Finite temperature Casimir effect of a Lorentz-violating scalar with higher order derivatives

TL;DR

This work analyzes the finite-temperature Casimir effect for a complex massive scalar field that breaks Lorentz invariance via a spacelike aether-like vector coupled to higher derivatives. Using the generalized zeta-function method, it derives analytic expressions for the free energy and Casimir pressure in the presence of Dirichlet and mixed boundary conditions on two parallel plates, for both orientations of the Lorentz-violating vector, in three asymptotic regimes: small plate distance, high temperature, and large mass. The results show orientation- and boundary-condition–dependent corrections that can either weaken or strengthen the Casimir force, with exponential suppression in the large-mass limit and Stefan-Boltzmann-like scaling at high temperature. The zero-temperature limit agrees with prior CPT-even Lorentz-violating analyses, and the findings provide concrete benchmarks for Lorentz-violating effects in quantum vacuum phenomena.

Abstract

In this work I study the finite temperature Casimir effect caused by a complex and massive scalar field that breaks Lorentz invariance in a CPT-even, aether-like manner. The Lorentz invariance breaking is caused by a constant space-like vector directly coupled to higher order field derivatives. This vector needs to be space-like in order to avoid non-causality problems that will arise with a time-like vector. I investigate the two scenarios of the scalar field satisfying either Dirichlet or mixed boundary conditions on a pair of flat parallel plates. I use the generalized zeta function technique that enables me to obtain the Helmholtz free energy and the Casimir pressure when the Casimir plates are in thermal equilibrium with a heat reservoir at finite temperature. I investigate two different directions of the unit vector, parallel and perpendicular to the plates. I examine both scenarios for both types of boundary conditions and, in both cases and for the two different boundary conditions, I obtain simple analytic expressions of the Casimir energy and pressure in the three asymptotic limits of small plate distance, high temperature, and large mass, examining all combinations of boundary conditions, unit vector direction, and asymptotic limits.