arXiv subjects

Dan Hooper

Publications and source records attributed to Dan Hooper.

At least 19 recordsLinked to original sources

arXiv2026

Solar Neutrino Constraints on Inelastic Dark Matter Scattering in Light of Recent LUX-ZEPLIN Observations

The LUX-ZEPLIN (LZ) Collaboration recently reported the detection of a single nuclear recoil candidate event with a very high recoil energy. The lack of any corresponding low-energy events motivates models in which dark matter scattering with nuclei has a nontrivial momentum dependence or proceeds inelastically, suppressing the rate of low-energy recoils. In this study, we consider the constraints on inelastic dark matter, including scenarios favored by the LZ event, from the absence of an excess of high-energy neutrinos from the Sun in IceCube observations. We confirm the results of Pospelov & Ramani and show, more generally, that the lack of an excess of high-energy neutrinos from the Sun strongly constrains the parameter space in this class of models.

hep-ph↗

arXiv2026

Low-energy antinuclei measurements for background-free indirect dark matter searches and PBH signatures

Light low-energy cosmic ray antinuclei constitute powerful probes for detecting dark matter or other sources of new physics in our Galaxy. This ASTRA Initiative Mission Concept reviews the theoretical motivation, highlighting the transformative potential and current experimental status. Motivated by exciting tentative results, it makes a clear case for the need for the next flagship mission to confirm or refute claims of cosmic antinuclei as signs of new physics.

astro-ph.HE↗

arXiv2026

Novel Signatures of Matter-Induced Dark Matter Decay in Large-Volume Neutrino Telescopes

Large-volume neutrino telescopes offer a unique opportunity to search for decaying dark matter through events containing a pair of energetic, highly non-collimated muon tracks emerging from a common vertex. Such events would have negligible Standard Model backgrounds and would constitute a striking signature of new physics. Conventional dark matter annihilation or decay, however, is too strongly constrained to produce an observable rate of such events. We therefore consider scenarios in which an excited dark matter state is extremely long-lived in vacuum but decays much more rapidly in the presence of ordinary matter. We present two realizations of this mechanism. In the first, a long-range scalar field sourced by ordinary matter modifies the dark-sector mass spectrum, kinematically opening the decay $\chi_2 \rightarrow \chi_1 Z'$ near the Earth while leaving it forbidden in vacuum. In the second, the scalar background induces kinetic mixing between a heavy $Z'$ and the photon, greatly enhancing the three-body decay $\chi_2\to\chi_1\mu^+\mu^-$ in matter-rich environments. We calculate the resulting distributions of muon energies and opening angles and show that viable regions of parameter space can yield observable event rates in IceCube, KM3NeT, and other large-volume neutrino telescopes while remaining consistent with existing constraints. We also briefly consider the sensitivity of IceCube to multi-muon events produced by the decays of cosmologically long-lived charged particles with masses $\gtrsim 1$ TeV.

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arXiv2026

A Multimessenger Analysis of the High-Energy Milky Way: Source Populations Contribute Significantly to IceCube's Galactic Neutrino Flux

We perform a joint analysis of the high-energy neutrino emission observed from the Galactic Plane by IceCube and the diffuse ultra-high-energy gamma-ray emission measured by LHAASO. We compare this data to models that include diffuse emission from cosmic-ray interactions in the interstellar medium, unresolved TeV halos, and unresolved Galactic neutrino sources. We find that the gamma-ray emission can be explained by a combination of diffuse processes and unresolved TeV halos. The observed neutrino emission cannot be generated by cosmic-ray interactions in the interstellar medium alone, but requires contributions from one or more unresolved source populations. Across a wide range of assumptions about Galactic cosmic-ray transport, we find that Galactic neutrino sources contribute significantly to the neutrino flux observed from the Galactic Plane and are likely responsible for most of this emission.

astro-ph.HE↗

arXiv2026

The Delta Resonance in the Neutrino Sky

Recent measurements of the diffuse cosmic neutrino flux by IceCube show evidence for a spectral break at an energy near $E_\nu \sim 30$ TeV. In this letter, we suggest that this feature may be due to the $\Delta$-baryon resonance in $p\gamma$ interactions. We show that the measured spectrum, including the observed break, can be naturally accommodated by a flux of protons accelerated with a spectrum $dN_p /dE_p \propto E_p^{-3.1}$ interacting with X-rays of typical energy $E_{\gamma} \sim 0.3\,{\rm keV}$. We also point out that the presence of this spectral break significantly reduces the contribution of neutrino sources to the isotropic gamma-ray background, alleviating the longstanding tension between these measurements. In the $\Delta$-resonance scenario, the gamma rays accompanying neutrino production cascade down to MeV-GeV energies and contribute at the $\sim 10\%$ level to the isotropic gamma-ray background at $\sim 3$~GeV. If our proposal is realized, it may imply that we have identified the dominant sources that produce the extragalactic cosmic rays.

