider neutral-current inelastic neutrino-nucleus and dark matter(DM)-nucleus scattering off $^{40}$Ar, $^{133}$Cs, and $^{127}$I nuclei that are relevant to a number of low-threshold neutrino experiments at pion decay-at-rest facilities. We carry out large scale nuclear shell model calculations of the inelastic cross sections considering the full set of electroweak multipole operators. Our results demonstrate that Gamow-Teller transitions provide the dominant contribution to the cross section and that the long-wavelength limit provides a reasonable approximation to the total cross section for neutrino sources. We show that future experiments will be sensitive to this channel and thus these results provide additional neutrino and DM scattering channels to explore at pion decay-at-rest facilities.

hep-ph↗

arXiv2022

Low-Mass dark matter (in)direct detection with inelastic scattering

We revisit the detection of luminous dark matter in direct detection experiments. In this scenario, dark matter scatters endothermically to produce an excited state, which decays to produce a photon. We explore ways in which the electron recoil signal from the decay photon can be differentiated from other potential electron recoil signals with a narrow spectral shape. We find that larger volume/exposure xenon detectors will be unable to differentiate the signal origin without significant improvements in detector energy resolution of around an order of magnitude. We also explore what can be learned about a generic luminous dark matter signal with a higher resolution detector. Motivated by the advancements in energy resolution by solid-state detectors, we find that sub-eV resolution enables the discovery of LDM in the presence of background levels that would otherwise make observation impossible. We also find that sub-eV resolution can be used to determine the shape of the luminous dark matter decay spectrum and thus constrain the dark matter mass and velocity distribution.

hep-ph↗

arXiv2022

Snowmass2021 Cosmic Frontier White Paper: Calibrations and backgrounds for dark matter direct detection

Future dark matter direct detection experiments will reach unprecedented levels of sensitivity. Achieving this sensitivity will require more precise models of signal and background rates in future detectors. Improving the precision of signal and background modeling goes hand-in-hand with novel calibration techniques that can probe rare processes and lower threshold detector response. The goal of this white paper is to outline community needs to meet the background and calibration requirements of next-generation dark matter direct detection experiments.

hep-ex↗

arXiv2022

Observing the Migdal effect from nuclear recoils of neutral particles with liquid xenon and argon detectors

In recent years, dark matter direct detection experiments have spurred interest in the Migdal effect, where it is employed to extend their sensitivity to lower dark matter masses. Given the lack of observation of the Migdal effect, the calculation of the signal is subject to large theoretical uncertainties. It is therefore desirable to attempt a first measurement of the Migdal effect, and to test the theoretical predictions of the Migdal effect for the calibration of the experimental response to a potential dark matter signal. In this work, we explore the feasibility of observing the Migdal effect in xenon and argon. We carry out proof-of-concept calculations for low-energy neutrons from a filtered source, and using a reactor, the Spallation Neutron Source, or $^{51}$Cr as potential neutrino sources. We perform a detector simulation for the xenon target and find that, with available technology, the low-energy neutron source is the most promising, requiring only a modest neutron flux, detector size, and exposure period.

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