arXiv subjects

Spencer Griffith

Publications and source records attributed to Spencer Griffith.

4 recordsLinked to original sources

arXiv2026

Inelastic Signatures of Electroweak Dark Matter

Minimal dark matter extended to include a Majorana and a Dirac multiplet coupled through the Higgs --- the HC-MDM model --- provides a compelling and predictive framework. We show that in certain limits of this model, the mass splitting and the inelastic interaction are representation-independent, while the thermal-relic masses are representation-dependent. We then show that this model can account for the high-energy recoil event recently reported by LUX-ZEPLIN (LZ) while also respecting thermal-relic, elastic-scattering, and solar-capture constraints. Generic inelastic DM models do not connect all these tests and generic Higgsino models do not survive them.

hep-ph↗

arXiv2026

Minimal Dark Matter: Generalized Framework and Direct-Detection Sensitivity

Minimal electroweak dark matter models are compelling due to their simplicity, though calculations of their freezeout abundance are complicated by nonperturbative effects due to Sommerfeld enhancement and bound-state formation. It has been shown that all individual multiplet scenarios beyond the doublet lead to direct-detection signals above the neutrino floor and thus within the reach of next-generation experiments. If no signals are found, would minimal dark matter be excluded? Yes for the simplest models, but it has been unknown for the important extension of two multiplets coupled by Higgs interactions (Higgs-coupled minimal dark matter). We present a generalized framework for calculating nonperturbative effects for such models that also covers the case of individual multiplets. In this framework, we calculate nonperturbative effects on freezeout as well as the prospects for direct detection, correcting shortcomings and omissions in the literature. Importantly, for the mixed Majorana (odd) and Dirac (even) multiplet combination 3M2D (and marginally the 5M4D), we find that the predicted direct-detection signals can extend below the neutrino floor. Fully testing minimal dark matter will thus require more than direct-detection experiments.

hep-ph↗

arXiv2024

Angular Distribution of Gamma Rays Produced in Proton-Proton Collisions

Accurate modeling of how high-energy proton-proton collisions produce gamma rays through the decays of pions and other secondaries is needed to correctly interpret astrophysical observations with the Fermi-LAT telescope. In the existing literature on cosmic-ray collisions with gas, the focus is on the gamma-ray yield spectrum, $d N_\gamma/dE$. However, in some situations, the joint energy and angular distribution can be observed, so one needs instead $d^2 N_\gamma/dE \, d\Omega$. We provide calculations of this distribution over the energy range from the pion production threshold to $100~{\rm GeV}$, basing our results on FLUKA simulations. We provide the results in tabular form and provide a Python tool on GitHub to aid in utilization. We also provide an approximate analytic formula that illuminates the underlying physics. We discuss simplified examples where this angular dependence can be observed to illustrate the necessity of taking the joint distribution into account.

hep-ph↗

arXiv2023

Small-Scale Magnetic Fields are Critical to Shaping Solar Gamma-Ray Emission

The Sun is a bright gamma-ray source due to hadronic cosmic-ray interactions with solar gas. While it is known that incoming cosmic rays must generally first be reflected by solar magnetic fields to produce outgoing gamma rays, theoretical models have yet to reproduce the observed spectra. We introduce a simplified model of the solar magnetic fields that captures the main elements relevant to gamma-ray production. These are a flux tube, representing the network elements, and a flux sheet, representing the intergranule sheets. Both the tube and sheet have a horizontal size of order $100~{\rm km}$ and serve as sites where cosmic rays are reflected and gamma rays are produced. While our simplified double-structure model does not capture all the complexities of the solar-surface magnetic fields, such as Alfv\'{e}n turbulence from wave interactions or magnetic fluctuations from convection motions, it improves on previous models by reasonably producing both the hard spectrum seen by Fermi-LAT at $\text{1--200}~{\rm GeV}$ and the considerably softer spectrum seen by HAWC at near $10^3~{\rm GeV}$. We show that lower-energy ($\lesssim 10~{\rm GeV}$) gamma rays are primarily produced in the network elements and higher-energy ($\gtrsim {\rm few} \times 10~{\rm GeV}$) gamma rays in the intergranule sheets. Notably, the spectrum softening observed by HAWC results from the limited effectiveness of capturing and reflecting $\sim 10^4~{\rm GeV}$ cosmic rays by the finite-sized intergranule sheets. Our study is important for understanding cosmic-ray transport in the solar atmosphere and will lead to insights about small-scale magnetic fields at the photosphere.

astro-ph.HE↗