arXiv subjects

E. Brito

Publications and source records attributed to E. Brito.

5 recordsLinked to original sources

arXiv2026

Distributed Topological Charge and Spinorial Holonomy in Yukawa-Regularized Graphene Disclinations

Conical geometries provide the standard description of disclinations, but they concentrate the curvature at a singular apex. We introduce a Yukawa-type regularization that replaces this singularity by a smooth curvature distribution while preserving the asymptotic topology of the defect. Exact expressions are obtained for the conformal factor, curvature, and enclosed topological charge. The resulting geometry exhibits a scale-dependent topological charge and a corresponding radius-dependent holonomy, establishing a direct connection between distributed curvature and geometric phases. We further investigate the dynamics of massless Dirac quasiparticles in this background and show that the regularized core modifies the spin connection while preserving the asymptotic topological signature of the defect. These results provide a finite-core extension of the conventional conical description and offer a natural framework for studying geometric and topological effects in graphene-like systems.

cond-mat.mes-hall↗

arXiv2026

Nonrotating and rotating black holes with secondary disformal hair in a ghost-free metric-affine parity-violating scalar-torsion theory

In this paper, we formulate a ghost-free metric-affine scalar-torsion model in which a pseudoscalar field is coupled to the Nieh--Yan density and derivatively coupled to the Einstein-Palatini tensor. The theory is projectively invariant and, in the shift-symmetric sector, depends on the scalar only through its gradient. After fixing the projective gauge, the independent connection is solved exactly: its symmetric part is the Levi-Civita connection associated with the metric $h_{\mu\nu}$, disformally related to the metric $g_{\mu\nu}$, while its antisymmetric part is a purely axial torsion sourced by $v_\mu=\partial_\mu\vartheta$. We identify a degenerate ghost-free branch, $\alpha=6\beta^2\kappa^2$, for which Ricci-flat geometries in the $h$-metric frame solve the metric equations and the Noether current vanishes identically. For example, we consider Schwarzschild and Kerr geometries in the $h$-metric frame, which generate disformal deformations on these geometries from the perspective of the $g$-metric frame. For the Schwarzschild black hole in the $h$-metric frame, we construct static and Babichev--Charmousis-like time-dependent scalar profiles, and discuss horizon regularity in Eddington--Finkelstein coordinates. For the Kerr black hole in the $h$-metric frame, we show that the fixed-norm scalar profile is generically axisymmetric, depending on both the radial and angular coordinates, and we construct a stationary future-regular profile in ingoing Kerr coordinates. The Kerr solution with the nontrivial scalar field is stealth only in the $h$-metric frame. In the $g$-metric frame, it produces disformal corrections stemming from the nontrivial scalar field profile and it represents secondary disformal scalar hair rather than primary Noether-charge hair.

gr-qc↗

arXiv2024

The Palatini formalism of the $f(R,\mathcal{L}_{m},T)$ theory of gravity

We present the first formulation of the recently proposed $f(R,\mathcal{L}_m,T)$ theory of gravity within the Palatini formalism, a well-known alternative variational approach where the metric and connection are treated as independent variables. By applying this formalism, we derive a new set of field equations that exhibit, as expected, distinct properties compared to their metric formalism counterparts. We particularly present the Newtonian limit of this formalism, as well as the resulting Friedmann-like equations. We highlight that potential observational signatures may distinguish between the metric and Palatini frameworks. Our results open new pathways for exploring the phenomenology of modified gravity theories and their testability with observational data.

gr-qc↗

arXiv2024

Hydrostatic equilibrium configurations of neutron stars in the $f(R,\mathcal{L},T)$ gravity theory

In the present work, we obtain the hydrostatic equilibrium configurations of neutron stars in the recently proposed $f(R,\mathcal{L},T)$ theory of gravity, for which $R$ is the Ricci scalar, $\mathcal{L}$ is the matter lagrangian density, $T$ is the trace of the energy-momentum tensor and $f$ is a function of the argument. This theory emerges in the present literature as a generalized geometry-matter coupling theory of gravity. We derive the Tolman-Oppenheimer-Volkoff-like equation for a particular functional form of the $f(R,\mathcal{L},T)$ function. Our solutions are obtained from realistic equations of state describing matter inside neutron stars. We obtain stable solutions for neutron stars and we show that for some values of the free parameter of the theory it is possible to be in agreement with both NICER and LIGO/Virgo observational data.

gr-qc↗

arXiv2023

Search for the $f(R,T)$ gravity functional form via gaussian processes

The $f(R,T)$ gravity models, for which $R$ is the Ricci scalar and $T$ is the trace of the energy-momentum tensor, elevate the degrees of freedom of the renowned $f(R)$ theories, by making the Einstein field equations of the theory to also depend on $T$. While such a dependence can be motivated by quantum effects, the existence of imperfect or extra fluids, or even a cosmological ``constant'' which effectively depends on $T$, the formalism can truly surpass some deficiencies of $f(R)$ gravity. As the $f(R,T)$ function is arbitrary, several parametric models have been proposed {\it ad hoc} in the literature and posteriorly confronted with observational data. In the present article, we use gaussian process to construct an $f(R,T)=R+f(T)$ model. To apply the gaussian process we use a series of measurements of the Hubble parameter. We then analytically obtain the functional form of the function. By construction, this form, which is novel in the literature, is well-adjusted to cosmological data. In addition, by extrapolating our reconstruction to redshift $z=0$, we were able to constrain the Hubble constant value to $H_0=69.97\pm4.13$$\rm \ km \ s^{-1} \ Mpc^{-1}$ with $5\%$ precision. Lastly, we encourage the application of the functional form herewith obtained to other current problems of observational cosmology and astrophysics, such as the rotation curves of galaxies.

gr-qc↗