Carlos Quimbay

Leptogenesis and tensor polarisation from a gravitational Chern-Simons term

Centro de Investigaciones, Universidad Antonio Narin˜o,Cll 58A # 37-94, Bogot´a D.C., ColombiaJanuary 2005AbstractWithin an effective field theory derived from string theory, the universal axionhas to be coupled to the the gravitational Chern-Simons (gCS) term. Duringany era when the axion field is varying, the vacuum fluctuation of the gravi-tational wave amplitude will then be circularly polarised, generating an expec-tation value for the gCS term. The polarisation may be observable throughthe Cosmic Microwave Background, and the vacuum expectation value of thegCS term may generate the baryon asymmetry of the Universe. We argue herethat such effects cannot be computed without further input from string theory,since the ‘vacuum’ in question is unlikely to be the field-theoretic one.

Spontaneous CP phases and flavour changing neutral currents in the left–right symmetric model

Abstract We study the behaviour of the flavour changing neutral currents in the left–right symmetric model related to the presence of spontaneous CP phases. To do this, we explore four cases corresponding to combinations of maximal and no CP violation in both the lepton and quark sector. We find that we can constrain the flavour changing neutral currents to the experimental limit, by adjusting the CP-violating phase of the quark sector, opening the possibility to obtain a large CP violation in the lepton sector as well as new Higgs bosons at the electroweak scale.

Fermionic dispersion relations at finite temperature and non-vanishing chemical potentials in the minimal standard model

Abstract We calculate the fermionic dispersion relations in the minimal standard model at finite temperature in presence of non-vanishing chemical potentials due to the CP-asymmetric fermionic background. The dispersion relations are calculated for a vacuum expectation value of the Higgs field equal to zero (unbroken electroweak symmetry). The calculation is performed in the real time formalism of the thermal field theory at one-loop order in a general ζ gauge. The fermionic self-energy is calculated at leading order in temperature and chemical potential and this fact permits us to obtain gauge-invariant analytical expressions for the dispersion relations.

Majorana Neutrino Oscillations in Vacuum

In the context of a type I seesaw scenario which leads to get light left-handed and heavy right-handed Majorana neutrinos, we obtain expressions for the transition probability densities between two flavor neutrinos in the cases of left-handed and right-handed neutrinos. We obtain these expressions in the context of an approach developed in the canonical formalism of Quantum Field Theory for neutrinos which are considered as superpositions of mass-eigenstate plane waves with specific momenta. The expressions obtained for the left-handed neutrino case after the ultra-relativistic limit is taking lead to the standard probability densities which describe light neutrino oscillations. For the right-handed neutrino case, the expressions describing heavy neutrino oscillations in the non-relativistic limit are different respect to the ones of the standard neutrino oscillations. However, the right-handed neutrino oscillations are phenomenologically restricted as is shown when the propagation of heavy neutrinos is considered as superpositions of mass-eigenstate wave packets.

Are the new physics contributions from the left-right symmetric model important for the indirect CP violation in the neutral B mesons?

No HeadingSeveral works analyzing the new physics contributions from the Left-Right Symmetric Model to the CP violation phenomena in the neutral B mesons can be found in the literature. These works exhibit interesting and experimentally sensible deviations from the Standard Model predictions but at the expense of considering a low right scale υR around 1 TeV. However, when we stick to the more conservative estimates for υR, which say that it must be at least 107 GeV, no experimentally sensible deviations from the Standard Model appear for indirect CP violation. This estimate for υR arises when the generation of neutrino masses is considered. In spite of the fact that this scenario is much less interesting and says nothing new about both the CP violation phenomenon and the structure of the Left-Right Symmetric Model, this possibility must be taken into account for the sake of completeness and when considering the see-saw mechanism that provides masses to the neutrino sector.