arXiv subjects

Euro Spallucci

Publications and source records attributed to Euro Spallucci.

At least 19 recordsLinked to original sources

arXiv2023

The Cornell black hole

The Cornell potential can be derived from a recently proposed non-local extension of Abelian electrodynamics. Non-locality can be alternatively described by an extended charge distributions in Maxwell electrodynamics. We state that in these models the energy momentum tensor necessarily requires the presence of the interaction term between the field and the charge itself. We show that this extended form of energy momentum tensor leads to an exact solution of the Einstein equations describing a charged AdS black hole. We refer to it as the "Cornell black hole"(CBH). Identifying the effective cosmological constant with the pressure of Van der Waals fluid, we study the gas-liquid phase transition and determine the critical parameters.

hep-th↗

arXiv2022

Double copy of spontaneously broken Abelian gauge theory

Similarity in the structure of scattering amplitudes in Yang-Mills theories and General Relativity led to the idea that graviton could be described as the double copy of a vector gauge field. In this letter we discuss a realization of this idea emerging directly from solutions of equations of General Relativity. A general form of the energy momentum tensor for the electric field is derived that leads to the metric tensor in terms of the double copy of a corresponding gauge potential. We than use this general property to find the double copy of spontaneously broken scalar electrodynamics. The result is a screened Reissner-Nordström-like metric. When the horizon radius and the Compton wavelength of the massive photon become comparable the black hole becomes a quantum object. An exact solution of the horizon wave equation is found and the corresponding energy spectrum is described. It turns out that highly excited states show a characteristic string-like behavior.

hep-th↗

arXiv2021

Regularization ambiguity and van der Waals black hole in 2+1 dimensions

Charged black holes in a ($2+1$)-dimensional anti-de Sitter space-time suffer from some limitations such as the ambiguity in the definition of the mass and the bad short distance behavior. In this paper we present a way to resolve such issues. By extending the parameter space of the BTZ geometry, we properly identify the integration constants in order to remove the conical singularity sitting at the origin. In such a way we obtain a well defined Minkowski limit and horizons also in the case of de Sitter background space. On the thermodynamic side, we obtain a proper internal energy, by invoking the consistency with the Area Law, even if the mass parameter does not appear in the metric coefficients. As a further improvement, we show that it is sufficient to assume a finite size of the electric charge to obtain a short scale regular geometry. The resulting solution, generalizing the charged BTZ metric, is dual to a van der Waals gas.

gr-qc↗

arXiv2021

Kalb-Ramond scalar QED multiple vacua

We study a model of interacting vector and Kalb-Ramond gauge fields in a non-trivial Higgs vacuum generated by a charged and a neutral scalar field. The system admits different vacua for different v.e.v. of the two Higgs fields. Our primary interest in this paper regards the "mixed phase" where both the photon and the Kalb-Ramond acquire a mass. In this phase we compute the interaction potential energy between static test charges. It turns out that the limit in which the photon becomes massless, while the Kalb-Ramond remains massive, leads to a Cornell confining potential between test charges.

hep-th↗

arXiv2021

Horizons and the Wave Function of Planckian Quantum black holes

At the Planck scale the distinction between elementary particles and black holes becomes fuzzy. The very definition of a "quantum black hole" (QBH) is an open issue. Starting from the idea that, at the Planck scale, the radius of the event horizon undergoes quantum oscillations, we introduce a black hole mass-radius Generalised Uncertainty Principle (GUP) and derive a corresponding gravitational wavelength. Next we recover a GUP encoding effective geometry. This semi-classical gravitational description admits black hole configurations only for masses higher than the Planck mass. Quantum corrections lead to a vanishing Hawking temperature when the Planck mass is approached from above. Finally we replace our semi-classical model by a relativistic wave equation for the "horizon wave function". The solution admits a discrete mass spectrum which is bounded from below by a stable ground state with energy close to the Planck mass. Interestingly higher angular momentum states fit onto Regge trajectories indicating their stringy nature.

hep-th↗

arXiv2020

Cornell potential in Kalb-Ramond scalar QED via Higgs mechanism

In this letter we derive the Cornell confining potential in a theory of interacting Abelian gauge vector and massive Kalb-Ramond tensor. The Kalb-Ramond mass is instrumental to obtain the linear confining behavior of the potential at large distances. The same model can be described via interaction with Higgs fields, alternatively, providing mass to the vector, or to the tensor fields. In the first case, the photon acquires mass, while the tensor remains massless. The resulting interaction potential is a screened Coulomb one. In the second case, the photon remains massless while Kalb-Ramond tensor acquires mass and the resulting potential is of the Cornell type with the mass parameter determining the slope of the linear part.

