arXiv subjects

Daniel Flores-Alfonso

Publications and source records attributed to Daniel Flores-Alfonso.

At least 19 recordsLinked to original sources

arXiv2026

Planar AdS multi-NUT spacetimes and Kaluza-Klein multi-monopoles

In higher-dimensional Einstein-AdS gravity, it is well known that planar and static anti-de Sitter black holes can be endowed with multiple rotation parameters via a large-gauge transformation. However, a similar prescription fails when multiple NUT parameters are added, thereby obstructing the study of holographic properties with more than one NUT charge. To pave the way towards this direction, we construct explicit planar AdS spacetimes having multiple NUT parameters in two simple ways that allow one to circumvent the strong restrictions imposed by the vacuum field equations. First, motivated by momentum relaxation holographic models, we construct multi-NUT spaces in AdS with flat horizons by adding free scalar fields possessing an axionic profile. In our second approach, we build similar configurations in Einstein gravity with quadratic-curvature corrections. We end by presenting planar versions of the Kaluza-Klein monopole in AdS with different magnetic charges. As a byproduct, our strategy yields a simple way to generalize the Gross-Perry-Sorkin monopole to include the cosmological constant.

hep-th↗

arXiv2026

The Gödel Universe as a Superconductor

Material science and engineering have benefited from the use of geometric and topological tools. A material medium can mimic effective gravitational fields while spacetime metrics serve as geometric models of physical media. Although analog models of optical, acoustic, and viscous media in curved spacetimes are well established, none have yet captured the hallmark constitutive properties of superconductors. In this work we show that the Gödel universe - an exact solution to Einstein's field equations - serves as the gravitational analog of a superconducting medium in its Meissner state.

physics.gen-ph↗

arXiv2025

The dyonic Kerr-Schild ansatz

We develop a geometric extension of the Kerr-Schild ansatz that incorporates both electric and magnetic sectors of the Maxwell field in a unified framework, without resorting to duality rotations. We start observing that the known purely electric solution satisfies Maxwell's equations due to a closedness condition obeyed by the Kerr-Schild null congruence. From the associated local exactness property, we construct a new one-form naturally linked to the congruence as a sort of Poincaré dualization. This leads us to propose a geometrically motivated dyonic vector potential within the Kerr-Schild ansatz, defined as a superposition of an electric contribution along the congruence and a magnetic one that aligns to the dualized one-form. We then show that for a stationary and axisymmetric Kerr-Schild ansatz, the electrovac circularity theorem uniquely constrains not only the scalar profile of the metric, but also those associated to the electric-magnetic splitting of the gauge field. The resulting formalism provides a transparent derivation of the dyonic Kerr-Newman solution and extends naturally to the (A)dS case, highlighting the intrinsic interplay between geometry and matter in a Kerr-Schild setting.

hep-th↗

arXiv2025

Ultrarelativistic limit of the Kerr theorem

The original Kerr theorem provides the foundation for Kerr-Schild transformations by classifying all shear-free and geodesic null congruences in flat spacetime; the key ingredient of the Kerr-Schild ansatz. However, due to the high level of degeneracy of the outcome it is often less practical than its symmetric refinements, which may single out congruences leading to physically significant spacetimes by imposing relevant symmetries. An illustrative example is the stationary axisymmetric version of Kerr theorem which has been shown to lead directly and uniquely to the Kerr black hole in vacuum. In this work, we propose a new symmetric refinement of the Kerr theorem by boosting the stationary symmetry into its ultrarelativistic limit to achieve invariance under null translations, while keeping axisymmetry. Under these assumptions, the classification yields only two distinct congruences. The first congruence is covariantly constant and, through the Kerr-Schild ansatz, evidently yields an axisymmetric pp-wave. The vacuum axisymmetric profile of this pp-wave displays a logarithmic dependence on the polar radius, characteristic of the exterior gravitational field of the Bonnor light beam, and includes as a special case the Aichelburg-Sexl ultrarelativistic limit of the Schwarzschild black hole. The Kerr-Schild transformation of the second congruence gives rise to a non-trivial vacuum solution recently reported in [Phys. Rev. D 112, 024020 (2025)]. Using circularity and appropriately fixing the reparameterization invariance of the orthogonal manifold to the Killing fields, we show that the latter solution corresponds to the well-known Taub-NUT spacetime with planar topology. These results emphasize how symmetry-based refinements of the Kerr theorem constitute a powerful tool to constructing physically essential spacetimes.

