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Garcia-Recio, C., Nieves, J., & Tolos, L. (2010). D mesic nuclei. Phys. Lett. B, 690(4), 369–375.
Abstract: The energies and widths of several D-0 meson bound states for different nuclei are obtained using a D-meson selfenergy in the nuclear medium, which is evaluated in a selfconsistent manner using techniques of unitarized coupled-channel theory. The kernel of the meson-baryon interaction is based on a model that treats heavy pseudoscalar and heavy vector mesons on equal footing, as required by heavy quark symmetry. We find D-0 bound states in all studied nuclei, from C-12 up to Pb-208. The inclusion of vector mesons is the keystone for obtaining an attractive D-nucleus interaction that leads to the existence of D-0-nucleus bound states, as compared to previous studies based on SU(4) flavor symmetry. In some cases, the half widths are smaller than the separation of the levels, what makes possible their experimental observation by means of a nuclear reaction. This can be of particular interest for the future PANDA@FAIR physics program. We also find a D+ bound state in C-12, but it is too broad and will have a significant overlap with the energies of the continuum.
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Gamermann, D., Nieves, J., Oset, E., & Ruiz Arriola, E. (2010). Couplings in coupled channels versus wave functions: Application to the X(3872) resonance. Phys. Rev. D, 81(1), 014029–14pp.
Abstract: We perform an analytical study of the scattering matrix and bound states in problems with many physical coupled channels. We establish the relationship of the couplings of the states to the different channels, obtained from the residues of the scattering matrix at the poles, with the wave functions for the different channels. The couplings basically reflect the value of the wave functions around the origin in coordinate space. In the concrete case of the X(3872) resonance, understood as a bound state of D-0(D) over bar*(0) and D+D*(-) (and c.c. From now on, when we refer to D-0(D) over bar*(0), D+D*(-), or D (D) over bar* we are actually referring to the combination of these states with their complex conjugate in order to form a state with positive C-parity), with the D-0(D) over bar*(0) loosely bound, we find that the couplings to the two channels are essentially equal leading to a state of good isospin I = 0 character. This is in spite of having a probability for finding the D-0(D) over bar*(0) state much larger than for D+D*(-) since the loosely bound channel extends further in space. The analytical results, obtained with exact solutions of the Schrodinger equation for the wave functions, can be useful in general to interpret results found numerically in the study of problems with unitary coupled channels methods.
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Yamagata-Sekihara, J., Nieves, J., & Oset, E. (2011). Couplings in coupled channels versus wave functions in the case of resonances: Application to the two A(1405) states. Phys. Rev. D, 83(1), 014003–15pp.
Abstract: In this paper we develop a formalism to evaluate wave functions in momentum and coordinate space for the resonant states dynamically generated in a unitary coupled channel approach. The on-shell approach for the scattering matrix, commonly used, is also obtained in quantum mechanics with a separable potential, which allows one to write wave functions in a trivial way. We develop useful relationships among the couplings of the dynamically generated resonances to the different channels and the wave functions at the origin. The formalism provides an intuitive picture of the resonances in the coupled channel approach, as bound states of one bound channel, which decays into open ones. It also provides an insight and practical rules for evaluating couplings of the resonances to external sources and how to deal with final state interaction in production processes. As an application of the formalism we evaluate the wave functions of the two A(1405) states in the pi Sigma, (K) over barN, and other coupled channels. It also offers a practical way to study three-body systems when two of them cluster into a resonance.
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Du, M. L., Baru, V., Dong, X. K., Filin, A., Guo, F. K., Hanhart, C., et al. (2022). Coupled-channel approach to T-cc(+) including three-body effects. Phys. Rev. D, 105(1), 014024–19pp.
Abstract: A coupled-channel approach is applied to the charged tetraquark state T-cc(+). recently discovered by the LHCb Collaboration. The parameters of the interaction are fixed by a fit to the observed line shape in the three-body (DD0)-D-0 pi(+) channel. Special attention is paid to the three-body dynamics in the T-cc(+) due to the finite life time of the D*. An approach to the T-cc(+) is argued to be self-consistent only if both manifestations of the three-body dynamics, the pion exchange between the D and D* mesons and the finite D* width, are taken into account simultaneously to ensure that three-body unitarity is preserved. This is especially important to precisely extract the pole position in the complex energy plane whose imaginary part is very sensitive to the details of the coupled-channel scheme employed. The (DD0)-D-0 and (DD+)-D-0 invariant mass distributions, predicted based on this analysis, are in good agreement with the LHCb data. The low-energy expansion of the D* D scattering amplitude is performed and the low-energy constants (the scattering length and effective range) are extracted. The compositeness parameter of the T-cc(+) is found to be close to unity, which implies that the T-cc(+) is a hadronic molecule generated by the interactions in the D*D-+(0) and D*D-0(+) channels. Employing heavy-quark spin symmetry, an isoscalar D* D* molecular partner of the T-cc(+) with J(P) = 1(+ )is predicted under the assumption that the DD* -D* D* coupled-channel effects can be neglected.
