Scalaron Decay in Perturbative Quantum Gravity

A certain quadratic gravity model provides a successfully inflationary scenario. The inflation is driven by the new scalar degree of freedom called scalaron. After the end of inflation the scalaron decays in matter and dark matter degrees of freedom reheating the Universe. We study new channels by which the scalaron can transfer energy to the matter sector. These channels are annihilation and decay via intermediate graviton states. Results are obtained within perturbative quantum gravity. In the heavy scalaron limit only scalar particles are produced by the annihilation channel. Scalaron decays in all types of particles are allowed. In the light scalaron limit decay channel is strongly suppressed. Boson production via the annihilation channel is expected to be dominant at the early stages of reheating, while fermion production will dominate later stages.