
Roca, L., & Oset, E. (2010). Asymmetry observables in e(+)e() > pi(+) pi() gamma in the phi region within a chiral unitary approach. Phys. Rev. D, 81(1), 014010–8pp.
Abstract: We make a theoretical study of the charge and forwardbackward pion asymmetries in the e(+)e() > pi(+) pi() gamma process on and off the phi resonance energy. These observables are rather sensitive to the inner details of the theoretical models to describe the reaction. In addition to the standard implementation of the initial state radiation and the bremsstrahlung contribution to the final state radiation, we use the techniques of the chiral unitary approach to evaluate the contribution from the mechanisms of phi decay into pi(+) pi() gamma. This contribution involves the implementation of final state interaction from direct chiral loops, the exchange of vector and axialvector resonances and the final state interaction through the consideration of the mesonmeson unitarized amplitudes, which were found important in a previous work describing the phi > pi pi gamma. We find a good reproduction of the experimental data from KLOE for the forwardbackward asymmetry, both at the phi peak and away from it. We also make predictions for the angular distributions of the charge asymmetry and show that this observable is very sensitive to the chiral loops involved in phi radiative decay.



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.



Sakai, S., Roca, L., & Oset, E. (2017). Charmbeauty meson bound states from B (B*)D(D*) and interaction B (B*)(D)overbar((D)overbar*). Phys. Rev. D, 96(5), 054023–9pp.
Abstract: We evaluate the swave interaction of pseudoscalar and vector mesons with both charm and beauty to investigate the possible existence of molecular BD, B* D, BD*, B* D*, B (D) over bar, B* (D) over bar, B (D) over bar*, or B* (D) over bar* meson states. The scattering amplitude is obtained implementing unitarity starting from a tree level potential accounting for the dominant vector meson exchange. The diagrams are evaluated using suitable extensions to the heavy flavor sector of the hidden gauge symmetry Lagrangians involving vector and pseudoscalar mesons, respecting heavy quark spin symmetry. We obtain bound states at energies above 7 GeV for BD (J(P) = 0(+)), B* D (1(+)), BD* (1(+)), and B* D* (0(+), 1(+,) 2(+)), all in isospin 0. For B (D) over bar (0(+)), B* (D) over bar (1(+)), B (D) over bar* (1(+)), and B* (D) over bar* (0(+), 1(+), 2(+)) we also find similar bound states in I = 0, but much less bound, which would correspond to exotic meson states with _ (b) over bar and (c) over bar quarks, and for the I = 1 we find a repulsive interaction. We also evaluate the scattering lengths in all cases, which can be tested in current investigations of lattice QCD.



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.



Roca, L., & Oset, E. (2010). Description of the f(2)(1270), rho(3)(1690), f(4)(2050), rho(5)(2350), f(6)(2510) resonances as multirho(770) states. Phys. Rev. D, 82(5), 054013–11pp.
Abstract: In a previous work regarding the interaction of two rho(770) resonances, the f(2)(1270) (J(PC) = 2(++)) resonance was obtained dynamically as a tworho molecule with a very strong binding energy, 135 MeV per rho particle. In the present work we use the rho rho interaction in spin 2 and isospin 0 channel to show that the resonances rho(3)(1690) (3()), f(4)(2050) (4(++)), rho(5)(2350) (5()), and f(6)(2510) (6(++)) are basically molecules of increasing number of rho(770) particles. We use the fixed center approximation of the Faddeev equations to write the multibody interaction in terms of the twobody scattering amplitudes. We find the masses of the states very close to the experimental values and we get an increasing value of the binding energy per rho as the number of rho mesons is increased.



Wang, G. Y., Roca, L., & Oset, E. (2019). Discerning the two K1 (1270) poles in D0 > pi(+) VP decay. Phys. Rev. D, 100(7), 074018–10pp.
Abstract: Within the chiral unitary approach, the axialvector resonance K1 (1270) has been predicted to manifest a twopole nature. The lowest pole has a mass of 1195 MeV and a width of 246 MeV and couples mostly to K*pi, and the highest pole has a mass of 1284 MeV and a width of 146 MeV and couples mostly to rho K. We analyze theoretically how this doublepole structure can show up in D0 > pi+VP decays by looking at the vectorpseudoscalar (VP) invariant mass distribution for different VP channels, exploiting the fact that each pole couples differently to different VP pairs. We find that the final (K) over bar*pi and rho(K) over tilde channels are sensible to the different poles of the K1 (1270) resonance and hence are suitable reactions to analyze experimentally the doublepole nature of this resonance.



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 nonquarkantiquark mesons since they would contain at least one b and one s quarks. The swave scattering matrix is evaluated implementing unitarity by means of the BetheSalpeter 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.



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.



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.



Roca, L., Liang, W. H., & Oset, E. (2022). Inconsistency of the data on the K1(1270) > pi K0*(1430) decay width. Phys. Lett. B, 824, 136827–3pp.
Abstract: We show, using the same Lagrangian for the K1(1270) > pi K0*(1430) and K0*(1430) > K1 (1270)pi decays, that the present PDG data on the partial decay width of K1 (1270) > pi K0*(1430) implies a width for K0*(1430) > K1 (1270)pi decay which is about one order of magnitude larger than the total K0*(1430) width. A discussion on this inconsistency is done, stressing its relationship to the existence of two K1(1270) states obtained with the chiral unitary theory, which are not considered in the experimental analyses of K pi pi data.

