Suppressing Quantum Fluctuations in Classicalization

TL;DR

This paper investigates how certain scalar field theories can suppress quantum fluctuations through classicalization, leading to a softer, red-tilted power spectrum at small scales, contrasting with traditional UV completions.

Contribution

It demonstrates that quantum fluctuation suppression and spectral softening occur only in theories that admit superluminal classical backgrounds, indicating a classicalization mechanism over standard UV completion.

Findings

Quantum fluctuations can be significantly suppressed in classicalizing theories.

The power spectrum can become red at small scales in these theories.

Suppression is linked to the existence of superluminal classical backgrounds.

Abstract

We study vacuum quantum fluctuations of simple Nambu-Goldstone bosons - derivatively coupled single scalar-field theories possessing shift-symmetry in field space. We argue that quantum fluctuations of the interacting field can be drastically suppressed with respect to the free-field case. Moreover, the power-spectrum of these fluctuations can soften to become red for sufficiently small scales. In quasiclassical approximation, we demonstrate that this suppression can only occur for those theories that admit such classical static backgrounds around which small perturbations propagate faster than light. Thus, a quasiclassical softening of quantum fluctuations is only possible for theories which classicalize instead of having a usual Lorentz invariant and local Wilsonian UV- completion. We illustrate our analysis by estimating the quantum fluctuations for the DBI-like theories.