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Alfredo Vega

Publications and source records attributed to Alfredo Vega.

At least 19 recordsLinked to original sources
arXiv2026

Thermodynamics of the Isospectral family of holographic vector mesons

We study the thermal behavior of the $ρ$ meson using the isospectral family of the softwall AdS/QCD model. By computing spectral functions at finite temperature and chemical potential for different members of this family, we isolate the effect of the ground-state electromagnetic decay constant $f_1$ on the melting temperature $T_m$ of the $ρ(770)$ meson. A clear monotonic increase of $T_m$ with $f_1$ is found, supporting the interpretation of $f_1$ as a key scale controlling quarkonium dissociation. For excited states, the same qualitative trend appears but is strongly suppressed as the radial quantum number increases. Using the isospectral parameter to fix $f_1$ to its experimental value ($226$ MeV) yields a holographic model whose spectral function gives a melting temperature $T_m = 157$ MeV and a smooth crossover from confinement to deconfinement. The thermal mass shows a mild decrease near the critical point, while the width grows monotonically. Our results demonstrate that the isospectral transformation provides a controlled way to adjust ground-state decay constants without altering the mass spectrum, enabling precise studies of medium effects on vector mesons.

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arXiv2026

Confining potential in holographic bottom-up QCD from WKB

By using the \emph{Rydberg--Klein--Rees} (RKR) formulas to solve the inverse Schrödinger problem, we found a confining bottom-up potential from a given eigenvalue spectrum. To illustrate this methodology, we consider the vector meson spectrum derived in the D3/D7 system as input data to derive the corresponding bottom-up confining potential that resembles the geometric structure of the so-called hardwall model. We compute some properties for this new bottom-up model, including the thermal deconfinement phase transition, the $ρ$ radial Regge trajectory, and the configurational entropy.

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arXiv2025

Holographic quark masses and radiative decays of heavy vector mesons

Holographic models of QCD provide the spectrum of heavy vector meson masses and electromagnetic decay constants through bulk computations of the current-current correlation function. Conversely, the phenomenology of heavy vector mesons is articulated by the constituent heavy quark model utilizing a non-relativistic approximation. By applying the Segre formula from non-relativistic quantum mechanics, we derive new observables from holography: the constituent quark mass, the three-photon decay width, the effective fine structure constant of the strong interaction, and the mixed one-photon and two-gluon decay width. We also derive the three-gluon decay width, the three-photon decay width, and the mixed one-photon and two-gluon decay width for the radially excited states of heavy quarkonia and compare them with available experimental data. The present results reveal a new paradigm of meson spectroscopy in AdS/QCD.

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arXiv2025

Engineering Confining Dilatons: A WKB Inverse Problem in Holographic QCD

This work presents a WKB-based inverse problem approach within the framework of holographic bottom-up QCD to engineer confining dilatons from hadronic mass spectra. Starting from a general parameterization of nonlinear radial Regge trajectories, $M_n^2=a(n+b)^ν$, we apply the Rydberg-Klein-Rees (RKR) formula to derive the large-z behavior of the corresponding holographic confining potential. This potential is inversely related to the dilaton field profile, leading naturally to a non-quadratic dilaton $Φ(z)=(κ\,z)^{2-α}$, where the parameters ($κ$, $α$) are uniquely determined by the spectral parameters ($a$,$ν$). We successfully test this method by fitting the spectra of heavy quarkonia ($c\bar{c}$ and $b\bar{b}$), achieving good agreement with experimental data. Furthermore, we extend this formalism to describe the spectroscopy of tetraquark states by superimposing an additional potential term, derived from the Bethe-Salpeter equation for diquarks, onto the standard mesonic confining potential. This work establishes a powerful and flexible bottom-up framework for deriving confinement directly from spectral data, applicable to both conventional and exotic hadrons.

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arXiv2025

Quantization Rules in Holographic QCD Models

In this paper, we investigate quasinormal modes in holographic QCD models from the perspective of the WKB approximation. We derive the generalized Bohr Sommerfeld quantization rules for quasi-stationary states in holographic QCD models. As a simple application of these formulas, we compute the quasinormal modes of scalar and vector fields in the soft wall model, where an analytic expression for the real part of the frequency can be found in the low temperature regime. Additionally, this study provides useful insights into the dissociation process in holographic QCD models.

