Person:
Rubiera García, Diego

First Name

Diego

Last Name

Rubiera García

Affiliation

Universidad Complutense de Madrid

Faculty / Institute

Ciencias Físicas

Department

Física Teórica

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Now showing 1 - 10 of 36

Singularity-free and cosmologically viable Born-Infeld gravity with scalar matter
(MDPI, 2021-11) Benisty, David; Olmo, Gonzalo J.; Rubiera García, Diego
The early cosmology, driven by a single scalar field, both massless and massive, in the context of Eddington-inspired Born-Infeld gravity, is explored. We show the existence of nonsingular solutions of bouncing and loitering type (depending on the sign of the gravitational theory's parameter, epsilon) replacing the Big Bang singularity, and discuss their properties. In addition, in the massive case, we find some new features of the cosmological evolution depending on the value of the mass parameter, including asymmetries in the expansion/contraction phases, or a continuous transition between a contracting phase to an expanding one via an intermediate loitering phase. We also provide a combined analysis of cosmic chronometers, standard candles, BAO, and CMB data to constrain the model, finding that for roughly |epsilon|& LSIM;5 & BULL;10-8m2 the model is compatible with the latest observations while successfully removing the Big Bang singularity. This bound is several orders of magnitude stronger than the most stringent constraints currently available in the literature.
An infinite class of exact rotating black hole metrics of modified gravity
(IOP Publishing, 2022-03) Afonso, Victor I.; Mora Pérez, Gerardo; Olmo, Gonzalo J.; Orazi, Emanuele; Rubiera García, Diego
We build an infinite class of exact axisymmetric solutions of a metric-affine gravity theory, namely, Eddington-inspired Born-Infeld gravity, coupled to an anisotropic fluid as a matter source. The solution-generating method employed is not unique of this theory but can be extended to other Ricci-Based Gravity theories (RBGs), a class of theories built out of contractions of the Ricci tensor with the metric. This method exploits a correspondence between the space of solutions of General Relativity and that of RBGs, and is independent of the symmetries of the problem. For the particular case in which the fluid is identified with non-linear electromagnetic fields we explicitly derive the corresponding axisymmetric solutions. Finally, we use this result to work out the counterpart of the Kerr-Newman black hole when Maxwell electrodynamics is set on the metric-affine side. Our results open up an exciting new avenue for testing new gravitational phenomenology in the fields of gravitational waves and shadows out of rotating black holes.
Junction conditions of Palatini f (R,T) gravity
(Amer Physical Soc, 2022-11-06) Rosa, Joao Luis; Rubiera García, Diego
We work out the junction conditions for the Palatini f(R, T) extension of general relativity, where f is an arbitrary function of the curvature scalar R of an independent connection, and of the trace T of the stress -energy tensor of the matter fields. We find such conditions on the allowed discontinuities of several geometrical and matter quantities, some of which depart from their metric counterparts, and in turn extend their Palatini f(R) versions via some new T-dependent terms. Moreover, we also identify some "exceptional cases " of f(R,T) Lagrangians such that some of these conditions can be discarded, thus allowing for further discontinuities in R and T and, in contrast with other theories of gravity, they are shown to not give rise to extra components in the matter sector, e.g., momentum fluxes and double gravitational layers. We discuss how these junction conditions, together with the nonconservation of the stress-energy tensor ascribed to these theories, may induce nontrivial changes in the shape of specific applications such as traversable thin-shell wormholes.
Multicenter solutions in Eddington-inspired Born-Infeld gravity
(Springer, 2020-11-04) Olmo, Gonzalo J.; Orazi, Emanuele; Rubiera García, Diego
We find multicenter (Majumdar-Papapetrou type) solutions of Eddington-inspired Born-Infeld gravity coupled to electromagnetic fields governed by a Born-Infeld-like Lagrangian. We construct the general solution for an arbitrary number of centers in equilibrium and then discuss the properties of their one-particle configurations, including the existence of bounces and the regularity (geodesic completeness) of these spacetimes. Our method can be used to construct multicenter solutions in other theories of gravity.
Prospects for fundamental physics with LISA.
(Springer/Plenum publishers, 2020-08-31) Martín Moruno, Prado; Rubiera García, Diego; otros, ...
In this paper, which is of programmatic rather than quantitative nature, we aim to further delineate and sharpen the future potential of the LISA mission in the area of fundamental physics. Given the very broad range of topics that might be relevant to LISA,we present here a sample of what we view as particularly promising fundamental physics directions. We organize these directions through a "science-first" approach that allows us to classify how LISA data can inform theoretical physics in a variety of areas. For each of these theoretical physics classes, we identify the sources that are currently expected to provide the principal contribution to our knowledge, and the areas that need further development. The classification presented here should not be thought of as cast in stone, but rather as a fluid framework that is amenable to change with the flow of new insights in theoretical physics.
Pre-main sequence evolution of low-mass stars in Eddington-inspired Born-Infeld gravity
(Springer, 2022-08-14) Guerrero Roman, Merce; Rubiera García, Diego; Wojnar, Aneta
