arXiv subjects

Nelson R. F. Braga

Publications and source records attributed to Nelson R. F. Braga.

At least 19 recordsLinked to original sources

arXiv2026

Frame-dependency of the confinement temperature in a strongly-coupled plasma under rotation: a holographic description

Recently, it was demonstrated that the disagreement between lattice calculations and holographic models, regarding rotational effects in the quark-gluon plasma (QGP), occurs due to different choices of reference frames. While a static observer measures a confinement temperature that decreases with rotation, one in a co-rotating frame finds the opposite behavior. Both results are correct, and a comprehension of the frame-dependency of the critical temperature is a significant step in the description of the QGP under rotation. In this article, we generalize this previous holographic result by describing the plasma through the most general Myers-Perry black hole solution. This breaks the spherical symmetry present in the equal angular momentum case, considered before. As a consequence, the local temperature measured by a co-rotating observer has a non-trivial angular dependence: it can decrease, increase or even behave non-monotonically when rotational velocity increases.

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arXiv2026

Non linear Regge trajectories of quarkonia from holography

We propose a holographic model for quarkonia using the WKB approximation with the Langer correction to properly reproduce nonlinear Regge trajectories of the form $m_n^2 = β(n + c_0)^{2/3} + c_1$. This form is expected from previous studies involving the solution of Cornell potential for heavy quark-antiquark interactions using a model based on the quadratic form of the spinless Salpeter-type equation (QSSE). The model fits experimental masses with very good accuracy. The corresponding decay constants also show a reasonable agreement with the results obtained from experimental data.

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arXiv2026

Unraveling the effect of rotation on the confinement/deconfinement transition of the quark-gluon plasma

There is an apparent contradiction in the current literature about the effect of rotation in the quark-gluon plasma (QGP). While results from lattice QCD predict an increase in the confinement/deconfinement critical temperature, approximated calculations and effective models, including holographic ones, lead to the opposite result. Noncentral heavy ion collisions form QGPs with relativistic rotational velocities. Thereby, a great interest was drawn into the effect of rotation in strongly interacting matter. In this work, we show that the apparent contradiction is associated with the choices of observer considered in each case. We consider a holographic description of a rotating plasma using a Myers-Perry black hole. For a static observer, the result is that the confinement/deconfinement temperature decreases with the angular velocity, while for an observer corotating with the plasma the opposite behavior is found, in agreement with lattice calculations.

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arXiv2026

Topological charges and confined-deconfined phase transition in holography

In recent years, many interesting works providing a topological description for black hole (BH) properties have appeared in the literature. In particular, in this framework BHs correspond to topological defects in an enlarged (off-shell) parameter space, with an associated total topological charge. In gauge/gravity duality the transition from the confined to the deconfined phase is mapped into the dominance of a BH phase in the gravity side. Here we show, using a holographic AdS/QCD model, that the introduction of an energy scale in anti-de Sitter (AdS) space results in a change in the topological class. Such a modification corresponds to the existence of confined and deconfined phases, separated by a Hawking Page transition at a finite critical temperature.

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arXiv2026

Spontaneous symmetry breaking in a non-Abelian topological gauge theory

We study the spontaneous symmetry breaking mechanism in a non-Abelian topological gauge field theory, built from the twisted $\mathcal{N} = 2$ super-Yang-Mills theory in the presence of a Fujikawa-type potential. Specifically, by employing Fujikawa's Becchi-Rouet-Stora-Tyutin method, local degrees of freedom are released from the introduction of a potential in the trivial sector of equivariant cohomology. Such a potential displays a nontrivial vacuum solution, which induces the spontaneous symmetry breaking of the gauge symmetry together with the original fermionic scalar supersymmetry of the topological action. In this case, not only massive vector bosons emerge, but also fermionic fields with massive poles. This result shows that the introduction of a topological phase in non-Abelian gauge theories could provide a mechanism of mass generation for fermions with their masses correlated to the mass of Higgs gauge bosons ($m_B$). For the SSB in the topological case, three different vacuum directions are required. Otherwise, the supersymmetry could not be broken, and mass generation for fermions will not occur. Starting with a theory with symmetry $G = SU(N)$, to obtain a gauge theory at the end of the process, we must have $N \geq 3$. We study a maximal symmetry breaking of the type $SU(3) \rightarrow U(1) \times U(1)$, and obtain their fermionic propagators with mass poles $m^2_F = m^2_B = v^2$ after SSB, being $v^2 $ the energy scale introduced by the Fujikawa-type potential.

