Spontaneous breaking of global U(1) symmetry in an interacting Bose gas under rigid rotation

TL;DR

This paper studies how rigid rotation affects the spontaneous breaking of U(1) symmetry in an interacting Bose gas, revealing rotation-dependent phase transition behavior and the importance of nonperturbative effects.

Contribution

It introduces a detailed analysis of the impact of rotation on U(1) symmetry breaking, including the derivation of the thermodynamic potential and the role of nonperturbative effects.

Findings

Critical temperature scales as Ω^{1/3}

Goldstone theorem holds with thermal corrections

Rotation influences phase transition order

Abstract

We investigate the impact of rigid rotation on the spontaneous breaking of U(1) symmetry in a Bose gas, which is described by a self-interacting complex scalar field Lagrangian. Rigid rotation is introduced through a specific metric that explicitly depends on the angular velocity $\Omega$. We begin by determining the free propagator for this model at finite temperature $T$ and chemical potential $\mu$. Using this propagator, we calculate the thermodynamic potential in terms of an energy dispersion relation $\epsilon_{k}$. It is found that in both the U(1) symmetric phase and the symmetry-broken phase, two energy branches emerge. In the symmetry-broken phase, they are identified with a massive phonon and a massless roton mode. Notably, rotation does not alter $\epsilon_{k}$ at low momentum. Setting $\mu=0$, we use the total thermodynamic potential, which includes classical, thermal, vacuum, and nonperturbative ring contributions, to explore how the condensate depends on $T$ and $\Omega$. We first focus on the classical and thermal parts of the thermodynamic potential and find that the critical temperature of the U(1) phase transition scales as $\Omega^{1/3}$. By identifying the (pseudo-)Goldstone and non-Goldstone modes of this model with $\pi$ and $\sigma$ mesons, we calculate the $T$ and $\Omega$ dependence of masses $m_{\pi}$ and $m_{\sigma}$. We demonstrate that the Goldstone theorem holds only when the one-loop (thermal) corrections to $m_{\sigma}$ and $m_{\pi}$ are taken into account. We further explore the $T$ and $\Omega$ dependence of the condensate, determine the $\sigma$ dissociation temperatures for fixed $\Omega$, and compare them with the critical temperature of the phase transition. Additionally, we emphasize the role played by the nonperturbative ring potential, especially in altering the order of the phase transition with and without rotation.