arXiv subjects

Alejandro Cabo

Publications and source records attributed to Alejandro Cabo.

At least 19 recordsLinked to original sources

arXiv2018

Can the symmetry breaking in the SM be determined by the "second minimum" of the Higgs potential?

The possibility that the spontaneous symmetry breaking in the Standard Model (SM) may be generated by the Top-Higgs Yukawa interaction (which determines the so called "second minimum" in the SM) is examined. A former analysis is extended about a QCD action only including the Yukawa interaction of a single quark with a scalar field. We repeat the calculation of the two loop effective action of the model for the scalar field. A correction of the evaluation allowed choosing a strong coupling $\alpha $($\mu,\Lambda_{QCD})=0.2254$ GeV at an intermediate scale $\mu=11.63$ GeV, in order to fix the minimum of the potential at a scalar field determining $175$ GeV for the quark mass. A scalar field mass $m=44$ GeV is following, which is of the order than the experimental Higgs mass. The effects of considering a running with momenta coupling are studied. For this, the finite part of the two loop potential contribution determined by the strong coupling, was represented as a momentum integral. Next, substituting in this integral the experimental values of the running coupling, the potential curve became very similar to the one for constant coupling. This happened after simply assuming that the low momentum dependence of the coupling is "saturated" to a constant value being close to its lowest experimental value.

hep-ph↗

arXiv2017

Can the symmetry breaking in the SM be determined by the Top-Higgs Yukawa interaction?

In this letter, we first resume the results of a previous article (EPJC(2011)71:1620). That work considered a simple model of QCD including a Yukawa interaction with a scalar field. Its two loop effective potential for the scalar field, predicted a 126 GeV Higgs mass after the minimum of the potential was fixed at a mean scalar field giving a 175 GeV Top quark mass. However, a high value of the strong coupling was required (\alpha=g^2/(4 \pi) close to 1) to get these values. After reviewing the results of this study, an idea for extending the work is simply advanced here: to consider the running strong coupling, in order to decide whether or not, the usual values of the strong interactions have the chance of justifying the experimentally known values of the Higgs and Top quark masses. It is underlined that a positive result of the proposed task will suggests the possibility of basing the SM breaking of symmetry, on the so called "second minimum" of this model. This could also identify the essential role of QCD in this effect. Results of the further examination of this question will be presented elsewhere.

hep-ph↗

arXiv2016

About the effects of diffusion in electric tomography

The Maxwell equations for an homogeneous medium in which electric currents are composed of Ohmic, diffusive and impressed currents are written in the static approximation in which displacements currents are neglected. Closed exact expressions are given for the solutions of the charge density, electric field potential and the magnetic field intensity as functions of the impressed currents and densities. Also, approximate formulae for these magnitudes are derived. The solutions correctly reproduce the conclusions of a previous work in which the relevance of Yukawa like potentials determined by diffusion effects were identified. Within the approximate solutions, the effective potential generated by the impressed sources is given by the superposition of Yukawa potentials created by the impressed charges concentrated in a given volume element. This representation makes evident that at small spatial regions, the experimental detectors are able to measure spherically symmetrical signals, indicating the presence of electric monopoles. The discussion also allows to argue that the magnetic field tomographic signal becomes completely independent of the presence of diffusion in the medium. The analysis also permits to determine the range of space and temporal frequencies in which the diffusion effects might become important in justifying the detection of monopole signals.

physics.bio-ph↗

arXiv2014

How the active and diffusional nature of brain tissues can generate monopole signals at micrometer sized measures

We investigate mechanisms which could generate transient monopole signals in measuring current source density (CSD), as it had been indicated to occur in recent small volume experiments. A simple model is defined for this purpose. It is emphasized that the active nature of the neural biological activity, with its ability to generate ionic density imbalances, might be able to induce appreciable monopole signals in CSD detectors at micrometer scales. Thus, it follows that when both diffusive and ohmic transport are considered to be present in neural tissues, potential measures in micrometer regions can include appreciable electric monopole signals, for sufficiently small values of the ratio (\sigma a^{2})/(\epsilon D), where "\sigma" is the conductivity, "\epsilon" is the dielectric constant, "D" is the diffusion constant and "a" is the linear dimension of the ionic charge densities generated by the neural processes. Ranges of possible magnitudes for these parameters in the considered experimental studies are estimated. The analysis indicates values for the ratio between the dipolar and monopole signals which are close to the ones measured in Pyramidal cells in recent experiments. The measured results for Spiny Stellate cells are also qualitatively described by the model by predicting a finite monopole signal in combination with vanishing dipolar and quadrupole ones.

