arXiv subjects

Thomas Schwemberger

Publications and source records attributed to Thomas Schwemberger.

7 recordsLinked to original sources

arXiv2026

Moving a Detector to Probe New Neutrino Interactions: IWCD at Hyper-Kamiokande

Moving a detector through a beam with a spatially varying energy spectrum exposes the same target and apparatus to distinct incident spectra, enabling interaction spectroscopy. While movable neutrino detectors were put forth primarily to control systematic uncertainties, we show that detector motion enables probing the structure of fundamental interactions. We demonstrate this with the Intermediate Water Cherenkov Detector (IWCD), the movable detector of Hyper-Kamiokande in the J-PARC off-axis beam, considering neutrino non-standard interactions (NSI) as a benchmark. Exploiting ratios of neutral current to charged current event rates reduces common normalization uncertainties, while measurements at multiple off-axis positions can break degeneracies that persist for a single incident spectrum. Combining three off-axis positions and adopting a $5\%$ correlated normalization uncertainty benchmark, we project $95\%$ CL sensitivities to axial neutral current NSI of $-0.07 \lesssim \varepsilon^{uA}_{\mu\mu} \lesssim 0.06$ and vector NSI of $-0.10 \lesssim \varepsilon^{uV}_{\mu\mu} \lesssim 0.12$, as well as for charged current NSI of $-0.05 \lesssim \varepsilon^{udL}_{\mu\mu} \lesssim 0.05$. Axial NSI, which do not contribute to the ordinary matter potential, are complementary to neutrino oscillation and high energy scattering measurements. More broadly, detector motion provides a new way to distinguish interactions with different energy dependence.

hep-ph↗

arXiv2025

Multimessenger Constraints on Supermassive Dark Stars and Their Black Hole Remnants

Dark matter (DM) annihilation can power the first generation of stars as long lived dark stars (DSs) that grow to supermassive scales $M_{\rm DS}\gtrsim 10^{5} M_{\odot}$ and eventually collapse into heavy black holes that could seed the supermassive black holes observed at high redshifts. We compute the diffuse electromagnetic emission from a cosmological population of such supermassive DSs and their black hole remnants, tracking the entire DS history and including thermal surface radiation, DM annihilation in adiabatically contracted halos as well as late-time emission from DM overdensity spikes around the resulting black holes. After accounting for photon attenuation, we find that DS related contributions can exceed the Fermi-LAT extragalactic $\gamma$-ray background for thermal relic annihilation cross-sections and DM masses below $\sim 1$ TeV. Our results constitute the first population integrated diffuse multimessenger constraints on supermassive DSs as progenitors of early black holes and demonstrate that diffuse photon and neutrino backgrounds offer a powerful and complementary avenue for probing the role of DM in the formation of the earliest massive structures.

astro-ph.CO↗

arXiv2025

Clash of the Titans: ultra-high energy KM3NeT event versus IceCube data

KM3NeT has reported the detection of a remarkably high-energy through-going muon. Lighting up about a third of the detector, this muon likely originated from a neutrino exceeding 10 PeV in energy. The crucial question we need to answer is where this event comes from and what its source is. Intriguingly, IceCube has been operating with a much larger effective area for a considerably longer time, yet it has not reported neutrinos above 10~PeV. We quantify the tension between the KM3NeT event and the absence of similar high-energy events in IceCube. Through a detailed analysis, we determine the most likely neutrino energy to be in the range of 23 - 2400 PeV. We find a $3.5\sigma$ tension between the two experiments, assuming the neutrino is from the diffuse isotropic neutrino flux. Alternatively, assuming the event is of cosmogenic origin and considering three representative models, this tension still falls within 3.1 - 3.6$\sigma$. The least disfavored scenario is a steady or transient point source, though still leading to $2.9\sigma$ and $2.0\sigma$ tensions, respectively. The lack of observation of high-energy events in IceCube seriously challenges the explanation of this event coming from any known diffuse fluxes. Our results indicate the KM3NeT event is likely the first observation of a new astrophysical source.

