# Will Gravitational Wave Sirens Determine the Hubble Constant?

## TL;DR

This paper discusses the challenges in accurately estimating the Hubble constant using gravitational wave standard sirens due to uncertainties in the universe's expansion history and emphasizes the need for model-agnostic statistical methods.

## Contribution

It highlights the impact of background expansion model uncertainties on Hubble constant estimation and advocates for model-independent statistical techniques.

## Key findings

- Biases in $H_0$ estimation can reach 3$\sigma$ in non- extit{LCDM} cosmologies.
- Fitting for matter density alone reduces precision from 1 extbackslash% to 5 extbackslash%.
- Model assumptions significantly affect $H_0$ estimates at high precision levels.

## Abstract

Lack of knowledge about the background expansion history of the Universe from independent observations makes it problematic to obtain a precise and accurate estimation of the Hubble constant $H_0$ from gravitational wave standard sirens, even with electromagnetic counterpart redshifts. Simply fitting simultaneously for the matter density in a flat \lcdm\ model can reduce the precision on $H_0$ from 1\% to 5\%, while not knowing the actual background expansion model of the universe (e.g.\ form of dark energy) can introduce substantial bias in estimation of the Hubble constant. When the statistical precision is at the level of 1\% uncertainty on $H_0$, biases in non-\lcdm\ cosmologies that are consistent with current data could reach the 3$\sigma$ level. To avoid model-dependent biases, statistical techniques that are appropriately agnostic about model assumptions need to be employed.