physics.bio-ph↗

arXiv2011

Scattering solution of a ball by a bat

The problem of the mechanical evolution of a shock between a cylindrically symmetric bat and a spherical ball is solved in the strict rigid approximation for arbitrary values of the initial conditions. The friction during the impact is assumed to satisfy the standard rules. When the only source of energy dissipation is friction, the problem is fully solved by determining the separation point between the bodies. It also follows that whatever the character of any additional form of dissipation is, it only affects the ending value of the net impulse I done by the normal force of the bat on the ball at separation, but not the dynamical evolution with the value of I during the shock process. A relation determining whether the contact points of the two bodies slides between them or become at rest (to be pure rotation state) at the end of the impact, is determined for the case of the purely frictional energy dissipation. The solution is also generalized to include losses in addition to the frictional ones and then applied to the description of experimental measures of the scattering of a ball by a bat. The evaluations satisfactorily reproduce the measured curves for the output center of mass and angular velocities of the ball as functions of the scattering angle and the impact parameter, respectively.

physics.class-ph↗

arXiv2010

Dilaton stabilization by massive fermion matter

The study started in a former work about the Dilaton mean field stabilization thanks to the effective potential generated by the existence of massive fermions, is here extended. Three loop corrections are evaluated in addition to the previously calculated two loop terms. The results indicate that the Dilaton vacuum field tend to be fixed at a high value close to the Planck scale, in accordance with the need for predicting Einstein gravity from string theory. The mass of the Dilaton is evaluated to be also a high value close to the Planck mass, which implies the absence of Dilaton scalar signals in modern cosmological observations. These properties arise when the fermion mass is chosen to be either at a lower bound corresponding to the top quark mass, or alternatively, at a very much higher value assumed to be in the grand unification energy range. One of the three 3-loop terms is exactly evaluated in terms of Master integrals. The other two graphs are however evaluated in their leading logarithm correction in the perturbative expansion. The calculation of the non leading logarithmic contribution and the inclusion of higher loops terms could made more precise the numerical estimates of the vacuum field value and masses, but seemingly are expected not to change the qualitative behavior obtained. The validity of the here employed Yukawa model approximation is argued for small value of the fermion masses with respect to the Planck one. A correction to the two loop calculation done in the previous work is here underlined.

hep-th↗

arXiv2010

Is the Tsallis q-mean value instable?

The recent argue about the existence of an instability in the definition of the mean value appearing in the Tsallis non extensive Statistical Mechanic is reconsidered. Here, it is simply underlined that the pair of probability distributions employed in constructing the instability statement have a discontinuous limit when the number of states tends to infinity. That is, although for an arbitrary but finite number of states W, both probability distributions are normalized to the unit, their limits W tending to infinity do not satisfy the normalization condition and thus are not allowed "escort" probabilities for the q-mean value. However, similar distributions converging to the former ones when a parameter W_o is tending to infinity are defined here. They both satisfy the normalization to the unity in the limit W tending to infinity. This simple change allows to show that the stability condition becomes satisfied, for whatever large but fixed value of W_o is chosen.

cond-mat.stat-mech↗

arXiv2010

Effect of Laughlin correlations on crystalline mean field solutions of the 2DEG in FQHE regime

The energy per particle of many body wavefunctions that mix Laughlin liquid with crystalline correlations for periodic samples in the Haldane-Rezayi configuration is numerically evaluated for periodic samples. The Monte Carlo algorithm is employed and the wave functions are constructed in such a way that have the same zeroes as the periodic Laughlin states. Results with up to 16 particles show that these trial wavefunctions have lower energy than the periodic Laughlin states for finite samples even at $\nu=1/3$. Preliminary results for 36 particles suggest that this tendency could reach the thermodynamic limit. These results get relevance in view of the very recent experimental measures that indicate the presence of periodic structures in the 2DEG for extremely small temperatures and clean samples, inclusive at main FQHE filling fractions $\nu=1/3,2/3 $.

