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 $3\sigma$ 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.
