arXiv subjects

R. Gonzalez Felipe

Publications and source records attributed to R. Gonzalez Felipe.

At least 55 records · Page 3Linked to original sources

arXiv2004

Sneutrino brane inflation and leptogenesis

Modifications to the Friedmann equation in brane cosmology can have important implications for early universe phenomena such as inflation and the generation of the baryon asymmetry. We study a simple scenario of chaotic brane inflation where, in a minimal supersymmetric seesaw model, the scalar superpartner of a heavy singlet Majorana neutrino drives inflation and, simultaneously, generates the required lepton asymmetry through its direct out-of-equilibrium decays after the inflationary era. For a gravitino mass in the range 100 GeV - 1 TeV, we find that successful nucleosynthesis and leptogenesis in this framework require that the 5D Planck mass is in the range M5 ~ 10^10 - 10^13 GeV and the reheating temperature Trh ~ 10^6 - 10^8 GeV.

hep-ph↗

arXiv2003

Polychromatic Grand Unification

The possibility of achieving a gauge coupling grand unification by increasing the QCD degrees of freedom at higher energies is investigated. When confronted with precision low-energy data, the generic weak-mixing angle relation sin^2(theta_W) = N/2(N+1) requires N=7 colors at the GUT scale M_U ~ 10^17 GeV. With the exclusive addition of light Higgs doublets to the standard model particle content, such a unification may also occur if N=5 at M_U ~ 10^16 GeV.

hep-ph↗

arXiv2003

Removing Ambiguities in the Neutrino Mass Matrix

We suggest that the weak-basis independent condition det(M_nu)=0 for the effective neutrino mass matrix can be used in order to remove the ambiguities in the reconstruction of the neutrino mass matrix from input data available from present and future feasible experiments. In this framework, we study the full reconstruction of M_nu with special emphasis on the correlation between the Majorana CP-violating phase and the various mixing angles. The impact of the recent KamLAND results on the effective neutrino mass parameter is also briefly discussed.

hep-ph↗

arXiv2003

Minimal Scenarios for Leptogenesis and CP Violation

The relation between leptogenesis and CP violation at low energies is analyzed in detail in the framework of the minimal seesaw mechanism. Working, without loss of generality, in a weak basis where both the charged lepton and the right-handed Majorana mass matrices are diagonal and real, we consider a convenient generic parametrization of the Dirac neutrino Yukawa coupling matrix and identify the necessary condition which has to be satisfied in order to establish a direct link between leptogenesis and CP violation at low energies. In the context of the LMA solution of the solar neutrino problem, we present minimal scenarios which allow for the full determination of the cosmological baryon asymmetry and the strength of CP violation in neutrino oscillations. Some specific realizations of these minimal scenarios are considered. The question of the relative sign between the baryon asymmetry and CP violation at low energies is also discussed.

hep-ph↗

arXiv2002

Flavor-dependent CP violation and electroweak baryogenesis in supersymmetric theories

We analyze electroweak baryogenesis in supersymmetric theories with flavor-dependent CP-violating phases. We generalize the standard approach to include the flavor dependence of the CP-violating sources and obtain an analytical approximate expression for the baryon asymmetry of the universe induced by these sources. It is shown that in the framework where the $μ$-term is real and the chargino sources vanish, large flavor mixing might lead to a substantial baryon asymmetry through the squark contributions, once the condition to have a strong first-order phase transition induced by light right-handed up squarks is relaxed. We derive model independent bounds on the relevant up-squark left-right mass insertions. We show that in supersymmetric models with non-minimal flavor structure these bounds can be reached and the required baryon asymmetry can be generated, while satisfying the constraints coming from the electric dipole moments.

hep-ph↗

arXiv2002

Leptogenesis, CP violation and neutrino data: What can we learn?

A detailed analytic and numerical study of baryogenesis through leptogenesis is performed in the framework of the standard model of electroweak interactions extended by the addition of three right-handed neutrinos, leading to the seesaw mechanism. We analyze the connection between GUT-motivated relations for the quark and lepton mass matrices and the possibility of obtaining a viable leptogenesis scenario. In particular, we analyze whether the constraints imposed by SO(10) GUTs can be compatible with all the available solar, atmospheric and reactor neutrino data and, simultaneously, be capable of producing the required baryon asymmetry via the leptogenesis mechanism. It is found that the Just-So^2 and SMA solar solutions lead to a viable leptogenesis even for the simplest SO(10) GUT, while the LMA, LOW and VO solar solutions would require a different hierarchy for the Dirac neutrino masses in order to generate the observed baryon asymmetry. Some implications on CP violation at low energies and on neutrinoless double beta decay are also considered.

hep-ph↗

arXiv2001

Is right-handed neutrino degeneracy compatible with the solar and atmospheric neutrino data?