gr-qc↗

arXiv2025

Inhomogeneous metrics on complex bundles in Lovelock gravity

We consider Lovelock gravity in arbitrary, even dimensions. We find a large class of new gravitational instantons by considering extended nontrivial circle bundles over Kähler manifolds. Concretely, we generalize the Page-Pope metric in the presence of higher-curvature corrections of the Lovelock class. A subset of these spaces admits analytic continuation into the Lorentzian sector, producing new stationary solutions in Lovelock gravity. The geometries are fully determined by a single algebraic equation. We also obtain necessary and sufficient conditions for Lovelock-constant Kähler manifolds to exist in Lovelock gravity. Finally, we find a wide class of Lovelock-Maxwell solutions beyond staticity, allowing us to obtain the electrovacuum extension of these instantons.

hep-th↗

arXiv2025

Non-Abelian black holes in conformal gravity

The first black hole solutions of the SU(N) Bach-Yang-Mills equations are presented. Static generalizations breaking spherical symmetry are also constructed. These constitute the first examples in the literature of C-metrics sourced by a Yang-Mills field.

hep-th↗

arXiv2024

Nonlinearly charging the conformally dressed black holes preserving duality and conformal invariance

We start this paper by concisely rederiving ModMax, which is nothing but the unique nonlinear extension of Maxwell's equations preserving conformal and duality invariance. The merit of this new derivation is its transparency and simplicity since it is based on an approach where the elusive duality invariance is manifest. In the second part, we couple the ModMax electrodynamics to Einstein gravity with a cosmological constant together with a standard conformal scalar field, and new stationary spacetimes with dyonic charges are found. These solutions are later used as seed configurations to generate nonlinearly charged (super-)renormalizably dressed spacetimes by means of a known generating method that we extend to include any nonlinear conformal electrodynamics. We end by addressing the issue of how to generalize some of these results to include the recently studied non-Noetherian conformal scalar fields, whose equation of motion still enjoys conformal symmetry even though its action does not. It turns out that the static non-Noetherian conformally dressed black holes also become amenable to being charged by ModMax.

hep-th↗

arXiv2024

Self-gravitating solutions in Yang-Mills-Chern-Simons theory coupled to 3D massive gravity

We study self-gravitating solutions of 3-dimensional massive gravity coupled to Yang-Mills-Chern-Simons gauge theory. Among these, there is a family of asymptotically Warped-Anti de Sitter black holes that come to generalize previous solutions found in the literature and studied in the context of WAdS$_3$/CFT$_2$. We also present self-gravitating solutions to the 3-dimensional Einstein-Yang-Mills theory, as well as other self-gravitating solutions in the presence of higher-curvature terms.

hep-th↗

arXiv2024

The geometry of induced currents in two dimensional media

We present a framework that allows us to clearly identify the geometric features underlying the phenomenon of superconductivity in two dimensional materials. In particular, we show that any such medium whose response to an externally applied electromagnetic field is a geodesically flowing induced current, must be a superconductor. In this manner, we conclude that the underlying geometry of this type of media is that of a Lorentzian contact manifold. Moreover, we show that the macroscopic hallmark of their superconducting state is a purely topological condition equivalent to the geodesic nature of the induced current: the non-vanishing of its helicity.

cond-mat.supr-con↗

arXiv2024

Gravitational Waves from Thurston Geometries

It has been established that the famous three-dimensional Thurston geometries have four intrinsically Lorentzian analogs. We explore these spacetimes in three-dimensional general relativity nonminimally coupled to a scalar field together with electromagnetic matter. We find that three of these spacetimes support electromagnetic radiation, while, the other is partially sourced by a nonnull field and supports gravitational radiation. By addressing this problem we have also found a novel type of gravitational Cheshire effect.

gr-qc↗

arXiv2023

Axial anomaly in nonlinear conformal electrodynamics

We study the axial anomaly of Dirac spinors on gravitational instanton backgrounds in the context of nonlinear electrodynamics. In order to do so, we consider Einstein gravity minimally coupled to a recently proposed conformal electrodynamics that enjoys duality transformation invariance. These symmetries allow us to generalize the Eguchi-Hanson configuration while preserving its geometry. We then compute the Dirac index of the nonlinearly charged Eguchi-Hanson and Taub-NUT configurations. We find that there is an excess of positive chiral Dirac fermions over the negative ones which triggers the anomaly.

