### Abstract

In a class of generalized Proca theories, we study the existence of neutron star solutions with a nonvanishing temporal component of the vector field Aμ approaching 0 toward spatial infinity, as they may be the endpoints of tachyonic instabilities of neutron star solutions in general relativity with Aμ=0. Such a phenomenon is called spontaneous vectorization, which is analogous to spontaneous scalarization in scalar-tensor theories with nonminimal couplings to the curvature or matter. For the nonminimal coupling βXR, where β is a coupling constant and X=-AμAμ/2, we show that there exist both 0-node and 1-node vector-field solutions, irrespective of the choice of the equations of state of nuclear matter. The 0-node solution, which is present only for β=-O(0.1), may be induced by some nonlinear effects such as the selected choice of initial conditions. The 1-node solution exists for β=-O(1), which suddenly emerges above a critical central density of star and approaches the general relativistic branch with the increasing central density. We compute the mass M and radius rs of neutron stars for some realistic equations of state and show that the M-rs relations of 0-node and 1-node solutions exhibit a notable difference from those of scalarized solutions in scalar-tensor theories. Finally, we discuss the possible endpoints of tachyonic instabilities.

Original language | English |
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Article number | 024067 |

Journal | Physical Review D |

Volume | 102 |

Issue number | 2 |

DOIs | |

Publication status | Published - 2020 Jul 15 |

### ASJC Scopus subject areas

- Physics and Astronomy (miscellaneous)

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## Cite this

*Physical Review D*,

*102*(2), [024067]. https://doi.org/10.1103/PhysRevD.102.024067