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arXiv2024

Isospectrality and configurational entropy as testing tools for bottom-up AdS/QCD

This work discusses the connection between isospectrality and configurational entropy in holographic bottom-up models. We analyze the effect of monoparametric isospectral transformation in holographic decay constants and configurational entropy for a set of softwall-like models at zero temperature. We conclude that the isospectral parameter $λ$ defines a window of possible holographic models suitable to describe spectroscopy.

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arXiv2024

Holographic stability for non-$q\bar{q}$ candidates

In the context of bottom-up AdS/QCD models, we discuss how the configurational entropy can describe heavy non-$q\,\bar{q}$ states. Using the non-quadratic softwall model, introduced to describe non-linear Regge trajectories, we parametrize different multiquark and exotic meson structures to describe $Z_c$, $ψ$, and $Z_b$ states as non-$q\,\bar{q}$ hadrons in terms of stability. We found that $Z_c$ is better described as a hybrid meson with one gluon tube, $ψ$ as hadrocharmonium, and $Z_b$ as hadronic molecule.

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arXiv2022

A holographic bottom-up description of light nuclide spectroscopy and stability

This work explores a holographic proposal to describe light nuclide spectroscopy by considering extensions to the well-known bottom-up AdS/QCD proposals, the hardwall and softwall models. We also propose an alternative description inspired by the Woods-Saxon potential. We find the static dilaton associated with this potential in this Wood-Saxon-like model. We compute the nuclide spectra finding that, despite their pure AdS/QCD origin, hardwall and softwall, as monoparametric models, have good accuracy and precision since the RMS error is near 11 $\%$ and 4 $\%$ respectively. In the case of the Wood-Saxon model, the RMS was around 1 $\%$. We also discuss configurational entropy as a tool to categorize which model is suitable to describe nuclides in terms of stability. We found that configurational entropy resembles a stability line, independent from nuclear spin, for symmetric light nuclides when considering softwall and Wood-Saxon-like models. For the hardwall case, configurational entropy, despite increasing with the constituent number, depends on the nuclear spin. Thus, the Woods-Saxon-like model emerges as the best choice to describe light nuclide spectroscopy in the bottom-up scenario.

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arXiv2022

Fermionic DIS from a deformed string/gauge correspondence model

From a deformed AdS$_5$ space, we used the string/gauge duality to study the deep inelastic scattering for unpolarized fermions with spin 1/2, considering the large Bjorken $x$ parameter regime. Here, we also took into account an anomalous dimension of an operator which represents fermions at the boundary. From this analysis, we compute the corresponding structure functions, which are dependent on $x$ and on the photon virtuality $q$. The results achieved are in agreement with the experimental data.

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arXiv2022

Drag Force in the Vacuum of Confining Gauge Theories

The complete absence of isolated quarks reaching particle detectors after high energy collisions suggests that some physical mechanism generates resistance to their propagation in the vacuum. In order to reveal such a mechanism, we analyze the fate of an infinitely heavy quark that is initially propagating in the vacuum with inertial motion. The non-perturbative structure of the vacuum is treated here using the gauge/ gravity correspondence, the isolated quark on the boundary gauge theory is dual to a trailing string moving in the bulk of a higher dimensional curved space. We find that, for a large class of non-conformal gauge theories with a holographic dual, the geometrical structure of the bulk geometry induces a drag force on the quark that moves in the vacuum. In addition, we show that for these gauge theories there will be the presence of such a drag force due to its vacuum whenever the dual bulk geometry generates a linear potential for a $q\bar{q}$ pair. The relation of the linear $q\bar{q}$ potential with the drag force on the isolated quark is a holographic piece of evidence that both phenomena are different manifestations of the confinement of quarks.

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arXiv2022

Pion form factor from an AdS deformed background

We consider a bottom-up AdS/QCD model with a conformal exponential deformation $e^{k\,z^2}$ on a Lorentz invariant AdS background. In this model, we assume the conformal dimension associated with the operator that creates pions at the boundary as $Δ=3$. Regarding the infrared scale related to photon field $k_γ$, we analyze two cases: constant and depending on the transferred momentum $q$. In these two cases, we computed the electromagnetic pion form factor as well as the pion radius. We compare our results with experimental data as well as other theoretical (holographic and non-holographic) models. In particular, for the momentum-dependent infrared scale, we find good agreement with the available experimental data as well as non-holographic models.

