# Constraint on cosmological parameters by Hubble parameter from gravitational wave standard sirens of neutron star binary system

## TL;DR

This paper proposes a novel method to measure the Hubble parameter using gravitational wave standard sirens from neutron star binaries, demonstrating its potential for precise cosmological constraints with future detectors.

## Contribution

The paper introduces a new approach utilizing GW anisotropy of luminosity distance to measure H(z), validated through simulations for upcoming GW detectors like DECIGO.

## Key findings

- DECIGO provides accurate H(z) measurements.
- Mock data significantly tightens cosmological parameter constraints.
- Future GW observations could vastly improve cosmological parameter estimation.

## Abstract

In this paper, we present a new method of measuring Hubble parameter($H(z)$), making use of the anisotropy of luminosity distance($d_{L}$), and the analysis of gravitational wave(GW) of neutron star(NS) binary system. The method has never been put into practice before due to the lack of the ability of detecting GW. LIGO's success in detecting GW of black hole(BH) binary system merger announced the possibility of this new method. We apply this method to several GW detecting projects, including Advanced LIGO(Adv-LIGO), Einstein Telescope(ET) and DECIGO, finding that the $H(z)$ by Adv-LIGO and ET is of bad accuracy, while the $H(z)$ by DECIGO shows a good accuracy. We use the error information of $H(z)$ by DECIGO to simulate $H(z)$ data at every 0.1 redshift span, and put the mock data into the forecasting of cosmological parameters. Compared with the available 38 observed $H(z)$ data(OHD), mock data shows an obviously tighter constraint on cosmological parameters, and a concomitantly higher value of Figure of Merit(FoM). For a 3-year-observation by standard sirens of DECIGO, the FoM value is as high as 834.9. If a 10-year-observation is launched, the FoM could reach 2783.1. For comparison, the FoM of 38 actual observed $H(z)$ data is 9.3. These improvement indicates that the new method has great potential in further cosmological constraints.