cond-mat.mes-hall↗

arXiv2009

Exact eigenfunctions of FQHE systems at fractional filling factors 1/q. I. Formal results

Eigenstates of the FQHE hamiltonian problem after to be projected on the LLL are determined for filling factors 1/q, with q an odd number. The solutions are found for an infinite class of finite samples in which the Coulomb potential is periodically extended. Therefore, a thermodynamic limit solution is also identified. The results suggest the presence of integrability properties in FQHE systems. The many particle states are simple Slater determinants constructed with special single particle states. These orbitals are defined as powers of order q of "composite fermion" like wavefunctions associated to a reduced magnetic field B/q. At the same time, those "composite fermion" states were obtained by factorizing and canceling fixed position (quasi-momentum independent) zeros in previously derived exact Hartree-Fock orbitals. A formula for the energy per particle of the FQHE states is given for finite samples as well as for the thermodynamic limit state. As a side result, the same "composite fermions" like orbitals are employed to construct variational wavefunctions of the system, showing zeros of order q as two electrons approach each other, as Laughlin states do. The long range spatial correlation associated to the starting HF solutions may further reduce the energy of these states.

cond-mat.mes-hall↗

arXiv2009

Stationary density matrix of a pumped polariton system

The density matrix, ρ, of a model polariton system is obtained numerically from a master equation which takes account of pumping and losses. In the stationary limit, the coherences between eigenstates of the Hamiltonian are three orders of magnitude smaller than the occupations, meaning that the stationary density matrix is approximately diagonal in the energy representation. A weakly distorted grand canonical Gibbs distribution fits well the occupations.

cond-mat.mes-hall↗

arXiv2008

Could Fermion Masses Play a Role in the Stabilization of the Dilaton in Cosmology?

We study the possibility that the Dilaton is stabilized by the contribution of fermion masses to its effective potential. We consider the Dilaton gravity action in four dimensions to which we add a mass term for a Dirac fermion. Such an action describes the interaction of the Dilaton with the fermions in the Yang-Mills sector of the coupled supergravity/super-Yang-Mills action which emerges as the low energy effective action of superstring theory after the extra spatial dimensions have been fixed. The Dilaton couples to the Fermion mass term via the usual exponential factor of this field which multiplies the non-kinetic terms of the matter Lagrangian, if we work in the Einstein frame. In the kinetic part of the Fermion action in the Einstein frame the Dilaton does not enter. Such masses can be generated in several ways: they can arise as a consequence of flux about internal spatial dimensions, they may arise as thermal fermion masses in a quasi-static phase in the early universe, and they will arise after the breaking of supersymmetry at late times. The vacuum contribution to the potential for the Dilaton is evaluated up to two loops. The result shows a minimum which could stabilize the Dilaton for reasonable ranges of parameter values.

hep-th↗

arXiv2007

On the statistical physics of metastable and non-equilibrium stationary states

The optimization problems defining meta-stable or stationary equilibrium are explored. The Gibbs scheme is modified aiming to describe the statistical properties of a class of non-equilibrium and metastable states. The system is assumed to maximize the usual definition of the Entropy, subject to the standard constant energy and norm restrictions, plus additional constraints. The central assumption is that the existence of the considered metastable state is determined by the action of this additional dynamical constraint, that blocks the evolution of the system up to its maximum Entropy state, thus maintaining it in the metastable or stationary configuration. After requiring from the statistical description to be valid for the combination of two nearly independent subsystems, it follows that the eigenvalues of the constraint operators C should have the restricted homogeneous form C(p{i})=p{i}^{q}, in terms of the eigenvalues of the density matrix p{i}, where q is a fixed real number. Therefore, the distribution of the eigenvalues of the constraint function have the Tsallis structure. This conclusion suggests the interpretation of the q parameter as reflecting the homogeneous dependence of the constraint determining the metastable state on the density matrix. An application to the plasma experiments of Huang and Driscoll is expected to be considered elsewhere in order to compare the results with Tsallis scheme and the minimal Enstrophy one.

