TwInflation

TL;DR

This paper introduces Twinflation, a natural, EFT-controlled hybrid inflation model with a discrete twin symmetry that addresses the hierarchy problem and avoids fine-tuning, providing a viable low-scale inflation scenario.

Contribution

It proposes a novel Twinflation model incorporating a twin symmetry to solve the hierarchy problem in hybrid inflation, ensuring natural parameters and EFT control.

Findings

Twinflation reduces quadratic sensitivity to UV physics.

The model achieves inflation without fine-tuning initial conditions.

Parameters remain below EFT cutoff scales.

Abstract

The general structure of Hybrid Inflation remains a very well-motivated mechanism for lower-scale cosmic inflation in the face of improving constraints on the tensor-to-scalar ratio. However, as originally modeled, the "waterfall" field in this mechanism gives rise to a hierarchy problem ($\eta-$problem) for the inflaton after demanding standard effective field theory (EFT) control. We modify the hybrid mechanism and incorporate a discrete "twin" symmetry, thereby yielding a viable, natural and EFT-controlled model of non-supersymmetric low-scale inflation, "Twinflation". Analogously to Twin Higgs models, the discrete exchange-symmetry with a "twin" sector reduces quadratic sensitivity in the inflationary potential to ultra-violet physics, at the root of the hierarchy problem. The observed phase of inflation takes place on a hilltop-like potential but without fine-tuning of the initial inflaton position in field-space. We also show that all parameters of the model can take natural values, below any associated EFT-cutoff mass scales and field values, thus ensuring straightforward theoretical control. We discuss the basic phenomenological considerations and constraints, as well as possible future directions.