# Imprint of a scalar era on the primordial spectrum of gravitational waves

## TL;DR

Future gravitational wave observations could reveal signatures of a scalar-dominated era before Big Bang nucleosynthesis, offering insights into early Universe physics beyond the Standard Model.

## Contribution

This paper investigates how a scalar field-driven early era affects the primordial gravitational wave spectrum, providing a new way to probe pre-Big Bang physics.

## Key findings

- Scalar era leaves distinctive imprints on GW spectrum
- Future GW detectors can test models with early scalar domination
- Complementary frequency coverage enhances detection prospects

## Abstract

Upcoming searches for the stochastic background of inflationary gravitational waves (GWs) offer the exciting possibility to probe the evolution of our Universe prior to Big Bang nucleosynthesis. In this spirit, we explore the sensitivity of future GW observations to a broad class of beyond-the-Standard-Model scenarios that lead to a nonstandard expansion history. We consider a new scalar field whose coherent oscillations dominate the energy density of the Universe at very early times, resulting in a scalar era prior to the standard radiation-dominated era. The imprint of this scalar era on the primordial GW spectrum provides a means to probe well-motivated yet elusive models of particle physics. Our work highlights the complementarity of future GW observatories across the entire range of accessible frequencies.