Significance of Fabry-Perot cavities for space gravitational wave antenna DECIGO

Abstract: The future Japanese project for the detection of gravitational waves in space is planned as DECIGO. To achieve various scientific missions, including the verification of cosmic inflation through the detection of primordial gravitational waves as the main objective, DECIGO is designed to have high sensitivity in the frequency band from $0.1$ to $1$ Hz, with arms of length 1000 km. Furthermore, the use of the Fabry-Perot cavity in these arms has been established for the DECIGO project. In this paper, we scrutinize the significance of the Fabry-Perot cavity for promoting this project, with a focus on the possibility of observing gravitational waves from cosmic inflation and binary compact star systems as indicators. The results show that using the Fabry-Perot cavity is extremely beneficial for detecting them, and it is anticipated to enable the opening of a new window in gravitational wave astronomy.