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Albaladejo, M., Fernandez-Soler, P., Nieves, J., & Ortega, P. G. (2018). Contribution of constituent quark model c(s)over-bar states to the dynamics of the D*s0 (2317) and Ds1(2460) resonances. Eur. Phys. J. C, 78(9), 722–22pp.
Abstract: The masses of the D*(s0) (2317) and D-s1(2460) resonances lie below the DK and D* K thresholds respectively, which contradicts the predictions of naive quark models and points out to non-negligible effects of the D(*) K loops in the dynamics of the even-parity scalar (J(pi) = 0(+)) and axial-vector (J(pi) = 1(+)) c (s) over bar systems. Recent lattice QCD studies, incorporating the effects of the D(*) K channels, analyzed these spin-parity sectors and correctly described the D*(s0)(2317) – D-s1(2460) mass splitting. Motivated by such works, we study the structure of the D*(s0)(2317) and D-s1(2460) resonances in the framework of an effective field theory consistent with heavy quark spin symmetry, and that incorporates the interplay between D(*) K meson-meson degrees of freedom and bare P-wave c (s) over bar states predicted by constituent quark models. We extend the scheme to finite volumes and fit the strength of the coupling between both types of degrees of freedom to the available lattice levels, which we successfully describe. We finally estimate the size of the D(*) K two-meson components in the D*(s0)(2317) and D-s1(2460) resonances, and we conclude that these states have a predominantly hadronic-molecular structure, and that it should not be tried to accommodate these mesons within c (s) over bar constituent quark model patterns.
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Guo, F. K., Hidalgo-Duque, C., Nieves, J., & Pavon Valderrama, M. (2013). Consequences of heavy-quark symmetries for hadronic molecules. Phys. Rev. D, 88(5), 054007–5pp.
Abstract: Among the newly observed structures in the heavy-quarkonium mass region, some have been proposed to be hadronic molecules. We investigate the consequences of heavy- quark flavor symmetry on these heavy meson hadronic molecules. The symmetry allows us to predict new hadronic molecules on one hand, and test the hadronic molecular assumption of the observed structures on the other hand. We explore the consequences of the flavor symmetry assuming the X(3872) and Z(b)(10 610) as an isoscalar D (D) over bar* and isovector B (B) over bar* hadronic molecule, respectively. A series of hadronic molecules composed of heavy mesons are predicted. In particular, there is an isoscalar 1(++) B (B) over bar* bound state with a mass about 10 580 MeV which may be searched for in the Y(1S, 2S)pi(+) pi(-) pi(0) mass distribution; the isovector charmonium partners of the Z(b)(10 610) and the Z(b)(10 650) are also predicted, which probably corresponds to the very recently observed Z(c)(3900) and Z(c)(4025) resonances by the BESIII Collaboration.
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Garcia-Recio, C., Hidalgo-Duque, C., Nieves, J., Salcedo, L. L., & Tolos, L. (2015). Compositeness of the strange, charm, and beauty odd parity Lambda states. Phys. Rev. D, 92(3), 034011–14pp.
Abstract: We study the dependence on the quark mass of the compositeness of the lowest-lying odd parity hyperon states. Thus, we pay attention to Lambda-like states in the strange, charm, and beauty sectors which are dynamically generated using a unitarized meson-baryon model. In the strange sector we use a SU(6) extension of the Weinberg-Tomozawa meson-baryon interaction, and we further implement the heavy-quark spin symmetry to construct the meson-baryon interaction when charmed or beauty hadrons are involved. In the three examined flavor sectors, we obtain two J(P) = 1/2- and one J(P) = 3/2(-) Lambda states. We find that the. states which are bound states (the three Lambda(b)) or narrow resonances [one Lambda(1405) and one Lambda(c)(2595)] are well described as molecular states composed of s-wave meson-baryon pairs. The 1/2(-) wide Lambda(1405) and Lambda(c)(2595) as well as the 3/2(-) Lambda(1520) and Lambda(c)(2625) states display smaller compositeness so they would require new mechanisms, such as d-wave interactions.
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Albaladejo, M., & Nieves, J. (2022). Compositeness of S-wave weakly-bound states from next-to-leading order Weinberg's relations. Eur. Phys. J. C, 82(8), 724–12pp.
