arXiv subjects

Shanshan Rodriguez

Publications and source records attributed to Shanshan Rodriguez.

8 recordsLinked to original sources

arXiv2026

Energy Extraction via Magnetic Reconnection from a Rotating Dyonic Black Hole in $N = 2, \ U(1)^2$ Gauged Supergravity

We study energy extraction via magnetic reconnection from a rotating dyonic black hole in four-dimensional $N=2$, $U(1)^2$ gauged supergravity. Using the Comisso-Asenjo mechanism in the ZAMO frame, we derive the asymptotic hydrodynamic energy per unit enthalpy $\epsilon^{\infty}_\pm$ and determine when reconnection outflows attained negative energy at infinity. By varying the spin $a$, electric and magnetic charges, NUT parameter $N_g$, and gauge coupling $g$, we compute the cutoff magnetization $\sigma_0^{\rm cutoff}$ and map the region of parameter space that admits $\epsilon^{\infty}_-<0$. We find that $\sigma_0^{\rm cutoff}$ and the very existence of Comisso-Asenjo extraction are tightly controlled by $g$ and the dyonic charges: increasing $g$ or pushing the charges toward extremality raises $\sigma_0^{\rm cutoff}$ and shrinks the CA-active part of the ergoregion. Unlike Kerr, the spin enters through the normalization factor $\Xi$, and the quartic horizon function $\Delta_g$, so geometric effects from the AdS/NUT deformation dominate the usual frame-dragging enhancement. As a result, the extracted power and efficiency are non-monotonic in $a$ and peak at intermediate spin ($a\sim0.8$); near-extremal rotation is not required for high efficiency, provided $g$ is small and $Q$ is moderate. Efficient extraction further demands extreme magnetization and nearly radial outflows, confining the active reconnection layer to a thin shell, just outside the horizon.

gr-qc↗

arXiv2026

Superradiant Suppression of Non-minimally Coupled Scalar fields for a Rotating Charged dS Black Hole in Conformal Weyl Gravity

In this study, we present an analytical investigation of the superradiant scattering of a massive charged conformally coupled scalar field in rotating charged $de~Sitter$ black hole spacetimes within two gravitational theories: General Relativity (GR) and fourth-order Conformal (Weyl-squared) Gravity (CWG). For the massless charged conformally coupled scalar, we exploit a recently discovered correspondence between the Heun equation and the semiclassical limit of Belavin-Polyakov-Zamolodchikov (BPZ) equations in two-dimensional conformal field theory to solve for the superradiant amplification factors as controlled expansions in a small parameter scaling. For the massive charged conformally coupled scalar, we use WKB methods to derive an order of magnitude approximation for the amplification factors in the cosmological region in terms of those in the region $r_+\ll r \ll r_c$ where $r_+$ and $r_c$ are the outer and cosmological event horizons, respectively. For both the massless and massive sectors, suppression of superradiant amplification in CWG relative to that in GR is observed across the parameter regimes studied. Particularly, in the massive sector, we find strong exponential suppression of superradiant amplification on the order of $e^{-2\mu\Lambda^{-1/2}}$ in the cosmological region.

hep-th↗

arXiv2026

Plasma effects on gravitational lensing and shadow observables of a Kerr-like black hole in a dark matter halo

Plasma surrounding a black hole modifies light propagation and can alter the observed shadow, potentially affecting the interpretation of Event Horizon Telescope data. We study the effects of dark matter and nonmagnetized pressureless plasma on the shadow of a Kerr-like black hole by analyzing null geodesics in both homogeneous and inhomogeneous plasma distributions. For the homogeneous plasma profile, the asymptotic Bardeen coordinates acquire a refractive normalization factor arising from the leading-order coupling between the metric function $\Delta(r)$ and the radial plasma function $f_r(r)\propto r^2$. We show that increasing the black hole spin generally enlarges the shadow radius and increases its deformation, while moving the observer away from the equatorial plane decreases both quantities. For the parameter ranges considered, astrophysically reasonable dark matter densities in this model do not produce appreciable changes in the photon trajectories. Plasma effects, however, are significant: increasing the plasma density increases the shadow radius and deformation for homogeneous plasma, but decreases them for inhomogeneous plasma. The energy emission rate likewise depends strongly on the plasma model, with homogeneous plasma producing a substantially larger rate as the plasma strength increases. As an illustrative benchmark, we compare the resulting geometric critical-curve sizes with EHT-inferred shadow-size intervals for M87* and Sgr A*.

gr-qc↗

arXiv2024

Energy extraction through magnetic reconnection from a Kerr-Newman black hole in perfect fluid dark matter

In this work, we provide a thorough analysis of energy extraction via magnetic reconnection, a novel mechanism recently proposed by Comisso and Asenjo, for a Kerr-Newman black hole immersed in a perfect fluid dark matter (PFDM) background. Our studies focus on the impact of black hole spin $a$, electric charge $Q$ and PFDM parameter $\lambda$ on the horizons, ergoregion and circular geodesics at the equatorial plane of this black hole, and how they further influence the reconnection efficiency and energy extraction rate. Our results show that the outer horizon and the size of ergoregion do not vary monotonically with increasing dark matter parameters $\lambda$ until reaching its critical value $\lambda_c$ due to the combined counteracting effect between the black hole's charge and dark matter parameter. We identify the optimal combinations of $a$, $Q$ and $\lambda$ that allow for efficient energy extraction and high extracted power, even when the black hole is not spinning near its extremal limit. Our results ease the stringent conditions observed in other rotating black holes, where achieving comparable levels of extracted power and reconnection efficiency typically requires a near-extremal spin.

