Soft Gravitons Screen Couplings in de Sitter Space

TL;DR

This paper studies how soft gravitons in de Sitter space influence local matter field dynamics, showing that IR logarithms lead to time-dependent couplings without breaking Lorentz invariance.

Contribution

It demonstrates that IR logarithms from soft gravitons can be absorbed into wave function renormalization and induce gauge-invariant, physical time-dependent couplings in matter fields.

Findings

IR logarithms do not break Lorentz invariance.

Couplings in scalar and Yukawa theories become time-dependent.

Relative scaling exponents of couplings are gauge invariant.

Abstract

The scale invariance of the quantum fluctuations in de Sitter space leads to the appearance of de Sitter symmetry breaking infra-red logarithms in the graviton propagator. We investigate physical effects of soft gravitons on the local dynamics of matter fields well inside the cosmological horizon. We show that the IR logarithms do not spoil Lorentz invariance in scalar and Dirac field theory. The leading IR logarithms can be absorbed by a time dependent wave function renormalization factor in the both cases. In the interacting field theory with $\lambda \phi^4$ and Yukawa interaction, we find that the couplings become time dependent with definite scaling exponents. We argue that the relative scaling exponents of the couplings are gauge invariant and physical as we can use the evolution of a coupling as a physical time.