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We study the first-order in α′ corrections to non-extremal 4-dimensional dyonic Reissner-Nordström (RN) black holes with equal electric and magnetic charges in the context of Heterotic Superstring effective field theory (HST) compactified on a T6. The particular embedding of the dyonic RN black hole in HST considered here is not supersymmetric in the extremal limit. We show that, at first order in α′, consistency with the equations of motion of the HST demands additional scalar and vector fields become active, and we provide explicit expressions for all of them. We determine analytically the position of the event horizon of the black hole, as well as the corrections to the extremality bound, to the temperature and to the entropy, checking that they are related by the first law of black-hole thermodynamics, so that ∂S/∂M = 1/T. We discuss the implications of our results in the context of the Weak Gravity Conjecture, clarifying that entropy corrections for fixed mass and charge at extremality do not necessarily imply corrections to the extremal charge-to-mass ratio, This work has been supported in part by the MCIU, AEI, FEDER (UE) grant PGC2018- 095205-B-I00, CONACyT grant 237351 and by the Spanish Research Agency (Agencia Estatal de Investigación) through the grant IFT Centro de Excelencia Severo Ochoa SEV- 2016-0597. PAC was mostly funded by Fundación La Caixa through a La Caixa - Severo Ochoa" International pre-doctoral grant. In the last stages of this project PAC was supported by the KU Leuven grant \Bijzonder Onderzoeksfonds C16/16/005

In this work the spontaneous symmetry breaking in certain nonlinear theories with second-class constraints is explored. Using the Dirac's method we perform an analysis of the constraints and the counting of the degrees of freedom. The corresponding effective Hamiltonian is constructed explicitly. It is shown that on the surfaces where the effective Hamiltonian takes critical values the symplectic structure becomes degenerate. In particular, we demonstrate that under the condition of spontaneous symmetry breaking, which implies non trivial vacuum surfaces, second-class constraints behave as first-class ones on certain regions of the phase space, leading to undefined Dirac's brackets and to the modification of the number of degrees of freedom. As a physical consequence, these models can suffer from certain pathologies such as the existence of modes with an acausal propagation. Concrete examples where this phenomena occurs are described in detail., Comment: 10 pages, no figures

In the present study we analyse, within the scalar sector of the Standard-Model Extension (SME) framework, the influence of a spontaneous Lorentz symmetry breaking on gravitational quantum states of ultracold neutrons. The model is framed according to the laboratory conditions of the recent high-sensitivity GRANIT and $q$Bounce experiments. The high-precision data achieved in such experiments allow us to set bounds on the symmetry breaking parameters of the model. The effective Hamiltonian governing the neutron's motion along the axis of free fall is derived explicitly. It describes a particle in a gravitational field with an effective gravitational constant controlled non-trivially by the Lorentz-violating parameters. In particular, using the exact wave functions and the energy spectrum, we evaluate both the heights associated with the quantum states and the transition frequencies between neighborhoring quantum states. By comparing our theoretical results with those reported in the GRANIT and the $q$Bounce experiments, upper bounds on the Lorentz-violating parameters are determined. We also consider for the first time the gravity-induced interference pattern in a COW-type experiment to test Lorenz-invariance. In this case, an upper bound for the parameters is established as well., Comment: 12 Pages, 5 Figures

Following a field-theoretical approach, we study the scalar Casimir effect upon a perfectly conducting cylindrical shell in the presence of spontaneous Lorentz symmetry breaking. The scalar field is modeled by a Lorentz-breaking extension of the theory for a real scalar quantum field in the bulk regions. The corresponding Green's functions satisfying Dirichlet boundary conditions on the cylindrical shell are derived explicitly. We express the Casimir pressure (i.e. the vacuum expectation value of the normal-normal component of the stress-energy tensor) as a suitable second-order differential operator acting on the corresponding Green's functions at coincident arguments. The divergences are regulated by making use of zeta function techniques, and our results are successfully compared with the Lorentz invariant case. Numerical calculations are carried out for the Casimir pressure as a function of the Lorentz-violating coefficient, and an approximate analytical expression for the force is presented as well. It turns out that the Casimir pressure strongly depends on the Lorentz-violating coefficient and it tends to diminish the force., 15 pages, 8 figures