In light of the recent solar and atmospheric neutrino data, we investigate the possibility of having an exactly degenerate spectrum for heavy right-handed Majorana neutrinos at the grand unification scale. The analysis is performed in the context of the minimal supersymmetric standard model with unbroken R-parity and extended with three heavy Majorana neutrino fields in order to implement the seesaw mechanism. In the absence of a Dirac-type leptonic mixing, the only source of lepton flavour violation is the right-handed neutrino sector. Inspired by GUT-motivated relations among the quark, charged-lepton and Dirac neutrino Yukawa coupling matrices, and after the inclusion of the radiative effects, we determine the effective neutrino mass matrix at the electroweak scale. Using then the latest global analyses of the solar and atmospheric data at 99% C.L., we conclude that, within this framework, the only solar solutions compatible with the experimental data are the LOW and LMA solutions, being the latter the most favoured one. At 90% C.L., only the LMA solution is allowed.

hep-ph↗

arXiv2001

Dynamical CP Violation and Flavour-Changing Processes

We investigate the phenomenological constraints on a model where, besides the standard model Higgs sector, there is an effective new strong interaction acting on the third generation of quarks and characterized by a $θ$-like term. This $θ$ term induces electroweak symmetry breaking and leads to dynamical spontaneous CP violation. We show that the constraints coming from K physics and the electric dipole moment of the neutron impose that the new physics scale should be of the order of 35 TeV. Contrary to naive expectations, the predictions of the model for B physics are very close to the standard model ones. The main differences appear in processes involving the up quarks such as $D^0-\bar{D}^0$ mixing and in the electric dipole moment of the neutron, which should be close to the experimental limit. Possible deviations from the standard model predictions for CP asymmetries in B decays are also considered.

hep-ph↗

arXiv2000

Radiatively Induced Lorentz and CPT Violation in Schwinger Constant Field Approximation

The Schwinger proper-time method is an effective calculation method, explicitly gauge invariant and nonperturbative. We make use of this method to investigate the radiatively induced Lorentz and CPT-violating effects in quantum electrodynamics when an axial vector interaction term is introduced in the fermionic sector. The induced Lorentz and CPT-violating Chern-Simons term coincides with the one obtained using a covariant derivative expansion but differs from the result usually obtained in other regularization schemes. A possible ambiguity in the approach is also discussed.

hep-th↗

arXiv2000

Yukawa Structure with Maximal Predictability

A simple Ansatz for the quark mass matrices is considered, based on the assumption of a power structure for the matrix elements and the requirement of maximal predictability. A good fit to the present experimental data is obtained and the position of the vertex of the unitarity triangle, i.e. (\barρ,\barη), is predicted.

hep-ph↗

arXiv1999

Texture Zeros and Weak Basis Transformations

We investigate the physical meaning of some of the "texture zeros" which appear in most of the Ansatze on quark masses and mixings. It is shown that starting from arbitrary quark mass matrices and making a suitable weak basis transformation one can obtain some of these sets of zeros which therefore have no physical content. We then analyse the physical implications of a four-texture zero Ansatz which is in agreement with all present experimental data.

hep-ph↗

arXiv1998

Electroweak Baryogenesis in the Presence of an Isosinglet Quark

We consider the possibility of electroweak baryogenesis in a simple extension of the standard model with an extra singlet complex scalar and a vector-like down quark. We show that in the present model the first-order electroweak phase transition can be strong enough to avoid the baryon asymmetry washout by sphalerons and that the CP-violating effects can be sufficient to explain the observed baryon-to-entropy ratio nB/s ~ 10^(-10). Other appealing features of the model include the generation of a CKM phase from spontaneous CP breaking at a high energy scale and a possible solution of the strong CP problem through the natural suppression of the parameter theta.

hep-ph↗

arXiv1997

On the Chern-Simons topological term at finite temperature

The parity-violating topological term in the effective action for 2+1 massive fermions is computed at finite temperature in the presence of a constant background field strength tensor. Gauge invariance of the finite-temperature effective action is also discussed.

hep-th↗

arXiv1997

Equivalence of the sine-Gordon and massive Thirring models at finite temperature

Using the path-integral approach, the quantum massive Thirring and sine-Gordon models are proven to be equivalent at finite temperature. This result is an extension of Coleman's proof of the equivalence between both theories at zero temperature. The usual identifications among the parameters of these models also remain valid at $T \neq 0$.

hep-th↗

arXiv1997

A Dynamical Scheme for a Large CP-Violating Phase

A dynamical scheme where the third generation of quarks plays a distinctive role is implemented. New interactions with a $θ$ term induce the breaking of the electroweak symmetry and the top-bottom mass splitting. A large CP-violating phase naturally follows from the latter.

hep-ph↗

arXiv1996

Behaviour of the Absorptive Part of the W Electromagnetic Vertex

The absorptive part of the $WWγ$ vertex induced by massive fermion loops is considered for different kinematical configurations. We show that the axial part of this vertex is different from zero not only when massive fermions are involved but also for massless fermion loops, if one of the W bosons is space-like and the other is time-like. We also discuss in what sense Low's soft photon theorem is satisfied.

hep-ph↗

arXiv1996

A light stop and electroweak baryogenesis

The possibility of creating baryon asymmetry at the electroweak phase transition in the minimal supersymmetric standard model is considered for the case when right-handed squarks are much lighter than left-handed ones. It is shown that the usual requirement v(T_c)/T_c > 1 for baryogenesis can be satisfied in a range of the parameters of the model, consistent with present experimental bounds.

hep-ph↗

arXiv1996

Spinning Relativistic Particle in an External Electromagnetic Field

The Hamiltonian formulation of the motion of a spinning relativistic particle in an external electromagnetic field is considered. The approach is based on the introduction of new coordinates and their conjugated momenta to describe the spin degrees of freedom together with an appropriate set of constraints in the Dirac formulation. For particles with gyromagnetic ratio $g=2$, the equations of motion do not predict any deviation from the standard Lorentz force, while for $g \neq 2$ an additional force, which corresponds to the magnetic dipole force, is obtained.

hep-th↗