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arXiv2025

Hawking-Page transition in anti-de Sitter massive gravity with non-compact spatial boundary

In gauge/gravity duality, the Hawking Page (HP) process plays the important role of representing a confined/deconfined phase transition. For spaces that are asymptotically anti-de Sitter (AdS) with planar spatial boundary there is no HP transition, unless some infrared energy scale is introduced. Massive gravity theories have been applied in the context of holography in order to represent systems with momentum dissipation. In this work we study the HP transition for massive gravity in an asymptotically AdS space with $\mathbb{R}^n\times\, $S$^1 $ boundary. It is shown that the graviton mass term produces an HP transition at a finite critical temperature.

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arXiv2025

Holographic QCD phase diagram for a rotating plasma in the Hawking-Page approach

We investigate the combined effect of rotation and finite chemical potential in the confinement/deconfinement transition of strongly interacting matter. The holographic description consists of a five-dimensional geometry that contains a black hole (BH) in the deconfined (plasma) phase. The geometry is equipped with some cut-off that introduces an infrared energy scale. We consider two possibilities: the so-called hard wall and soft wall AdS/QCD models. The transition between the plasma and hadronic phases is represented holographically as a Hawking-Page transition between geometries with and without a black hole. The gravitational dual of the rotating plasma at finite density is given by a Reissner-Nordström (RN) charged anti-de Sitter (AdS) BH with non-zero angular momentum. This analysis provides the critical temperature of deconfinement as a function of the quark chemical potential and the plasma rotational velocity. For the case of very low temperatures, the dependence of the critical values of the chemical potential for the transition to occur at $ T \to 0 $ on the rotation is found.

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arXiv2025

Holography and the internal structure of charmonium

Holographic models that consider classical vector fields in a 5-d background provide successful effective descriptions for heavy vector meson spectra. This holds both in the vacuum and in a thermal medium, like the quark gluon plasma. However, it is somehow mysterious the way that these phenomenological models work. In particular, what is the role of the fifth dimension and what is the relation between the holographic 5-d background and the physical (4-d) heavy mesons. Hadrons, in contrast to leptons, are composite particles with some internal structure, that depends on the energy at which they are observed. In this work, a static meson is represented by a heavy quark-antiquark pair with an interaction described by a Nambu Goto string living in the same 5-d background that provides field solutions leading to masses and decay constants of charmonium states. The interaction potential that shows up is linear for large distances with a string tension consistent with the effective Cornell potential. Introducing temperature $T$ in the background it is found, for the $J/ψ$ case, that there is a deconfining transition at some critical value of $T$. The results obtained indicate that the 5-d background is effectively representing the internal structure of the (static) charmonium (quasi) states.

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arXiv2025

Holography and charmonium structure in a finite density plasma

It has recently been proposed that the extra dimension in holographic models for charmoniun is related to its internal structure. Representing the interaction between the quark anti-quark pair by a string inside the background used in these models, the linear term of the Cornell potential was obtained. More than that, the dissociation in the thermal medium is also described in a consistent way. Here we extend this study to the case of a plasma with finite density. The combined effects of density and temperature are analyzed from the point of view of quark anti-quark interaction and the results obtained are consistent with the ones derived previously using spectral functions.

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arXiv2024

Hawking-Page transition in holographic QCD at finite density

We study the confinement/deconfinement transition of QCD matter for a quark-gluon plasma at finite density using AdS/QCD duality. In order to determine the critical temperature and its dependence on the quark chemical potential, the semi-classical Hawking-Page approach is considered for a charged AdS black hole. The result obtained is consistent with the QCD phase diagram, with the critical temperature decreasing as the chemical potential increases. Using the soft wall holographic model, the value of quark density in which the phase transition occurs at zero temperature is estimated. For higher densities the QCD matter is deconfined, independent of the temperature.