In this work we study the so-called ModMax nonlinear electrodynamics, which is a novel model designed to preserve duality rotations and conformal transformations, such as the Maxwell's equations do. This model allows to study diverse gravitational phenomena when is coupled to General Relativity, in particular charged black holes and gravitational waves. In the present work we focus in the dynamics and Hamiltonian analysis of the model. Specifically, we analyze the propagation of the discontinuities of the field and obtain the corresponding dispersion relations. To perform the Hamiltonian analysis we adopt the first order formalism develop by Pleba\'nski and follow the Dirac method for theories with constraints. We derive the effective Hamiltonian, classify all the constraints and identify the degrees of freedom. We prove that the effective Hamiltonian is strictly bounded from below and investigate the existence of non trivial minima., Comment: 10 Pages, No Figures, Accepted to publication in IJMP A

We construct a deformed adS-Einstein-Born-Infeld black hole from noncommutative gauge theory of gravity and determine the metric coefficients up to second order on the noncommutative parameter. We analyse the modifications on the thermodynamical properties of the black hole due to the noncommutative contributions, and we show that noncommutativity has as a direct consequence, the removal of critical points., 11 pages, 10 figures

We analyze noncommutative deformations of a higher dimensional anti-de Sitter-Einstein-Born-Infeld black hole. Two models based on noncommutative inspired distributions of mass and charge are discussed and their thermodynamical properties such as the equation of state are explicitly calculated. In the (3 + 1)-dimensional case the Gibbs energy function of each model is used to discuss the presence of phase transitions.

In this paper we revisit the classification of the gauge transformations in the Euler top system using the generalized classical Hamiltonian dynamics of Nambu. In this framework the Euler equations of motion are bi-Hamiltonian and $SL(2, \mathbb{R})$ linear combinations of the two Hamiltonians leave the equations of motion invariant, although belonging to inequivalent Lie-Poisson structures. Here we give the explicit form of the Hamiltonian vector fields associated to the components of the angular momentum for every single Lie-Poisson structure including both the asymmetric rigid bodies and its symmetric limits. We also give a detailed classification of the different Lie-Poisson structures recovering all the ones reported previously in the literature.

Maxwell's equations are invariant under both duality rotations and conformal transformations. Recently Bandos, Lechner, Sorokin, and Townsend have found a nonlinear generalisation of electrodynamics which possesses both of these symmetries. We couple this theory to General Relativity and explore self-gravitating configurations with a clear physical interpretation. We find charged black holes and exact gravitational waves. The black hole geometry is Reissner-Nordstr\"om, however, the non-linearity parameter acts as a screening factor allowing extremal configurations where the mass of the black hole is smaller than its charge. Furthermore, we also discuss the phenomenon of birefringence and determine the optical metrics associated to the propagation of photons., Comment: 9 pages, 1 figure

Recent work has shown the existence of a unique nonlinear extension of electromagnetism which preserves conformal symmetry and allows for the freedom of duality rotations. Moreover, black holes and gravitational waves have been found to exist in this nonlinearly extended electrovacuum. We generalise these dyonic black holes in two major ways: with the relaxation of their horizon topology and with the inclusion of magnetic mass. Motivated by recent attention to traversable wormholes, we use this new family of Taub-NUT spaces to construct AdS wormholes. We explore some thermodynamic features by using a semi-classical approach. Our results show that a phase transition between the nut and bolt configurations arises in a similar way to the Maxwellian case.

