Covariantly Quantum Galileon

TL;DR

This paper calculates the one-loop effective action of the cubic Galileon coupled to quantum gravity using a covariant, gauge-independent approach, revealing new non-Galileon interactions induced by gravity that could impact phenomenology.

Contribution

It introduces a covariant, gauge-invariant method to derive the effective action of Galileons coupled to gravity, uncovering non-Galileon terms not seen in previous non-covariant analyses.

Findings

Gravity induces an effective mass for the scalar field.

Novel non-Galileon higher-derivative interactions are discovered.

These interactions are not Planck suppressed and could influence phenomenology.

Abstract

We derive the 1-loop effective action of the cubic Galileon coupled to quantum-gravitational fluctuations in a background and gauge-independent manner, employing the covariant framework of DeWitt and Vilkovisky. Although the bare action respects shift symmetry, the coupling to gravity induces an effective mass to the scalar, of the order of the cosmological constant, as a direct result of the non-flat field-space metric, the latter ensuring the field-reparametrization invariance of the formalism. Within a gauge-invariant regularization scheme, we discover novel, gravitationally induced non-Galileon higher-derivative interactions in the effective action. These terms, previously unnoticed within standard, non-covariant frameworks, are not Planck suppressed. Unless tuned to be sub-dominant, their presence could have important implications for the classical and quantum phenomenology of the theory.