Possibility of Direct Measurement of the Acceleration of the Universe Using 0.1 Hz Band Laser Interferometer Gravitational Wave Antenna in Space

TL;DR

This work proposes DECIGO, a space-based interferometer optimized for $f\sim0.1$ Hz, to directly measure the Universe's acceleration and probe primordial gravitational waves. It derives a cosmological phase correction $X(z)$ that encodes acceleration and curvature, and shows how combining $d_L(z)$ with $X(z)$ enables constraints on $\Omega_{k0}$ from NS-NS binaries at $z\sim1$; a detailed parameter study indicates that long-term observations could yield high-precision measurements of $X(z)$ even with optimistic timelines. The authors further argue that cross-correlation of DECIGO pairs could detect a primordial stochastic background down to $\Omega_{GW}\sim10^{-20}$, linking late-time cosmology to early-Universe physics, provided the instrument achieves $h_{rms}\sim2\times10^{-27}$ at $f\sim0.1$ Hz. The paper discusses design targets, potential noise and confusion challenges, and the broader cosmological impact of directly observing cosmic acceleration with gravitational waves.

Abstract

It may be possible to construct a laser interferometer gravitational wave antenna in space with $h_{rms}\sim 10^{-27}$ at $ f\sim 0.1{\rm Hz}$ in this century. We show possible specification of this antenna which we call DECIGO. Using this antenna we show that 1) typically $ 10^5$ ($10^4\sim 10^6$) chirp signals of coalescing binary neutron stars per year may be detected with S/N $\sim 10^4$. 2) We can directly measure the acceleration of the universe by ten years observation of binary neutron stars. 3) The stochastic gravitational waves of $Ω_{GW}\gsim 10^{-20}$ predicted by the inflation may be detected by correlation analysis for which effects of the recent cosmic acceleration would become highly important. Our formula for phase shift due to accelerating motion might be also applied for binary sources of LISA.

Figures (1)

• Figure 1: Sensitivity (effectively S/N=1) for various detectors (LISA, DECIGO, LIGOII and a detector $10^3$ times less sensitive than DECIGO) in the form of $h_{rms}$ (solid lines). The dashed line represents evolution of the characteristic amplitude $h_c$ for NS-NS binary at $z=1$ (filled triangles; wave frequencies at 1yr and 10 yr before coalescence). The dotted lines represent the required sensitivity for detecting stochastic background with $\Omega_{GW}=10^{-16}$ and $\Omega_{GW}=10^{-20}$ by ten years correlation analysis (S/N=1).