We consider the classical 3-body system with $d$ degrees of freedom $(d>1)$ at zero total angular momentum. The study is restricted to potentials $V$ that depend solely on relative (mutual) distances $r_{ij}=\mid {\bf r}_i - {\bf r}_j\mid$ between bodies. Following the proposal by J. L. Lagrange, in the center-of-mass frame we introduce the relative distances (complemented by angles) as generalized coordinates and show that the kinetic energy does not depend on $d$, confirming results by Murnaghan (1936) at $d=2$ and van Kampen-Wintner (1937) at $d=3$, where it corresponds to a 3D solid body. Realizing $\mathbb{Z}_2$-symmetry $(r_{ij} \rightarrow -r_{ij})$ we introduce new variables $\rho_{ij}=r_{ij}^2$, which allows us to make the tensor of inertia non-singular for binary collisions. In these variables the kinetic energy is a polynomial function in the $\rho$-phase space. The 3 body positions form a triangle (of interaction) and the kinetic energy is $\mathcal{S}_3$-permutationally invariant wrt interchange of body positions and masses (as well as wrt interchange of edges of the triangle and masses). For equal masses, we use lowest order symmetric polynomial invariants of $\mathbb{Z}_2^{\otimes3} \oplus \mathcal{S}_3$ to define new generalized coordinates, they are called the {\it geometrical variables}. Two of them of the lowest order (sum of squares of sides of triangle and square of the area) are called {\it volume variables}. We study three examples in some detail: (I) 3-body Newton gravity in $d=3$, (II) 3-body choreography in $d=2$ on the algebraic lemniscate by Fujiwara et al where the problem becomes one-dimensional in the geometrical variables, and (III) the (an)harmonic oscillator., Comment: 32 pages, 2 figures

Se presenta un equipo de soporte de vida neonatal (ESVIN) que emplea la terapia termica y terapia ventilatoria (neumatica) en un solo equipo para proveer ventilacion pulmonar con aire caliente, humedecido y enriquecido con oxigeno, en un ambiente caliente, humidificado y esteril. El equipo es capaz de simultaneamente dar ventilacion pulmonar e incubar, siendo una de sus caracteristicas principales la minimizacion de la condensacion del agua en el corrugado y ofrece la caracteristica adicional de evitar la movilizacion y/o desconexion del neonato para realizar ciertos procedimientos tales como: cirugias e intubaciones, entre otras. Los principales resultados son el tiempo de acceso al neonato menor a 2 s y minimizacion de la condensacion de agua. Asimismo, los resultados del control termico son de tiempo de estabilizacion en el habitaculo de 75 minutos para la temperatura de 36 °C y tiempo de estabilizacion de la temperatura de la piel del neonato de 58 minutos

The noncommutative baby Skyrme model is a Moyal deformation of the two-dimensional sigma model plus a Skyrme term, with a group-valued or Grassmannian target. Exact abelian solitonic solutions have been identified analytically in this model, with a singular commutative limit. Inside any given Grassmannian, we establish a BPS bound for the energy functional, which is saturated by these baby Skyrmions. This asserts their stability for unit charge, as we also test in second-order perturbation theory., Comment: 1+8 pages, no figures

Recently Randjbar-Daemi and Shaposhnikov put forward a 4-dimensional effective QED coming from a Nielsen-Olesen vortex solution of the abelian Higgs model with fermions coupled to gravity in D=6. However, exploring possible physical consequences of such an effective QED was left open. In this letter we study the corresponding effective Casimir effect. We find that the extra dimensions yield fifth and third inverse powers in the separation between plates for the modified Casimir force which are in conflict with known experiments, thus reducing the phenomenological viability of the model., Comment: 12 pages, references added, comparison with experimental data clarified. v4 published version

We exhibit a new way to perform the group-manifold reduction of pure Einstein gravity in the vielbein formulation when the compactification group manifold is S3. The new Bianchi IX group-manifold reduction is obtained by exploiting the two three-dimensional Lie algebras that the S3 group manifold admits. As an application of the new reduction we show that there exists a domain wall solution to the lower-dimensional theory which upon uplifting to the higher-dimension turns out to be the self-dual (in the nonvanishing components of both curvature and spin connection) Kaluza–Klein monopole.

In this contribution we exhibit a new consistent group-manifold reduction of pure Einstein gravity in the vielbein formulation when the compactification group manifold is S3. The novel feature in the reduction is to consider the two 3-dimensional Lie algebras that S3 admits. We discuss the characteristics of the lower-dimensional theory and we emphasize the results generated by the new group-manifold reduction. As an application we show that the lower-dimensional theory admits a domain wall solution which upon uplifting to the higherdimension results to be the self-dual (in both curvature and spin connection) Kaluza-Klein monopole.

