Search results for "electrodynamics"

Radiative decays in bottomonium beyond the long wavelength approximation

2019

We revisit the nonrelativistic quark model description of electromagnetic radiative decays in bottomonium. We show that even for the simplest spectroscopic quark model the calculated widths can be in good agreement with data once the experimental masses of bottomonium states and the photon energy are properly implemented in the calculation. For transitions involving the lower lying spectral states this implementation can be easily done via the Long Wave Length approximation. For transitions where this approximation does not apply we develop a new method of implementing the experimental energy dependencies.

Response functions for infinite fermion systems with velocity dependent interactions

1992

Response functions of infinite Fermi systems are studied in the framework of the self-consistent random phase approximation (RPA). Starting from an effective interaction with velocity and density dependence, or equivalently from a local energy density functional, algebraic expressions for the RPA response function are derived. Simple formulae for the energy-weighted and polarizability sum rules are obtained. The method is illustrated by applications to nuclear matter and liquid 3 He. In nuclear matter, it is shown that existing Skyrme interactions give spin-isospin response functions close to those calculated with finite range interactions. The different renormalization of longitudinal and …

Numerical integration of subtraction terms

2016

Numerical approaches to higher-order calculations often employ subtraction terms, both for the real emission and the virtual corrections. These subtraction terms have to be added back. In this paper we show that at NLO the real subtraction terms, the virtual subtraction terms, the integral representations of the field renormalisation constants and -- in the case of initial-state partons -- the integral representation for the collinear counterterm can be grouped together to give finite integrals, which can be evaluated numerically. This is useful for an extension towards NNLO.

Multi-longitudinal mode emission in a bidirectional laser model

2011

Multi-longitudinal mode emission is a fundamental issue in laser physics. Interestingly enough, the mechanisms responsible for the transition from single- to multi-longitudinal mode emission have not been completely clarified yet. For example, it is well known that in unidirectional ring lasers the Rabi splitting of the lasing transition can lead to multimode emission even in a homogeneously broadened medium, the so called Risken-Nummedal—Graham-Haken instability (RNGHI) [1]. In spite of being known since the late sixties, only in the recent years a couple of experiments have demonstrated “dressed” versions of the RNGHI [2], i.e., up to day there are not clear demonstrations of this basic m…

Model Dependence of Nucleon Resonance Parameters

2004

Nucleon resonance parameters as mass, width, branching ratios and electromagnetic helicity amplitudes cannot be determined in a model independent way. The best way to obtain such elementary quantities is in terms of a partial wave analysis and a separation of resonance and background. In this work we have concentrated on the extraction of the e.m. helicity amplitudes A l p and A312 from electric and magnetic multipole analyses that were obtained from different groups with different techniques. We make a comparison of our results for the resonances P11(1440), 013(1520) and s11(1535). The variation that we find can be considered as a measure of the model uncertainty in these quantities.

Spurious Singularities in Quasipotential Amplitudes

1973

Analytical description of the transverse Anderson localization of light

2017

Dynamical bar-mode instability in spinning bosonic stars

2020

Spinning bosonic stars (SBSs) can form from the gravitational collapse of a dilute cloud of scalar/Proca particles with nonzero angular momentum, via gravitational cooling. The scalar stars are, however, transient due to a nonaxisymmetric instability which triggers the loss of angular momentum. By contrast, no such instability was observed for the fundamental ( m = 1 ) Proca stars. In [N. Sanchis-Gual et al., Phys. Rev. Lett. 123, 221101 (2019)] we tentatively related the different stability properties to the different toroidal/spheroidal morphology of the scalar/Proca models. Here, we continue this investigation, using three-dimensional numerical-relativity simulations of the Einstein-(mas…

Electric-Field-Induced Symmetry Breaking of Angular Momentum Distribution in Atoms

2006

We report the experimental observation of alignment to orientation conversion in the 7D_3/2 and 9D_3/2 states of Cs in the presence of an external dc electric field, and without the influence of magnetic fields or atomic collisions. Initial alignment of angular momentum states was created by two-step excitation with linearly polarized laser radiation. The appearance of transverse orientation of angular momentum was confirmed by the observation of circularly polarized light. We present experimentally measured signals and compare them with the results of a detailed theoretical model based on the optical Bloch equations.

Strongly correlated states of trapped ultracold fermions in deformed Landau levels

2015

We analyze the strongly correlated regime of a two-component trapped ultracold fermionic gas in a synthetic non-Abelian U(2) gauge potential, that consists of both a magnetic field and a homogeneous spin-orbit coupling. This gauge potential deforms the Landau levels (LLs) with respect to the Abelian case and exchanges their ordering as a function of the spin-orbit coupling. In view of experimental realizations, we show that a harmonic potential combined with a Zeeman term, gives rise to an angular momentum term, which can be used to test the stability of the correlated states obtained through interactions. We derive the Haldane pseudopotentials (HPs) describing the interspecies contact inte…