arXiv subjects

F. Fernandez

Publications and source records attributed to F. Fernandez.

At least 19 recordsLinked to original sources

arXiv2026

Exploring $T_{\Upsilon\Upsilon}$ tetraquark candidates in a coupled-channels formalism

We investigate the spectrum of $T_{\Upsilon\Upsilon}$ tetraquark candidates within a coupled-channels framework. The analysis includes all $L\leq2$ combinations of $\Upsilon(1S)$, $\Upsilon(2S)$, $\eta_b(1S)$, and $\eta_b(2S)$ in the $J^P = 0^\pm, 1^\pm, 2^\pm$ sectors. The meson-meson interaction is derived from an underlying constituent quark model through the resonating group method, and the properties of the states are obtained from poles of the scattering matrix. We find a rich spectrum of resonant, and virtual, states distributed between the $\eta_b(1S)\eta_b(1S)$ and $\Upsilon(2S)\Upsilon(2S)$ thresholds. The pattern of poles exhibits approximate heavy-quark spin symmetry multiplets. Several states are dominated by a single channel and can be associated with threshold-driven structures, while higher-mass resonances show sizable mixing among channels involving radially excited bottomonia. The predicted widths range from tens to several hundred MeV. Branching ratios indicate that many states couple predominantly to final states with at least one excited bottomonium, whereas only a subset of the spectrum is expected to be visible in the $\eta_b(1S)\eta_b(1S)$, $\eta_b(1S)\Upsilon(1S)$ and $\Upsilon(1S)\Upsilon(1S)$ channels. These results provide quantitative guidance for experimental searches of fully heavy tetraquarks and offer a test of coupled-channel dynamics and heavy-quark spin symmetry in the $bb\bar b\bar b$ sector.

hep-ph↗

arXiv2024

Revisiting the proton-antiproton scattering using a constituent-quark-model based coupled-channels calculation

Motivated by the last experimental and theoretical advances in the analysis of possible baryonium resonances, the $X(1835)$ and their partners, we perform a constituent-quark-model based coupled-channels calculation of the proton-antiproton scattering in order to analyze the possible existence of bound states or near-threshold structures. The used $N\overline N$ potential is derived from a $G$-parity transformation of the quark-model-based $NN$ interaction which has described well deuteron properties, $NN$ phase shifts, and even hadron-hadron phenomenology. The additional $N\overline N$ annihilation is taken into account by a complex phenomenological potential whose real part is generated by one-pion and one-gluon exchange annihilation potentials and its imaginary part is an energy-independent potential of Gaussian form. Then, all the parameters of the interaction are constrained by the $NN$ sector except those determining the imaginary part of the annihilation potential. Our study concludes that the nucleon-antinucleon dynamics is complex and rich in scattering singularities near the proton-antiproton and neutron-antineutron thresholds.

hep-ph↗

arXiv2024

Exploring doubly-heavy tetraquarks in constituent-quark-model based meson-meson coupled-channels approach

The LHCb Collaboration announced in 2021 the discovery of a new tetraquark-like state, named $T_{cc}^+$, with minimum quark content $cc\bar u\bar d$, close to the $D^0D^{*+}$ threshold. This has motivated countless theoretical works trying to identify the dynamics which is responsible of the formation of such state; in particular, the one performed by us in Ref. \cite{Ortega:2022efc}, where a $D^0D^{*+}$ molecular candidate whose mass, width, scattering length and effective ranges are in reasonable agreement with experimental measurements. We explore herein the possibility of having $T_{cc}^+$ partners in all doubly-heavy tetraquark sectors, considering doubly represented light antiquarks $u$, $d$ or $s$, and taking into account all possible spin-parity quantum numbers. The computation is done using a constituent-quark-model based meson-meson coupled-channels framework which has been tested many times in the last fifteen years describing conventional heavy mesons and baryons, their coupling with hadron-hadron thresholds but also in exploring its application to compact multiquark structures. The advantage of using an approach with such a relatively large history is that it allows us to make predictions because all the parameters have already been constrained from our previous works. Then, from this perspective, we present a parameter-free model-dependent prediction of doubly-heavy tetraquarks that may be partners of the discovered $T_{cc}^+$ state.

