Gravitational waves from inflation in LISA: reconstruction pipeline and physics interpretation

TL;DR

This paper develops a template-based analysis pipeline for detecting and interpreting gravitational wave signals from inflation with LISA, enabling insights into fundamental physics models of the early universe.

Contribution

It introduces a classification of inflationary gravitational wave templates, forecasts LISA's reconstruction capabilities, and explores implications for inflationary physics models.

Findings

LISA can reconstruct inflationary signals with specific parameter accuracy.

Seven template classes effectively describe diverse inflationary scenarios.

Reconstructed signals can inform models of axions, graviton mass, and primordial black holes.

Abstract

Various scenarios of cosmic inflation enhance the amplitude of the stochastic gravitational wave background (SGWB) at frequencies detectable by the LISA detector. We develop tools for a template-based analysis of the SGWB and introduce a template databank to describe well-motivated signals from inflation, prototype their template-based searches, and forecast their reconstruction with LISA. Specifically, we classify seven templates based on their signal frequency shape, and we identify representative fundamental physics models leading to them. By running a template-based analysis, we forecast the accuracy with which LISA can reconstruct the template parameters of representative benchmark signals, with and without galactic and extragalactic foregrounds. We identify the parameter regions that can be probed by LISA within each template. Finally, we investigate how our signal reconstructions shed light on fundamental physics models of inflation: we discuss their impact for measurements of \emph{e.g.,} ~the couplings of inflationary axions to gauge fields; the graviton mass during inflation; the fluctuation seeds of primordial black holes; the consequences of excited states during inflation, and the presence of small-scale spectral features.