Based on a dispersive approach, we apply the inverse amplitude method to unitarize one-loop SU(2) and SU(3) Chiral Perturbation Theory. Numerically, find that this unitarization technique yields correct complex analytic structure in terms of cuts poles. Indeed, using chiral parameter estimates obtained from low energy experiments obtain poles associated with rho(770) K^*(982) resonances. Just by fixing their actual masses parametrization pi-pi pi-K phase shifts eight different channels. With...

In the context of $f(R)$ theories gravity, we address problem finding static and spherically symmetric black hole solutions. Several aspects constant curvature solutions with without electric charge are discussed. We also study general case (without imposing curvature). Following a perturbative approach around Einstein-Hilbert action, it is found that only Schwarzschild-(anti) de Sitter type present up to second order in perturbations. Explicit expressions for effective cosmological obtained...

In this work we consider the possibility of describing current evolution universe, without introduction any cosmological constant or dark energy (DE), by modifying Einstein-Hilbert (EH) action. context $f(R)$ gravities within metric formalism, show that it is possible to find an action which exactly reproduces behavior EH with constant. addition analytical at origin having Minkowski and Schwarzschild solutions as vacuum solutions. The found highly nontrivial must be written in terms...

We apply the one-loop results of $\mathrm{SU}{(3)}_{L}\ifmmode\times\else\texttimes\fi{}\mathrm{SU}{(3)}_{R}$ chiral perturbation theory supplemented with inverse-amplitude method to fit available experimental data on $\ensuremath{\pi}\ensuremath{\pi}$ and $\ensuremath{\pi}K$ scattering. With essentially only three parameters we describe accurately corresponding six different channels: namely, $(I, J)=(0, 0), (2, (1, 1), (\frac{1}{2}, (\frac{3}{2}, \mathrm{and} 1)$. In addition reproduce...

We show that, in the context of brane-world scenarios with low tension tau=f(4), massive brane fluctuations (branons) are natural dark matter candidates. calculate present abundances for both hot (warm) and cold branons terms branon mass M scale f. The results compared current experimental bounds on these parameters. also study prospects their detection direct search experiments comment characteristic signals indirect ones.

In the context of $f(R)$ theories gravity, we study evolution scalar cosmological perturbations in metric formalism. Using a completely general procedure, find exact fourth-order differential equation for matter density longitudinal gauge. case sub-Hubble modes, expression reduces to second-order which is compared with standard (quasistatic) used literature. We show that functions quasistatic approximation not justified. However, those adequately describing present phase accelerated...

Annihilation of different dark matter (DM) candidates into Standard Model (SM) particles could be detected through their contribution to the gamma ray fluxes that are measured on Earth. The magnitude such contributions depends particular DM candidate, but certain imprints produced photon spectra may analyzed in a model-independent fashion. In this work we provide fitting formulae for generated by WIMP annihilation quarks, leptons and gauge bosons channels wide range masses.

We report a calculation of the shear viscosity in relativistic multicomponent meson gas as function temperature and chemical potentials. approximately solve Uehling-Uhlenbeck transport equation kinetic theory, appropriate for boson gas, with kinematics. Since at low temperatures can be taken mostly composed pions, fraction kaons etas, we explore region where binary elastic collisions least one pion are dominant scattering processes. Our input phase shifts fits to experimental data obtained...

In General Relativity without a cosmological constant non-positive contribution from the space-time geometry to Raychaudhuri equation is found provided that particular energy conditions are assumed and regardless considered solution of Einstein's equations. This fact usually interpreted as manifestation attractive character gravity. Nevertheless, positive should occur since this case in an accelerated expanding Robertson-Walker model for congruences followed by fundamental observers....

In this work we deal with the critical behavior of bulk viscosity in linear sigma model (LSM) as an example a system which can be treated by using different techniques. Starting from Boltzmann-Uehling-Uhlenbeck equation compute over entropy density LSM large-N limit. We search for possible maximum at temperature chiral phase transition. The information about temperature, well effective masses, is obtained potential. find that expected (as measure conformality loss) absent large N agreement...

We consider a general brane-world model parametrized by the brane tension scale f and branon mass M. For low compared to fundamental gravitational scale, we calculate relic abundance its contribution cosmological dark matter. compare this result with current observational limits on total hot matter energy densities derive corresponding bounds Using nucleosynthesis number of relativistic species, also set limit light branons in terms tension. Finally, estimate coming from loss rate supernovae...

In the context of brane-world scenarios with compactified large extra dimensions, we study production possible massive brane oscillations (branons) in electron-positron colliders. We compute their contribution to electroweak gauge bosons decay width and single-photon single-Z processes. With CERN LEP-I results assuming nonobservation at LEP-II present exclusion plots for tension $\ensuremath{\tau}{=f}^{4}$ branon mass M. Prospects next generation colliders are also considered.

If the Electroweak Symmetry Breaking Sector turns out to be strongly interacting, actively investigated effective theory for longitudinal gauge bosons plus Higgs can efficiently extended cover regime of saturation unitarity (where perturbative expansion breaks down). This is achieved by dispersion relations, whose subtraction constants and left cut contribution approximately obtained in different ways giving rise unitarization procedures. We illustrate ideas with Inverse Amplitude Method,...