arXiv subjects

Fernando S. Navarra

Publications and source records attributed to Fernando S. Navarra.

At least 19 recordsLinked to original sources

arXiv2026

Probing the $G(3900)$ State in Heavy-Ion Collisions

We investigate the interactions of the recently confirmed exotic hadron $G(3900)$ with the hadronic medium composed of light mesons produced in heavy-ion collisions. Using an effective Lagrangian approach, we compute both vacuum and thermally averaged cross sections for processes such as $G(3900) + \pi \to D^{(\ast)} + \bar{D}^{(\ast)}$ and their inverse reactions. Following recent proposals, the $G(3900)$ is interpreted as a $P$-wave $D\bar{D}^*/D^*\bar{D}$ molecular state. The resulting thermally averaged cross sections are employed in a rate equation to determine the time evolution of the $G(3900)$ multiplicity, with initial conditions provided by statistical and coalescence hadronization models. We compute the number of $G(3900)$'s produced in central Pb-Pb collisions at $\sqrt{s_{NN}} = 5.02$ TeV and compare it with the number of produced $Z_c(3900)$'s . We obtain a considerably smaller final yield of $G(3900)$ compared to $Z_c(3900)$.

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arXiv2024

Studying the nature of the lightest charmed axial mesons via femtoscopy

In this work we discuss how femtoscopic analysis can shed light on the nature of the two lightest axial charmed mesons, denominated as $D_1(2430)$ and $D_1(2420)$, whose masses are similar but widths are different. Their properties are reasonably described taking into account meson-meson coupled channel dynamics and a bare quark-model pole constituting the lowest-order amplitudes. Two different bare quark-model states are used in order to accommodate the different scattering lengths coming from the lattice QCD calculations for the $Dπ$ and $D^*π$ systems and the data from the ALICE Collaboration on the $Dπ$ system. The amplitudes are employed as inputs to determine the correlation functions for the $D^{*}π$ and $Dρ$ channels and identify the signatures associated with the lowest-lying axial charmed mesons.

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arXiv2022

Multiplicity of the doubly charmed state $T_{cc} ^+$ in heavy-ion collisions

We study the evolution of the doubly charmed state $T_{cc}^+$ in a hot hadron gas produced in the late stage of heavy-ion collisions. We use effective Lagrangians to calculate the thermally averaged cross sections of $T_{cc}^+$ production in reactions such as $ D^{(*)} D^{(*)} \rightarrow T_{cc}^+ π, T_{cc}^+ ρ$ and its absorption in the corresponding inverse processes. We then solve the rate equation to follow the time evolution of the $T_{cc}^+$ multiplicity, and determine how it is affected by the considered reactions during the expansion of the hadronic matter. We compare the evolution of the $T_{cc}^+$ abundance treated as a hadronic $S$-wave molecule and as a tetraquark state. Our results show that the tetraquark yield increases by a factor of about 2 at freeze-out, but it is still one order of magnitude smaller than the final yield of molecules formed from hadron coalescence. Also, the results indicate that $N_{T_{cc}}$ is more affected by interactions with hadronic medium than $ N_{X(3872)} $ in similar conditions. We also show that yields depend very weakly on the system size, represented by $\mathcal{N} = \left[ d N_{ch} / d η(η< 0.5)\right]^{1/3}$.

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arXiv2019

QCD Sum Rules Approach to the $X,~Y$ and $Z$ States

In the past decade, due to the experimental observation of many charmonium-like states, there has been a revival of hadron spectroscopy. In particular, the experimental observation of charged charmonium-like, $Z_c$ states, and bottomonium-like, $Z_b$ states, represents a challenge since they can not be accommodated within the naive quark model. These charged states are good candidates of either tetraquark or molecular states and their observation motivated a vigorous theoretical activity. This is a rapidly evolving field with enormous amount of new experimental information. In this work, we review the current experimental progress and investigate various theoretical interpretations of these candidates of the multiquark states. The present review is written from the perspective of the QCD sum rules approach, where we present the main steps of concrete calculations and compare the results with other approaches and with experimental data.