We construct maximal D = 8 gauged supergravities by the reduction of D = I I supergravity over three-dimensional group manifolds. Such manifolds are classified into two classes, A and B, and eleven types. This Bianchi classification carries over to the gauged supergravities. The class A theories have 1/2 BPS domain wall solutions that uplift to purely gravitational solutions consisting of 7D Minkowski and a 4D Euclidean geometry. These geometries are generically singular. The two regular exceptions correspond to the near-horizon limit of the single- or double-centre Kaluza-Klein monopole. In contrast, the class B supergravities are defined by a set of equations of motion that cannot be integrated to an action and allow for no 1/2 BPS domain walls.

We construct five massive deformations of the unique nine–dimensional N = 2 supergravity, each with two parameters. All of these deformations have a higher–dimensional origin via Scherk–Schwarz reduction and correspond to gauged supergravities. The gauge groups we encounter are SO(2), SO(1, 1)+, R, R+ and the unique two–dimensional non–Abelian Lie group CR1, which consists of scalings and translations in one dimension. We make a systematic search for two classes of vacuum solutions: maximally symmetric solutions with constant scalars and half-supersymmetric domain wall solutions. In the first category we find explicit solutions in the form of (non-supersymmetric) de Sitter space solutions. In the second category we find precisely the three classes of domain wall solutions that were given in an earlier work.

In this paper, we present a deformed model of Einstein-Proca spacetime based on the replacement of pointlike sources by noncommutative smeared distributions. We discuss the solutions to the set of noncommutative Einstein-Proca equations thus obtained, with emphasis on the issue of singularities and horizons.

In this work we review the classification of geodesics of massive test particles in the gravitational background of the black hole solutions of Einstein-Born-Infeld spacetime. Even though some features are quite similar to those of Reissner-Nordstr\"{o}m spacetime there are also important differences, particularly those related to the effective potential governing the geodesic motion. Explicit solutions involving Weierstrass functions are given for a pair of specific scenarios., Comment: 10 pages, 8 figures

Conformal invariant new forms of $p$-brane and D$p$-brane actions are proposed. The field content of these actions are: an induced metric, gauge fields, an auxiliary metric and an auxiliary scalar field that implements the Weyl invariance. This scalar field transforms with a conformal weight that depends on the brane dimension. The proposed actions are Weyl invariant in any dimension and the elimination of the auxiliary metric and the scalar field reproduces the Nambu-Goto action for $p$-branes and the Born-Infeld action for D$p$-branes. As a consequence of the fact that in the $p$-brane case, the action is quadratic in $\partial_0 X$, we develop a complete construction for the associated canonical formalism, solving the problem in previous formulations of conformal $p$-brane actions where the Hamiltonian can not be constructed. We obtain the algebra of constraints and identify the generator of the Weyl symmetry. In the construction of the corresponding supersymmetric generalization of this conformal $p$-brane action we show that the associated $\kappa$-symmetry is consistent with the conformal invariance. In the D$p$-brane case, the actions are quadratic in the gauge fields. These actions can be used to construct new conformal couplings in any dimension $p$ to the auxiliary scalar field now promoted as a dynamical variable., Comment: 12 pages, one additional section

The exact solution of the Schwinger model with compact gauge group U(1) is presented. The compactification is imposed by demanding that the only surviving true electromagnetic degree of freedom has angular character. Not surprinsingly, this topological condition defines a version of the Schwinger model which is different from the standard one, where $c$ takes values on the line. The main consequences are: the spectra of the zero modes is not degenerated and does not correspond to the equally spaced harmonic oscillator, both the electric charge and a modified gauge invariant chiral charge are conserved (nevertheless, the axial-current anomaly is still present) and, finally, there is no need to introduce a $\theta$-vacuum. A comparison with the results of the standard Schwinger model is pointed out along the text., Comment: 14 pages, 2 figures. Accepted for publication in Mod. Phys. Letts. A

