Particle mass generation from physical vacuum

We present an approach for particle mass generation in which the physical vacuum is assumed as a medium at zero temperature and where the dynamics of the vacuum is described by the Standard Model without the Higgs sector. In this approach fermions acquire masses from interactions with vacuum and gauge bosons from charge fluctuations of vacuum. The obtained results are consistent with the physical mass spectrum, in such a manner that left-handed neutrinos are massive. Masses of electroweak gauge bosons are properly predicted in terms of experimental fermion masses and running coupling constants of strong, electromagnetic and weak interactions. An existing empirical relation between the top quark mass and the electroweak gauge boson masses is explained by means of this approach.Comment: 28 pages. arXiv admin note: substantial text overlap with arXiv:hep-ph/0702145, arXiv:0805.2116, arXiv:hep-ph/010920

Quantum phase transition in the chirality of the (2+1)-dimensional Dirac oscillator

We study the (2+1)-dimensional Dirac oscillator in the presence of an external uniform magnetic field ($B$). We show how the change of the strength of $B$ leads to the existence of a quantum phase transition in the chirality of the system. A critical value of the strength of the external magnetic field ($B_c$) can be naturally defined in terms of physical parameters of the system. While for $B=B_c$ the fermion can be considered as a free particle without defined chirality, for $BB_c$) the chirality is left (right) and there exist a net potential acting on the fermion. For the three regimes defined in the quantum phase transition of chirality, we observe that the energy spectra for each regime is drastically different. Then, we consider the $z$-component of the orbital angular momentum as an order parameter that characterizes the quantum phase transition.Comment: 15 page

Graphene physics via the Dirac oscillator in (2+1) dimensions

We show how the two-dimensional Dirac oscillator model can describe some properties of electrons in graphene. This model explains the origin of the left-handed chirality observed for charge carriers in monolayer and bilayer graphene. The relativistic dispersion relation observed for monolayer graphene is obtained directly from the energy spectrum, while the parabolic dispersion relation observed for the case of bilayer graphene is obtained in the non-relativistic limit. Additionally, if an external magnetic field is applied, the unusual Landau-level spectrum for monolayer graphene is obtained, but for bilayer graphene the model predicts the existence of a magnetic field-dependent gap. Finally, this model also leads to the existence of a chiral phase transition.Comment: 11 pages, some references adde

Electroweak standard model at finite temperature in presence of a bosonic chemical potential

We study the electroweak standard model at finite temperature in presence of a bosonic chemical potential associated with the conserved electromagnetic current. To preserve the thermodynamic equilibrium of the system, the thermal medium is neutralized by the introduction of four background charges related to the four gauge bosons of this model. Using the mean-field approximation, in the high temperature limit, we find that there exists a difference between the effective mass of the spatial and temporal components of the W boson. A W boson condensation induced via the background charges allows to vanish this difference.Comment: 18 pages, LATEX, changed content, corrected typos, added referenc

Rest masses of elementary particles as effective masses at zero temperature

We introduce a new approach to generate dinamically the masses of elementary particles in the $SU(3)_C \times SU(2)_L \times U(1)_Y$ Standard Model without Higgs Sector (SMWHS). We start from the assumption that rest masses correspond to the effective masses of particles in an elementary quantum fluid at zero temperature. These effective masses are obtained through radiative corrections, at one-loop order, in the context of the real time formalism of quantum field theory at finite temperature and density. The quantum fluid is described in structure and dynamics by the SMWHS and it is characterized by non-vanishing chemical potentials associated to the different fermion flavour species. Starting from the experimental mass values for quarks and leptons, taking the top quark mass as $m_t = 172.916$ GeV, we can compute, as an evidence of the consistency of our approach, the experimental central mass values for the $W^{\pm}$ and $Z^0$ gauge bosons. Subsequently we introduce in the SMWHS a massless scalar field leading to Yukawa coupling terms in the Lagrangian density. For this case we can also compute the experimental mass central values of the $W^{\pm}$ and $Z^0$ gauge bosons using a top quark mass value in the range 169.2 GeV $< m_{t} < 178.6$ GeV; this range for the top quark mass implies that the scalar boson mass must be in the range $0 < M_{H} < 152$ GeV.Comment: LATEX file, 25 pages, 3 eps figures. Corrected typo

