arXiv subjects

James B. Dent

Publications and source records attributed to James B. Dent.

At least 19 recordsLinked to original sources

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

Primordial black holes from Q-balls produced in a first-order phase transition

We consider the formation of Q-balls in false vacuum remnants during a cosmological first-order phase transition. We find that under certain circumstances Q-balls can collapse to form primordial black holes. This scenario can produce multimessenger signals that may be observed at upcoming experiments, including 1-100 nHz gravitational waves from the phase transition, and gamma-rays emitted from primordial black holes as Hawking radiation and as superradiance. These signals are quite distinctive, and differ markedly from signals expected from Fermi-balls. The reheating of the dark sector from the phase transition may address the Hubble tension.

hep-ph↗

arXiv2026

Gravitational Waves and Cosmological Observables from First-Order Phase Transitions: Thermal Corrections at Low Temperature

We consider the impact on cosmological first-order phase transitions (FOPTs) of low-temperature thermal corrections to the effective potential. These are corrections from degrees of freedom whose field-dependent masses in the true vacuum are much larger than the nucleation temperature, though in the false vacuum the field-dependent masses may be much smaller than the nucleation temperature. We focus on the regime in which the thin-wall approximation is valid, and in which these corrections are small enough that they do not alter the vacuum structure of the theory. Although the general form of these corrections to the thermal effective potential can be quite complicated, we argue that the net effect of all such corrections can be well-modeled in this limit with a single new parameter. We determine the shift in the parameters of the FOPT in terms of this new parameter, and the impact on gravitational wave signals and cosmological observables.

hep-ph↗

arXiv2026

Gravitational Waves from a Black Hole Falling Radially into a Thin-Shell Traversable Wormhole

We compute the gravitational-wave signal generated by the radial infall of a stellar-mass black hole into a thin-shell Schwarzschild traversable wormhole. Modeling the black hole as a test particle, we derive analytic expressions for the emitted waveform, including contributions from the mass quadrupole and higher-order multipoles. The resulting signal exhibits a characteristic pulse-gap structure associated with repeated throat crossings. We further compute the amplitude spectral density and compare it with representative ground-based detector sensitivities, finding that such signals could lie within the sensitivity range for optimally oriented sources at distances of order ~500 Mpc. These results provide a potential observational signature of traversable wormholes in gravitational-wave data.

gr-qc↗

arXiv2026

Direct Collapse Black Hole Candidates from Decaying Dark Matter

Injecting 1-13.6 eV photons into the early universe can suppress the molecular hydrogen abundance and alter the star formation history dramatically enough to produce direct collapse black holes. These, in turn, could explain the recently observed population of puzzling high-redshift supermassive black holes that appear to require super-Eddington accretion. We show that axion dark matter decay in the intergalactic medium can account for this energy injection. We use a single zone model of the gas core and semi-analytically evolve its chemo-thermal properties to track the conditions for which the system becomes an atomic cooling halo-a necessary precursor for the production of heavy black hole seeds to explain the high-redshift black hole population. Windows of axions masses between 24.5-26.5 eV with photon couplings as low as $4\times 10^{-12}$/GeV may realize this atomic cooling halo condition. We highlight the significance of the band structure of molecular hydrogen on the effectiveness of this process and discuss estimates of the heavy seed population and prospects for testing this model.

hep-ph↗

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

Primordial Black Holes at the Junction

Primordial black holes (PBHs) formed during first-order phase transitions provide a powerful link between the early-universe microphysics and observable signatures today, including dark matter and gravitational waves. In this work we develop a unified description of PBH formation based on the Israel junction conditions, which capture collapse dynamics without relying on conventional overdensity or pressure-balance arguments. As a first application, we show that exotic objects such as Fermi-balls can collapse into PBHs even when most of the vacuum energy is trapped in solitonic cores, leading to a different gravitational-wave signal relative to vacuum-only scenarios. As a second application, we study multiple phase transitions in a hidden sector, which generate correlated gravitational-wave spectra and PBH abundances across transitions. Our framework, while analytically controlled, is broadly applicable to hidden-sector models with general vacuum, radiation, and matter contributions. We present the resulting predictions for PBH mass spectra, dark matter fractions, and gravitational-wave signals, highlighting parameter regions that remain open in current searches and motivating future probes.

hep-ph↗

arXiv2025

Gravitational wave signatures of primordial black hole accretion during early matter domination

We present a scenario in which primordial black holes (PBHs) form in a post-inflationary radiation-dominated (RD) phase and then experience significant accretion during a phase of early matter dominated (EMD). We show that PBH masses could grow by up to two orders of magnitude. Restricting to the linear perturbation regime, we compute the gravitational wave (GW) spectrum that features two peaks. The high-frequency peak is associated with the PBH formation in the RD phase, while the low-frequency peak is due to the sudden transition from EMD to the later, standard RD phase. We identify a PBH mass range where one or both peaks can be observed by a combination of different GW detectors. Finally, we show the signal-to-noise ratio of the total GW spectrum for PBHs in the asteroid mass window, where they could comprise the totality of dark matter.

hep-ph↗

arXiv2025

Imprints of Early Universe Cosmology on Gravitational Waves

We explore the potential of gravitational waves (GWs) to probe the pre-BBN era of the early universe, focusing on the effects of energy injection. Specifically, we examine a hidden sector alongside the Standard Model that undergoes a strong first-order phase transition (FOPT), producing a GW signal. Once the phase transition has completed, energy injection initiates reheating in the hidden sector, which positions the hidden sector field so that additional phase transitions can occur. This can result in a total of three distinct phase transitions with a unique three-peak GW spectrum. Among these transitions, the first and third are of the standard type, while the intermediate second transition is inverted, moving from a broken to an unbroken phase. Using polynomial potentials as a framework, we derive analytical relations among the phase transition parameters and the resulting GW spectrum. Our results indicate that the second and third transitions generate GWs with higher amplitudes than the first, with a peak frequency ratio differing by up to an order of magnitude. This three-peak GW spectrum is detectable by upcoming facilities such as LISA, BBO, and UDECIGO. Notably, the phenomenon is robust across various potentials and model parameters, suggesting that hidden sector GWs provide a powerful tool for exploring new physics scenarios in the pre-BBN era.

