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R. Dick

Publications and source records attributed to R. Dick.

13 recordsLinked to original sources
arXiv2022

Snowmass2021 Cosmic Frontier: The landscape of low-threshold dark matter direct detection in the next decade

The search for particle-like dark matter with meV-to-GeV masses has developed rapidly in the past few years. We summarize the science case for these searches, the recent progress, and the exciting upcoming opportunities. Funding for Research and Development and a portfolio of small dark matter projects will allow the community to capitalize on the substantial recent advances in theory and experiment and probe vast regions of unexplored dark-matter parameter space in the coming decade.

hep-ph↗
arXiv2019

Enhanced Edelstein effect and interdimensional effects in an electron gas with Rashba spin-orbit coupling interface

We examine the bound-state and free-state contributions to the density of states in a three-dimensional electron gas with a two-dimensional interface with Rashba spin-orbit coupling. Confinement of electrons to the interface is achieved through the inclusion of an attractive potential in the interface. Motivation for our research comes from interest in heterostructure materials that exhibit the Edelstein and inverse Edelstein effects on surfaces or interfaces due to large Rashba spin-orbit coupling. By modifying the Hamiltonian of a three-dimensional free electron gas to include an interface with Rashba spin-orbit coupling and an attractive potential, we are able to calculate the bound-state and free-state wavefunctions and corresponding density of states analytically. We find that one of the spin-split energy bands in the interface has an upper bound, resulting in an enhancement of the Edelstein and inverse Edelstein effect.

cond-mat.mes-hall↗
arXiv2015

Dimensional Effects on the Density of States in Systems with Quasi-Relativistic Dispersion Relations and Potential Wells

Motivated by the recent discoveries of materials with quasi-relativistic dispersion relations, we determine densities of states in materials with low dimensional substructures and relativistic dispersion relations. We find that these dimensionally hybrid systems yield quasi-relativistic densities of states that are a superposition of the corresponding two- and three-dimensional densities of states.

cond-mat.mes-hall↗
arXiv2009

Radiation pressure on a dielectric boundary: was Poynting wrong?

When a plane electromagnetic wave in air falls on a flat dielectric boundary, the dielectric body is pulled toward the air as predicted by Poynting a century ago. According to Noether's theorem, the momentum in the direction parallel to the boundary must be conserved among the incident, reflected and transmitted waves. This uniquely determines the expression for the wave momentum in the dielectric medium which agrees with the Minkowski form. The inward force recently predicted and accompanied by Abraham's momentum are not consistent with Fresnel's formulae and basic symmetry principles.

physics.class-ph↗
arXiv2007

Dimensionally hybrid Green's functions and density of states for interfaces

The energy dependent Green's function for an interface Hamiltonian which interpolates between two and three dimensions can be calculated explicitly. This yields an expression for the density of states on the interface which interpolates continuously between the two-dimensional behavior for high energies and the three-dimensional behavior for low energies.

cond-mat.other↗
arXiv2005

Superheavy dark matter and ultrahigh energy cosmic rays

The phase of inflationary expansion in the early universe produces superheavy relics in a mass window between 10^{12} GeV and 10^{14} GeV. Decay or annihilation of these superheavy relics can explain the observed ultrahigh energy cosmic rays beyond the Greisen-Zatsepin-Kuzmin cutoff. We emphasize that the pattern of cosmic ray arrival directions with energies beyond 20 EeV will decide between the different proposals for the origin of ultrahigh energy cosmic rays.

hep-ph↗
arXiv2005

Ultrahigh energy cosmic rays from collisional annihilation revisited

We re-examine collisional annihilation of superheavy dark matter particles in dark matter density spikes in the galactic halo as a possible source of ultrahigh energy cosmic rays. We estimate the possible flux in a way that does not depend on detailed assumptions about the density profiles of dark matter clumps. The result confirms that collisional annihilation is compatible with annihilation cross sections below the unitarity bounds for superheavy dark matter if the particles can form dense cores in dark matter substructure, and it provides estimates for core sizes and densities. The ensuing clumpy source distribution in the galactic halo will be tested within a few years of operation of the Pierre Auger observatory.

astro-ph↗
arXiv2004

Variation of the fine structure constant in QSO spectra from coherent dark matter oscillations

We consider the problem of the evolution of the fine structure coefficient alpha under the assumption that the scalar field coupling to the Maxwell term satisfies the condition mt>>1 for coherent dark matter oscillations. In this case we find that the coupling scale f in the leading order coupling -(phi/4f)F^2 affects the cosmological evolution of alpha according to ln(alpha/alpha_0) xi(m_{Pl}/f)ln(tanh(t/2 tau)/tanh(t_0/2 tau)). A fit to the QSO observations by Murphy et al. yields f/xi= 2.12^{+0.58}_{-0.37} 10^5m_{Pl}. Here m_{Pl} is the reduced Planck mass, and xi^2=rho_phi/rho_m parametrizes the contribution of phi to the matter density in the universe.

astro-ph↗
arXiv2002

Hamiltonians and Green's functions which interpolate between two and three dimensions

I propose to use Hamiltonians which contain two-dimensional and three-dimensional kinetic terms for the description of two-dimensional systems in physics. As a model system the evolution of three-dimensional wavefunctions in the presence of an infinitely thin layer is studied. The model predicts distance laws for correlation functions which interpolate between two-dimensional and three-dimensional behavior. It also predicts that in certain cases transmission probabilities through thin layers should depend not only on the transverse, but also on the longitudinal momentum of the infalling particles. The model also yields a static potential which interpolates between the two-dimensional logarithmic potential at small distances and the three-dimensional (1/r)-potential at large distances.

cond-mat↗
arXiv2002

A photon mass on the brane

We discuss the impact of a bulk photon mass in a Dvali-Gabadadze-Porrati type brane model with Maxwell terms both on the brane and in the bulk, as proposed by Dvali, Gabadadze and Shifman. The motivation to include the bulk photon mass is to suppress radiation loss into the bulk. We point out that this modifies the photon propagator in such a way that it generates a small photon mass on the brane. Compatibility with present bounds on a photon mass imply that the transition to five-dimensional distance laws for the electromagnetic potentials would appear only at super-horizon length scales, thus excluding any direct detection possibility of a transition from four-dimensional to five-dimensional distance laws in electromagnetic interactions. We also include results on fermion propagators with Dirac terms on the brane and in the bulk.

hep-th↗
arXiv1998

Superstrings and dark matter

We point out that the spectrum and interactions of light states of the heterotic string indicate a string scale close to the GUT scale, and a mass generating scale for the gravitationally interacting states around 10^9 GeV if these states contribute a large fraction to dark matter.

hep-ph↗
arXiv1998

Cosmological implications of a light dilaton

Supersymmetric Peccei-Quinn symmetry and string theory predict a complex scalar field comprising a dilaton and an axion. These fields are massless at high energies, but it is known since long that the axion is stabilized in an instanton dominated vacuum. Instantons and axions together also provide a mechanism to stabilize a dilaton, thus accounting for a dilaton as a possible cold dark matter component accompanying the axion. We briefly review the prospects of this scenario and point out further implications.

hep-ph↗