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arXiv2018

Supersymmetry in the Double-Heavy Hadronic Spectrum

Relativistic light-front bound-state equations for double-heavy mesons, baryons and tetraquarks are constructed in the framework of supersymmetric light front holographic QCD. Although heavy quark masses strongly break conformal symmetry, supersymmetry and the holographic embedding of semiclassical light-front dynamics still holds. The theory, derived from five-dimensional anti-de Sitter space, predicts that the form of the confining potential in the light-front Hamiltonian is harmonic even for heavy quarks. Therefore, the basic underlying supersymmetric mechanism, which transforms meson-baryon and baryon-tetraquark wave functions into each other, can also be applied to the double-heavy sector; one can then successfully relate the masses of the double-heavy mesons to double-heavy baryons and tetraquarks. The dependence of the confining potential on the hadron mass scale agrees completely with the one derived in heavy light systems from heavy quark symmetry. We also make predictions for higher excitations of the charmonium and bottomonium states. In particular, the remarkable equality of the Regge slopes in the orbital angular momentum, $L$, and the principal quantum number, $n$, is predicted to remain valid.

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arXiv2015

Strangeness At Extremes

We study the properties of strange mesons in vacuum and in the hot nuclear medium within unitarized coupled-channel effective theories. We determine transition probabilities, cross sections and scattering lengths for strange mesons. These scattering observables are of fundamental importance for understanding the dynamics of strangeness production and propagation in heavy-ion collisions.

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arXiv2014

Factorization breaking of four-quark condensates in the Nambu Jona Lasinio model

We investigate the factorization hypothesis of the four-quark condensate $\langle q \bar{q} q \bar{q} \rangle = \, A \, \langle q \bar{q} \rangle^2$ with the help of the Nambu Jona-Lasinio Model supplemented with eighth order interactions. For that purpose we use the bosonization method with multiple auxiliary variables. We find that in a simplified U(1) version of the model factorization holds, whereas in the full SU(3)-flavor version of the model factorization is broken by terms which are related to the 't Hooft interactions.

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arXiv2014

Charged Exotic Charmonium States

In this short review we present and discuss all the experimental information about the charged exotic charmonium states, which have been observed over the last five years. We try to understand their properties such as masses and decay widths with QCD sum rules. We describe this method, show the results and compare them with the experimental data and with other theoretical approaches.

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arXiv2010

Investigating different structures for the $X(3872)$

Using the QCD spectral sum rule approach we investigate different currents with $J^{PC}=1^{++}$, which could be associated with the $X(3872)$ meson. Our results indicate that, with a four-quark or molecular structure, it is very difficult to explain the narrow width of the state unless the quarks have a special color configuration.

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arXiv2010

New Charmonium States in QCD Sum Rules: a Concise Review

In the past years there has been a revival of hadron spectroscopy. Many interesting new hadron states were discovered experimentally, some of which do not fit easily into the quark model. This situation motivated a vigorous theoretical activity. This is a rapidly evolving field with enormous amount of new experimental information. In the present report we include and discuss data which were released very recently. The present review is the first one written from the perspective of QCD sum rules (QCDSR), where we present the main steps of concrete calculations and compare the results with other approaches and with experimental data.

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arXiv2008

QCD sum rules study of the meson Z^+(4430)

We use QCD sum rules to study the recently observed meson $Z^+(4430)$, considered as a $D^*D_1$ molecule with $J^{P}=0^{-}$. We consider the contributions of condensates up to dimension eight and work at leading order in $α_s$. We get $m_Z=(4.40\pm0.10) \GeV$ in a very good agreement with the experimental value. We also make predictions for the analogous mesons $Z_{s}$ and $Z_{bb}$ considered as $D_s^*D_1$ and $B^*B_1$ molecules respectively. For $Z_{s}$ we predict $m_{Z_{s}}= (4.70\pm 0.06) {\rm GeV}$, which is above the $D_s^*D_1$ threshold, indicating that it is probably a very broad state and, therefore, difficult to be experimentally seen. For $Z_{bb}$ we predict $m_{Z_{bb}}= (10.74\pm 0.12) {\rm GeV}$, in agreement with quark model predictions.