gr-qc↗

arXiv2024

Geometrodynamics of a 2D Curved Surface due to a Constrained Quantum Particle via its Gravitational Dual: $\mathbf{\mathcal{S}^2}$ Analytical Model Calculations

We provide a unique and novel extension of da Costa's calculation of a quantum mechanically constrained particle. This is achieved by analyzing the perturbative back reaction of the quantum confined particle's eigenstates and spectra upon the geometry of the curved surface itself, thereby addressing the problem of shape optimization in this model. We do this by first formulating a two-dimensional action principle of the quantum constrained particle, which upon variation of the wave function reproduces Schr\"odinger's equation including da Costa's surface curvature-induced potentials. We further demonstrate that our derived action principle is dual to a two-dimensional dilation gravity theory and we vary its functional with respect to the embedded two-dimensional inverse-metric to obtain the respective geometrodynamical Einstein equation. We solve this resulting Einstein equation perturbatively by first solving the da Costa's Schr\"odinger equation to obtain an initial eigensystem, which is used as initial-input data for a perturbed metric inserted into the derived Einstein equation. As a proof of concept, we perform this calculation on a two-sphere and show its first iterative perturbed shape evolution. We also turn on external electromagnetic fields and formulate the full field theoretic field equations for future investigation. The external fields manifest themselves via a surface induced, pulled-back $U(1)$ coupling in our two-dimensional dual gravity theory, thereby revealing interesting and rich new surface physics in this specific paradigm.

hep-th↗

arXiv2022

N\"other Currents, Black Hole Entropy Universality and CFT Duality in Conformal Weyl Gravity

In this paper we study black hole entropy universality within the Conformal Weyl gravity paradigm. We do this by first computing the entropy of specific vacuum and non-vacuum solutions, previously unexplored in Conformal Weyl gravity via both the N\"other current method and Wald's entropy formula. For the vacuum case, we explore the near horizon near extremal Kerr metric, which is also a vacuum solution to Conformal Weyl gravity and not previously studied in this setting. For the non-vacuum case we couple the conformal Weyl gravity field equations to a near horizon (linear) $U(1)$ gauge potential and analyze the respective found solutions. We highlight the non-universality of black hole entropy between our studied black hole solutions of varying symmetries. However despite non-universality, the respective black hole entropies are in congruence with Wald's entropy formula for the specific gravity theory. Finally and despite non-universality, we comment on the construction of a near horizon CFT dual to one of our unique non-vacuum solutions. Due to the non-universality, we must introduce a parameter (similarly to entropy calculations in LQG) which we also call $\gamma$ and relating to the Weyl anomaly coefficient. The construction follows an $AdS_2/CFT_1$ correspondence in the near horizon, which enables the computation of the full asymptotic symmetry group of the chosen non-vacuum conformal Weyl black hole and its near horizon quantum CFT dual. We conclude with a discussion and outlook for future work.

hep-th↗

arXiv2019

Exploration of The Duality Between Generalized Geometry and Extraordinary Magnetoresistance

We outline the duality between the extraordinary magnetoresistance (EMR), observed in semiconductor-metal hybrids, and non-symmetric gravity coupled to a diffusive $U(1)$ gauge field. The corresponding gravity theory may be interpreted as the generalized complex geometry of the semi-direct product of the symmetric metric and the antisymmetric Kalb-Ramond field: ($g_{\mu\nu}+\beta_{\mu\nu}$). We construct the four dimensional covariant field theory and compute the resulting equations of motion. The equations encode the most general form of EMR within a well defined variational principle, for specific lower dimensional embedded geometric scenarios. Our formalism also reveals the emergence of additional diffusive pseudo currents for a completely dynamic field theory of EMR. The proposed equations of motion now include terms that induce geometrical deformations in the device geometry in order to optimize the EMR. This bottom-up dual description between EMR and generalized geometry/gravity lends itself to a deeper insight into the EMR effect with the promise of potentially new physical phenomena and properties.

hep-th↗

arXiv2017

On the Near Horizon Canonical Quantum Microstates from $AdS_2/CFT_1$ and Conformal Weyl Gravity

We compute the full asymptotic symmetry group of black holes belonging to the same equivalence class of solutions within the Conformal Weyl Gravity formalism. We do this within an $AdS_2/CFT_1$ correspondence and by performing a Robinson-Wilczek two dimensional reduction, thus enabling the construction of an effective quantum theory of the remaining field content. The resulting energy momentum tensors generate asymptotic Virasoro algebras, to $s$-wave, with calculable central extensions. These centers in conjunction with their proper regularized lowest Virasoro eigen-modes yield the Bekenstein-Hawking black hole entropy via the statistical Cardy formula. We also analyze quantum holomorphic fluxes of the dual CFTs in the near horizon, giving rise to finite Hawking temperatures weighted by the central charges of the respective black hole spacetimes. We conclude with a discussion and outlook for future work.

hep-th↗