Structure of compact stars in R-squared Palatini gravity

Abstract

We analyse configurations of neutron stars in the so-called R-squared gravity in the Palatini formalism. Using a realistic equation of state we show that the mass-radius configurations are lighter than their counterparts in General Relativity. We also obtain the internal profiles, which run in strong correlation with the derivatives of the equation of state, leading to regions where the mass parameter decreases with the radial coordinate in a counter-intuitive way. In order to analyse such correlation, we introduce a parametrisation of the equation of state given by multiple polytropes, which allows us to explicitly control its derivatives. We show that, even in a limiting case where hard phase transitions in matter are allowed, the internal profile of the mass parameter still presents strange features and the calculated M −R configurations also yield neutron stars lighter than those obtained in General Relativity.2 Teppa Pannia et al.

Astrophysical Constraints on Strong Modified Gravity

“…where u t (r) and u φ (r) are the t and φ components of the four-velocity of the particle, respectively. Formulas (36), (37), and (38) can also be written in terms of the metric coefficients (see Harko et al 108 or Pérez et al 99 for the corresponding expressions). In order to compute the heat emitted by a thin accretion disk around a black hole, we first have to study the circular orbits of massive particles in such spacetime geometry.…”

Towards New Constraints in Extended Theories of Gravity: Cosmography and Gravitational-Wave Signals from Neutron Stars

“…Thanks to the discovery of a neutron star with mass 1.974M [49]-confirmed later on by other measurements [50][51][52][53], the precise sighting [54] through binary system measurements, double neutron stars features and pulsar systems [55], the validity of GR standard predictions have been indeed put into question. Thus the interest for such configurations in extended theories of gravity, mainly in scalar-tensor theories [56][57][58][59][60][61][62][63][64][65][66][67][68][69][70][71], has aimed to reconcile predictions with astrophysical results.…”

Palatini f(R) gravity in the solar system: Post-Newtonian equations of motion and complete PPN parameters

“…Several astrophysical aspects of Palatini gravity were considered in the literature, such as black holes [1][2][3][4][5][6], wormholes [7][8][9] and stellar objects [10][11][12][13][14]. Although problems for stars in Palatini f (R) gravity were reported [15][16][17][18], these issues depend on matter assumptions that need not to be true [19][20][21][22].…”