Assessing the potential of LIGO-India in resolving the Hubble Tension

Determining the Hubble constant (H0), a fundamental parameter describing cosmic expansion, remains a challenge due to conflicting measurements from the early and late universe. Gravitational wave (GW) observations from binary neutron star (BNS) mergers, with identified host galaxies through electromagnetic (EM) follow-up, offer an independent method to measure H0. However, this requires detection of numerous events, which could take decades with current GW detectors. LIGO-India can dramatically accelerate this effort. With sensitivity comparable to the existing LIGO detectors, its addition to the LIGO-Virgo network could increase detected events by 70%. This improvement nearly doubles when accounting for the detector’s 70% duty cycle, increasing the probability of simultaneous operation of three detectors by a factor of ~2. We perform end-to-end simulations to estimate triple-coincidence detection rates and sky localization, considering realistic BNS populations, lightcurves, and EM observatory specifications. Our findings suggest LIGO-India could increase BNS events with observed kilonovae by ~2-7 times. The factor of few improvements in source localization precision with LIGO-India can allow much deeper EM follow-up campaigns (not considered in the simulations), potentially increasing the overall rate of detection of EM counterparts by a factor of ~20, which can have an enormous impact in addressing critical questions in different areas of astronomy. We evaluate the impact of LIGO-India in the context of H0 measurement and argue that it can cut down the required observation time of several decades by a factor of few and possibly to just few years with regular sensitivity upgrades.