Influence on observation from IR divergence during inflation -- Multi field inflation --

TL;DR

This paper extends a method for regularizing IR divergences in inflationary fluctuations from single to multi-field models, emphasizing the importance of quantum decoherence in observable predictions.

Contribution

It demonstrates that IR divergences can be regularized in multi-field inflation models with finite-duration non-linear interactions, incorporating quantum decoherence effects.

Findings

IR divergences are regularized in multi-field inflation with finite interaction duration.

Quantum decoherence influences observable fluctuations in multi-field inflation.

The approach aligns multi-field results with previous single-field regularization methods.

Abstract

We propose one way to regularize the fluctuations generated during inflation, whose infrared (IR) corrections diverge logarithmically. In the case of a single field inflation model, recently, we proposed one solution to the IR divergence problem. There, we introduced new perturbative variables which better mimic actual observable fluctuations, and proved the regularity of correlation functions with respect to these variables. In this paper, we extend our previous discussions to a multi field inflation model. We show that, as long as we consider the case that the non-linear interaction acts for a finite duration, observable fluctuations are free from IR divergences in the multi field model, too. In contrast to the single field model, to discuss observables, we need to take into account the effects of quantum decoherence which pick up a unique history of the universe from various possibilities contained in initial quantum state set naturally in the early stage of the universe.