Search results for "quantum electrodynamics"

EP-1186: Accuracy of the TG-43 dose calculation formalism for HDR skin brachytherapy

2013

On the interdependence between ground and one-phonon RPA states

1998

Working within a schematic model and in a boson formalism, we provide a descrip tion of the ground and first-excited states of a nuclear system in terms of two independent phonon operators. The description reveals itself quite effective in reproducing the energies of the states. A comparison between these two phonon operators allows us to localize a region where a correct description of these states is compatible with the Random Phase Approximation (RPA) requirement of a single phonon. This region is found to coincide approximately with that spanned by the standard RPA. Outside this region, the two phonons start differing rapidly therefore making the application of the RPA scheme impossible…

Erratum: “Fitted dosimetric parameters of high dose-rate 192Ir sources according to the AAPM TG43 formalism” [Med. Phys. 28 (4), 654-660 (2001)]

2001

Dark Photon Oscillations in Our Inhomogeneous Universe

2020

A dark photon may kinetically mix with the ordinary photon, inducing oscillations with observable imprints on cosmology. Oscillations are resonantly enhanced if the dark photon mass equals the ordinary photon plasma mass, which tracks the free electron number density. Previous studies have assumed a homogeneous Universe; in this Letter, we introduce for the first time an analytic formalism for treating resonant oscillations in the presence of inhomogeneities of the photon plasma mass. We apply our formalism to determine constraints from Cosmic Microwave Background photons oscillating into dark photons, and from heating of the primordial plasma due to dark photon dark matter converting into …

Self-consistency conditions for localized magnetic moments in a free electron gas

1969

The self-consistent conditions for a localized magnetic moment in a metal are studied in the case where the density of states of the host metal is free electron like. A method is outlined which in principle allows to determine self-consistently in the Hartree-Fock approximation the relevant parameters of the magnetic ground state of the system. A numerical example is approximately worked out to show how the theory gives reasonable answers in spite of the crudeness of some of the approximations used.

Friedel Oscillations in Relativistic Nuclear Matter

1994

We calculate the low-momentum N-N effective potential obtained in the OBE approximation, inside a nuclear plasma at finite temperature, as described by the relativistic $ \sigma $-$ \omega $ model. We analyze the screening effects on the attractive part of the potential in the intermediate range as density or temperature increase. In the long range the potential shows Friedel-like oscillations instead of the usual exponential damping. These oscillations arise from the sharp edge of the Fermi surface and should be encountered in any realistic model of nuclear matter.

Electroweak precision data and right-handed gauge bosons

1998

The implication of recent electroweak precision data for left-right symmetric models is examined. We establish a lower bound on the charged and neutral right-handed gauge bosons independent of the right-handed neutrino mass and of any restrictions or implied symmetries on the right KM matrix.

Quantum simulation of gauge potentials with cold atoms in optical lattices: a tunable platform for relativistic fermions and axions

2014

We offer here a brief introduction to the idea of quantum simulations with cold atomic gases, with focus on the recent efforts towards artificial gauge potentials and fields. This is mainly intended as a sort of “pedestrian guide” for people not yet working in the field, but curious to get a first contact with it; longer and deeper reviews are addressed for deeper details. As a special case, we focus here on reviewing some own previous contributions about a flexible toolbox based on bichromatic optical lattices and Raman assisted tunnelling. Such a scheme would allow good control on the mass and kinetic terms of a lattice Hamiltonian in different effective dimensions. If realized with fermi…

Direct perturbation theory in terms of energy derivatives: Fourth-order relativistic corrections at the Hartree–Fock level

2011

In this work, the quantum-chemical treatment of relativistic effects by means of direct perturbation theory is extended from its lowest order, DPT2, to the next higher order, DPT4. The required theory is given in terms of energy derivatives with the DPT4 energy correction defined as the corresponding second derivative with respect to the relativistic perturbation parameter λ(rel) = c(2) and c as the speed of light. To facilitate the implementation in standard quantum-chemical program packages, a general formulation of DPT starting from a nonrelativistic Lagrangian is developed, thereby expanding both wave function and operators in terms of λ(rel). The corresponding expressions, which incorp…

Coherent magneto-elastic oscillations in superfluid magnetars

2016

We study the effect of superfluidity on torsional oscillations of highly magnetised neutron stars (magnetars) with a microphysical equation of state by means of two-dimensional, magnetohydrodynamical- elastic simulations. The superfluid properties of the neutrons in the neutron star core are treated in a parametric way in which we effectively decouple part of the core matter from the oscillations. Our simulations confirm the existence of two groups of oscillations, namely continuum oscillations that are confined to the neutron star core and are of Alfv\'enic character, and global oscillations with constant phase and that are of mixed magneto-elastic type. The latter might explain the quasi-…