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arXiv2007

QCD sum rules study of $QQ-\bar{u}\bar{d}$ mesons

We use QCD sum rules to study the possible existence of $QQ-\bar{u}\bar{d}$ mesons, assumed to be a state with $J^{P}=1^{+}$. For definiteness, we work with a current with an axial heavy diquark and a scalar light antidiquark, at leading order in $α_s$. We consider the contributions of condensates up to dimension eight. For the $b$-quark, we predict $M_{T_{bb}}= (10.2\pm 0.3) {\rm GeV}$, which is below the $\bar{B}\bar{B}^*$ threshold. For the $c$-quark, we predict $M_{T_{cc}}= (4.0\pm 0.2) {\rm GeV}$, in agreement with quark model predictions.

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arXiv2005

Can the meson cloud explain the nucleon strangeness?

We use the meson cloud model, including the kaon and the $K^*$ contributions, to estimate the electric and magnetic strange form factors of the nucleon. We compare our results with the recent measurements of the strange quark contribution to parity-violating asymmetries in the forward G0 electron-proton scattering experiment. We conclude that it is not possible to explain the data using this model.

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arXiv2004

QCD sum rule approach for the light scalar mesons as four-quark states

We study the two point-function for the scalar mesons $σ, κ, f_0(980)$ and $a_0(980)$ as diquak-antidiquark states. We also study the decays of these mesons into $ππ$, $Kπ$ and $K\bar{K}$. We found that the couplings are consistent with existing experimental data, pointing in favor of the four-quark structure for the light scalar mesons.

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arXiv2003

The structure of $f_0(980)$ from charmed mesons decays

We use the QCD sum rules to evaluate the form factors associated with the semileptonic decays of $D_s$ and $D$ mesons into $f_0(980)$. We consider the $f_0(980)$ meson as a quark-antiquark state with a mixture of strange and light components. The decay rates are evaluated in terms of the mixing angle. Using the same form factors to evaluate nonleptonic decays in the framework of the factorization approximation we conclude that the importance of the light quarks in $f_0(980)$ is not negligible.

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arXiv2003

$J/ψ$ dissociation by pions in QCD

We compute the $J/ψπ\to {charmed mesons}$ cross section using QCD sum rules. This cross section is important to distinguish the suppression in the production of $J/ψ$ through the dissociation by comoving pions and through the formation of quark-gluon plasma. Our sum rules for the $J/ψπ\to \bar{D} D^*$, $D \bar{D}^*$, ${\bar D}^* D^*$ and ${\bar D} D$ hadronic matrix elements are constructed by using vaccum-pion correlation functions, and we work up to twist-4 in the soft-pion limit. After doing a thermal average we get $<σ^{πJ/ψ} v>\sim 0.2 - 0.4$ mb at $T=150\MeV$

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arXiv2002

Progress in the determination of the $J/ψ-π$ cross section

Improving previous calculations, we compute the $J/ψπ\to {charmed mesons}$ cross section using QCD sum rules. Our sum rules for the $J/ψπ\to \bar{D} D^*$, $D \bar{D}^*$, ${\bar D}^* D^*$ and ${\bar D} D$ hadronic matrix elements are constructed by using vaccum-pion correlation functions, and we work up to twist-4 in the soft-pion limit. Our results suggest that, using meson exchange models is perfectly acceptable, provided that they include form factors and that they respect chiral symmetry. After doing a thermal average we get $<σ^{πJ/ψ} v>\sim 0.3$ mb at $T=150\MeV$.

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arXiv2001

Space-time evolution of the \lap model: classical and quantum aspects

A time dependent variational approach is used to derive the equations of motion for the λϕ^4 model. The simultaneous evolution of the quantum fluctuations and of the classical part of the field is considered in a lattice of 1+1 dimensions. Different initial conditions corresponding to non equilibrium situations are considered and evolved in time. Such high energy localized configurations expand in the lattice by ``bumps'' which may change with time. The quantum fluctuations make the peaks be smoother and the expansion faster.

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