arXiv subjects

Alejandro Cabo Montes de Oca

Publications and source records attributed to Alejandro Cabo Montes de Oca.

32 records · Page 2Linked to original sources

arXiv2009

Can the particle mass spectrum be explained within the Standard Model?

A modified version of PQCD considered in previous works is investigated here in the case of retaining only the quark condensate. The Green functions generating functional is expressed in a form in which Dirac's delta functions are now absent from the free propagators. The new expansion implements the dimensional transmutation effect through a single interaction vertex in addition to the standard ones in mass less QCD. The new vertex suggests a way for constructing an alternative to the SM in which the mass and CKM matrices could be generated by the instability of masslesss QCD under the production of the top quark and other fermions condensates, in a kind of generalized Nambu Jona Lasinio mechanism. The results of a two loop evaluation of the vacuum energy indicate that the quark condensate is dynamically generated. However, the energy as a function of the condensate parameter is again unbounded from below in this approximation. Assuming the existence of a minimum of the vacuum energy at the experimental value of the top quark mass mq=173 GeV, we evaluate the two particle propagator in the quark anti-quark channel in zero order in the coupling and a ladder approximation in the condensate vertex. Adopting the notion from the former top quark models, in which the Higgs field corresponds to the quark condensate, the results suggest that the Higgs particle could be represented by a meson which might appear at energies around two times the top quark mass.

hep-ph↗

arXiv2007

Static Universe model existing due to the Matter-Dark Energy coupling

The work investigate a static, isotropic and almost homogeneous Universe containing a real scalar field modeling the Dark-Energy (quintaessence) interacting with pressureless matter. It is argued that the interaction between matter and the Dark Energy, is essential for the very existence of the considered solution. Assuming the possibility that Dark-Energy can be furnished by the Dilaton (a scalar field reflecting the condensation of string states with zero angular momentum) we fix the value of scalar field at the origin to the Planck scale. It became possible to fix the ratio of the amount of Dark Energy to matter energy, in the currently estimated value 0.7/0.3, and also the observed magnitude of the Hubble constant. The value of the mass for the scalar field chosen for fixing the above ratio and Hubble effect strength, results to be of the order of 10^{-29}cm^{-1}, a small mass which seems to be compatible with the zero mass of the Dilaton in the lowest approximations.

gr-qc↗

arXiv2007

Vacuum polarization of massive spinor fields in static black-string backgrounds

The renormalized mean value of the quantum Lagrangian and the corresponding components of the Energy-Momentum tensor for massive spinor fields coupled to an arbitrary gravitational field configuration having cylindrical symmetry are analytically evaluated using the Schwinger-DeWitt approximation, up to second order in the inverse mass value. The general results are employed to explicitly derive compact analytical expressions for the quantum mean Lagrangian and Energy- Momentum tensor in the particular background of the Black-String space-time.

gr-qc↗

arXiv2007

Renormalized Wick expansion for a modified PQCD

The renormalization scheme for the Wick expansion of a modified version of the perturbative QCD introduced in previous works is discussed. Massless QCD is considered, by implementing the usual multiplicative scaling of the gluon and quark wave functions and vertices. However, also massive quark and gluon counter-terms are allowed in this mass less theory since the condensates are expected to generate masses. A natural set of expansion parameters of the physical quantities is introduced: the coupling itself and to masses $m_q$ and $m_g$ associated to quarks and gluons respectively. This procedure allows to implement a dimensional transmutation effect through these new mass scales. A general expression for the new generating functional in terms of the mass parameters $m_q$ and $m_g$ is obtained in terms of integrals over arbitrary but constant gluon or quark fields in each case. Further, the one loop potential, is evaluated in more detail in the case when only the quark condensate is retained. This lowest order result again indicates the dynamical generation of quark condensates in the vacuum.

hep-ph↗

arXiv2007

Quantization of massive scalar fields over static black string backgrounds

The renormalized mean value of the corresponding components of the Energy-Momentum tensor for massive scalar fields coupled to an arbitrary gravitational field configuration having cylindrical symmetry are analytically evaluated using the Schwinger-DeWitt approximation, up to second order in the inverse mass value. The general results are employed to explicitly derive compact analytical expressions for the Energy-Momentum tensor in the particular background of the Black-String spacetime. In the case of the Black String considered in this work, we proof that a violation of the weak energy condition occur at the horizon of the space-time for values of the coupling constant, that include as particular cases the most interesting of minimal and conformal coupling.

gr-qc↗

arXiv2007

Quantization of massive scalar fields over axis symmetric space-time backgrounds

The renormalized mean value of the quantum Lagrangian and the Energy-Momentum tensor for scalar fields coupled to an arbitrary gravitational field configuration are analytically evaluated in the Schwinger-DeWitt approximation, up to second order in the inverse mass value. The cylindrical symmetry situation is considered. The results furnish the starting point for investigating iterative solutions of the back-reaction problem related with the quantization of cylindrical scalar field configurations. Due to the homogeneity of the equations of motion of the Klein-Gordon field, the general results are also valid for performing the quantization over either vanishing or non-vanishing mean field configurations. As an application, compact analytical expressions are derived here for the quantum mean Lagrangian and Energy-Momentum tensor in the particular background given by the Black-String space-time.

