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

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 $3σ$ confidence level. The direct detection is also possible for natural inflation with the potential $V(ϕ)=Λ^4 [1-\cos(ϕ/f)]$, 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 $V(ϕ)=λϕ^4/4$ with a non-minimal coupling $ξ$ between the inflaton field $ϕ$ and the Ricci scalar $R$ gives rise to a detectable level of gravitational waves for $|ξ|$ smaller than the order of 0.01, irrespective of the reheating temperature.