cond-mat.stat-mech↗

arXiv2007

Crystal mean field based trial wavefunctions for the FQHE ground states

Employing the Haldane-Rezayi periodic representation, the crystalline determinantal Hall crystal mean field solutions derived in previous works are used to construct variational wavefunctions for the FQHE at $ν=1/q$. The proposed states optimize the short range correlations in a similar measure as the Laughlin ones, since the zero of the states when the coordinates of two particles join is of order $q$. However, the proposed wavefunctions also incorporate the crystalline correlations of the mean field problem, through a determinantal mean field function entering their construction. The above properties, lead to the expectation that the considered states can be competitive in energy per particle with the Laughlin ones. Their similar structure also could explain way the breaking of the translation invariance in the FQHE ground states can result to be a weak one, which after disregarded, produce the Laughlin states as good approximations. Calculation for checking these possibilities are under consideration.

cond-mat.mes-hall↗

arXiv2007

Mean field exact solutions showing charge density wave crossover at low fillings in the fractional quantum Hall regime

A general analytical framework for the determination of the mean field states at arbitrary rational filling factors for the 2DEG in FQHE regime is given. Its use allows to obtain analytic expressions for the solutions at filling factors of the form $ν=1/q$ for arbitrary odd $q$. The analysis can be performed for two general classes of states characterized by $γ=1$ or $γ={1/2}$ particles per unit cell. Instead of the periodic peaks of the Wigner solid solution, the new states show electron densities forming percolating ridges that may favor an energy decrease through correlated ring of exchange contributions. Therefore, we estimate that they can realize mean field versions of the so called Hall Crystal (HC) states. The obtained analytic HC solution shows the same crystalline symmetry that the corresponding WC state in its class $γ=1$, but a qualitatively different charge density distribution. The energy dependence of the corresponding HC and WC states on the filling factor is also evaluated here for the class $γ=1/2$. The results show a crossover between HC state and the Wigner crystal, close to filling 1/7. Therefore, transitions may occur from one to the other as the electron density is varied. This result is consistent with recent experimental findings.

cond-mat.mes-hall↗

arXiv2006

Photon emission as a source of coherent behaviour of polaritons

We show that the combined effect of photon emission and Coulomb interactions may drive an exciton-polariton system towards a dynamical coherent state, even without phonon thermalization or any other relaxation mechanism. Exact diagonalization results for a finite system (a multilevel quantum dot interacting with the lowest energy photon mode of a microcavity) are presented in support to this statement.

cond-mat.mes-hall↗

arXiv2005

Gauge invariance properties and singularity cancellations in a modified PQCD

The gauge-invariance properties and singularity elimination of the modified perturbation theory for QCD introduced in previous works, are investigated. The construction of the modified free propagators is generalized to include the dependence on the gauge parameter $α$. Further, a functional proof of the independence of the theory under the changes of the quantum and classical gauges is given. The singularities appearing in the perturbative expansion are eliminated by properly combining dimensional regularization with the Nakanishi infrared regularization for the invariant functions in the operator quantization of the $α$-dependent gauge theory. First-order evaluations of various quantities are presented, illustrating the gauge invariance-properties.

hep-ph↗

arXiv2005

Can the cosmological constant undergo abrupt changes?

The existence of a simple spherically symmetric and static solution of the Einstein equations in the presence of a cosmological constant vanishing outside a definite value of the radial distance is investigated. A particular succession of field configurations, which are solutions of the Einstein equations in the presence of the considered cosmological term and auxiliary external sources, is constructed. Then, it is shown that the associated succession of external sources tend to zero in the sense of the generalized functions. The type of weak solution that is found becomes the deSitter homogeneous space-time for the interior region, and the Schwartzschild space in the outside zone.

gr-qc↗

arXiv2005

Phase diagram of two dimensional electron gas in a perpendicular magnetic field around Landau level filling factors ν=1 and ν=3

The measured melting curve $T_{m}(ν)$ between the crystal and liquid phases is analyzed using thermodynamics to extract the change of magnetization $ΔM$ as a function of the Landau level filling factor \ $ν,$ near $ν=1$. \ An explanation of $ΔM$($ν)$ is proposed \ in terms of Skyrmions. \ Near $ν=3$, a Wigner crystal is the most probable solid phase, experiments excluding Skyrmions.

cond-mat.mes-hall↗