Braneworld models may yield interesting effects ranging from high-energy physics to cosmology, or even some low-energy physics. Their mode structure modifies standard results in these physical realms that can be tested and used to set bounds on the models parameters. Now, to define braneworld deviations from standard 4D physics, a notion of matter and gravity localization on the brane is crucial. In this work we investigate the localization of universal massive scalar fields in a de Sitter thick tachyonic braneworld generated by gravity coupled to a tachyonic bulk scalar field. This braneworld possesses a 4D de Sitter induced metric and is asymptotically flat despite the presence of a negative bulk cosmological constant, a novel and interesting peculiarity that contrasts with previously known models. Universal scalar fields can be localized in this expanding braneworld if their bulk mass obeys an upper bound, otherwise they delocalize: The dynamics of the scalar field is governed by a Schroedinger equation with an analog quantum mechanical potential of modified Poeschl-Teller type that depends on the bulk curvature of the braneworld system and the value of the bulk scalar field mass. For masses satisfying a certain upper bound, the potential displays a negative minimum and possesses a single massless bound state separated from the Kaluza-Klein (KK) massive modes by a mass gap defined by the Hubble (expansion scale) parameter of the 3-brane. As the bulk scalar field mass increases, the minimum of the quantum mechanical potential approaches a null value and, eventually, it becomes positive, transforming into a potential barrier and leading to delocalization of the bulk scalar field from the brane. The general solution of the Schroedinger equation is given in terms of general Heun functions, giving rise to a new application of these special functions., Comment: 9 pages in latex, 4 figures

A Wheeler-DeWitt equation for the Kantowski-Sachs model is derived within the framework of the minimal quantum gravity theory proposed by Ho\v{r}ava. We study the solution to this equation in the ultraviolet limit for the specific case where the {\lambda} parameter of the theory takes its relativistic value {\lambda} = 1. It is observed that the minisuperspace variables switch their role compared with their usual infrared (General Relativity) behavior., Comment: 5 pages, 2 figures. This work was presented at the 8th Workshop of the Gravitation and Mathematical Physics Division of the Mexican Physical Society, Tuxtla Gutierrez, Chiapas, Mexico, November 22-26, 2010

In brane world models, combining the extra dimensional field modes with the standard four dimensional ones yields interesting physical consequences that have been proved from high energy physics to cosmology. Even some low energy phenomena have been considered along these lines to set bounds on the brane model parameters. In this work we extend to the gravitational realm a previous result which gave finite electromagnetic and scalar potentials and self energies for a source looking pointlike to an observer sitting in a 4D Minkowski subspace of the single brane of a Randall-Sundrum spacetime including compact dimensions. We calculate here the gravitational field for the same type of source by solving the linearized Einstein equations. Remarkably, it turns out to be also non singular. Moreover, we use gravitational experimental results of the Cavendish type and the Parameterized Post Newtonian (PPN) coefficients, to look for admissible values of the brane model parameters. The anti de Sitter radius hereby obtained is concordant with previous results based on Lamb shift in hydrogen. However, the resulting PPN parameters lie outside the acceptable value domain., Comment: 24 pages

We present the study of two 3-brane system embedded in a 5-dimensional space-time in which the fifth dimension is compactified on a $S^{1}/Z_{2}$ orbifold. Assuming isotropic, homogeneous, and static branes, it can be shown that the dynamics of one brane is dominated by the other one when the metric coefficients have a particular form. We study the resulting cosmologies when one brane is dominated by a given single-fluid component., This work was presented at the VIII Taller of the DGFM, Tuxtla Gutierrez, Chiapas, Mexico noviembre 22-26, 2010

We determine the finite temperature Casimir effect of an Abelian vector field for a pair of parallel perfectly conducting plates in a Randall-Sundrum II model extended by p compact dimensions. We implement perfectly conducting conditions as a codimension one problem in the higher dimensional theory. The resulting Casimir force encodes the structure of the field modes as vacuum fluctuations and so it is sensitive to the extra dimensions of brane worlds. It can be neatly expressed in terms of two four-dimensional Casimir force contributions: one for the massless mode and the other for a tower of massive modes associated with the extra dimensions.

