Primordial Gravitational Wave Signals in Modified Cosmologies

TL;DR

This paper explores how modified gravity theories alter primordial gravitational wave spectra, affecting detection prospects across different observatories and enabling potential differentiation between models.

Contribution

It analyzes PGW signals in scalar-tensor and extradimensional modified gravity theories, highlighting their distinct detection signatures and prospects.

Findings

Scalar-tensor PGWs detectable by high-frequency laser interferometers

Extradimensional PGWs potentially observable with pulsar timing arrays

Multi-frequency GW observations can distinguish between modified gravity models

Abstract

Modified expansion rates in the early Universe prior to big bang nucleosynthesis are common in modified gravity theories, and can have a significant impact on the generation of dark matter, matter-antimatter asymmetry, primordial black holes and the primordial gravitational wave (PGW) spectrum. Here we study the PGW spectrum in modified gravity theories, in early Universe cosmology. In particular, we consider scalar-tensor and extradimensional scenarios, investigating the detection prospects in current and future GW observatories. For the scalar-tensor case, PGW could be potentially observed by laser interferometers operating in the high-frequency range, while for the extradimensional case they could be detected even at low frequencies with pulsar timing arrays. We find that data from the planned network of several GW detectors operating across various frequency ranges could be able to distinguish between various modified gravity scenarios.