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arXiv2023

Inhomogeneity of a rotating quark-gluon plasma from holography

Rotation affects the transition temperature between confined (hadronic) and deconfined (quark-gluon plasma) phases of the strongly interacting matter produced in non-central heavy ion collisions. A holographic description of this effect was presented recently, considering an AdS black hole with cylindrical symmetry in rotation. Here we extend this approach in order to analyse the more realistic case of strongly interacting matter that, rather than living in a cylindrical shell, spreads over a region around the rotational axis. In this case, the confined and deconfined phases may coexist. The holographic description of the plasma behaviour under rotation is shown to be consistent with the concept of local temperature for rotating frames developed by Tolman and Ehrenfest.

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arXiv2023

Configuration entropy of a rotating quark-gluon plasma from holography

The configuration entropy (CE) provides a measure of the stability of physical systems that are spatially localized. An increase in the CE is associated with an increase in the instability of the system. In this work we apply a recently developed holographic description of a rotating plasma, in order to investigate the behaviour of the CE when the plasma has angular momentum. Considering the holographic dual to the plasma, namely a rotating AdS black hole, the CE is computed at different rotational speeds and temperatures. The result obtained shows not only an increase with the rotational speed $ v$ but, in particular, a divergence of the CE as $v$ approaches the speed of light: $\, v \to 1 $. We discuss the results obtained showing that they are consistent with the change in the geometry of the black hole caused by the rotation and the corresponding variation of the volume of the dual plasma. We also connect the results found here with those obtained in a recent work, where it was shown that the complete dissociation of heavy mesons in a plasma is represented by a positive singularity in the CE.

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arXiv2023

Bottomonium Dissociation in a Rotating Plasma

Heavy vector mesons provide important information about the quark gluon plasma (QGP) formed in heavy ion collisions. This happens because the fraction of quarkonium states that are produced depends on the properties of the medium. The intensity of the dissociation process in a plasma is affected by the temperature, the chemical potential and the presence of magnetic fields. These effects have been studied by many authors in the recent years. Another important factor that can affect the dissociation of heavy mesons, and still lacks of a better understanding, is the rotation of the plasma. Non central collisions form a plasma with angular momentum. Here we use a holographic model to investigate the thermal spectrum of bottomonium quasi-states in a rotating medium in order to describe how a non vanishing angular velocity affects the dissociation process.

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arXiv2022

Configuration entropy and stability of bottomonium radial excitations in a plasma with magnetic fields

Heavy vector mesons produced in a heavy ion collision are important sources of information about the quark gluon plasma (QGP). For instance, the fraction of bottomonium states observed in such a collision is altered by the dissociation effect caused by the plasma. So, it is very important to understand how the properties of the plasma, like temperature $(T)$, density and the presence of background magnetic fields $(eB)$, affect the dissociation of bottomonium in the thermal medium. AdS/QCD holographic models provide a tool for investigating the properties of heavy mesons inside a thermal medium. The meson states are represented by quasinormal modes in a black hole geometry. In this work we calculate the quasinormal modes and the associated complex frequencies for the four lowest levels of radial excitation of bottomonium inside a plasma with a magnetic field background. We also calculate the differential configuration entropy (DCE) for all these states and investigate how the dissociation effect produced by the magnetic field is translated into a dependence of the DCE on $eB$. An interesting result obtained in this study is that the DCE increases with the radial excitation level $n$. Also, a nontrivial finding of this work is that the energy density associated with the bottomonium quasinormal modes presents a singularity near the black hole horizon for some combination of values of $T, eB$ and $n$. As we show here, it is possible to separate the singular factor and define a square integrable quantity that provides a DCE that is always finite. In addition, we discovered that, working with the potentially singular energy density, one finds a very interesting way to use the DCE as a tool for determining the dissociation temperature of the meson quasisates.

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arXiv2022

Confinement/Deconfinement temperature for a rotating quark-gluon plasma

Non-central heavy ion collisions lead to the production of a quark gluon plasma with angular momentum. We investigate, using holographic AdS/QCD models, how does rotation of the medium affects the confinement/deconfinement transition temperature $T_c$. In holographic models, this transition is represented by a Hawking-Page process involving two asymptotically anti-de Sitter spaces. The plasma is represented here by extending the holographic approach to anti-de Sitter spaces with cylindrical symmetry. Then, the rotation of the medium is introduced through a Lorentz boost. We consider hard and soft wall AdS/QCD models. In both cases we find it out that, as the rotational velocity $v$ increases, $T_c$ decreases, following the expression $T_c(v) = T_c(0)/γ(v)$, where $γ(v)$ is the Lorentz factor.