astro-ph.HE↗

arXiv2026

WIMP-like Dark Matter Without Thermalization At Freeze-Out

In the standard thermal relic scenario, dark matter remains in chemical equilibrium with the Standard Model radiation bath until freeze-out occurs at $T \sim m_X/20$, where $m_X$ is the dark matter mass. In this familiar class of models, the observed relic density is obtained for annihilation cross sections of order $\sigma v \sim 10^{-26}$ cm$^3$/s. We show that comparable cross sections can naturally be realized in hidden-sector models in which the dark matter and Standard Model sectors decouple at a very high temperature, $T \gg m_X$, and subsequently evolve with separate thermal histories. Despite this decoupling, the two sectors have similar temperatures during freeze-out, leading to the usual thermal relic abundance. As a consequence, the coupling between the Standard Model and hidden sectors can be extremely small, potentially placing direct detection and collider signals far below foreseeable sensitivities.

hep-ph↗

arXiv2026

Constraining The Neutrino-Nucleon Cross Section with the Ultrahigh-Energy KM3NeT Event

KM3NeT's detection of a muon track produced by a $\sim 220 \, {\rm PeV}$ neutrino provides an opportunity to probe physics at center-of-momentum energies greater than those probed by the Large Hadron Collider or other existing particle accelerators. In this study, we use this single event to place an upper limit on the neutrino-nucleon cross section of $\sigma_{\nu N} < 40 \, \sigma_{\nu N}^{\rm SM}$ at $E_{\rm CM} \sim 20 \, {\rm TeV}$. This result can be used to constrain a variety of scenarios beyond the Standard Model. With future very large volume neutrino telescopes, constraints on the neutrino-nucleon scattering cross section are expected to become substantially more stringent and, in some scenarios, could become competitive with accelerator probes of new physics.

hep-ph↗

arXiv2026

Ultrahigh-Energy Gamma-Ray Sources Need Not Be Hadronic PeVatrons

Ultrahigh-energy gamma rays ($E_{\gamma}>100 \, {\rm TeV}$) have been detected from a handful of astrophysical sources. Due to the Klein-Nishina suppression of inverse Compton scattering at such high energies, it has sometimes been argued that these sources must be accelerators of PeV-scale protons, making them the long-sought-after Galactic ''PeVatrons.'' Here, we challenge this conclusion, demonstrating that these sources can be straightforwardly explained by simple leptonic models. In this context, we consider the microquasar SS 433, the Galactic Center, and TeV halos, showing in each case that the observation of PeV-scale gamma rays from these sources does not indicate that they are accelerators of hadronic cosmic rays. We also note that the measured angular extension of SS 433 is in good agreement with the predictions of our model, favoring a leptonic origin for the gamma-ray emission from this source. A definitive identification of a PeVatron would require additional information, such as the combined observation of the pion bump and synchrotron peak, the spatial correlation of gamma-ray emission with gas, or the detection of neutrinos with $E_{\nu} \gtrsim 100 \, {\rm TeV}$.

astro-ph.HE↗

arXiv2026

Dark Matter, Baryon Number, and Cosmic-Ray Antinuclei

Antideuterons and antihelium nuclei in the cosmic-ray spectrum have long been considered a smoking gun signature of dark matter annihilation, making the tentative observation of several such events by AMS highly intriguing. Conventional dark matter models, however, can produce only up to O(1) antideuteron events at AMS and are not capable of generating observable fluxes of antihelium. In this letter, we propose a class of models in which dark matter annihilates into particles carrying baryon and lepton number, whose subsequent decays produce enhanced fluxes of antinucleons and antinuclei. Such scenarios are motivated by Grand Unified Theories and can lead to an order-of-magnitude or larger enhancement in the resulting antideuteron and antihelium-3 fluxes, providing a means by which to potentially explain the events reported by the AMS Collaboration.

hep-ph↗

arXiv2026

Evaluating the Contribution of Active Galactic Nuclei to the Diffuse High-Energy Neutrino Flux

