Prospects of determination of reheating temperature after inflation by DECIGO

If the tensor-to-scalar ratio $r$ of cosmological perturbations takes a large value $r\sim 0.1$, which may be inferred by recent BICEP2 result, we can hope to determine thermal history, in particular, the reheating temperature, $T_R$, after inflation by space-based laser interferometers. It is shown that upgraded and upshifted versions of DECIGO may be able to determine $T_R$ if it lies in the range $6\times {10}^6<T_R<5\times {10}^7$GeV and $3\times 10^7<T_R<2\times 10^8$GeV, respectively. Although these ranges include predictions of some currently plausible inflation models, since each specification can probe $T_R$ of at most a decade range, we should determine the specifications of DECIGO with full account of constraints on inflation models to be obtained by near-future observations of temperature anisotropy and B-model polarization of the cosmic microwave background radiation.