# V-mode Polarization in Axion Inflation and Preheating

## TL;DR

This paper investigates the generation of primordial circular polarization during axion inflation, revealing a blue-tilted spectrum with index 4, regardless of the dominant decay channel, and explores implications for preheating.

## Contribution

It provides a detailed calculation of the V-mode polarization power spectrum in axion inflation, highlighting its independence from decay channels and its distinctive spectral tilt.

## Key findings

- V-mode polarization spectrum is blue-tilted with index 4
- The spectrum shape is independent of decay channels
- Implications for observational signatures of axion inflation

## Abstract

We study the production of primordial circular ("V-mode") polarization in axion inflation coupled to fermions and gauge fields, with special attention paid to (p)reheating. We construct the power spectrum of $V$, and find a blue-tilted spectrum with index $n_V=4$. This is independent of the dominant decay channel of the inflaton (direct fermion vs. direct photon production)