The detection of high-energy neutrinos from NGC 1068 and TXS-0506+56 suggests that active galactic nuclei (AGN) may contribute significantly to the the diffuse neutrino flux measured by IceCube. Using 10 years of publicly available IceCube data, we performed a systematic population analysis of X-ray-bright and gamma-ray-bright AGN to evaluate the extent to which this diffuse flux could originate from these sources. We find that gamma-ray-bright blazars can account for no more than 16\% of IceCube's total diffuse flux. Although we find no evidence of neutrino emission from gamma-ray-bright, non-blazar AGN, we cannot exclude the possibility that these sources contribute significantly to the diffuse flux. In contrast, we report (pre-trials) evidence of neutrino emission from several nearby, X-ray-bright, Seyfert-type AGN, including \mbox{NGC 1068} ($4.9\sigma$), SWIFT J1041.4-1740 ($2.6\sigma$), SWIFT J0202.4+6824A/B ($2.6\sigma$), SWIFT J0744.0+2914 (2.6$\sigma$), NGC 4151 ($2.5\sigma$), and NGC 3079 ($2.5\sigma$). Although not fully conclusive, these results suggest that IceCube may be detecting neutrinos from a larger population of Seyfert galaxies. The fact that these sources are not gamma-ray bright indicates that their neutrino production must be taking place in optically thick environments, such as in the coronae surrounding these galaxies' supermassive black holes. We also identify a $4.2\sigma$ correlation between the neutrinos detected by IceCube and members of the Swift-BAT catalog of X-ray-bright AGN, although this correlation is dominated by NGC 1068. We estimate that this class of sources contributes between 11.2\% and the entirety of IceCube's total diffuse neutrino flux. These results strengthen the emerging case for the prevalence of gamma-ray-obscured AGN as significant sources of high-energy neutrinos.

astro-ph.HE↗

arXiv2025

The Sensitivity of PUEO to Cosmogenic Neutrinos and Exotic Physics Scenarios

Several observatories designed to detect ultrahigh-energy neutrinos are planned for the next decade. The most imminent of these is the Payload for Ultrahigh Energy Observations (PUEO), a long-duration balloon-based experiment that will provide unprecedented sensitivity to neutrinos with energies in the range of ~ 1 - 1000 EeV. In this work, we assess the scientific reach of PUEO. In particular, we evaluate the sensitivity of this observatory to cosmogenic neutrinos and, in turn, to the proton fraction of the ultrahigh-energy cosmic-ray spectrum. We also consider the potential of PUEO to probe scenarios in which neutrinos are produced through the decays of ultraheavy dark matter particles or are radiated from cosmic strings. We find that PUEO will be able to constrain the proton composition of ultrahigh-energy cosmic rays in scenarios that feature very strong source evolution and in which protons are accelerated to extremely high energies. Although gamma-ray observations are generally more sensitive to decaying particles than neutrino observations, PUEO is expected to set the strongest neutrino-detector constraints above 10^19 eV. PUEO will also provide the strongest constraints on some models of cosmic strings.

astro-ph.HE↗

arXiv2025

A Thermal Relic Encyclopedia: Dark Matter Candidates Coupled to Quarks

Thermal freeze-out is a compelling framework for naturally generating the dark matter abundance. We systematically study a broad range of dark matter and mediator particle combinations that can viably realize thermal freeze-out, focusing on models in which the mediator couples to Standard Model quarks. In each case, we calculate the relic density and consider existing constraints from accelerators, cosmology, direct detection, and indirect detection over the full range of dark matter and mediator masses. We present an encyclopedic catalog of matrix elements, cross sections, and decay rates which can be used as a reference for future studies of dark matter phenomenology.

hep-ph↗

arXiv2025

The Impact of Muon and Pion Cooling on the Neutrino Spectrum of NGC 1068

The IceCube Neutrino Observatory has detected a flux of $\sim 1-10 \, {\rm TeV}$ neutrinos from the active galaxy, NGC 1068. The soft spectral index of these neutrinos has previously been interpreted as an indication that this source accelerates protons only up to energies of several hundred TeV. Here, we propose that this source might instead accelerate protons to significantly higher energies, but that the charged pions and muons produced in their interactions undergo significant synchrotron energy losses before they can decay, leading to a cutoff in the neutrino spectrum at TeV-scale energies. This scenario would require very strong magnetic fields to be present in the acceleration region of NGC 1068, on the order of $B \sim 10^7 \, {\rm G}$. We point out that this synchrotron cooling would impact the flavor ratios of the neutrinos from this source, providing a means to test this scenario with future very-large volume neutrino telescopes.

