Kavli Affiliate: Salvatore Vitale

| First 5 Authors: Sylvia Biscoveanu, Colm Talbot, Salvatore Vitale, ,

| Summary:

The binary neutron star (BNS) mass distribution measured with

gravitational-wave observations has the potential to reveal information about

the dense matter equation of state, supernova physics, the expansion rate of

the universe, and tests of General Relativity. As most current

gravitational-wave analyses measuring the BNS mass distribution do not

simultaneously fit the spin distribution, the implied population-level spin

distribution is the same as the spin prior applied when analyzing individual

sources. In this work, we demonstrate that introducing a mismatch between the

implied and true BNS spin distributions can lead to biases in the inferred mass

distribution. This is due to the strong correlations between the measurements

of the mass ratio and spin components aligned with the orbital angular momentum

for individual sources. We find that applying a low-spin prior which excludes

the true spin magnitudes of some sources in the population leads to

significantly overestimating the maximum neutron star mass and underestimating

the minimum neutron star mass at the population level with as few as six BNS

detections. The safest choice of spin prior that does not lead to biases in the

inferred mass distribution is one which allows for high spin magnitudes and

tilts misaligned with the orbital angular momentum.

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