Alfonso R. Zerwekh

The axigluon, a four-site model and the top quark forward–backward asymmetry at the Tevatron

Abstract Very recently, it has been shown by other authors that the CDF measurement of the top quark forward–backward asymmetry can be explained by means of a heavy and broad axigluon. In order to work, this mechanism needs that the axigluon coupling to the top quark must be different than the coupling to light quarks and both must be stronger than the one predicted in classical axigluon models. In this Letter, we argue that this kind of axigluon can be accommodated in an extended chiral color model we proposed previously. Additionally, we show that the desired features can be derived from a simple four-site model with delocalized fermions.

Gauge invariance, color octet vector resonances and double technieta production at the Tevatron

Abstract We show that the usual vector meson dominance method does not apply directly to the mixing of a color-octet vector boson (color-octet technirho) with the gluon because of gauge invariance. We propose a gauge invariant method where one works in a physical basis with mass eigenstate fields. As a result, we show that the physical technirho does not couple to two gluons, contrary to the general belief. Consequences for the production of a pair of color-octet, isosinglet technipions (technietas) at Fermilab is analyzed by means of a simulation of the signal and background, including kinematical cuts. We find that the signal is too small to be observed.

Quark masses and mixings in the RS1 model with a condensing 4th generation

A bstractWe study the hierarchy of quark masses and mixings in a model based on a 5-dimensional spacetime with constant curvature of Randall-Sundrum type with two branes, where the Electroweak Symmetry Breaking is caused dynamically by the condensation of a 4th generation of quarks, due to underlying physics from the 5D bulk and the first KK gluons. We first study the hierarchy of quark masses and mixings that can be obtained from purely adjusting the profile localizations, finding that realistic masses are not reproduced unless non trivial hierarchies of underlying 4-fermion interactions from the bulk are included. Then we study global U(1) symmetries that can be imposed in order to obtain non-symmetric modified Fritzsch-like textures in the mass matrices that reproduce reasonably well quark masses and CKM mixings.

Study of a neutrino mass texture generated in supergravity with bilinear R-parity violation

Abstract.We study a particular texture of the neutrino mass matrix generated in supergravity with non-universal bilinear R-parity violation parameters. The relatively high value of

Comments on the compatibility of thermodynamic equilibrium conditions with lattice propagators

tanbeta

Triple photon production at the Tevatron in technicolor models

makes the one-loop contribution to the neutrino mass matrix as important as the tree-level one. The atmospheric angle is nearly maximal, and its deviation from maximal mixing is related to the small size of the ratio between the solar and atmospheric mass scales. There is also a common origin for the small values of the solar and reactor angles, but the latter is much smaller due the large mass ratio between the heaviest two neutrinos. There is a high dependence of the neutrino mass differences on the scalar mass m0 and the gaugino mass M1/2, but a smaller dependence of the mixing angles on the same Sugra parameters. Measurements of branching ratios for the neutralino decays can give important information on the parameters of the model. There are good prospects at a future linear collider for these measurements, but a more detailed analysis is necessary for the LHC.

On infrared problems of effective Lagrangians of massive spin 2 fields coupled to gauge fields

In this paper the compatibility is analyzed of the non-perturbative equations of state of quarks and gluons arising from the lattice with some natural requirements for self-gravitating objects at equilibrium: the existence of an equation of state (namely, the possibility to define the pressure as a function of the energy density), the absence of superluminal propagation and Le Chatelier’s principle. It is discussed under which conditions it is possible to extract an equation of state (in the above sense) from the non-perturbative propagators arising from the fits of the latest lattice data. In the quark case, there is a small but non-vanishing range of temperatures in which it is not possible to define a single-valued functional relation between density and pressure. Interestingly enough, a small change of the parameters appearing in the fit of the lattice quark propagator (of around 10xa0%) could guarantee the fulfillment of all the three conditions (keeping alive, at the same time, the violation of positivity of the spectral representation, which is the expected signal of confinement). As far as gluons are concerned, the analysis shows very similar results. Whether or not the non-perturbative quark and gluon propagators satisfy these conditions can have a strong impact on the estimate of the maximal mass of quark stars.

The Linear BESS model at the LHC

Abstract We study the process p p →γγγ as a signal for associated photon–technipion production at the Tevatron. This is a clean signature with relatively low background. Resonant and non-resonant contributions are included and we show that technicolor models can be effectively probed in this mode.

ON THE QUANTUM CHROMODYNAMICS OF A MASSIVE VECTOR FIELD IN THE ADJOINT REPRESENTATION

Abstract In this paper we analyze the interactions of massive spin-2 particles charged under both Abelian and non-Abelian group using the Porrati–Rahman Lagrangian. This theory is valid up to an intrinsic cutoff scale. Phenomenologically a theory valid up to a cutoff scale is sensible as all known higher spin particles are non-fundamental and it is shown that indeed this action can be used to estimate some relevant cross section. Such action necessarily includes Stuckelberg field and therefore it is necessary to fix the corresponding gauge symmetry. We show that this theory, when the Stuckelberg symmetry is gauge-fixed, possesses a non-trivial infrared problem. A gauge fixing ambiguity arises which is akin to the Gribov problem in QCD in the Abelian case as well. In some cases (such as when the space–time is the four-dimensional torus) the vacuum copies can be found analytically. A similar phenomenon also appears in the case of Proca fields. A very interesting feature of these copies is that they arise only for “large enough” gauge potentials. This opens the possibility to avoid the appearance of such gauge fixing ambiguities by using a Gribov–Zwanziger like approach.

Classical sum rules and spin correlations in photoabsorption and photoproduction processes

Abstract In this work we consider the Linear BESS model at the LHC. This model can be seen as an adequated benchmark for exploring the phenomenological consequences of a composite Higgs sector since its particle content is the one we would expect in a realistic low energy description of modern (Technicolor inspired) dynamical electroweak symmetry breaking scenarios. Additionally, the model exhibits the property of decoupling, producing a good ultraviolet behavior. We focus on the limits on the masses of the new heavy vector particles imposed by direct resonance searches, recent measurements of the decay of the Higgs boson into two photons and the electroweak precision tests. We found that the model is capable to accommodate the existing experimental constrains provided that the spin-1 resonances are heavier than 3.4 TeV.