hep-th↗

arXiv2022

Higher-curvature generalization of Eguchi-Hanson spaces

We construct higher-dimensional generalizations of the Eguchi-Hanson gravitational instanton in the presence of higher-curvature deformations of general relativity. These spaces are solutions to Einstein gravity supplemented with the dimensional extension of the quadratic Chern-Gauss-Bonnet invariant in arbitrary even dimension $D=2m\geq 4$, and they are constructed out of non-trivial fibrations over $(2m-2)$-dimensional Kähler-Einstein manifolds. Different aspects of these solutions are analyzed; among them, the regularization of the on-shell Euclidean action by means of the addition of topological invariants. We also consider higher-curvature corrections to the gravity action that are cubic in the Riemann tensor and explicitly construct Eguchi-Hanson type solutions for such.

hep-th↗

arXiv2022

Phase transitions of black strings in dynamical Chern-Simons modified gravity

We study conserved charges and thermodynamics of analytic rotating anti-de Sitter black holes with extended horizon topology -- also known as black strings -- in dynamical Chern-Simons modified gravity. The solution is supported by a scalar field with an axionic profile that depends linearly on the coordinate that spans the string. We compute conserved charges by making use of the renormalized boundary stress-energy tensor. Then, by adopting the Noether-Wald formalism, we compute the black string entropy and obtain its area law. Indeed, the reduced Euclidean Hamiltonian approach shows that these methods yield a consistent first law of thermodynamics. Additionally, we derive a Smarr formula using a radial conservation law associated to the scale invariance of the reduced action and obtain a Cardy formula for the black string. A first-order phase transition takes place at a critical temperature between the ground state and the black string, above which the black string is the thermodynamically favored configuration.

hep-th↗

arXiv2021

Analytic non-homogeneous condensates in the $(2+1)$-dimensional Yang-Mills-Higgs-Chern-Simons theory at finite density

We construct the first analytic examples of non-homogeneous condensates in the Georgi-Glashow model at finite density in $(2+1)$ dimensions. The non-homogeneous condensates, which live within a cylinder of finite spatial volume, possess a novel topological charge that prevents them from decaying in the trivial vacuum. Also the non-Abelian magnetic flux can be computed explicitly. These solutions exist for constant and non-constant Higgs profile and, depending on the length of the cylinder, finite density transitions occur. In the case in which the Higgs profile is not constant, the full system of coupled field equations reduce to the Lamé equation for the gauge field (the Higgs field being an elliptic function). For large values of this length, the energetically favored configuration is the one with a constant Higgs profile, while, for small values, it is the one with non-constant Higgs profile. The non-Abelian Chern-Simons term can also be included without spoiling the integrability properties of these configurations. Finally, we study the stability of the solutions under a particular type of perturbations.

hep-th↗

arXiv2021

Nonlinear extensions of gravitating dyons: from NUT wormholes to Taub-Bolt instantons

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.

gr-qc↗

arXiv2020

Black holes and gravitational waves sourced by non-linear duality rotation-invariant conformal electromagnetic matter

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-Nordström, 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.

gr-qc↗

arXiv2020

Meronic AdS Black Holes in Gauss-Bonnet Theory

We examine analytical, intrinsically non-Abelian, black holes with SU(2) Yang-Mills matter content. Working in the extended thermodynamics scenario of Lovelock black holes we study the phase structure of a four and a five-dimensional spherically symmetric configuration. We work in Gauss-Bonnet-Einstein-Yang-Mills gravity with negative cosmological constant and use Euclidean methods to explore the thermodynamics of the systems. We observe that the solutions belong to the expected universality class of van der Waals and find a reentrant phase transition.

gr-qc↗

arXiv2019

Flux quantization in dilatonic Taub-NUT dyons

Spacetimes that include a boundary at infinity have a non-trivial topology. The homology of the background influences gauge fields living on them and lead to topological charges. We investigate the charges and fluxes of fields over a Taub--NUT background in Einstein--Maxwell dilaton--axion gravity, by using the relative homology and de Rham cohomology. It turns out that the electromagnetic sector is devoid of restrictions from a topological viewpoint. There are, however, flux quanta for the axion and dilaton fields. These results are obtained from the absolute homology of the spacetime boundary. The solutions we probe originate in the four dimensional low energy limit of heterotic string theory. So our results are complemented by the stringy coupling present in the fields. The quantization has a bundle theoretic interpretation as the axion's flux corresponds to the topological index of an underlying 2-bundle.

hep-th↗