A model of compact and ultracompact objects in $$f(\mathcal {R})$$-Palatini theory

Abstract

We present the features of a model which generalizes Schwarzschild’s homogeneous star by adding a transition zone for the density near the surface. By numerically integrating the modified TOV equations for the $$f(\mathcal {R})=\mathcal {R}+\lambda \mathcal {R}^2$$ f ( R ) = R + λ R 2 Palatini theory, it is shown that the ensuing configurations are everywhere finite. Depending on the values of the relevant parameters, objects more, less or as compact as those obtained in GR with the same density profile have been shown to exist. In particular, in some region of the parameter space the compactness is close to that set by the Buchdahl limit.

The gravitational field of a star in quadratic gravity

“…Albeit many extensions of the R+R 2 theory have been considered, as more complex f (R) theories [29], the use of Palatini formalism [33,34], or f (G) theories [35,36], the inclusion of terms quadratic in the Weyl (or equivalently the Ricci) tensor has attracted relatively little interest [34,37,38]. Considering the key role played by the Weyl term in black hole solutions of quadratic gravity, we believe that it is crucial to study in detail the effect of such term on self gravitating fluids.…”

“…As we will see, this term actually has major consequences on the solutions, while the R 2 term has only limited impact. In the end, the final goal of this work is to bring together these two lines of research: the more theoretically driven one [10][11][12][13][14][15][16][17][18][19][20][21], and the more astrophysical and phenomenological one [25][26][27][28][29][30][31][32][33][34][35][36]. At practical level, this reduces to link the explicit Yukawa corrections to the Newtonian potential of [10] to a perfect fluid stress-energy tensor, by means of the numerical methods already implemented in [20].…”

R2-gravity quark stars from perturbative QCD

“…In the last decade, compact stars were studied in f (R) theories of gravity in the metric [33,[35][36][37][38][39][40][41][42][43][44][45][46][47] and Palatini [48][49][50][51] frameworks. Within the metric formalism, the stellar structure equations are solved either perturbatively, i.e.…”

Gravitational wave echoes from compact stars in $f(\mathcal{R},T)$ gravity

“…in ATGs and compare the obtained properties of such objects with the experimentally observed ones. These sorts of studies have been carried out for the last many years using different ATGs [20][21][22][23][24][25]. Specifically, the literature survey shows that over the last few years a plethora of articles are focusing on compact stars in the context of f (R, T ) gravity from various astrophysical points of view.…”