Technicolor contribution to lepton + photon + missing energy events at the Tevatron

Events with one lepton, one photon and missing energy are the subject of recent searches at the Fermilab Tevatron. We compute possible contributions to these type of events from the process p pbar --> photon l nu_l nu_tau nubar_tau, where l=e,mu in the context of a Low Scale Technicolor Model. We find that with somewhat tighter cuts than the ones used in the CDF search, it could be possible to either confirm or exclude this model in a small region of its parameter space.Comment: 4 pages, 3 figures. Improved text and figures, including comments and new reference

The Effect of Composite Resonances on Higgs decay into two photons

In scenarios of strongly coupled electroweak symmetry breaking, heavy composite particles of different spin and parity may arise and cause observable effects on signals that appear at loop levels. The recently observed process of Higgs to $\gamma \gamma$ at the LHC is one of such signals. We study the new constraints that are imposed on composite models from $H\to \gamma\gamma$, together with the existing constraints from the high precision electroweak tests. We use an effective chiral Lagrangian to describe the effective theory that contains the Standard Model spectrum and the extra composites below the electroweak scale. Considering the effective theory cutoff at $\Lambda = 4\pi v \sim 3$ TeV, consistency with the $T$ and $S$ parameters and the newly observed $H\to \gamma\gamma$ can be found for a rather restricted range of masses of vector and axial-vector composites from $1.5$ TeV to $1.7$ TeV and $1.8$ TeV to $1.9$ TeV, respectively, and only provided a non-standard kinetic mixing between the $W^{3}$ and $B^{0}$ fields is included.Comment: 30 pages, 10 figures. Version for publication in European Physical Journal

Neutrino emission rates in highly magnetized neutron stars revisited

Magnetars are a subclass of neutron stars whose intense soft-gamma-ray bursts and quiescent X-ray emission are believed to be powered by the decay of a strong internal magnetic field. We reanalyze neutrino emission in such stars in the plausibly relevant regime in which the Landau band spacing of both protons and electrons is much larger than kT (where k is the Boltzmann constant and T is the temperature), but still much smaller than the Fermi energies. Focusing on the direct Urca process, we find that the emissivity oscillates as a function of density or magnetic field, peaking when the Fermi level of the protons or electrons lies about 3kT above the bottom of any of their Landau bands. The oscillation amplitude is comparable to the average emissivity when the Landau band spacing mentioned above is roughly the geometric mean of kT and the Fermi energy (excluding mass), i. e., at fields much weaker than required to confine all particles to the lowest Landau band. Since the density and magnetic field strength vary continuously inside the neutron star, there will be alternating surfaces of high and low emissivity. Globally, these oscillations tend to average out, making it unclear whether there will be any observable effects.Comment: 7 pages, 2 figures; accepted for publication in Astronomy & Astrophysic

Hadronic structure aspects of K+→π−+l1++l2+K^+\to \pi^-+ l^{+}_1 + l^{+}_2 decays

As is known from previous studies the lepton number violating decays $K^+\to \pi^- + l^{+}_1 + l^{+}_2$ have good prospects to probe new physics beyond the Standard Model and provide valuable information on neutrino masses and mixing. We analyze these processes with an emphasis on their hadronic structure aspects applying relativistic constituent quark model. We conclude that the previously ignored contribution associated with the t-channel Majorana neutrino exchange is comparable with the s-channel one in a wide range of neutrino masses. We also estimated model independent absolute upper bounds on neutrino contribution to these decays.Comment: 15 pages, 1 figure. Version to appear in PRD, normalization factor in Eq. (25) is correcte

RANDOM MAGNETIC FIELD EFFECTS ON ELECTRONIC PROPERTIES IN SUBSTITUTIONALLY AND TOPOLOGICALLY DISORDERED ALLOYS

We numerically investigate the effects of the random static magnetic field on a variety of electronic properties (localization of electron wavefunctions, spectral correlations and electrical conductance) in substitutionally and topologically disordered alloys. For this, we generate two-dimensional substitutionally disordered alloys and simulate three-dimensional amorphous structures by a molecular dynamics algorithm. As Hamiltonian models, we use the usual Anderson tight-binding model for the  substitutional  disorder and  a  tight-binding model with a set of explicit s-type orbitals for the topological disorder. We particularly focus on the effect of the random magnetic field on the localization of electron wavefunctions. In the presence of the substitutional disorder, we establish that the random magnetic field tends to delocalize the electron wavefunctions at the band center less than does the uniform magnetic field and it enhances the localization at the band edges. But, in the presence of the topological disorder, we observe the opposite effect. We show that the random magnetic field tends to delocalize the electron wavefunctions more than does the uniform magnetic field. In this respect, we demonstrate that the effect of the random magnetic field on the electron wavefunctions depends on the nature of the disorder.We numerically investigate the effects of the random static magnetic field on a variety of electronic properties (localization of electron wavefunctions, spectral correlations and electrical conductance) in substitutionally and topologically disordered alloys. For this, we generate two-dimensional substitutionally disordered alloys and simulate three-dimensional amorphous structures by a molecular dynamics algorithm. As Hamiltonian models, we use the usual Anderson tight-binding model for the  substitutional  disorder and  a  tight-binding model with a set of explicit s-type orbitals for the topological disorder. We particularly focus on the effect of the random magnetic field on the localization of electron wavefunctions. In the presence of the substitutional disorder, we establish that the random magnetic field tends to delocalize the electron wavefunctions at the band center less than does the uniform magnetic field and it enhances the localization at the band edges. But, in the presence of the topological disorder, we observe the opposite effect. We show that the random magnetic field tends to delocalize the electron wavefunctions more than does the uniform magnetic field. In this respect, we demonstrate that the effect of the random magnetic field on the electron wavefunctions depends on the nature of the disorder

A new signature for color octet pseudoscalars at the LHC

Color octet (pseudo)scalars, if they exist, will be copiously produced at the CERN Large Hadron Collider (LHC). However, their detection can become a very challenging task. In particular, if their decay into a pair of top quarks is kinematically forbidden, the main decay channel would be into two jets, with a very large background. In this Brief Report we explore the possibility of using anomaly-induced decays of the color octet pseudoscalars into gauge bosons to find them at the LHC.Comment: 4 pages, 2 figures. New references adde