hep-ph↗

arXiv2023

Solar Radio Imaging at Arecibo: The Brightness Temperature and Magnetic Field of Active Regions

Strong solar magnetic fields are the energy source of intense flares and energetic coronal mass ejections of space weather importance. The key issue is the difficulty in predicting the occurrence time and location of strong solar eruptions, those leading to high impact space weather disturbances at the near-Earth environment. Here, we report regular solar mapping made at X-band (8.1 -- 9.2 GHz) with the Arecibo 12-m radio telescope. This has demonstrated its potential for identifying active regions, about one half to a day in advance, when they rotate on to the central meridian of the Sun, and predicting the strongest flares and coronal mass ejections directed towards the Earth. Results show (i) a good correlation between the temporal evolution of brightness temperature of active regions and their magnetic configurations; (ii) the ability of the mapping data to provide a better picture of the formation sites of active regions and to accurately track their evolution across the solar disk, giving forewarning of intense solar eruptions leading to severe space weather consequences; (iii) the importance of long-term monitoring of the Sun at X-band for understanding the complex three-dimensional evolution of solar features as a function of solar activity. The key point in this study is the identification of the magnetic properties of active regions on the solar disk to aid in improving forecast strategies for extreme space-weather events.

astro-ph.SR↗

arXiv2023

Unraveling the nature of the novel $\mathbf{T_{cs}}$ and $\mathbf{T_{c\bar s}}$ tetraquark candidates

Using proton-proton collisions at centre-of-mass energies $7$, $8$, and $13$ TeV, with a total integrated luminosity of $9\,\text{fb}^{-1}$, the LHCb collaboration has performed amplitude analyses of the $B^+\to D^+D^-K^+$, $B^+\to D^- D_s^+ \pi^+$ and $B^0\to \bar{D}^0 D_s^+ \pi^-$ decays, observing that new $T_{cs}$ and $T_{c\bar s}$ resonances are required in order to explain the experimental data. These signals could be the first observation of tetraquark candidates that do not contain a heavy quark-antiquark pair; in fact, they consist of four different flavours of quarks, one of which is a doubly charged open-charm state. We present herein an analysis of the $T_{cs}$ and $T_{c\bar s}$ states, which is an extension of our recently published study of similar $T_{cc}^+$ exotic candidates. Our theoretical framework is a constituent-quark-model-based coupled-channels calculation of $qq^\prime \bar s \bar c$ and $cq\bar s\bar q^{\prime}$ tetraquark sectors for $T_{cs}$ and $T_{c\bar s}$ structures, respectively. We explore the nature, and pole position, of the singularities that appear in the scattering matrix with spin-parity quantum numbers: $J^P=0^\pm$, $1^\mp$, and $2^\pm$. The constituent quark model has been widely used in the heavy quark sector, and thus all model parameters are already constrained from previous works. This makes our predictions robust and parameter-free. We find many singularities in the solution of various scattering-matrix problems which are either virtual states or resonances, but not bound states. Some of them fit well with the experimental observations of the spin-parity, mass and width of $T_{cs}$ and $T_{c\bar s}$ candidates, and thus tentative assignments are made; however, with caution, because the experimental Breit-Wigner parameters are related to the pole characteristics.

