## [0908.3283] DECIGO/BBO as a probe to constrain alternative theories of gravity

Authors: Kent Yagi, Takahiro Tanaka

Date: 23 Aug 2009

Abstract: We calculate how strongly one can constrain the alternative theories of gravity with deci-Hz gravitational wave interferometers such as DECIGO and BBO. Here we discuss Brans-Dicke theory and massive graviton theories as typical examples. We consider the inspiral of compact binaries composed of a neutron star (NS) and an intermediate mass black hole (IMBH) for Brans-Dicke (BD) theory and those composed of a super massive black hole (SMBH) and a black hole (SMBH) for massive graviton theories. Using the restricted 2PN waveforms including spin effects and taking the spin precession into account, we perform the Monte Carlo simulations of $10ˆ4$ binaries to estimate the determination accuracy of binary parameters including the Brans-Dicke parameter $\omega_{\mathrm{BD}}$ and the graviton Compton length $\lambda_g$. Assuming a $(1.4+10)M_{\odot}$ NS/BH binary of SNR=$\sqrt{200}$, the constraint on $\omega_{\mathrm{BD}}$ is obtained as $\omega_{\mathrm{BD}}>1.68\times 10ˆ6$, which is 200 times stronger than the estimated constraint from LISA observation. Furthermore, we find that, due to the expected large merger rate of NS/BH binaries of $O(10ˆ4)$ yr$ˆ{-1}$, a statistical analysis yields $\omega_{\mathrm{BD}}>5.74\times10ˆ7$, which is three orders of magnitude stronger than the current strongest bound obtained from the solar system experiment. For massive graviton theories, assuming a $(10ˆ6+10ˆ5)M_{\odot}$ BH/BH binary at 3Gpc, one can put a constraint $\lambda_g>2.24\times10ˆ{20}$cm, on average. This is three orders of magnitude stronger than the one obtained from the solar system experiment. From these results, it is understood that DECIGO/BBO is a very powerful tool for constraining alternative theories of gravity.

#### Jun 21, 2010

0908.3283 (/preprints)
2010-06-21, 18:02