Implications of the B-mode Polarization Measurement for Direct Detection of Inflationary Gravitational Waves

TL;DR

This paper evaluates the potential for future interferometric detectors to directly measure inflationary gravitational waves inferred from B-mode polarization, focusing on various inflationary models and their detectability conditions.

Contribution

It provides detailed predictions for the detectability of inflationary gravitational waves by DECIGO and BBO, considering different inflationary potentials and reheating temperatures.

Findings

Detection possible for high reheating temperatures in chaotic inflation.

Natural inflation detectable if decay constant exceeds 4.2 times Planck mass.

Detectability of non-minimal coupling models for small coupling values.

Abstract

The prospects for direct measurements of inflationary gravitational waves by next generation interferometric detectors inferred from the possible detection of B-mode polarization of the cosmic microwave background are studied. We compute the spectra of the gravitational wave background and the signal-to-noise ratios by two interferometric detectors (DECIGO and BBO) for large-field inflationary models in which the tensor-to-scalar ratio is greater than the order of 0.01. If the reheating temperature $T_{\rm RH}$ of chaotic inflation with the quadratic potential is high ($T_{\rm RH}>7.9\times10^6$ GeV for upgraded DECIGO and $T_{\rm RH}> 1.8\times 10^{6}$ GeV for BBO), it will be possible to reach the sensitivity of the gravitational background in future experiments at $3\sigma$ confidence level. The direct detection is also possible for natural inflation with the potential $V(\phi)=\Lambda^4 [1-\cos(\phi/f)]$, provided that $f>4.2 M_{\rm pl}$ (upgraded DECIGO) and $f>3.6 M_{\rm pl}$ (BBO) with $T_{\rm RH}$ higher than $10^8$ GeV. The quartic potential $V(\phi)=\lambda \phi^4/4$ with a non-minimal coupling $\xi$ between the inflaton field $\phi$ and the Ricci scalar $R$ gives rise to a detectable level of gravitational waves for $|\xi|$ smaller than the order of 0.01, irrespective of the reheating temperature.