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Oset, E., Bayar, M., Dote, A., Hyodo, T., Khemchandani, K. P., Liang, W. H., et al. (2016). Two-, Three-, Many-body Systems Involving Mesons. Multimeson Condensates. Acta Phys. Pol. B, 47(2), 357–365.
Abstract: In this paper, we review results from studies with unconventional many-hadron systems containing mesons: systems with two mesons and one baryon, three mesons, some novel systems with two baryons and one meson, and finally, systems with many vector mesons, up to six, with their spins aligned forming states of increasing spin. We show that in many cases, one has experimental counterparts for the states found, while in some other cases, they remain as predictions, which we suggest to be searched in BESIII, Belle, LHCb, FAIR and other facilities.
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Roca, L., Mai, M., Oset, E., & Meissner, U. G. (2015). Predictions for the Lambda(b) -> J/psi Lambda (1405) decay. Eur. Phys. J. C, 75(5), 218–9pp.
Abstract: We calculate the shape of the pi Sigma and (K) over bar N invariant mass distributions in the Lambda(b) -> J/psi pi Sigma and Lambda(b) -> J/psi (K) over bar N decays that are dominated by the Lambda (1405) resonance. The weak interaction part is the same for both processes and the hadronization into the different meson-baryon channels in the final state is given by symmetry arguments. The most important feature is the implementation of the meson-baryon final-state interaction using two chiral unitary models from different theoretical groups. Both approaches give a good description of antikaon-nucleon scattering data, the complex energy shift in kaonic hydrogen and the line shapes of pi Sigma K in photoproduction, based on the two-pole scenario for the Lambda (1405). We find that this reaction reflects more the higher mass pole and we make predictions of the line shapes and relative strength of the meson-baryon distributions in the final state.
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Roca, L., & Oset, E. (2016). On the hidden charm pentaquarks in Lambda(b) -> J/psi K- p decay. Eur. Phys. J. C, 76(11), 591–12pp.
Abstract: In a previous work we presented a theoretical analysis of the Lambda(b) -> J/psi K- p reaction based on which a recent experiment by the LHCb collaboration at CERN claimed the existence of two hidden charm pentaquarks, P-c(4380)(+) and P-c(4450)(+). In that work we focused only on the Lambda(1405) and P-c(4450)(+) signals and discussed the possible explanation of this pentaquark state within the picture of a dynamical meson-baryon molecule made up mostly from (D) over bar*Sigma(c) and (D) over bar*Sigma(c)* components. In the present work we improve upon the previous one by considering the total K- p and J/psi p data including all the relevant resonances contributing to the spectra, and discuss the possible nature of both P-c(4380)(+) and P-c(4450)(+). We also discuss several important topics, like the effect of the contact term in the reaction, the viability of reproducing the data without the P-c(4380)(+) and the possible quantum number assignment to these pentaquarks.
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Wang, G. Y., Roca, L., Wang, E., Liang, W. H., & Oset, E. (2020). Signatures of the two K1(1270) poles in D – plus ve plus V P decay. Eur. Phys. J. C, 80(5), 388–7pp.
Abstract: We analyze theoretically the D+ ye+ pK and D+ pe+ K*7 decays to see the feasibility to check the double pole nature of the axial -vector resonance Kt(1270) predicted by the unitary extensions of chiral perturbation theory (UChPT). Indeed, within UChPT the K1(1270) is dynamically generated from the interaction of a vector and a pseudoscalar meson, and two poles are obtained for the quantum numbers of this resonance. The lower mass pole couples dominantly to 10 and the higher mass pole to pK, therefore we can expect that different reactions weighing differently these channels in the production mechanisms enhance one or the other pole. We show that the different final V P channels in D pe+ V P weigh differently both poles, and this is reflected in the shape of the final vector-pseudoscalar invariant mass distributions. Therefore, we conclude that these decays are suitable to distinguish experimentally the predicted double pole of the Kt(1270) resonance.
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Dai, L. R., Roca, L., & Oset, E. (2020). Tau decay into tau(t) and a(1)(1260), b(1)(1235), and two K-1(1270). Eur. Phys. J. C, 80(7), 673–9pp.
Abstract: We study the tau -> nu(tau). A decay, with A an axialvector meson. We produce the a(1) (1260) and b(1) (1235) resonances in the Cabibbo favored mode and two K-1 (1270) states in the Cabibbo suppressed mode. We take advantage of previous chiral unitary approach results where these resonances appear dynamically from the vector and pseudoscalar meson interaction in s-wave. Actually two different poles were obtained associated to the K-1(1270) quantum numbers. We find that the unmeasured rates for b(1)(1235) production are similar to those of the a(1)(1260) and for the two K-1 states we suggest to separate the present information on the (K) over bar pi pi invariant masses into (K) over bar*pi and rho K modes, the channels to which these two resonances couple most strongly, predicting that thesemodes peak at different energies and have different widths. These measurements should shed light on the existence of these two K-1 states. In addition, we have gone one step further making a comparison with experimental results of three meson decay channels, letting the vector mesons of our approach decay into pseudoscalars, and we find an overall good agreement with experiment.
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Oset, E., & Roca, L. (2022). Exotic molecular meson states of B(*) K(*) nature. Eur. Phys. J. C, 82(10), 882–9pp.