hep-ph↗

arXiv2020

The Cornell potential in Lee-Wick inspired electrodynamics

In the seventies, Lee and Wick proposed an interesting modification of classical electrodynamics that renders it finite at the quantum level. At the classical level, this modified theory leads to a regular linear potential at short distances while also reproducing the Coulomb potential at large distances. It is shown that a suitable modification of the Lee-Wick idea can also lead to a linear potential at large distances. For this purpose, we study an Abelian model that ``simulates" the QCD confining phase while maintaining the Coulomb behavior at short distances. This paper is organized in three parts. In the first part, we present a pedagogical derivation of the static potential in the Lee-Wick model between two heavy test charges using the Hamiltonian formulation. In the second part, we describe a modification of the Lee-Wick idea leading to the standard Cornell potential. In the third part, we consider the effect of replacing a point-like charge with a smeared Gaussian-type source, that renders the electrostatic potential finite as r--> 0.

physics.gen-ph↗

arXiv2019

Quantum Corrected Black Holes from String T-Duality

In this paper we present some stringy corrections to black hole spacetimes emerging from string T-duality. As a first step, we derive the static Newtonian potential by exploiting the relation between the T-duality and the path integral duality. We show that the intrinsic non-perturbative nature of stringy corrections introduce an ultraviolet cutoff known as zero-point length in the path integral duality literature. As a result, the static potential is found to be regular. We use this result to derive a consistent black hole metric for the spherically symmetric, electrically neutral case. It turns out that the new spacetime is regular and is formally equivalent to the Bardeen metric, apart from a different ultraviolet regulator. On the thermodynamics side, the Hawking temperature admits a maximum before a cooling down phase towards a thermodynamically stable end of the black hole evaporation process. The findings support the idea of universality of quantum black holes.

gr-qc↗

arXiv2018

Quantum black holes and the Higgs mechanism at the Planck scale

In this paper we present a suitably adjusted Higgs-like mechanism producing black holes at, and beyond, the Planck energy. Planckian objects are difficult to classify either as "particles", or as "black holes", since the Compton wavelength and the Schwarzschild radius are comparable. Due to this unavoidable ambiguity, we consider more appropriate a quantum field theoretical (QFT) approach rather than General Relativity (GR), which is known to break down as the Planck scale is approached. A posteriori, a connection between the two description can be established for masses large enough with respect to the Planck mass, though always describing black holes at the microscopic level. We adopt a QFT inspired by the Higgs mechanism, in the sense that a massive scalar field develops a non-trivial vacuum for m>μ_{Pl}. Exictations around this vacuum are Planckian objects we name "black particles" to remark the ambiguous identity of these objects, as it has been mentioned above. A black particle eventually turns into a "quantum black hole" when the Schwarzschild radius becomes larger than its Compton wavelength. However, for m=μ_{Pl} the scalar field is massless at the tree-level, but develops a non-trivial vacuum at one-loop through a Coleman-Weinberg mechanism. In this case, excitations describe Planck mass black particles.

hep-th↗

arXiv2017

Gaussian black holes in Rastall Gravity

In this short note we present the solution of Rastall gravity equations sourced by a Gaussian matter distribution. We find that the black hole metric shares all the common features of other regular, General Relativity BH solutions discussed in the literature: there is no curvature singularity and the Hawking radiation leaves a remnant at zero temperature in the form of a massive ordinary particle.

gr-qc↗

arXiv2017

Remarks on regular black holes

Recently it has been claimed by Chinaglia and Zerbini that the curvature singularity is present even in the so-called regular black hole solutions of the Einstein equations. In this brief note we show that this criticism is devoid of any physical content.

gr-qc↗

arXiv2017

Regular black holes from semi-classical down to Planckian size

In this paper we review various models of curvature singularity free black holes. In the first part of the review we describe semi-classical solutions of the Einstein equations which, however, contains a "quantum" input through the matter source. We start by reviewing the early model by Bardeen where the metric is regularized by-hand through a short-distance cut-off, which is justified in terms of non-linear electro-dynamical effects. This a toy-model model useful to point-out the common features shared by all regular semi-classical black holes. Then, we solve Einstein equations with a Gaussian source encoding the quantum spread of an elementary particle. We identify, the a priori arbitrary, Gaussian width with the Compton wavelength of the quantum particle. This Compton-Gauss model leads to the estimate of a terminal density that a gravitationally collapsed object can achieve. We identify this density to be the Planck density, and reformulate the Gaussian model assuming this as its peak density. All these models, are physically reliable as long as the black hole mass is big enough with respect to the Planck mass. In the truly Planckian regime, the semi-classical approximation breaks down. In this case, a fully quantum black hole description is needed. In the last part of this paper, we propose a non-geometrical quantum model of Planckian black hole implementing the Holographic Principle and realizing the "classicalization" scenario recently introduced by Dvali and collaborators. The classical relation between the mass and radius of the black hole emerges only in the classical limit, far away from the Planck scale.

hep-th↗

arXiv2017

The bosonized version of the Schwinger model in four dimensions: a blueprint for confinement?

