Measuring the primordial gravitational waves from cosmic microwave background and stochastic gravitational wave background observations

TL;DR

This paper constrains primordial gravitational waves using CMB and SGWB data, combining LIGO observations and forecasting capabilities of LISA and PTA, to improve parameter constraints and understand early universe physics.

Contribution

It integrates multiple observational methods to constrain primordial gravitational waves and forecasts future detector sensitivities, advancing understanding of early universe cosmology.

Findings

SGWB observations improve constraints on tensor-to-scalar ratio and spectral index.

FAST projects significantly tighten bounds on gravitational wave parameters.

Combined data suggest slight parameter shifts in the cosmological model.

Abstract

We constrain the primordial gravitational waves from cosmic microwave background (CMB) and stochastic gravitational wave background (SGWB) observations. SGWB provides the latest way to explore the early universe and the cosmological evolution which can be reflected by primordial gravitational waves. We not only combine LIGO observations with CMB to measure primordial gravitational waves, but also forecast the potential abilities of the LISA detector and PTA projects. In the $\Lambda$CDM+$r$+$n_t$ model, the standard six parameters change slightly from SGWB observations. While the constraints on tensor-to-scalar ratio and tensor spectral index are improved obviously from SGWB observations. FAST projects have a significant impact on tensor-to-scalar ratio and tensor spectral index, namely $r<0.028$ and $n_t=-0.41^{+0.64}_{-0.96}$ at $95\%$ confidence level.