hep-ph↗

arXiv2021

The strange partner of the $Z_{c}$ structures in a coupled-channels model

The discovery of a new charged structure in the $K^+$ recoil-mass spectrum near the $D^-_s D^{*0}/D^{*-}_sD^0$ threshold, dubbed $Z_{cs}(3985)^-$, reinforce the idea that the structure of hadrons goes beyond the naive $qqq$ and the $q\bar q$ structures. The existence of this state, with quark content $c\bar c s\bar u$, can be expected from the well-established $Z_c(3900)^\pm$ and $Z_c(4020)$ states using SU(3) flavor symmetry. The $Z_c$ structures have been explained using the chiral constituent quark model in a coupled-channels calculation and, in this work, we undertake the study of the $Z_{cs}(3985)^-$ using the same model. We are able to reproduce the $K^+$ recoil-mass spectrum without any fine tuning of the model parameters. The study of the analytical structure of the S-matrix allows us to conclude that the structure is due to the presence of one virtual pole. A second state, the SU(3) flavor partner of the $Z_c(4020)$ is predicted at $\sim\!\! 4110$ MeV/$c^2$. New states in the hidden bottom strange sector are also predicted.

hep-ph↗

arXiv2018

Acoustically driven x-ray emission and matter collapse in lead

The action of focused underwater weak shock waves on a lead sample is revealed to be not restricted by a mechanical influence only. A strong unexpected x-ray emission was registered from the lead foil exposed to shock waves ({\it sound into x-rays}) which were extremely adiabatic compared to processes of x-ray generation. The lead foil, exposed to shock waves, lost a part of its area having the shape of a polygonal hole of the size of $\sim 2mm$. The missing polygon of lead foil looks as a delicately removed part with no damage at the hole surroundings as it should be after a mechanical breaking. This points to a non-mechanical mechanism of hole formation. That missing polygonal lead matter seems to be "disappeared" because the total lead volume was reduced by that amount after exposure to acoustic waves ({\it matter collapse}). Both paradoxical phenomena cannot be explained by a combination of known effects and a fundamentally new mechanism is required to underlie them. The concept of electron anomalous states, which encouraged the experiments and specified main features of them, is likely that mechanism.

physics.gen-ph↗

arXiv2018

An extreme magneto-ionic environment associated with the fast radio burst source FRB 121102

Fast radio bursts (FRBs) are millisecond-duration, extragalactic radio flashes of unknown physical origin. FRB 121102, the only known repeating FRB source, has been localized to a star-forming region in a dwarf galaxy at redshift z = 0.193, and is spatially coincident with a compact, persistent radio source. The origin of the bursts, the nature of the persistent source, and the properties of the local environment are still debated. Here we present bursts that show ~100% linearly polarized emission at a very high and variable Faraday rotation measure in the source frame: RM_src = +1.46 x 10^5 rad m^-2 and +1.33 x 10^5 rad m^-2 at epochs separated by 7 months, in addition to narrow (< 30 mus) temporal structure. The large and variable rotation measure demonstrates that FRB 121102 is in an extreme and dynamic magneto-ionic environment, while the short burst durations argue for a neutron star origin. Such large rotation measures have, until now, only been observed in the vicinities of massive black holes (M_BH > 10^4 MSun). Indeed, the properties of the persistent radio source are compatible with those of a low-luminosity, accreting massive black hole. The bursts may thus come from a neutron star in such an environment. However, the observed properties may also be explainable in other models, such as a highly magnetized wind nebula or supernova remnant surrounding a young neutron star.

astro-ph.HE↗

arXiv2016

Partners of the $X(3872)$ and HQSS breaking

Since the discovery of the $X(3872)$ the study of heavy meson molecules has been the subject of many investigations. On the experimental side different experiments have looked for its spin partners and the bottom analogs. On the theoretical side different approaches have been used to understand this state. Some of them are EFT that impose HQSS and so they make predictions for the partners of the $X(3872)$, suggesting the existence of a $J^{PC}=2^{++}$ partner in the charm sector or $J^{PC}=1^{++}$ or $2^{++}$ analogs in the bottom. In our work, in order to understand the $X(3872)$, we use a Chiral quark model in which, due to the proximity to the $DD^*$ threshold, we include $c\bar c$ states coupled to $DD^*$ molecular components. In this coupled channel model the relative position of the bare $c\bar c$ states with two meson thresholds are very important. We have looked for the $X(3872)$ partners and we don't find a bound state in the $D^*D^*$ $J^{PC}=2^{++}$. In the bottom sector we find the opposite situation where the $B^*B^*$ with $J^{PC}=2^{++}$ is bounded while the $J^{PC}=1^{++}$ is not bounded. These results shows how the coupling with $c\bar c$ states can induced different results than those expected by HQSS. The reason is that this symmetry is worse in the open heavy meson sector than in the hidden heavy meson sector.

