Binary neutron star mergers in massive scalar-tensor theory: Quasiequilibrium states and dynamical enhancement of the scalarization
Hao-Jui Kuan, Karim Van Aelst, Alan Tsz-Lok Lam, Masaru Shibata
Abstract
We study quasiequilibrium sequences of binary neutron stars in the framework of Damour-Esposito-Farese-type scalar-tensor theory of gravity with a massive scalar field, paying particular attention to the case where neutron stars are already spontaneously scalarized at distant orbits, i.e., in the high-coupling constant case. Although scalar effects are largely quenched when the separation $a$ is $\ensuremath{\gtrsim}3--6$ times of the Compton length scale that is defined by the scalar mass, we show that the interaction between the scalar fields of the two neutron stars generates a scalar cloud surrounding the binary at the price of orbital energy when $a\ensuremath{\lesssim}3--6$ times of the Compton length scale. This enables us to constrain the scalar mass ${m}_{\ensuremath{\phi}}$ from gravitational wave observations of binary neutron star mergers by inspecting the dephasing due to such phenomenon. In particular, the event GW170817 is suggestive of a constraint of ${m}_{\ensuremath{\phi}}\ensuremath{\gtrsim}{10}^{\ensuremath{-}11}\text{ }\text{ }\mathrm{eV}$ and the coupling strength should be mild if the neutron stars in this system were spontaneously scalarized.