http://arxiv.org/abs/1711.08713
We study neutron star solutions in second-order generalized Proca theories characterized by a $U(1)$-breaking vector field with derivative couplings. Depending on the signs of derivative coupling constants, the mass and radius of neutron stars can be either larger or smaller than those in general relativity. There is a tendency that a neutron star with a smaller mass is not gravitationally bound for a small central density and hence dynamically unstable, but that with a larger mass is gravitationally bound. Even with an equation of state where the mass of neutron stars in general relativity is smaller than the largest observed mass $M_{\ast} \simeq 2M_\odot$ ($M_{\odot}$ is the solar mass), the cubic and quartic derivative couplings with a large temporal vector component allow the possibility for realizing the mass $M_*$ greater than $2M_\odot$. This phenomenon is mostly attributed to the increase of the neutron star radius induced by a slower decrease of the matter pressure compared to general relativity. On the other hand, we show that the intrinsic vector-mode couplings give rise to general relativistic solutions with a trivial field profile, so the mass and radius are not modified from those in general relativity.
R. Kase, M. Minamitsuji and S. Tsujikawa
Mon, 27 Nov 2017
32/78
Comments: 21 pages, 8 figures