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

Yuki Kawasaki,Shuichiro Yokoyama,Shoki Iwaguchi,Koji Nagano,Izumi Watanabe,Bin Wu,Ryuma Shimizu,Seiji Kawamura,Tomohiro Ishikawa

doi:10.3390/galaxies10010025

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.

Highlights

The DECi-hertz Interferometer Gravitational-Wave Observatory (DECIGO) is a space gravitational wave (GW) detector [1,2]
One of the most important DECIGO goals is the observation of the primordial GW background (PGW) from the early Universe
We have found that we can obtain an extremely good signal-to-noise ratio (SNR) from the most optimistic model among all models we treated in this paper (Figure 3b)

Summary

Introduction

The DECi-hertz Interferometer Gravitational-Wave Observatory (DECIGO) is a space gravitational wave (GW) detector [1,2]. One of the most important DECIGO goals is the observation of the primordial GW background (PGW) from the early Universe. In the low-frequency band less than 0.1 Hz, GWs from several astrophysical sources impede the detection of the PGW [3]. DECIGO, which has a frequency band between 0.1 Hz and 10 Hz, is optimized for the PGW observation. Direct detection of PGW could contribute to the determination of inflation models in the early Universe. DECIGO was originally designed to be sensitive enough to observe the PGW, under the assumption that the normalized GW energy density Ωgw of the PGW is Ωgw ≈ 2 × 10−15 [4]. Recent observations of CMB by Planck satellite and BICEP/Keck collaboration have lowered the upper limit for the PGW to Ωgw ≈ 10−16, and this limit requires improvement of DECIGO’s sensitivity [5–7]

Objectives

Methods

Conclusion