Horndeski-Proca stars with vector hair

Abstract

We study Proca stars in a vector-tensor gravity model inspired by Horndeski's generalized Einstein-Maxwell field equations, supplemented with a mass term for the vector field. We discuss the effects of the nonminimal coupling term on the properties of the resulting Proca stars. We show that the sign of the coupling constant is crucial in determining the generic properties of these generalized Proca star solutions, as soon as the magnitude of the coupling constant is sufficiently large to allow for significant deviations from the standard Proca star case. For negative coupling constant we observe a new type of limiting behavior for the generalized Proca stars, where the spacetime splits into an interior region with matter fields and an exterior Schwarzschild region.

Horizon-scale tests of gravity theories and fundamental physics from the Event Horizon Telescope image of Sagittarius A ∗

“…While not sharing the same success as its scalar-tensor counterpart, the theory has started re-gaining interest recently (see e.g. [1440][1441][1442][1443][1444][1445][1446][1447][1448][1449][1450][1451][1452][1453][1454][1455][1456][1457][1458][1459]). The theory allows for the coupling of vector fields to gravity through their field-strength tensors, and this can be done for any vector field, including the gauge fields of the Standard Model.…”

To Half--Be or Not To Be?

“…While the equations of motion generically include higher derivatives away from that limit, the presence of a non-trivial constraint ensures that the theory propagates the correct D − 1 number of degrees of freedom in D dimensions. These derivative self-interactions were shown to be responsible for genuinely new properties in relation to the screening mechanisms and the coupling to alternative theories of gravity [7][8][9], although the main motivation for the development of the theory was aimed at applications to astrophysical systems [10][11][12][13][14][15][16][17][18][19][20][21][22][23][24][25] and cosmology [26][27][28][29][30][31][32][33][34][35][36][37][38][39][40][41][42].…”

Cosmology of Extended Proca-Nuevo

“…With astrophysical and cosmological applications in mind, the embedding of these effective field theories in a fully gravitational framework is an exciting problem connecting with the ongoing program of classifying viable extensions of general relativity (GR). Similarly to their scalartensor counterparts, generalized vector-tensor theories have been shown to exhibit intriguing phenomenological properties in astrophysical systems [1][2][3][4][5][6][7][8][9][10][11][12][13] and cosmology [14][15][16][17][18][19][20][21][22][23][24][25]. In the latter case, of particular interest is the fact that a time-dependent vector condensate could behave as a dark energy fluid, driving the observed accelerated cosmic expansion in the present-day universe, with a technically natural vector mass and dark energy scale [26,27].…”