Aceti, F., Oset, E., & Roca, L. (2014). Composite nature of the Lambda (1520) resonance. Phys. Rev. C, 90(2), 025208–8pp.
Abstract: Recently, the Weinberg compositeness condition of a bound state was generalized to account for resonant states and higher partial waves. We apply this extension to the case of the Lambda (1520) resonance and quantify the weight of the mesonbaryon components in contrast to other possible genuine building blocks. This resonance was theoretically obtained from a coupled channels analysis using the swave pi Sigma* and K Xi* and the dwave (K) over bar N and pi Sigma channels, applying the techniques of the chiral unitary approach. We obtain the result that this resonance is essentially dynamically generated from these mesonbaryon channels, leaving room for only 15% weight of other kinds of components in its wave function.

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 BetheSalpeter 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 lefthand cut contribution through loops in the crossed t, uchannels. 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 phaseshifts in the scalarisoscalar 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.

Dai, L. R., Oset, E., Feijoo, A., Molina, R., Roca, L., Martinez Torres, A., et al. (2022). Masses and widths of the exotic molecular B(s)(()*B)((s))(*()) states. Phys. Rev. D, 105(7), 074017–11pp.
Abstract: We study the interaction of the doubly bottom systems BB, B*B, BsB, Bs*B, B*B*, B*BS, B*Bs*, BsBs, BsBs*, Bs*Bs* by means of vector meson exchange with Lagrangians from an extension of the local hidden gauge approach. The full swave scattering matrix is obtained implementing unitarity in coupled channels by means of the BetheSalpeter equation. We find poles below the channel thresholds for the attractively interacting channels B*B in I = 0, Bs*B – B*Bs in I = 1/2, B* B* in I = 0, and Bs*B* in I = 1/2, all of them with J(P) = 1(+). For these cases the widths are evaluated identifying the dominant source of imaginary part. We find binding energies of the order of 1020 MeV, and the widths vary much from one system to the other: of the order of 10100 eV for the B* B system and Bs*B – B* Bs, about 6 MeV for the B*B* system and of the order of 0.5 MeV for the Bs*B* system.

Dai, L. R., Roca, L., & Oset, E. (2020). Tau decay into tau(t) and a(1)(1260), b(1)(1235), and two K1(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 K1 (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 swave. Actually two different poles were obtained associated to the K1(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 K1 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 K1 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.

Dai, L. R., Roca, L., & Oset, E. (2019). tau decay into a pseudoscalar and an axialvector meson. Phys. Rev. D, 99(9), 096003–14pp.
Abstract: We study theoretically the decay tau() > nu(tau)P()A, with P a pi() or K and A an axialvector resonance b(1)(1235), h(1) (1170), h(1) (1380), a(1) (1260), f(1) (1285) or any of the two poles of the K1 (1270). The process proceeds through a triangle mechanism where a vector meson pair is first produced from the weak current and then one of the vectors produces two pseudoscalars, one of which reinteracts with the other vector to produce the axial resonance. For the initial weak hadronic production we use a recent formalism to account for the hadronization after the initial quarkantiquark pair produced from the weak current, which explicitly filters Gparity states and obtain easy analytic formulas after working out the angular momentum algebra. The model also takes advantage of the chiral unitary theories to evaluate the vectorpseudoscalar (VP) amplitudes, where the axialvector resonances were obtained as dynamically generated from the vectorpseudoscalar interaction. We make predictions for invariant mass distribution and branching ratios for the channels considered.

Dias, J. M., Debastiani, V. R., Roca, L., Sakai, S., & Oset, E. (2017). Binding of the BD(D)overbar and BDD systems. Phys. Rev. D, 96(9), 094007–6pp.
Abstract: We study theoretically the BD (D) over bar and BDD systems to see if they allow for possible bound or resonant states. The threebody interaction is evaluated implementing the fixed center approximation to the Faddeev equations which considers the interaction of a D or (D) over bar particle with the components of a BD cluster, previously proved to form a bound state. We find an I(J(P)) = 1/2(0()) bound state for the BD (D) over bar system at an energy around 89258985 MeV within uncertainties, which would correspond to a bottom hiddencharm meson. In contrast, for the BDD system, which would be bottom doublecharm and hence manifestly exotic, we have found hints of a bound state in the energy region 89358985 MeV, but the results are not stable under the uncertainties of the model, and we cannot assure, nor rule out, the possibility of a BDD threebody state.

Dias, J. M., Roca, L., & Sakai, S. (2018). Prediction of new states from D(*)B(*)(B)overbar(*) threebody interactions. Phys. Rev. D, 97(5), 056019–8pp.
Abstract: We study threebody systems composed of D(*), B(*), and (B) over bar(*) in order to look for possible bound states or resonances. In order to solve the threebody problem, we use the fixed center approach for the Faddeev equations considering that the B*(B) over bar*(B (B) over bar) are clusterized systems, generated dynamically, which interact with a third particle D((D) over bar) whose mass is much smaller than the twobody bound states forming the cluster. In the DB*(B) over bar*, D*B*(B) over bar*, DB (B) over bar, and D*B (B) over bar systems with I = 1/2, we found clear bound state peaks with binding energies typically a few tens MeV and more uncertain broad resonant states about ten MeV above the threshold with widths of a few tens MeV.

Dias, J. M., Toledo, G., Roca, L., & Oset, E. (2021). Unveiling the K1(1270) doublepole structure in the (B)overbar > J/psi rho(K)overbar and (B)overbar > J/psi(K)overbar*pi decays. Phys. Rev. D, 103(11), 116019–13pp.
Abstract: By looking at the pseudoscalarvector meson spectra in the (B) over bar > J/psi rho(K) over bar and (B) over bar > J/psi(K) over bar*pi weak decays, we theoretically investigate the doublepole structure of the K1 (1270) resonance by using the chiral unitary approach to account for the finalstate interactions between the pseudoscalar (P) and vector (V) mesons. The K1 (1270) resonance is dynamically generated through these interactions in coupled channels and influences the shape of the invariant mass distributions under consideration. We show how these shapes are affected by the K1 (1270) doublepole structure to confront the results from our model with future experiments that might investigate the PV spectra in these decays.

Martinez Torres, A., Khemchandani, K. P., Roca, L., & Oset, E. (2020). Fewbody systems consisting of mesons. FewBody Syst., 61(4), 35–16pp.
Abstract: We present a work which is meant to inspire the fewbody practitioners to venture into the study of new, more exotic, systems and to hadron physicists, working mostly on twobody problems, to move in the direction of studying related fewbody systems. For this purpose we devote the discussions in the introduction to show how the input twobody 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 threebody 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 fewbody 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.

Oset, E., Bayar, M., Dote, A., Hyodo, T., Khemchandani, K. P., Liang, W. H., et al. (2016). Two, Three, Manybody Systems Involving Mesons. Multimeson Condensates. Acta Phys. Pol. B, 47(2), 357–365.
Abstract: In this paper, we review results from studies with unconventional manyhadron 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.