Abstract: We discuss a model-independent estimator of the likelihood of the compositeness of a shallow S-wave bound or virtual state. The approach is based on an extension of Weinberg's relations in Weinberg (Phys Rev 137:B672, 1965) and it relies only on the proximity of the energy of the state to the two-hadron threshold to which it significantly couples. The scheme only makes use of the experimental scattering length and the effective range low energy parameters, and it is shown to be fully consistent for predominantly molecular hadrons. As explicit applications, we analyse the case of the deuteron, the S-1(0) nucleon virtual state and the exotic D-so(*)(2317)(+/-) , and find strong support to the molecular interpretation in all cases. Results are less conclusive for the D* (s0)(2317)+/-, since the binding energy of this state would be significantly higher than that of the deuteron, and the approach employed here is at the limit of its applicability. We also qualitatively address the case of the recently discovered T + cc state, within the isospin limit to avoid the complexity of the very close thresholds (DD)-D-0*+ and D + D*(0), which could mask the ingredients of the approach proposed in this work.
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Xiao, C. W., Nieves, J., & Oset, E. (2013). Combining heavy quark spin and local hidden gauge symmetries in the dynamical generation of hidden charm baryons. Phys. Rev. D, 88(5), 056012–20pp.
Abstract: We present a coupled channel unitary approach to obtain states dynamically generated from the meson-baryon interaction with hidden charm, using constraints of heavy quark spin symmetry. As a basis of states, we use (D) over barB, (D) over bar *B states, with B baryon charmed states belonging to the 20 representations of SU(4) with J(P) = 1/2(+), 3/2(+). In addition we also include the eta N-c and J/psi N states. The inclusion of these coupled channels is demanded by heavy quark spin symmetry, since in the large m(Q) limit the D and D* states are degenerate and are obtained from each other by means of a spin rotation, under which QCD is invariant. The novelty in the work is that we use dynamics from the extrapolation of the local hidden gauge model to SU(4), and we show that this dynamics fully respects the constraints of heavy quark spin symmetry. With the full space of states demanded by the heavy quark spin symmetry and the dynamics of the local hidden gauge, we look for states dynamically generated and find four basic states that are bound, corresponding to (D) over bar Sigma(c), (D) over bar Sigma(c)*, (D) over bar*Sigma(c) and (D) over bar*Sigma*(c) decaying mostly into eta N-c and J/psi N. All the states appear in isospin I = 1/2, and we find no bound states or resonances in I = 3/2. The (D) over bar Sigma(c) state appears in J = 1/2 and the (D) over bar Sigma*(c) in J = 3/2; the (D) over bar*Sigma(c) appears nearly degenerate in J = 1/2, 3/2 and the (D) over bar*Sigma*(c) appears nearly degenerate in J = 1/2, 3/2, 5/2, with the peculiarity that in J = 5/2 the state has zero width in the space of states chosen. All the states are bound with about 50 MeV with respect to the corresponding (D) over barB thresholds, and the width, except for the J = 5/2 state, is also of the same order of magnitude. Finally, we discuss the uncertainties stemming from the expected breaking of SU(4) and the heavy quark spin symmetry.
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Du, M. L., Albaladejo, M., Guo, F. K., & Nieves, J. (2022). Combined analysis of the Z(c)(3900) and the Z(cs)(3985) exotic states. Phys. Rev. D, 105(7), 074018–20pp.
Abstract: We have performed a combined analysis of the BESIII data for both the Z(c)(3900) and Z(cs)(3985) structures, assuming that the latter is an SU(3) flavor partner of the former one. We have improved on the previous analysis of Albaladejo et al. [Phys. Lett. B 755, 337 (2016)] by computing the amplitude for the D-1(D) over barD* triangle diagram considering both D- and S-wave D1D*x couplings. We have also investigated effects from SU(3) light-flavor violations, which are found to be moderate and of the order of 20%. The successful reproduction of the BESIII spectra, in both the hidden-charm and hidden-charm strange sectors, strongly supports that the Z(cs)(3985) and Z(c)(3900) are SU(3) flavor partners placed in the same octet multiplet. The best results are obtained when an energy-dependent term in the diagonal D(*) (D) over bar ((s))((*)) interaction is included, leading to resonances (poles above the thresholds) to describe these exotic states. We have also made predictions for the isovector Z*c and isodoublet Z*(cs), D*(D) over bar*, and D*??D*s molecules, with J(PC) = 1(+-) and J(P) = 1(+), respectively. These states would be heavy-quark spin symmetry (HQSS) partners of the Z(c) and Z(cs). Besides the determination of the masses and widths of the Z(c)(3900) and Z(cs)(3985), we also predict those of the Z*(c) and Z*(cs) resonances.
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