astro-ph.HE↗

arXiv2025

Gamma-Rays and Gravitational Waves from Inelastic Higgs Portal Dark Matter

We explore a simple and predictive dark matter scenario involving a complex scalar field, $\phi$, coupled to the Higgs portal with no additional field content. In the UV, the field possesses a global $U(1)$ symmetry which is broken by mass terms and Higgs portal interactions. In the mass basis, the complex field splits into a pair of real scalars with a small mass splitting (in analogy to pseudo-Dirac fermions), such that the Higgs portal acquires both diagonal and off-diagonal terms with respect to these eigenstates. In the parameter space where the off-diagonal interaction predominates, this scenario is safe from direct detection constraints. Moreover, this model provides a viable explanation for the longstanding Galactic Center gamma-ray excess. Additionally, this model influences the Higgs potential in a way that could facilitate a strong first-order electroweak phase transition in the early universe, potentially leading to a stochastic gravitational wave background that could fall within the reach of upcoming space-based detectors.

hep-ph↗

arXiv2025

Searching for dark matter annihilation in the Sun with the IceCube Upgrade

The IceCube Upgrade will provide unprecedented sensitivity to dark matter particles annihilating in the core of the Sun. For dark matter candidates with spin-dependent couplings to nuclei and that annihilate significantly to tau leptons or neutrinos, we find that the IceCube Upgrade will be capable of testing parameter space that is beyond the reach of existing direct detection experiments. After calculating the sensitivity of the IceCube Upgrade to dark matter annihilation in the Sun, we explore dark matter models that could be tested by this experiment, identifying two classes of scenarios as promising targets for such searches.

hep-ph↗

arXiv2025

dSphobic Dark Matter

We present a mechanism that allows thermal relic dark matter to annihilate efficiently in the Galactic Halo and in galaxy clusters, but not in the lower-velocity environments of dwarf spheroidal (dSph) galaxies. We realize this within a complete model in which the dark matter consists of two distinct states separated by a small mass splitting. An indirect detection signal is generated only through the coannihilations of these two states, requiring both to be present. In the halo of the Milky Way, the dark matter particles in the lighter state can be excited into the long-lived heavier state through scattering. Once excited, these heavier particles can coannihilate with those in the lighter state, yielding a gamma-ray signal with little or no suppression. By contrast, the dark matter particles in dwarf galaxies do not possess enough kinetic energy to be excited, thereby suppressing the coannihilation rate and corresponding indirect detection signals from those systems. This framework breaks the predictive relationship that ordinarily exists between these respective gamma-ray signals and complicates our ability to interpret the results of indirect detection searches.

hep-ph↗

arXiv2025

Can a Breakdown of Hawking Evaporation Open a New Mass Window for Primordial Black Holes as Dark Matter?

Semi-classical Hawking evaporation is expected to break down at some point in a black hole's evolution as the effects of quantum gravity become important. In particular, it has been argued that the so-called memory-burden effect could cause black holes to become stabilized by the information that they carry, thereby suppressing the rate at which they undergo Hawking evaporation. It has furthermore been suggested that this opens a new mass window, between $10^{4}\,{\rm g} \lesssim M \lesssim 10^{10}\,{\rm g}$, over which primordial black holes could constitute the dark matter of our Universe. We show for the first time that this is true only if the transition from the semi-classical phase of a black hole to its memory-burdened phase is practically instantaneous. If this transition is instead more continuous, Hawking evaporation will persist at relevant levels throughout the eras of Big Bang Nucleosynthesis and recombination, leading to stringent constraints which rule out the possibility that black holes lighter than $\sim 4 \times 10^{16}\,{\rm g}$ could make up all or most of the dark matter. More broadly, our analysis demonstrates that even if departures from the semi-classical Hawking evaporation occur as proposed, they must be both drastic and abrupt to open viable new mass windows for primordial black hole dark matter.

astro-ph.CO↗

arXiv2025

Searching For Superheavy Decaying Particles With Ultra-High-Energy Neutrino Observatories

If there exist unstable but long-lived relics of the early universe, their decays could produce detectable fluxes of gamma rays and neutrinos. In this paper, we point out that the decays of superheavy particles, $m_{\chi} \gtrsim 10^{10} \, \text{GeV}$,would produce an enhanced flux of ultra-high-energy neutrinos through the processes of muon and pion pair production in the resulting electromagnetic cascades. These processes transfer energy from electromagnetic decay products into neutrinos, relaxing the constraints that can be derived from gamma-ray observations, and increasing the sensitivity of high-energy neutrino telescopes to superheavy particle decays. Taking this into account, we derive new constraints on long-lived superheavy relics from the IceCube Neutrino Observatory, and from the Fermi Gamma-Ray Space Telescope. We find that IceCube-Gen2, and other next generation neutrino telescopes, will provide unprecedented sensitivity to the decays of superheavy dark matter particles and other long-lived relics.

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