hep-ph↗

arXiv2015

Puzzles in quarkonium hadronic transitions with two pion emission

The anomalously large rates of some hadronic transitions from quarkonium are studied using QCD multipole expansion (QCDME) in the framework of a constituent quark model which has been successful in describing hadronic phenomenology. The hybrid intermediate states needed in the QCDME method are calculated in a natural extension of our constituent quark model based on the Quark Confining String (QCS) scheme. Some of the anomalies are explained due to the presence of an hybrid state with a mass near the mass of the decaying resonance whereas other are justified by the presence of molecular components in the wave function. Some unexpected results are pointed out.

hep-ph↗

arXiv2013

Molecular Structures in Hidden Charm Meson and Charmed Baryon Spectrum

Using a constituent quark model we study the mass and decay channels of meson meson and meson baryon structures in the charm sector. We show that the $X(3872)$ and $X(3940)$ resonances can be described as mixed charmonium-molecular states with $J^{PC}=1^{++}$, whereas the $X(3915)$ and the $Y(3940)$ can be assigned to similar mixed states with $J^{PC}=0^{++}$. In the baryon spectrum we identify the $Λ^+_c(2940)$ as a $D^*N$ molecule with $(I)J^P=(0)3/2^-$ and the recently reported $X_c(3250)$ as a $D^*Δ$ resonance with $(I)J^P=(1)5/2^-$ or $(I)J^P=(2)3/2^-$.

hep-ph↗

arXiv2013

Constituent quark model description of charmonium phenomenology

We review how quark models are able to describe the phenomenology of the charm meson sector. The spectroscopy and decays of charmonium and open charm mesons are described in a particular quark model and compared with the data and the results of other existing models in the literature. A quite reasonable global description of the heavy meson spectra is reached. A new assignment of the $\psi(4415)$ resonance as a 3D state leaving aside the 4S state to the X(4360) is tested through the analysis of the resonance structure in $e^{+}e^{-}$ exclusive reactions around the $\psi(4415)$ energy region. We make tentative assignments of some of the $XYZ$ mesons. To elucidate the structure of the $1^{+}$ $c\bar{s}$ states, i.e. $D_{s1}(2460)$ and $D_{s1}(2536)$, we study the strong decay properties of the $D_{s1}(2536)$ meson. We also perform a calculation of the branching fractions for the semileptonic decays of $B$ and $B_{s}$ mesons into final states containing orbitally excited charmed and charmed-strange mesons, which have become a very important source of information about the structure of heavy mesons. Analysis of the nonleptonic $B$ meson decays into $D^{(\ast)}D_{sJ}$ are also included.

hep-ph↗

arXiv2013

Strong charmonium decays in a microscopic model

Although the spectra of heavy quarkonium systems have been successfully explained by certain QCD motivated potential models, their strong decays are still an open problem. We perform a microscopic calculation of vector charmonium strong decays into open-charm mesons where the $q\bar{q}$ pairs are created from the same interquark interactions acting in the quark model that has been used to describe its spectrum, and also its leptonic and radiative decays. We compare the numerical results with those predicted by the $^{3}P_{0}$ decay model and with the available experimental data, and discuss the possible influence on the strong widths of the different terms of the potential. A comparison with other predictions from similar microscopic decay models is also included.