For a $(3+1)$-dimensional generalization of the Schwinger model, we compute the interaction energy between two test charges. The result shows that the static potential profile contains a linear term leading to the confinement of probe charges, exactly as in the original model in two dimensions. We further show that the same 4-dimensional model also appears as one version of the $ B \wedge F$ models in $(3+1)$ dimensions under dualization of Stueckelberg-like massive gauge theories. Interestingly, this particular model is characterized by the mixing between a $U(1)$ potential and an Abelian $3$-form field of the type that appears in the topological sector of QCD.

hep-th↗

arXiv2016

A particle-like description of Planckian black holes

In this paper we abandon the idea that even a "quantum" black hole, of Planck size, can still be described as a classical, more or less complicated, geometry. Rather, we consider a genuine quantum mechanical approach where a Planckian black hole is, by all means, just another "particle", even if with a distinguishing property: its linear size increases with the energy. The horizon dynamics is equivalently described in terms of a particle moving in gravitational potential derived from the horizon equation itself in a self-consistent manner. The particle turning-points match the radius of the inner and outer horizons of a charged black hole. This classical model pave the way towards the wave equation for a truly quantum black hole. We compute the exact form of the wave function and determine the energy spectrum. Finally, we describe the classical limit in which the quantum picture correctly approaches the classical geometric formulation. We find that the quantum-to-classical transition occurs far above the Planck scale.

hep-th↗

arXiv2016

A Dynamical model for non-geometric quantum black holes

It has been recently proposed that quantum black holes can be described as N-graviton Bose-Einstein condensates. In this picture the quantum properties of BHs "... can be understood in terms of the single number N". However, so far, the dynamical origin of the occupational number N has not been specified. This description is alternative to the usual one, where black holes are believed to be well described geometrically even at the quantum level. In this paper we pursue the former point of view and develop a non-geometrical dynamical model of quantum black holes (BHs). In our model the occupational number N is proportional to the principal quantum number n of a Planckian harmonic oscillator. The so-called "classicalization" corresponds to the large-n limit, where the Schwarzschild horizon is recovered.

hep-th↗

arXiv2015

Chern-Simons-Schwinger model of confinement in $QCD$

It has been shown that the mechanism of formation of glue-bags in the strong coupling limit of Yang-Mills theory can be understood in terms of the dynamics of a higher-rank abelian gauge field, namely, the 3-form dual to the Chern-Simons topological current. Building on this result, we show that the field theoretical interpretation of the Chern-Simons term, as opposed to its topological interpretation, also leads to the analytic form of the confinement potential that arises in the large distance limit of $QCD$. In fact, for a $(3+1)$-dimensional generalization of the Schwinger model, we explicitly compute the interaction energy. This generalization is due to the presence of the topological gauge field $A_{μνρ}$. Our results show that the static potential profile contains a linear term leading to the confinement of static probe charges. Once the quantum effects of the axial vector anomaly in $QCD$ are taken into account, the new gauge field and its matter-current counterpart provide an exact replica of the Schwinger mechanism of "charge-screening" that operates in $QED_2$.

hep-th↗

arXiv2015

Dynamically self-regular quantum harmonic black holes

The recently proposed UV self-complete quantum gravity program is a new and very interesting way to envision Planckian/trans-Planckian physics. in this new framework, high energy scattering is dominated by the creation of micro black holes, and it is experimentally impossible to probe distances shorter than the horizon radius. In this letter we present a model which realizes this idea through the creation of self-regular quantum black holes admitting a minimal size extremal configuration. Their radius provides a dynamically generated minimal length acting as a universal short-distance cut-off. We propose a quantisation scheme for this new kind of microscopic objects based on a Bohr-like approach, which does not require a detailed knowledge of quantum gravity. The resulting black hole quantum picture resembles the energy spectrum of a quantum harmonic oscillator. The mass of the extremal configuration plays the role of zero-point energy. Large quantum number re-establish the classical black hole description. Finally, we also formulate a "quantum hoop conjecture" which is satisfied by all the mass eigen-states and sustains the existence of quantum black holes sourced by Gaussian matter distributions.

hep-th↗

arXiv2014

Semi-classical approach to quantum black holes

In this Chapter we would like to review a "~phenomenological~" approach taking into account the most fundamental feature of string theory or, more in general, of quantum gravity, whatever its origin, which is the existence of a minimal length in the space-time fabric. This length is generally identified with the Planck length, or the string length, but it could be also much longer down to the TeV region. A simple and effective way to keep track of the effects the minimal length in black hole geometries is to solve the Einstein equations with an energy momentum tensor describing non point-like matter. The immediate consequence is the absence of any curvature singularity. Where textbook solutions of the Einstein equations loose any physical meaning because of infinite tidal forces, we find a de Sitter vacuum core of high, but finite, energy density and pressure. An additional improvement regards the final stage of the black hole evaporation leading to a vanishing Hawking temperature even in the neutral, non-rotating, case. In spite of th simplicity of this model we are able to describe the final stage of the black hole evaporation, resulting in a cold remnant with a degenerate, extremal, horizon of radius of the order of the minimal length. In this chapter we shall describe only neutral, spherically symmetric, regular black holes although charged, rotating and higher dimensional black holes can be found in the literature.

gr-qc↗