Effective model for particle mass generation

We present an effective model for particle mass generation in which we extract generic features of the Higgs mechanism that do not depend on its interpretation in terms of a Higgs field. In this model the physical vacuum is assumed as a medium at zero temperature which is formed by virtual fermions and antifermions interacting among themselves through the intermediate gauge bosons of the standard model without Higgs sector. As a consequence the fermions acquire their masses from theirs interactions with the vacuum and the gauge bosons from the charge fluctuations of the vacuum. This effective model is completely consistent with the physical mass spectrum, in such a way that the left-handed neutrinos are massive. The masses of the electroweak gauge bosons are properly predicted in terms of the experimental fermions masses and the running coupling constants of the strong, electromagnetic and weak interactions.Comment: 25 pages; LATEX; changed content, corrected typos, added reference

Dispersion relations at finite temperature and density for nucleons and pions

We calculate the nucleonic and pionic dispersion relations at finite temperature T and non-vanishing chemical potentials $(\mu_f)$ in the context of an effective chiral theory that describes the strong and electromagnetic interactions for nucleons and pions. The dispersion relations are calculated in the broken chiral symmetry phase, where the nucleons are massive and pions are taken as massless. The calculation is performed at lowest order in the energy expansion, working in the framework of the real time formalism of thermal field theory in the Feynman gauge. These one-loop dispersion relations are obtained at leading order with respect to T and $\mu_f$. We also evaluate the effective masses of the quasi-nucleon and quasi-pion excitations in thermal and chemical conditions as the ones of a neutron star.Comment: LaTeX File, 10 pages, 2 Postscript figure

Some classical properties of the non-abelian Yang-Mills theories

We present some classical properties for non-abelian Yang-Mills theories that we extract directly from the Maxwell's equations of the theory. We write the equations of motion for the SU(3) Yang-Mills theory using the language of Maxwell's equations in both differential and integral forms. We show that vectorial gauge fields in this theory are non-fermionic sources for non-abelian electric and magnetic fields. These vectorial gauge fields are also responsible for the existence of magnetic monopoles. We build the continuity equation and the energy-momentum tensor for the non-abelian case.Comment: 12 page

Can large fermion chemical potentials suppress the electroweak phase transition ?

We calculate the critical temperature $(T_c$) of the electroweak phase transition in the minimal standard model considering simultaneously temperature ($T$) and fermion chemical potential ($\mu_f$) effects over the effective potential. The calculation is performed in the one-loop approximation to the effective potential at non-zero temperature using the real time formalism of the thermal field theory. We show that it exists a fermion chemical potential critical value ($\mu_f^c$) for which the Higgs boson condensate vanishes at T=0. If $T$ and $\mu_f$ effects are considered simultaneously, it is shown that for $\mu_f \geq \mu_f^c$ then $T_c^2 \leq 0$, implying that the electroweak phase transition might not take place.Comment: LaTex File, 11 pages, 1 Postscript figur

Spreading of wave packets for neutrino oscillations in vacuum

The effects originated in dispersion with time on spreading of wave packets for the time-integrated two-flavor neutrino oscillation probabilities in vacuum are studied in the context of a field theory treatment. The neutrino flavor states are written as superpositions of neutrino mass eigenstates which are described by localized wave packets. This study is performed for the limit of nearly degenerate masses and considering an expansion of the energy until third order in the momentum. We obtain that the time-integrated neutrino oscillation probabilities are suppressed by a factor $1/L^2$ for the transversal and longitudinal dispersion regimes, where $L$ is the distance between the neutrino source and the detector.Comment: 13 pages, some types correcte