Search results for "S-matrix"
showing 10 items of 41 documents
Molecular Ω states
2018
Motivated by the recent finding of five Ωc states by the LHCb collaboration, and the successful reproduction of three of them in a recent approach searching for molecular states of meson–baryon with the quantum numbers of Ωc, we extend these ideas and make predictions for the interaction of meson–baryon in the beauty sector, searching for poles in the scattering matrix that correspond to physical states. We find several Ωb states: two states with masses 6405 MeV and 6465 MeV for JP=12−; two more states with masses 6427 MeV and 6665 MeV for 32−; and three states between 6500 and 6820 MeV, degenerate with JP=12−,32−, stemming from the interaction of vector–baryon in the beauty sector.
Chiral fermions and gauge fixing in five-dimensional theories
2001
We study in detail the issue of gauge-fixing in theories with one universal extra dimension, i.e. theories where both bosons and fermions display Kaluza-Klein (KK) excitations. The extra dimension is compactified using the standard orbifold construction for a massless chiral fermion. We carry out the gauge-fixing procedure at the level of the five-dimensional theory and determine the tree-level propagators and interaction vertices needed for performing perturbative calculations with the effective four-dimensional theory resulting after the compactification. The gauge-independence of the tree-level S-matrix involving massive KK modes is verified using specific examples. In order to obtain ma…
Three-body resonances in two-meson-one-baryon systems
2007
We report four $\Sigma$'s and three $\Lambda$'s, in the 1500 - 1800 MeV region, as two meson - one baryon S-wave $(1/2)^+$ resonances. We solve Faddeev equations in the coupled channel approach. The invariant mass of one of the meson-baryon pairs and that of the three particles have been varied and peaks in the squared three body $T$-matrix have been found very close to the existing $S$ = -1, $J^P= 1/2^+$ low lying baryon resonances. The input two-body $t$-matrices for meson-meson and meson-baryon interaction have been calculated by solving the Bethe-Salpeter equation with the potentials obtained in the chiral unitary approach.
Y(3940),Z(3930), and theX(4160)as dynamically generated resonances from the vector-vector interaction
2009
We apply a unitary approach together with a set of hidden‐gauge Lagrangians to study the vector‐vector interaction. Concretely, we focus on the sector with quantum numbers charm C = 0 and strangeness S = 0 in the region around 4000 MeV. We get five poles, three of which could be identified with the Y(3940), Z(3930) and X(4160). These poles appear with quantum numbers I = 0 and JPC = 0++,2++ and 2++, respectively, and can be considered as hadronic molecules made of D*D*, Ds*Ds*, decaying to a pair of light vectors, light‐heavy vector or pseudoscalar‐pseudoscalar.
Nucleon strangeness and unitarity
1996
The strange-quark vector current form factors of the nucleon are analyzed within the framework of dispersion relations. Particular attention is paid to contributions made by $K\bar{K}$ intermediate states to the form factor spectral functions. It is shown that, when the $K\bar{K}\to N\bar{N}$ amplitude is evaluated in the Born approximation, the $K\bar{K}$ contributions are identical to those arising from a one-loop calculation and entail a serious violation of unitarity. The mean square strangeness radius and magnetic moment are evaluated by imposing unitarity bounds on the kaon-nucleon partial wave amplitudes. The impact of including the kaon's form factor in the dispersion integrals is a…
Incoherent pion photoproduction on the deuteron with polarization observables II: Influence of final state rescattering
2005
Incoherent pion photoproduction on the deuteron is studied for photon energies from threshold up to 1 GeV with special emphasis on polarization observables. The elementary $\gamma N\to\pi N$ amplitude is taken from the MAID model. The influence of final state interactions on total and semi-exclusive cross sections $\vec d(\vec\gamma,\pi)NN$ is investigated by including complete rescattering in the final $NN$- and $\pi N$-subsystems. For charged pion-production the influence of $NN$-rescattering is moderate whereas $\pi N$-rescattering is almost negligible. Much stronger influences of $NN$-rescattering are seen in neutral pion production, which is due to the elimination of a significant spur…
Strategy to find the two $\Lambda(1405)$ states from lattice QCD simulations
2012
Theoretical studies within the chiral unitary approach, and recent experiments, have provided evidence of the existence of two isoscalar states in the region of the $\Lambda(1405)$. In this paper we use the same chiral approach to generate energy levels in a finite box. In a second step, assuming that these energies correspond to lattice QCD results, we devise the best strategy of analysis to obtain the two states in the infinite volume case, with sufficient precision to distinguish them. We find out that using energy levels obtained with asymmetric boxes and/or with a moving frame, with reasonable errors in the energies, one has a successful scheme to get the two $\Lambda(1405)$ poles.
Two-loop pinch technique in the electroweak sector
2002
The generalization of the two-loop Pinch Technique to the Electroweak Sector of the Standard Model is presented. We restrict ourselves to the case of conserved external currents, and provide a detailed analysis of both the charged and neutral sectors. The crucial ingredient for this construction is the identification of the parts discarded during the pinching procedure with well-defined contributions to the Slavnov-Taylor identity satisfied by the off-shell one-loop gauge-boson vertices; the latter are nested inside the conventional two-loop self-energies. It is shown by resorting to a set of powerful identities that the two-loop effective Pinch Technique self-energies coincide with the cor…
Determination of the ηHe3 threshold structure from the low energy pd→ηHe3 reaction
2017
We analyze the data on cross sections and asymmetries for the $pd\ensuremath{\rightarrow}\ensuremath{\eta}\phantom{\rule{0.16em}{0ex}}^{3}\mathrm{He}$ reaction close to threshold and look for bound states of the $\ensuremath{\eta}\phantom{\rule{0.16em}{0ex}}^{3}\mathrm{He}$ system. Rather than parameterizing the scattering matrix, as is usually done, we develop a framework in which the $\ensuremath{\eta}{\phantom{\rule{0.16em}{0ex}}}^{3}\mathrm{He}$ optical potential is the key ingredient, and its strength, together with some production parameters, are fitted to the available experimental data. The relationship of the scattering matrix to the optical potential is established using the Bethe…
Chiral symmetry amplitudes in the S-wave isoscalar and isovector channels and the σ, f[sub 0](980), a[sub 0](980) scalar mesons
1998
We use a nonperturbative approach which combines coupled channel Lippmann Schwinger equations with meson-meson potentials provided by the lowest order chiral Lagrangian. By means of one parameter, a cut off in the momentum of the loop integrals, which results of the order of 1 GeV, we obtain singularities in the S-wave amplitudes corresponding to the σ, f0 and a0 resonances. The ππ→ππ, ππ→KK phase shifts and inelasticities in the T=0 scalar channel are well reproduced as well as the π0η and KK mass distributions in the T=1 channel. Furthermore, the total and partial decay widths of the f0 and a0 resonances are properly reproduced. The results seem to indicate that chiral symmetry constraint…