hep-ph↗

arXiv2012

Scaling of the 3P0 strength in heavy meson strong decays

The phenomenological 3P0 decay model has been extensively applied to calculate meson strong decays. The strength \gamma\ of the decay interaction is regarded as a free flavor independent constant and is fitted to the data. We calculate through the 3P0 model the total strong decay widths of the mesons which belong to charmed, charmed-strange, hidden charm and hidden bottom sectors. The wave function of the mesons involved in the strong decays are given by a constituent quark model that describes well the meson phenomenology from the light to the heavy quark sector. A global fit of the experimental data shows that, contrarily to the usual wisdom, the \gamma\ depends on the reduced mass of the quark-antiquark pair in the decaying meson. With this scale-dependent strength \gamma, we are able to predict the decay width of orbitally excited B mesons not included in the fit.

hep-ph↗

arXiv2012

Molecular structures in charmonium spectrum: The $XYZ$ puzzle

We study in the framework of a constituent quark model the possible contributions of molecular structures to the XYZ charmonium like states. We analyze simultaneously the $c\bar{c}$ structures and the possible molecular components in a formalism which allows us to treat channels below and above thresholds. The only molecular state found in the $1^{++}$ sector correspond to the X(3872). Molecular resonances also appear with other quantum numbers. So, the so called Y(3940) and the X(3915) are suggested to be $J^{PC}=0^{++}$ charmonium states. In the $J^{PC}=1^{--}$ sector we also found significant contributions of the molecular structures which can affect the phenomenology.

hep-ph↗

arXiv2012

Nonleptonic $B \to D^{()}D_{sJ}^{()}$ decays and the nature of the orbitally excited charmed-strange mesons

The Belle Collaboration has recently reported a study of the decays $B \to D_{s1}(2536)^{+}\bar{D}^{(\ast)}$ and has given also estimates of relevant ratios between branching fractions of decays $B \to D^{(\ast)}D_{sJ}^{(\ast)}$ providing important information to check the structure of the $D_{s0}^{\ast}(2317)$, $D_{s1}(2460)$ and $D_{s1}(2536)$ mesons. The disagreement between experimental data and Heavy Quark Symmetry has been used as an indication that $D_{s0}^{\ast}(2317)$ and $D_{s1}(2460)$ mesons could have a more complex structure than the canonical $c\bar{s}$ one. We analyze these ratios within the framework of a constituent quark model, which allows us to incorporate the effects given by finite $c$-quark mass corrections. Our findings are that while the $D_{s1}(2460)$ meson could have a sizable non-$q\bar{q}$ component, the $D_{s0}^{\ast}(2317)$ and $D_{s1}(2536)$ mesons seem to be well described by a pure $q\bar{q}$ structure.

hep-ph↗

arXiv2011

Molecular effects in Charmonium Spectrum

We study the influence of possible molecular structures in the charmonium spectrum. We focus on the $0^{++}$ and $1^{--}$ sectors. In the first one we coupled the $2 ^3P_0$ $q\bar q$ pair with $DD$, $J/ψω$, $D_sD_s$ and $J/ψϕ$ channels and we obtain two states compatibles with the X(3945) and the Y(3940). In the second one we include the $3^3S_1$ and $2^3D_1$ charmonium states coupled to $DD$, $DD^*$, $D^*D^*$, $D_sD_s$, $D_sD_s^*$ and $D_s^*D_s^*$. In this calculation we obtain a new molecular state that could be the G(3900) or the controversial Y(4008) and two $c\bar c$ states dressed by the molecular components assigned to the $ψ(4040)$ and the $ψ(4160)$. The two $c\bar c$ states show interesting properties and in particular they solve the strong disagreement of the decay branching ratios measured by BABAR.

hep-ph↗

arXiv2011

Renormalization approach to constituent quark models of Quarkonium

Constituent quark models, while successful, require a great deal of fine tuning of the short distance interactions by introducing phenomenological gluonic form factors which are ultimately designed to accurately reproduce the spectrum. We apply and develop renormalization ideas to reduce the short distance sensitivity and show that, as naively expected, but not explicitly implemented in the models, the physics of binding is entirely linked to the string tension whereas leptonic decays depend more on the gluon exchange potential. We also show how the spectrum of S- and D- $1^{--}$ states is successfully intertwined through the singular tensor interaction.

hep-ph↗