A new mechanism to enhance primordial tensor fluctuations in single field inflation

TL;DR

This paper introduces a novel mechanism in single field inflation that temporarily amplifies primordial tensor fluctuations by utilizing a non-attractor phase, leading to potential observable signatures in the tensor spectrum.

Contribution

It presents a new tensor enhancement mechanism during non-attractor inflation, supported by a tensor duality framework and demonstrated in a kinetically driven inflation model.

Findings

Tensor fluctuations can be significantly amplified during non-attractor phases.

The tensor duality provides a new theoretical tool to analyze inflationary tensor modes.

The mechanism is exemplified in a kinetically driven inflation scenario with non-minimal couplings.

Abstract

We discuss a new mechanism to enhance the spectrum of primordial tensor fluctuations in single field inflationary scenarios. The enhancement relies on a transitory non-attractor inflationary phase, which amplifies the would-be decaying tensor mode, and gives rise to a growth of tensor fluctuations at superhorizon scales. We show that the enhancement produced during this phase can be neatly treated via a tensor duality between an attractor and non-attractor phase, which we introduce. We illustrate the mechanism and duality in a kinetically driven scenario of inflation, with non-minimal couplings between the scalar and the metric.