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arXiv2022

Melting of heavy vector mesons and quasinormal modes in a finite density plasma from holography

In this work, we investigate the melting of charmonium states within a holographic QCD model in the context of Einstein-Maxwell-Dilaton (EMD) theory. In the dual field theory, the model describes the heavy mesons inside a finite temperature and density medium. First, we calculate the spectrum at zero temperature. Then, at finite temperature, we obtain the spectral functions, where the heavy vector meson are represented by peaks. We show that the charmonium melts down at temperatures above the confinement/deconfinement temperature of the quark-gluon plasma. We also observe that the chemical potential speeds up the melting process. This finding is in agreement with results previously reported in the literature. In the gravitational side of the theory, we solve the perturbation equations in the hydrodynamics limit. From this result, we read off the diffusion coefficient by comparing the dispersion relation against the corresponding result obtained in the dual field theory. We also investigate the behavior of the diffusion coefficient as a function of the temperature. The perturbation equations are solved numerically, in order to get the quasinormal frequencies. We report the emergence of a new mode whose real part increases rapidly at a certain value of the chemical potential while its imaginary part decreases with the increasing of the chemical potential. Finally, by comparing against results obtained in the conformal plasma, we observe that the real part of the frequency increases, while the imaginary part decreases when we consider the non-conformal plasma.

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arXiv2021

Configuration entropy in the soft wall AdS/QCD model and the Wien law

The soft wall AdS/QCD holographic model provides simple estimates for the spectra of light mesons and glueballs satisfying linear Regge trajectories. It is also an interesting tool to represent the confinement/deconfinement transition of a gauge theory, that is pictured as a Hawking-Page transition from a dual geometry with no horizon to a black hole space. A very interesting tool to analyze stability of general physical systems that are localized in space is the configuration (or complexity) entropy (CE). This quantity, inspired in Shannon information entropy, is defined in terms of the energy density of the system in momentum space. The purpose of this work is to use the CE to investigate the stability of the soft wall background as a function of the temperature. A nontrivial aspect is that the geometry is an anti-de Sitter black hole, that has a singular energy density. In order to make it possible to calculate the CE, we first propose a regularized form for the black hole energy density. Then, calculating the CE, it is observed that its behavior is consistently related to the black hole instability in anti-de Sitter space. Another interesting result that emerges from this analysis is that the regularized energy density shows a behavior similar to the Wien law, satisfied by black body radiation. That means: the momentum $ k_{max} $ where the energy density is maximum, varies with the temperature $T$ obeying the relation: $ T / k_{max} = constant $ in the deconfined phase.

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arXiv2021

Configuration entropy and confinement/deconfinement transiton in holographic QCD

In the holographic AdS/QCD approach, the confinement/deconfinement transition is associated with the Hawking-Page transition of a thermal anti-de Sitter (AdS) space to an AdS black hole. In the case of the hard wall model, the thermal transition takes place in the planar AdS thanks to the introduction of an infrared cut-off in the geometry. The corresponding thermodynamic entropy of the $SU(N) $ gauge theory jumps from proportional to $N^0$ in the confined hadronic phase to proportional to $N^2$ in the plasma phase, corresponding to the presence of the color degrees of freedom. The Hawking-Page transition is understood by considering a semiclassical picture of a system consisting of two different geometries that are asymptotically AdS. One is the AdS black hole and the other the thermal AdS space. The relative stability between these competing geometries varies with the temperature. So, the transition is essentially a problem of stability. An interesting tool to study stability of physical systems is the configuration entropy (CE), inspired in the Shannon informational entropy. In this work we investigate the CE for the case of the AdS/QCD hard wall model at finite temperature. We propose a regularized form for the energy densities of the black hole (BH) and of the thermal AdS geometries that makes it possible to calculate their CEs as a function of the temperature. We find a relation between stability and the value of the CE for the system of asymptotically AdS geometries. Remarkably, it is found that the CE is proportional to $\log(T)$, where $T$ is the temperature. This result makes it possible to write out a simple relation between the configuration and the thermodynamic entropies.

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