arXiv subjects

G. Hansen

Publications and source records attributed to G. Hansen.

7 recordsLinked to original sources

arXiv2024

On the fermionic van der Waals and Casimir-Polder interactions

We formulate fermionic versions, for any number of spatial dimensions, of the van der Waals and Casimir-Polder interactions, and study their properties. In both cases, the systems we introduce contain localized `atoms': two-level systems, coupled to a vacuum Dirac field. This Dirac field plays here a role akin to the electromagnetic field in the van der Waals case. In this context, bag-model conditions for the Dirac field serve as the analog of the 'mirror' in the Casimir-Polder effect. We found that, in this case, the resulting interaction is repulsive.

hep-th↗

arXiv2024

Fermionic dynamical Casimir effect: Magnus expansion

We study pair creation out of the vacuum, for a system consisting of a massive Dirac field in $1+1$ dimensions, contained between a pair of perfectly reflecting boundaries, one of them oscillating. After analyzing some general properties of the vacuum-decay process, we evaluate the corresponding transition amplitude in a Magnus expansion of the S-matrix. We show how this yields, besides the single-pair creation amplitude, multipair ones, as well as corrections to the single pair amplitude. We also apply it to obtain an approximate, yet explicitly unitary expression for the Bogoliubov transformation between the in and out Fock spaces.

hep-th↗

arXiv2023

Dynamical Casimir effect for fermions in 2+1 dimensions

We study the fermion pair creation phenomenon due to the time dependence of curves, where boundary conditions are imposed on a Dirac field in 2+1 dimensions. These conditions, which lead to non-trivial relations for the normal component of the fermionic current, depend on the value of a dimensionless parameter. We show that the pair creation effect is maximized for bag boundary conditions, obtained for a particular value of that parameter. The effect is studied in terms of the effective action to extract information on the probability of vacuum decay, using an expansion in powers of the deformation of the curves with respect to straight lines. We demonstrate that the first non-trivial contributions to this process can be obtained from the electromagnetic vacuum polarization tensor for a Dirac field coupled to static boundaries.

hep-th↗

arXiv2023

A functional approach to the Van der Waals interaction

Based on a microscopic model, we use a functional integral approach to evaluate the quantum interaction energy between two neutral atoms. Each atom is coupled to the electromagnetic (EM) field via a dipole term, generated by an electron bound to the nucleus via a harmonic potential. We show that the resulting expression for the energy becomes the Van der Waals interaction energy at the first non-trivial order in an expansion in powers of the fine structure constant, encompassing both the long and short distance behaviours. We also explore the opposite, strong-coupling limit, which yields a result for the interaction energy as well as a threshold for the existence of a vacuum decay probability, manifested here as an imaginary part for the effective action. In the weak-coupling limit, we also study the effect of using a general central potential for the internal structure of the atoms.

quant-ph↗

arXiv2021

Dynamical Casimir effect from fermions in an oscillating bag in 1+1 dimensions

We evaluate dissipative effects for a system consisting of a massive Dirac field confined between two walls, one of them oscillating, in 1+1 dimensions. In the model that we consider, a dimensionless parameter characterizing each wall is tuned so that bag-boundary conditions are attained for a particular value. We present explicit results for the probability of creating a fermion pair out of the vacuum, and relate the total vacuum decay probability to the imaginary part of the effective action.

hep-th↗

arXiv2016

Phase rotation of muon beams for producing intense low-energy muon beams

Low-energy muon beams are useful for rare decay searches, which provide access to new physics that cannot be addressed at high-energy colliders. However, muons are produced within a broad energy spread unmatched to the low-energy required. In this paper we outline a phase rotation method to significantly increase the intensity of low-energy muons. The muons are produced from a short pulsed proton driver, and develop a time-momentum correlation in a drift space following production. A series of rf cavities is used to bunch the muons and phase-energy rotate the bunches to a momentum of around 100 MeV/c. Then another group of rf cavities is used to decelerate the muon bunches to low-energy. This obtains ~0.1 muon per 8 GeV proton, which is significantly higher than currently planned Mu2e experiments, and would enable a next generation of rare decay searches, and other intense muon beam applications.

physics.acc-ph↗

arXiv2009

Measurement of the Spin-Dependence of the pbar-p Interaction at the AD-Ring

We propose to use an internal polarized hydrogen storage cell gas target in the AD ring to determine for the first time the two total spin-dependent pbar-p cross sections sigma_1 and sigma_2 at antiproton beam energies in the range from 50 to 450 MeV. The data obtained are of interest by themselves for the general theory of pbar-p interactions since they will provide a first experimental constraint of the spin-spin dependence of the nucleon-antinucleon potential in the energy range of interest. In addition, measurements of the polarization buildup of stored antiprotons are required to define the optimum parameters of a future, dedicated Antiproton Polarizer Ring (APR), intended to feed a double-polarized asymmetric pbar-p collider with polarized antiprotons. Such a machine has recently been proposed by the PAX collaboration for the new Facility for Antiproton and Ion Research (FAIR) at GSI in Darmstadt, Germany. The availability of an intense stored beam of polarized antiprotons will provide access to a wealth of single- and double-spin observables, thereby opening a new window on QCD spin physics.

nucl-ex↗