Optimization of Design Parameters for Gravitational Wave Detector DECIGO Including Fundamental Noises

TL;DR

This paper optimizes DECIGO's design parameters, including mirror size and thermal noise considerations, to enhance its sensitivity to gravitational waves, especially from primordial backgrounds and white dwarf sources.

Contribution

It introduces a comprehensive optimization of DECIGO's parameters considering realistic noise sources and mirror geometry effects, improving its potential sensitivity.

Findings

Optimal mirror size and mass for maximum SNR identified.

Thick, large-radius mirrors enhance detector sensitivity.

Design recommendations for future DECIGO configurations provided.

Abstract

The DECi hertz Interferometer Gravitational-Wave Observatory (DECIGO) is a space gravitational wave (GW) detector. DECIGO was originally designed to be sensitive enough to observe primordial GW background (PGW). However, due to the lowered upper limit of the PGW by the Planck observation, further improvement of the target sensitivity of DECIGO is required. In the previous studies, DECIGO's parameters were optimized to maximize the signal-to-noise ratio (SNR) of the PGW to quantum noise including the effect of diffraction loss. To simulate the SNR more realistically, we optimize DECIGO's parameters considering the GWs from double white dwarfs (DWDs) and the thermal noise of test masses. We consider two cases of the cutoff frequency of GWs from DWDs. In addition, we consider two kinds of thermal noise: thermal noise in a residual gas and internal thermal noise. To investigate how the mirror geometry affects the sensitivity, we calculate it by changing the mirror mass, keeping the mirror thickness, and vice versa. As a result, we obtained the optimums for the parameters that maximize the SNR that depends on the mirror radius. This result shows that a thick mirror with a large radius gives a good SNR and enables us to optimize the design of DECIGO based on the feasibility study of the mirror size in the future.