"Stairway to Heaven" -- Spectroscopy of Particle Couplings with Gravitational Waves

TL;DR

This paper explores how stochastic gravitational wave backgrounds can reveal particle couplings through a stairway-like spectral signature, enabling spectroscopy of high-energy particle interactions in the early universe.

Contribution

It introduces the concept of spectral stairways in SGWBs as a method to measure particle couplings, demonstrated through a preheating scenario with multiple coupled fields.

Findings

Stairway signatures can be detected in SGWB spectra.

Couplings of particles can be reconstructed from spectral features.

Multiple detectors can identify the staircase pattern.

Abstract

We discuss the possibility to measure particle couplings with stochastic gravitational wave backgrounds (SGWBs). Under certain circumstances a sequence of peaks of different amplitude and frequency -- a $stairway$ -- emerges in a SGWB spectrum, with each peak probing a different coupling. The detection of such signature opens the possibility to reconstruct couplings (spectroscopy) of particle species involved in high energy phenomena generating SGWBs. Stairway-like signatures may arise in causally produced backgrounds in the early Universe, e.g. from preheating or first order phase transitions. As a proof of principle we study a preheating scenario with an inflaton $\phi$ coupled to multiple $daughter$ fields $\lbrace \chi_j \rbrace$ with different coupling strengths. As a clear stairway signature is imprinted in the SGWB spectrum, we reconstruct the relevant couplings with various detectors.