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arXiv2022

Holographic Confinement of the Solitary Quark

Single quarks moving in the vacuum of confining gauge theories are stopped by a drag force. The holographic description relates the confining scale in the bulk geometry with a range of physical values for the drag force in the vacuum. The vacuum drag force acting on the isolated quark directly manifests quark confinement since it prevents the quark from walking freely in the vacuum. However, analytical expressions for the drag force as a function of the quark velocity were lacking. In the present work, we propose that the vacuum drag force is given by the regularized zero-temperature limit of the corresponding thermal drag force. Within this approach, we obtain the desired analytic expressions in two different holographic models: the quadratic dilaton and the D-instanton. In both cases, we find well-behaved functions belonging to their physical range of values.

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arXiv2021

Proton and neutron form factors from deformed gravity/gauge duality

In this work, we study the electric and magnetic Sachs form factors for proton and neutron by using a deformed gravity/gauge model. We describe holographically baryons as well as gauge bosons which are ruled by the parameters $k_{B}$ and $k_γ$, associated with confinement and kinematical energy scales, respectively. Then, we construct the interaction action and calculate the electric and magnetic form factors for the proton and the neutron, and their electromagnetic sizes. The obtained results are compatible with those found in the literature from experimental and theoretical data.

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arXiv2021

Heavy quarkonia spectroscopy at zero and finite temperature in bottom-up AdS/QCD

S-wave states of charmonium and bottomonium are described using bottom-up AdS/QCD. We propose a holographic model that unifies the description of masses and decay constants, leading to a precise match with experimental data on heavy quarkonia. Finite temperature effects are considered by calculating the current-current spectral functions of heavy vector mesons. The identification of quasi-particle states as Breit-Wigner resonances in the holographic spectral function was made. We develop a prescription to subtract background contributions from the spectral function to isolate the Breit-Wigner peak. The quasi-particle holographic thermal evolution is described, allowing us to estimate the melting temperature for vector charmonia and bottomonia. Our holographic model predicts that $J/Ψ$ melts at $415$ MeV $(\sim 2.92 ~T_c)$ and $Υ$ melts at $465$ MeV $(\sim 3.27~ T_c)$)

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arXiv2020

Proton Structure Functions from an AdS/QCD model with a deformed background

In this work we study unpolarized spin $1/2$ baryonic deep inelastic scattering (DIS) in the regime of large Bjorken parameter $x$. We calculate the corresponding structure functions $F_{1,2}(x,q^2)$. Our approach is based on an AdS/QCD model with a deformed background, where we consider an exponential factor in the AdS$_5$ metric. Such a deformation implies the introduction of an anomalous dimension in the model. Our results for the structure functions are consistent with those found in the literature from experimental data.

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arXiv2020

Non-linear Regge trajectories with AdS/QCD

In this work, we consider a non-quadratic dilaton $Φ(z)=(κ\,z)^{2-α}$ in the context of the static soft wall model to describe the mass spectrum of a wide range of vector mesons from the light up to the heavy sectors. The effect of this non-quadratic approach is translated into non-linear Regge trajectories with the generic form $M^2=a\,(n+b)^ν$. We apply this sort of fits for the isovector states of $ω$, $ϕ$, $J/ψ$ and $Υ$ mesons and compare with the corresponding holographic duals. We also extend these ideas to the heavy-light sector by using the isovector set of parameters to extrapolate the proper values of $κ$ and $α$ through the average constituent mass $\bar{m}$ for each mesonic specie considered. In the same direction, we address the description of possible non-$q\,\bar{q}$ candidates using $\bar{m}$ as a holographic threshold, associated with the structure of the exotic state, to define the values of $κ$ and $α$. We study the $π_1$ mesons in the light sector, and the $Z_c$, $Y$ and $Z_b$ mesons in the heavy sector as possible exotic vector states. Finally, the RMS error for describing these twenty-seven states with fifteen parameters (four values for $κ$ and $α$ respectively and seven values for $\bar{m}$) is $12.61\%$.

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arXiv2020

Light Pseudoscalar and Axial Spectroscopy using AdS/QCD Modified Soft Wall Model

We study light pseudoscalar and axial states using a soft wall model that is modified by introducing two extra parameters: an UV-cutoff and an anomalous term in the conformal dimension of the fields involved such that meson fields with different parities are easily distinguishable. We find that 23 of these light mesonic states, including the scalars and vector states analyzed with one of our previous results, are fitted within the RMS error bounds given for this model, whose parameters are given by the quadratic dilaton profile, the UV locus $z_{0}$ and the anomalous term $Δ_{P}$. Our results show that Regge trajectories for pseudoscalar and axial mesons are linear in the radial quantum number $n$, as expected for these sort of regular $q\overline{q}$ mesons.

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