Recently, it has been shown that maximal supergravity allows for non-supersymmetric AdS critical points that are perturbatively stable. We investigate this phenomenon of stability without supersymmetry from the sGoldstino point of view. In particular, we calculate the projection of the mass matrix onto the sGoldstino directions, and derive the necessary conditions for stability. Indeed we find a narrow window allowing for stable SUSY breaking points. As a by-product of our analysis, we find that it seems impossible to perturb supersymmetric critical points into non-supersymmetric ones: there is a minimal amount of SUSY breaking in maximal supergravity., 27 pages, 1 figure. v2: two typos corrected, published version

Models for the internal composition of Dense Compact Stars are reviewed as well as macroscopic properties derived by observations of relativistic processes. Modeling of pure neutron matter Neutron Stars is presented and crust properties are studied by means of a two fluid model., Proceedings from the VIII Workshop of the Gravitation and Mathematical Physics Division of the Mexican Physical Society, December 2010, Chiapas, Mexico (6 pages, 2 figures); added references

Physical effects in brane worlds models emerge by the incorporation of field modes coming from extra dimensions with the usual four dimensional ones. Such effects can be tested with well established experiments to set bounds on the parameters of the brane models. In this work we extend a previous result which gave finite electromagnetic potentials and self energies for a source looking pointlike to an observer sitting in a 4D Minkowski subspace of a single brane of a Randall-Sundrum spacetime including compact dimensions, and along which the source stretches uniformly. We show that a scalar particle produces a nonsingular static potential, possess a finite self-energy and that technically its analysis is very similar to the electrostatic case. As for the latter, we use the deviations from the Coulomb potential to set bounds on the anti de Sitter radius of the brane model on the basis of two experiments, namely, one of the Cavendish type and other being the scattering of electrons by Helium atoms. We found these are less stringent than others previously obtained using the Lamb shift in Hydrogen., 23 pages, 4 figures

Constraints to the mass of a scalar field and the strength of its self-interacting coupling constant are obtained. This was done using observations of stellar dynamics at the center of our galaxy and by assuming that the dark compact object responsible of such dynamics is a boson star and not a supermassive black hole. We show that if such scalar field represents a spin-zero particle with cross section high enough to be considered collisional dark matter, there is a region of parameters compatible with both conditions: that the scalar field play the role of collisional dark matter and that it can form objects with the mass and compactness compatible with stellar kinematics., To appear in the Procceedings of the VIII Workshop of the Gravitation and Mathematical Physics Division of the Mexican Physical Society

Deformation quantization is applied to quantize gravitational systems coupled with matter. This quantization procedure is performed explicitly for quantum cosmology of these systems in a flat minisuper(phase)space. The procedure is employed in a quantum string minisuperspace corresponding to an axion-dilaton system in an isotropic FRW Universe. The Wheeler-DeWitt-Moyal equation is obtained and its corresponding Wigner function is given analytically in terms of Meijer's functions. Finally, this Wigner functions is used to extract physical information of the system., Comment: 12 pages, 4 figures, to appear in the Proceedings of the VIII Mexican Workshop on Gravitation and Mathematical Physics

We give a brief overview of several models in brane‐world cosmology. In particular, we focus on the asymmetric DGP and Regge‐Teiltelboim models. We present the associated equations of motion governing the dynamics of the brane and their corresponding Friedmann‐like equations. In order to develop the quantum Regge‐Teiltelboim type cosmology we construct its Ostrogradski Hamiltonian formalism which naturally leads to the corresponding Wheeler‐DeWitt equation. In addition, we comment on possible generalizations for these models including second order derivative geometrical terms.

To consider GRBs as standard candles, the circularity problem should be surmounted. To do this GRBs are calibrated at low redshifts using SNIa data and then extrapolating the calibration to higher redshifts. In this work we apply GRBs calibration to estimate the Hubble parameter, H(z), from the luminosity distance extracted from the calibration and, knowing H(z), we study the parameter w(z) of the equation of state of dark energy.

This is a brief review of the standard model of cosmology. We first introduce the FRW models and their flat solutions for energy fluids playing an important role in the dynamics at different epochs. We then introduce different cosmological lengths and some of their applications. The later part is dedicated to the physical processes and concepts necessary to understand the early and very early Universe and observations of it., 25 pages, 2 figures, v2: a typo corrected

We introduce, at a basic level, the concepts that are necessary to get acquainted with two of the most interesting fields of research which emerged from classical general relativity: black holes and gravitational waves.