Parity Violation from Emergent Non-Locality During Inflation

TL;DR

This paper investigates how parity violation during inflation, caused by massive spinning particles with a helical chemical potential, can produce observable non-local effects in the primordial trispectrum, especially under reduced sound speed conditions.

Contribution

It introduces a novel effective non-local description of parity violation in the inflationary trispectrum, revealing new oscillatory signals and features in the presence of a reduced sound speed.

Findings

Parity violation can be significantly large with a reduced sound speed.

A new oscillatory signal pattern in the trispectrum is identified.

The effective theory provides a compact template for the parity-violating trispectrum.

Abstract

Parity violation in the early universe holds great promise for uncovering new physics. In particular, the primordial scalar four-point correlation function is allowed to develop a parity-violating component when massive spinning particles coupled to a helical chemical potential are present during inflation. In this paper, we explore the rich physics of such a parity-violating trispectrum in the presence of a reduced speed of sound for the Goldstone boson of broken time translations. We show that this signal can be significantly large while remaining under perturbative control, offering promising observational prospects for future cosmological surveys. In the limit of a reduced sound speed, the dynamics admits an effective non-local description organized as a time-derivative expansion. This reveals that parity violation arises due to emergent non-locality in the single-field effective theory. At leading order, this effective theory yields a compact trispectrum template, written in terms of elementary functions. We then conduct a comprehensive analysis of the kinematic dependence of this parity-violating trispectrum and reveal new features. In addition to the low-speed collider resonance, we find a new class of signals lying in the internal soft-limit of the correlator. This signal is characterized by an oscillatory pattern periodic in the momentum ratio, with a frequency determined by the speed of sound and the chemical potential, making it drastically distinct from the conventional cosmological collider signal.