Measuring the spectrum of primordial gravitational waves with CMB, PTA and Laser Interferometers

TL;DR

This paper assesses the potential to measure primordial gravitational waves across a vast frequency range using CMB, PTA, and laser interferometers, highlighting promising joint detection prospects.

Contribution

It develops a comprehensive framework for sensitivity calculations across multiple GW detection methods and evaluates their combined capabilities for primordial GW detection.

Findings

Strong joint detection prospects between CMB and space-based interferometers.

Sensitivity curves for various experiments across 21 decades of frequency.

Evaluation of astrophysical foreground effects on primordial GW measurements.

Abstract

We investigate the possibility of measuring the primordial gravitational wave (GW) signal across 21 decades in frequencies, using the cosmic microwave background (CMB), pulsar timing arrays (PTA), and laser and atomic interferometers. For the CMB and PTA experiments we consider the LiteBIRD mission and the Square Kilometer Array (SKA), respectively. For the interferometers we consider space mission proposals including the Laser Interferometer Space Antenna (LISA), the Big Bang Observer (BBO), the Deci-hertz Interferometer Gravitational wave Observatory (DECIGO), the $\mu$Ares experiment, the Decihertz Observatory (DO), and the Atomic Experiment for Dark Matter and Gravity Exploration in Space (AEDGE), as well as the ground-based Einstein Telescope (ET) proposal. We implement the mathematics needed to compute sensitivities for both CMB and interferometers, and derive the response functions for the latter from the first principles. We also evaluate the effect of the astrophysical foreground contamination in each experiment. We present binned sensitivity curves and error bars on the energy density parameter, $\Omega_{GW}h^2$, as a function of frequency for two representative classes of models for the stochastic background of primordial GW: the quantum vacuum fluctuation in the metric from single-field slow-roll inflation, and the source-induced tensor perturbation from the spectator axion-SU(2) inflation models. We find excellent prospects for joint measurements of the GW spectrum by CMB and space-borne interferometers mission proposals.