Quantum Backgrounds from Coherent States

Coherent states provide a bridge between classical and quantum field theories. In this talk, I will explore how studying the quantum dynamics of field backgrounds through the evolution of their associated coherent states can provide insight into their stability. Focusing on a complex scalar field theory with quartic interactions, I will present the quantum evolution of two Lorentz-breaking states. Although both describe stationary configurations in the classical limit, they behave differently once quantum effects are included: one becomes unstable, while the other remains stable. The first example is a zero-charge condensate, which is depleted by number-changing processes among its constituent particles. The second is a finite-charge condensate, or superfluid, which remains stable and closely follows its classical evolution, albeit with a quantum-corrected chemical potential. Through these examples, I will discuss the challenges of consistently formulating coherent states in interacting quantum field theories and the connection between their evolution and more standard semiclassical methods.