Abstract: We evaluate theoretically the interaction of the open bottom and strange systems (B) over bar (K) over bar, (B) over bar * (K) over bar, (B) over bar (K) over bar * and (B) over bar* (K) over bar* to look for possible bound states which could correspond to exotic non-quark-antiquark mesons since they would contain at least one b and one s quarks. The s-wave scattering matrix is evaluated implementing unitarity by means of the Bethe-Salpeter equation, with the potential kernels obtained from contact and vector meson exchange mechanisms. The vertices needed are supplied from Lagrangians derived from suitable extensions of the hidden gauge symmetry approach to the bottom sector. We find poles below the respective thresholds for isospin 0 interaction and evaluate the widths of the different obtained states by including the main sources of imaginary part, which are the B *-> B gamma decay in the (B) over bar * (K) over bar channels, the K *-> K pi in the channels involving a K *, plus the box diagrams with (B) over bar (K) over bar and (B) over bar * (K) over bar intermediate states for the (B) over bar * (K) over bar * channels.
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Song, J., Duan, M. Y., Roca, L., & Oset, E. (2024). Pentaquark molecular states with hidden bottom and double strangeness. Eur. Phys. J. C, 84(10), 1055–8pp.
Abstract: We investigate the meson-baryon interaction in coupled channels with the quantum numbers of the pentaquarks Pbss and Pbsss. The interaction is derived from an extension of the local hidden gauge approach to the heavy quark sector, which has demonstrated accurate results compared to experiments involving Ωb, Ξb states, and pentaquarks Pc and Pcs. In our study, we identify several molecular states with small decay widths within the chosen set of coupled channels. The spin-parity (JP) of these states is as follows: JP=12− for pseudoscalar-baryon (12+) coupled channels, JP=32− for pseudoscalar-baryon (32+) coupled channels, JP=12− and 32− for vector-baryon (12+) coupled channels, and JP=12−, 32−, 52− for vector-baryon (32+) coupled channels. We search for the poles of these states and evaluate their couplings to the different channels.
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Roca, L., Morais Dias, J., & Oset, E. (2025). The Ds1(2460)→Dsπ plus π- decay from a Ds1 molecular perspective. European Physical Journal C, 85(7), 808.
Abstract: We conduct a theoretical study of the Ds1(2460)-> Ds pi+pi- decay from the perspective that the Ds1 is a molecular state, built mostly from the D*K and Ds* components. The D* and Ds* mesons are allowed to decay into two pseudoscalars, with one of them merging with the other pseudoscalar that forms the Ds1 state, ultimately leading to the pi+pi-Ds final state. This results in a triangle diagram mechanism where all theoretical ingredients are well-known, leading to a free parameter framework. We evaluate the mass distributions of particle pairs and find good agreement with the experimental distributions of a recent LHCb experiment, providing strong support to the molecular picture of the Ds1(2460) state. We also discuss the role played by the scalar mesons f0(500) and f0(980), at odds with the interpretation of the experimental analysis.
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Martinez Torres, A., Khemchandani, K. P., Roca, L., & Oset, E. (2020). Few-body systems consisting of mesons. Few-Body Syst., 61(4), 35–16pp.
Abstract: We present a work which is meant to inspire the few-body practitioners to venture into the study of new, more exotic, systems and to hadron physicists, working mostly on two-body problems, to move in the direction of studying related few-body systems. For this purpose we devote the discussions in the introduction to show how the input two-body amplitudes can be easily obtained using techniques of the chiral unitary theory, or its extensions to the heavy quark sector. We then briefly explain how these amplitudes can be used to solve the Faddeev equations or a simpler version obtained by treating the three-body scattering as that of a particle on a fixed center. Further, we give some examples of the results obtained by studying systems involving mesons. We have also addressed the field of many meson systems, which is currently almost unexplored, but for which we envisage a bright future. Finally, we give a complete list of works dealing with unconventional few-body systems involving one or several mesons, summarizing in this way the findings on the topic, and providing a motivation for those willing to investigate such systems.
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Albaladejo, M., Oller, J. A., Oset, E., Rios, G., & Roca, L. (2012). Finite volume treatment of pi pi scattering and limits to phase shifts extraction from lattice QCD. J. High Energy Phys., 08(8), 071–22pp.
Abstract: We study theoretically the effects of finite volume for pi pi scattering in order to extract physical observables for infinite volume from lattice QCD. We compare three different approaches for pi pi scattering (lowest order Bethe-Salpeter approach, N/D and inverse amplitude methods) with the aim of studying the effects of the finite size of the box in the potential of the different theories, specially the left-hand cut contribution through loops in the crossed t, u-channels. We quantify the error made by neglecting these effects in usual extractions of physical observables from lattice ()CD spectrum. We conclude that for pi pi phase-shifts in the scalar-isoscalar channel up to 800 MeV this effect is negligible for box sizes bigger than 2,5m(pi)(-1) and of the order of 5% at around 1.5 – 2m(pi)(-1). For isospin 2 the finite size effects can reach up to 10% for that energy. We also quantify the error made when using the standard Luscher method to extract physical observables from lattice QCD, which is widely used in the literature but is an approximation of the one used in the present work.
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