astro-ph.HE↗

arXiv2024

Diffuse Neutrino Signals from Dark Stars Seeding Super-Massive Black Holes

Dark stars (DSs) -- first stars powered by dark-matter (DM) heating rather than fusion -- could form in the early Universe. They can grow to $\gtrsim 10^5 M_{\odot}$ masses and collapse into seeds of supermassive black holes (SMBHs). We demonstrate that diffuse neutrino flux generated by DSs can be observable in existing experiments and have energies reaching hundreds of MeV, providing novel window for probing SMBH progenitors. We establish first constraints on DSs and DM annihilations powering them using data from Super-Kamiokande and IceCube neutrino experiments, and consistent with James Webb Space Telescope observations. Upcoming experiments such as Hyper-Kamiokande, DUNE, JUNO will be able to explore DS properties with enhanced sensitivity.

hep-ph↗

arXiv2024

Hunting Nonstandard Neutrino Interactions and Leptoquarks in Dark Matter Experiments

Next generation direct dark matter (DM) detection experiments will have unprecedented capabilities to explore coherent neutrino-nucleus scattering (CE$ν$NS) complementary to dedicated neutrino experiments. We demonstrate that future DM experiments can effectively probe nonstandard neutrino interactions (NSI) mediated by scalar fields in the scattering of solar and atmospheric neutrinos. We set first limits on $S_1$ leptoquark models that result in sizable $μ-d$ and $τ-d$ sector neutrino NSI CE$ν$NS contributions using LUX-ZEPLIN (LZ) data. As we show, near future DM experiments reaching $\sim \mathcal{O}(100)$ton-year exposure, such as argon-based ARGO and xenon-based DARWIN, can probe parameter space of leptoquarks beyond the reach of current and planned collider facilities. We also analyze for the first time prospects for testing NSI in lead-based detectors. We discuss the ability of leptoquarks in the parameter space of interest to also explain the neutrino masses and $(g-2)_μ$ observations.

hep-ph↗

arXiv2022

Detecting Beyond the Standard Model Interactions of Solar Neutrinos in Low-Threshold Dark Matter Detectors

As low-threshold dark matter detectors advance in development, they will become sensitive to recoils from solar neutrinos which opens up the possibility to explore neutrino properties. We predict the enhancement of the event rate of solar neutrino scattering from Beyond the Standard Model interactions in low-threshold DM detectors, with a focus on silicon, germanium, gallium arsenide, xenon, and argon-based detectors. We consider a set of general neutrino interactions, which fall into five categories: the neutrino magnetic moment as well as interactions mediated by four types of mediators (scalar, pseudoscalar, vector, and axial vector), and consider coupling these mediators to either quarks or electrons. Using these predictions, we place constraints on the mass and couplings of each mediator and the neutrino magnetic moment from current low-threshold detectors like SENSEI, Edelweiss, and SuperCDMS, as well as projections relevant for future experiments such as DAMIC-M, Oscura, Darwin, and ARGO. We find that such low-threshold detectors can improve current constraints by up to two orders of magnitude for vector mediators and one order of magnitude for scalar mediators.

hep-ph↗

arXiv2019

Direct detection of primordial black hole relics as dark matter

If dark matter is composed of primordial black holes, such black holes can span an enormous range of masses. A variety of observational constraints exist on massive black holes, and black holes with masses below $10^{15}\,\mathrm{g}$ are often assumed to have completely evaporated by the present day. But if the evaporation process halts at the Planck scale, it would leave behind a stable relic, and such objects could constitute the entirety of dark matter. Neutral Planck-scale relics are effectively invisible to both astrophysical and direct detection searches. However, we argue that such relics may typically carry electric charge, making them visible to terrestrial detectors. We evaluate constraints and detection prospects in detail, and show that if not already ruled out by monopole searches, this scenario can be largely explored within the next decade using existing or planned experimental equipment. A single detection would have enormous implications for cosmology, black hole physics, and quantum gravity.

hep-ph↗