Adam Ritz

We explore the aggregate effect of binary systems on the Milky Way's dark matter (DM) velocity distribution with Monte Carlo simulations. Through gravitational interactions with binaries, transiting DM particles can gain substantial energy. We analyze this mechanism across a range of galactic binaries, and find it to be most effective for double black holes, where ejection speeds can reach ∼ 2000 km/s while attaining a large ejection rate. We assess the expected binary-boosted DM flux from synthetic populations of black hole binaries in the galaxy, and show direct detection experiments can be sensitive to it. In particular, we demonstrate that large noble liquid detectors such as Lux-Zeplin and PandaX-4T can extend their mass sensitivity down to the sub-GeV scale, and potentially become competitive with other lower-threshold experiments when the full galactic black hole binary population is taken into account. This boosting mechanism, being gravitational in nature, is largely model- and mass-independent.

We explore the sensitivity of neutrino observatories and direct dark matter detection experiments to boosted sub-GeV dark matter produced by inelastic cosmic ray collisions in the atmosphere. We revisit earlier approaches and extend the sensitivity to higher mass by modeling the proton bremsstrahlung production mode via initial state radiation. For vector-mediated dark matter models, the peak of the cosmic ray flux allows for enhanced DM production for mediator masses near the ρ / ω resonances. We determine and compare the ensuing sensitivity of direct detection experiments LZ and PandaX-4T and the neutrino detectors Borexino and Super-K.

We investigate the impact of residual annihilation from sub-GeV mass thermal relic dark matter candidates during big bang nucleosynthesis (BBN). Focusing on candidates with p -wave annihilation channels, we show that the hadronic injection of pions and kaons beyond freeze-out, and their subsequent interaction with protons and neutrons prior to the deuterium bottleneck, provides a sensitivity to annihilation that surpasses that of the cosmic microwave background (CMB) and indirect detection in the galaxy.

We explore the sensitivity of collider experiments to a broad class of GeV-scale dark vector models of new physics via production in proton and neutron bremsstrahlung and initial state radiation. This is achieved using a new physically motivated model for timelike vector form factors with generic charges for both protons and neutrons, which is fit to a variety of timelike and spacelike data with quantified uncertainties. The production model for both proton and neutron bremsstrahlung is applied to recast and extend the reach of existing FASER data to GeV-mass dark photons, U ( 1 ) B , U ( 1 ) B − L , and protophobic vectors, as well as forecasts for millicharged particles at FORMOSA.

We investigate the null geodesics, in particular the stable and unstable light rings and shadows, of a Kerr–Newman black hole immersed in an asymptotically uniform magnetic field as described by the Ernst-Wild (Melvin–Kerr–Newman) spacetime. Through numerical ray tracing, we demonstrate that both the black hole rotation and the magnetized Melvin geometry impact the light rings and shadows non-trivially and in compensating ways. In addition, we use a perturbative expansion in the magnetic field B to analyze the deviation of the observable shadow relative to the Kerr result analytically, and determine connections between Lyapunov exponents for light ring instabilities and quasinormal modes in the eikonal limit.

We analyze the quasinormal mode spectrum for Kerr black holes surrounded by an asymptotically uniform magnetic field, modeled with the Ernst-Wild geometry. A perturbative expansion in both the rotation parameter a and the magnetic field B allows the analysis of perturbations with Kerr- like asymptotics well inside the Melvin radius, and we obtain the spectrum for a variety of scalar quasinormal modes over a range of parameters using the continued fraction method. We then interpolate the low-lying mode spectrum to construct an Ernst-Wild template for the ringdown, and use the LIGO-Virgo-KAGRA analysis tool pyRing to assess the impact of the magnetosphere on the extraction of ringdown signatures from several observed binary black hole mergers.

High luminosity colliders and fixed target facilities using proton beams are sensitive to new weakly coupled degrees of freedom across a broad mass range. Among the various production modes, bremsstrahlung is particularly important for dark sector degrees of freedom with masses between 0.5 and 2.0 GeV, due to mixing with hadronic resonances. In this paper, we revisit the calculation of dark vector production via initial state radiation in non-single-diffractive scattering, using an improved treatment of the splitting functions and timelike electromagnetic form factors. The approach is benchmarked by applying an analogous calculation to model inclusive ρ -meson production, indicating consistency with data from NA27 in the relevant kinematic range.

High luminosity colliders and fixed target facilities using proton beams are sensitive to new weakly coupled degrees of freedom across a broad mass range. Among the various production modes, bremsstrahlung is particularly important for dark sector degrees of freedom with masses between 0.5 and 2.0 GeV, due to mixing with hadronic resonances. In this paper, we revisit the calculation of dark vector production via initial state radiation in non-single diffractive scattering, using an improved treatment of the splitting functions and timelike electromagnetic form-factors. The approach is benchmarked by applying an analogous calculation to model inclusive $ρ$-meson production, indicating consistency with data from NA27 in the relevant kinematic range.