We study three aspects of the early-evolutionary phases in low-mass stars within Eddington-inspired Born-Infeld (EiBI) gravity, a viable extension of General Relativity. These aspects are concerned with the Hayashi tracks (i.e. the effective temperature-luminosity relation); the minimum mass required to belong to the main sequence; and the maximum mass allowed for a fully convective star within the main sequence. Using analytical models accounting for the most relevant physics of these processes, we find in all cases a dependence of these quantities not only on the theory's parameter, but also on the star's central density, a feature previously found in Palatini f(R) gravity. Using this, we investigate the evolution of these quantities with the (sign of the) EiBI parameter, finding a shift in the Hayashi tracks in opposite directions in the positive/negative branches of it, and an increase (decrease) for positive (negative) parameter in the two masses above. We use these results to elaborate on the chances to seek for traces of new physics in low-mass stars within this theory, and the limitations and difficulties faced by this approach.
Some recent results on Ricci-based gravity theories
(World Scientific, 2022-05) Olmo, Gonzalo J.; Rubiera García, Diego
In this paper, metric-afline theories in which the gravity Lagrangian is built using (projectively invariant) contractions of the Ricci tensor with itself and with the metric (Ricci-based gravity theories, or RBGs for short) are reviewed. The goal is to provide a contextualized and coherent presentation of some recent results. In particular, we focus on the correspondence that exists between the field equations of these theories and those of general relativity, and comment on how this can be used to build new solutions of physical interest. We also discuss the formalism of junction conditions in the f (R) case, and provide a brief summary on current experimental and observational bounds on model parameters.
Shadows and optical appearance of black bounces illuminated by a thin accretion disk
(IOP Publishing, 2021-08) Guerrero Roman, Merce; Olmo, Gonzalo J.; Rubiera García, Diego; Sáez Chillón Gómez, Diego
We study the light rings and shadows of an uniparametric family of spherically symmetric geometries interpolating between the Schwarzschild solution, a regular black hole, and a traversable wormhole, and dubbed as black bounces, all of them sharing the same critical impact parameter. We consider the ray-tracing method in order to study the impact parameter regions corresponding to the direct, lensed, and photon ring emissions, finding a broadening of all these regions for black bounce solutions as compared to the Schwarzschild one. Using this, we determine the optical appearance of black bounces when illuminated by three standard toy models of optically and geometrically thin accretion disks viewed in face-on orientation.
Multiring images of thin accretion disk of a regular naked compact object.
(Amer Physical Soc, 2022-08-30) Guerrero Roman, Merce; Olmo Gonzalo, J.; Rubiera García, Diego; Sáez Chillón Gómez, Diego
We discuss the importance of multiring images in the optical appearance of a horizonless spherically symmetric compact object, when illuminated by an optically thin accretion disk. Such an object corresponds to a subcase of an analytically tractable extension of the Kerr solution dubbed as the "eye of the storm" by Simpson and Visser in [J. Cosmol. Astropart. Phys. 03 (2022) 011], which merits in removing curvature singularities via an asymptotically Minkowski core, while harboring both a critical curve and an infinite potential barrier at the center for null geodesics. This multiring structure is induced by light rays winding several times around the object, and whose luminosity is significantly boosted as compared to the Schwarzschild solution by the modified shape of the potential. Using three toy profiles for the emission of an infinitely thin disk, truncated at its inner edge (taking its maximum value there) and having different decays with the distance, we discuss the image created by up to eight rings superimposed on top of the direct emission of the disk as its edge is moved closer to the center of the object. Our results point to the existence of multiring images with a non-negligible luminosity in shadow observations when one allows for the existence of other compact objects in the cosmic zoo beyond the Schwarzschild solution. Such multiring images could be detectable within the future projects on very long baseline interferometry.
Nonsingular black holes in nonlinear gravity coupled to Euler-Heisenberg electrodynamics.
(Amer Physical Soc, 2020-07-01) Guerrero Roman, Merce; Rubiera García, Diego
We study static, spherically symmetric black holes supported by the Euler-Heisenberg theory of electrodynamics and coupled to two different modified theories of gravity. Such theories are the quadratic f (R) model and Eddington-inspired Born-Infeld gravity, both formulated in metric-affine spaces, where the metric and affine connection are independent fields. We find exact solutions of the corresponding field equations in both cases, characterized by mass, charge, the Euler-Heisenberg coupling parameter, and the modified gravity one. For each such family of solutions, we characterize its horizon structure and the modifications in the innermost region, finding that some subclasses are geodesically complete. The singularity regularization is achieved under two different mechanisms: either the boundary of the manifold is pushed to an infinite affine distance, not being able to be reached in finite time by any geodesic, or the presence of a wormhole structure allows for the smooth extension of all geodesics overcoming the maximum of the potential barrier.