hep-ph↗

arXiv2025

Multi-messenger Probes of Asteroid Mass Primordial Black Holes: Superradiance Spectroscopy, Hawking Radiation, and Microlensing

Superradiance provides a unique opportunity for investigating dark sectors as well as primordial black holes, which themselves are candidates for dark matter over a wide mass range. Using axion-like particles as an example, we show that line signals emerging from a superradiated axion cloud combined with black hole Hawking radiation in extragalactic and galactic halos, along with microlensing observations lead to complementary constraints on parameter space combinations including the axion-photon coupling, axion mass, black hole mass, and its dark matter fraction, $f_{\rm PBH}$. For the asteroid mass range $\sim10^{16}-10^{22}~{\rm g}$, where primordial black holes can provide the totality of dark matter, we demonstrate that ongoing and upcoming observations such as SXI, JWST, and AMEGO-X will be sensitive to possible line and continuum signals, respectively, providing probes of previously inaccessible regions of $f_{\rm PBH}$ parameter space. Further complementarity from a stochastic gravitational-wave background emerging from the black hole formation mechanism is also considered.

hep-ph↗

arXiv2023

Bragg-Primakoff Axion Photoconversion in Crystal Detectors

Axions and axion-like pseudoscalar particles with dimension-5 couplings to photons exhibit coherent Primakoff scattering with ordered crystals at keV energy scales, making for a natural detection technique in searches for solar axions. We find that there are large suppressive corrections, potentially greater than a factor of $\mathcal{O}(10^3)$, to the coherent enhancement when taking into account absorption of the final state photon. This effect has already been accounted for in light-shining-through-wall experiments through the language of Darwin classical diffraction, but is missing from the literature in the context of solar axion searches that use a matrix element approach. We extend the treatment of the event rate with a heuristic description of absorption effects to bridge the gap between these two languages. Furthermore, we explore the Borrmann effect of anomalous absorption in lifting some of the event rate suppression by increasing the coherence length of the conversion. We study this phenomenon in Ge, NaI, and CsI crystal experiments and its impact on the the projected sensitivities of SuperCDMS, LEGEND, and SABRE to the solar axion parameter space. Lastly, we comment on the reach of multi-tonne scale crystal detectors and strategies to maximize the discovery potential of experimental efforts in this vein.

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

Sensitivity to Dark Sector Scales from Gravitational Wave Signatures

We consider gravitational wave signals produced by a first-order phase transition in a theory with a generic renormalizable thermal effective potential of power law form. We find the frequency and amplitude of the gravitational wave signal can be related in a straightforward manner to the parameters of the thermal effective potential. This leads to a general conclusion; if the mass of the dark Higgs is less than 1% of the dark Higgs vacuum expectation value, then the gravitational wave signal will be unobservable at all upcoming and planned gravitational wave observatories.

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.

hep-ph↗

arXiv2021

Cosmic-ray upscattered inelastic dark matter

Light non-relativistic components of the galactic dark matter halo elude direct detection constraints because they lack the kinetic energy to create an observable recoil. However, cosmic-rays can upscatter dark matter to significant energies, giving direct detection experiments access to previously unreachable regions of parameter-space at very low dark matter mass. In this work we extend the cosmic-ray dark matter formalism to models of inelastic dark matter and show that previously inaccessible regions of the mass-splitting parameter space can be probed. Conventional direct detection of non-relativistic halo dark matter is limited to mass splittings of $δ\sim10~\mathrm{keV}$ and is highly mass dependent. We find that including the effect of cosmic-ray upscattering can extend the reach to mass splittings of $δ\sim100~\mathrm{MeV}$ and maintain that reach at much lower dark matter mass.

hep-ph↗

arXiv2021

Low-mass inelastic dark matter direct detection via the Migdal effect

We consider searches for the inelastic scattering of low-mass dark matter at direct detection experiments, using the Migdal effect. We find that there are degeneracies between the dark matter mass and the mass splitting that are difficult to break. Using XENON1T data we set bounds on a previously unexplored region of the inelastic dark matter parameter space. For the case of exothermic scattering, we find that the Migdal effect allows xenon-based detectors to have sensitivity to dark matter with ${\cal O}(\mathrm{MeV})$ mass, far beyond what can be obtained with nuclear recoils alone.

hep-ph↗

arXiv2021

Solar Gamma Ray Constraints on Dark Matter Annihilation to Secluded Mediators

We consider the indirect detection of dark matter that is captured in the Sun and subsequently annihilates to long-lived dark mediators. If these mediators escape the Sun before decaying, they can produce striking gamma ray signals, either via the decay of the mediators directly to photons, or via bremsstrahlung and hadronization of the mediator decay products. Using recent measurements from the HAWC Observatory, we determine model-independent limits on heavy dark matter that are orders of magnitude more powerful than direct detection experiments, for both spin-dependent and spin-independent scattering. We also consider a well-motivated model in which fermionic dark matter annihilates to dark photons. For such a realistic scenario, the strength of the solar gamma ray constraints are reduced, compared to the idealistic case, because the dark matter capture cross section and mediator lifetime are related. Nonetheless, solar gamma ray constraints enable us to exclude a previously unconstrained region of dark photon parameter space.

hep-ph↗