Exact RG Flow in an Expanding Universe and Screening of the Cosmological Constant

TL;DR

This paper derives an exact renormalization group flow equation for a scalar field in an expanding universe, revealing a quantum screening mechanism that reduces the effective cosmological constant as the IR cutoff is lowered.

Contribution

It provides the first exact RG flow equation in an expanding cosmological background and analyzes the impact of expansion on the cosmological constant and scalar interactions.

Findings

The cosmological constant decreases as the IR cutoff is removed.

Expansion alters the running of the quartic coupling, affecting quantum triviality.

Supports a quantum screening mechanism for the cosmological constant.

Abstract

We obtain the exact renormalization group (RG) flow equation for a self interacting real scalar field in an expanding cosmological background. The beta functional for the potential in the local potential approximation is determined in terms of the mode functions defining the vacuum of the theory. For a scalar in an inflating universe, which is released in the Bunch-Davies vacuum, the flow equation is analyzed in detail using the optimized cutoff function for the quartically truncated potential. In that case, the constant term in the potential, which can in fact be viewed as the cosmological constant, decreases as the IR cutoff is removed, supporting the existence of a quantum mechanical screening mechanism. On the other hand, the running of the quartic coupling constant at IR is altered by the expansion, which seems to affect the quantum triviality of the theory.