José Ramón Peláez Sagredo

Pion-pion scattering amplitude. IV. Improved analysis with once subtracted Roy-like equations up to 1100 MeV

We improve our description of π π scattering data by imposing additional requirements on our previous fits, in the form of once-subtracted Roy-like equations, while extending our analysis up to 1100 MeV. We provide simple and ready to use parametrizations of the amplitude. In addition, we present a detailed description and derivation of these once-subtracted dispersion relations that, in the 450 to 1100 MeV region, provide an additional constraint which is much stronger than our previous requirements of forward dispersion relations and standard Roy equations. The ensuing constrained amplitudes describe the existing data with rather small uncertainties in the whole region from threshold up to 1100 MeV, while satisfying very stringent dispersive constraints. For the S0 wave, this requires an improved matching of the low and high energy parametrizations. Also for this wave we have considered the latest low energy K_(l4) decay results, including their isospin violation correction, and we have removed some controversial data points. These changes on the data translate into better determinations of threshold and subthreshold parameters which remove almost alldisagreement with previous chiral perturbation theory and Roy equation calculations below 800 MeV. Finally, our results favor the dip structure of the S0 inelasticity around the controversial 1000 MeV region.

Varying the light quark mass: Impact on the nuclear force and big bang nucleosynthesis

The quark mass dependences of light-element binding energies and nuclear scattering lengths are derived using chiral perturbation theory in combination with nonperturbative methods. In particular, we present new, improved values for the quark mass dependence of meson resonances that enter the nuclear force. A detailed analysis of the theoretical uncertainties arising in this determination is presented. As an application, we derive from a comparison of observed and calculated primordial deuterium and helium abundances a stringent limit on the variation of the light quark mass, δm_q/mq = 0:02 ± 0.04. Inclusion of the neutron lifetime modification, under the assumption of a variation of the Higgs vacuum expectation value that translates into changing quark, electron, and weak gauge boson masses, leads to a stronger limit |δm_q|< 0.009.

CERN LHC sensitivity to the resonance spectrum of a minimal strongly interacting electroweak symmetry breaking sector

We present a unified analysis of the two main production processes of vector boson pairs at the CERN LHC, VV-fusion and q (q) over bar annihilation, in a minimal strongly interacting electroweak symmetry breaking sector. Using a unitarized electroweak chiral Lagrangian formalism and modeling the final VLVL strong rescattering effects by a form factor, we describe q (q) over bar annihilation processes in terms of the two chiral parameters that govern elastic VLVL scattering. Depending on the values of these two chiral parameters, the unitarized amplitudes may present resonant enhancements in different angular momentum-isospin channels. Scanning this two parameter space, wt: generate the general resonance spectrum of a minimal strongly interacting electroweak symmetry breaking sector and determine the regions that can be probed at the CERN LHC.

Thermal rho and sigma mesons from chiral symmetry and unitarity

We study the temperature evolution of the rho and sigma mass and width, using a unitary chiral approach. The one-loop pipi scattering amplitude in chiral perturbation theory at Tnot equal0 is unitarized via the inverse amplitude method. Our results predict a clear increase with T of both the rho and sigma widths. The masses decrease slightly for high T, while the rhopipi coupling increases. The rho behavior seems to be favored by experimental results. In the sigma case, it signals chiral symmetry restoration.

Two-meson cloud contribution to the baryon antidecuplet binding

We study the two-meson virtual cloud contribution to the self-energy of the SU(3) antidecuplet, to which the Thet (+) pentaquark is assumed to belong. This is motivated by the large branching ratio of the N(1710) decay into two pions and one nucleon. We derive effective Lagrangians that describe the N(1710) decay into N pi pi with two pions in s or p wave. We obtain increased binding for all members of the antidecuplet and a contribution to the mass splitting between states with different strangeness which is at least 20% of the empirical one. We also provide predictions for three-body decays of the pentaquark antidecuplet.

Nonordinary light meson couplings and the 1/N_c expansion

We study the large N_c behavior of couplings among light meson states with different compositions in terms of quarks and gluons. We shortly review the most common compositions of mesons, which are of interest for the understanding of low-lying meson resonances, namely, the ordinary quark-antiquark states as well as the nonordinary glueball, tetraquark, and other states. We dedicate special attention to Jaffes generalization of the tetraquark with N_c - 1 q -q over bar q pairs, which is the only type of state we have identified whose width does not necessarily vanish with N_c, though it does decouple exponentially with N_c from the ππ channel, so that it is weakly coupled to the meson-meson system.

Improved unitarized heavy baryon chiral perturbation theory for pi N scattering to fourth order

We extend our previous analysis of the unitarized pion-nucleon scattering amplitude including up to fourth order terms in heavy baryon chiral perturbation theory. We pay special attention to the stability of the generated Delta(1232) resonance, the convergence problems, and the power counting of the chiral parameters.

New dispersion relations in the description of π π scattering amplitudes

We present a set of once subtracted dispersion relations which implement crossing symmetry conditions for the

Chiral Extrapolations of light resonances from dispersion relations and Chiral Perturbation Theory

\pi\pi

Once subtracted Roy-like dispersion relations and a precise analysis of pion-pion scattering data

scattering amplitudes below 1 GeV. We compare and discuss the results obtained for the once and twice subtracted dispersion relations, known as Roys equations, for three