gr-qc↗

arXiv2005

Particle dynamics in a relativistic invariant stochastic medium

The dynamics of particles moving in a medium defined by its relativistically invariant stochastic properties is investigated. For this aim, the force exerted on the particles by the medium is defined by a stationary random variable as a function of the proper time of the particles. The equations of motion for a single one-dimensional particle are obtained and numerically solved. A conservation law for the drift momentum of the particle during its random motion is shown. Moreover, the conservation of the mean value of the total linear momentum for two particles repelling each other according with the Coulomb interaction is also following. Therefore, the results indicate the realization of a kind of stochastic Noether theorem in the system under study. Possible applications to the stochastic representation of Quantum Mechanics are advanced.

quant-ph↗

arXiv2005

About the role of 2D screening in High Temperature Superconductivity

The 2D screening is investigated in a simple single band square tight-binding model which qualitatively resembles the known electronic structure in high temperature superconductors. The Coulomb kernel for the two particle Bethe-Salpeter equation in the single loop (RPA) approximation for the polarization can be evaluated in a strong tight binding limit. The results indicate an intense screening of the Coulomb repulsion between the particles, which becomes stronger and anisotropic when the Fermi level approach half filling (or equivalently, when the Fermi surface approach the Van Hove singularities) and rapidly decreases away it. The effect is also more pronounced for quasi-momenta regions near the corners of the Brillouin cell, which correspond to dual spatial distances of the order few unit cells. Therefore, a possible mechanism is identified which could explain the existence of extremely small Cooper pairs in these materials, as bounded anisotropic composites joined by residual super-exchange or phonon interactions.

cond-mat.supr-con↗

arXiv2005

Can mass-less QCD dynamically generate heavy quarks?

As it was suggested by previous works on a modified perturbation expansion for QCD, the possibility for the generation of large quark condensates in the mass-less version of the theory is explored. For this purpose, it is firstly presented a way of well define the Feynman diagrams at any number of loops by just employing dimensional regularization. After that, the calculated zero and one loop corrections to the effective potential indicate a strong instability of the system under the generation of quark condensates. The also evaluated quark condensate dependence of particular two loop terms does not modify the instability picture arising at one loop. The results suggest a possible mechanism for a sort of Top Condensate Model to be a dynamically fixed effective action for mass-less QCD. The inability of lattice calculations in detecting this possibility could be related with the limitations in treating the fermion determinants.

hep-ph↗

arXiv2002

Non-reciprocity and heat transfer in far from equilibrium processes

A non-reciprocal phonon model for microwave or optical isolators is considered. It gives a simpler framework to further investigate the formerly argued possibility for a heat transfer between black bodies at common temperatures. While the non-dissipative device retains the Detailed Balance property, the presence of dissipation breaks it. This property allows a net transfer of heat between the two black bodies at common temperatures, whenever the absorptive elements are at lower temperatures than the one being common to the bodies.

cond-mat.stat-mech↗

arXiv2002

On the gauge invariant and topological nature of the localization determining the Quantum Hall Effect plateaus

It is shown how the electromagnetic response of the 2DEG under Quantumm Hall Effect regime, chracterized by the Chern-Simons topological action, transforms the sample impurities and defects in charge reservoirs that stabilize the the Hall conductivity plateaus. The results, determine the basic dynamical origin of the singular properties of localization under the occurrence of the QHE obtained in the pioneering works of Laughlin and of Joynt and Prange, by means of a gauge invariance argument and a purely electronic analysis, respectively. The common picture of electrons moving the equipotential lines gets an analytical realization through the Chern-Simons current and charge densities.

cond-mat.mes-hall↗

arXiv2000

Edge Modes Waves in Superlattices in Quantum Hall Effect Regime

The wave propagation of edge modes in a superlattice of 2D electron Gases in quantum Hall regime is investigated. After introducing surfaces charge and current densities at the edge, the Maxwell equations are solved for waves running along the boundary. The constitutive relations expressing the edge charge and current densities in terms of the fields at the boundary are derived. One of them is similar to the London equation for superconductor currents. The dispersion relation and wave polarizations for the momenta region $w/c<k$ are also obtained for propagation along the borderlines of the electron gases. It follows that the modes have no dispersion at any frequency. The static limit solutions complete the definition at the boundary of the formerly determined interior field configurations showing a Meissner like effect. The results underline that various of the current theoretical approaches to edge excitations could be appropriate for superlattice structures but can fail to describe standard planar samples.

cond-mat.mes-hall↗

arXiv1998

On the sign of the static dielectric function at T=0

The question of the allowed signs for the static dielectric function for exactly homogeneous ground states in many body systems is further analyzed. The discussion is restricted to zero temperature situation. Firstly, it is argued that the positivity is equivalent to the requirement that the work needed for to adiabatically connect a static charge density, be positive. In particular the rule seems to be a fully appropriate stability condition if the system interacts with a freely moving but coulomb interacting jellium. This situation is common in thermodynamical equilibrium discussions, in which the system can be stable or not in dependence of the relaxation of some external constraints. Further, an argument based in a quantized electromagnetic field treatment is also given. It requires the positivity of the dielectric function as an intrinsic stability condition for the charged system independently of the jellium dynamics.Possible inmplications for the more complex finite temperature situation are commented.

cond-mat.stat-mech↗

arXiv1998

On the magneto-roton gap and the Laughlin state stability

It is argued that the Girvin, MacDonald and Platzman (GMP) evaluation of the magneto-roton spectrum, in spite of probably being a sensible estimate of the excitation spectrum around the real ground state, is not implying the variational stability of the Laughlin state. The suplementary corrections needed to produce a variational calculation around the Laughlin state at 1/3 value of the filling factor are evaluated approximately. The results indicate, within the considered approximation, the existence of lower lying states for a range of wavevector values.

cond-mat.mes-hall↗