2,224 research outputs found
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.Comment: 8 pages, standard LaTe
Maximally restrictive leptonic texture zeros in two-Higgs-doublet models
The implementation of maximally restrictive texture zeros in the leptonic
sector is investigated in the context of two-Higgs-doublet models with Majorana
neutrinos. After analyzing all maximally restrictive pairs of leptonic mass
matrices with zero entries, we conclude that there are only four texture
combinations that are compatible with observations at 3 sigma confidence level
and can be implemented through Abelian symmetries in a two-Higgs-doublet model.
The compatibility of these textures with current constraints on
lepton-flavor-violating processes is also studied. The ultraviolet completion
of these models is discussed in the framework of the seesaw mechanism for
neutrino masses.Comment: 13 pages, 5 figures, 5 tables; comments and references added, final
version to appear in J. Phys.
Abelian realization of phenomenological two-zero neutrino textures
In an attempt at explaining the observed neutrino mass-squared differences
and leptonic mixing, lepton mass matrices with zero textures have been widely
studied. In the weak basis where the charged lepton mass matrix is diagonal,
various neutrino mass matrices with two zeros have been shown to be consistent
with the current experimental data. Using the canonical and Smith normal form
methods, we construct the minimal Abelian symmetry realizations of these
phenomenological two-zero neutrino textures. The implementation of these
symmetries in the context of the seesaw mechanism for Majorana neutrino masses
is also discussed.Comment: 11 pages; references added, version to appear in Nuclear Physics
Minimal string-scale unification of gauge couplings
We look for the minimal particle content which is necessary to add to the
standard model in order to have a complete unification of gauge couplings and
gravity at the weakly coupled heterotic string scale. Using the current
precision electroweak data, we find that the presence of a vector-like fermion
at an intermediate scale and a non-standard hypercharge normalization are in
general sufficient to achieve this goal at two-loop level. If one requires the
extra matter scale to be below the TeV scale, then it is found that the
addition of three vector-like fermion doublets with a mass around 700 GeV
yields a perfect string-scale unification, provided that the affine levels are
kY=13/3, k2=1 and k3=2, as in the SU(5) X SU(5) string-GUT. Furthermore, if
supersymmetry is broken at the unification scale, the Higgs mass is predicted
in the range 125 GeV - 170 GeV, depending on the precise values of the top
quark mass and tan(beta) parameter.Comment: 12 pages, 2 figures, references updated and comments added, final
version to appear in Phys. Lett.
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 .Comment: 9 pages, standard LaTe
A new bridge between leptonic CP violation and leptogenesis
Flavor effects due to lepton interactions in the early Universe may have
played an important role in the generation of the cosmological baryon asymmetry
through leptogenesis. If the only source of high-energy CP violation comes from
the left-handed leptonic sector, then it is possible to establish a bridge
between flavored leptogenesis and low-energy leptonic CP violation. We explore
this connection taking into account our present knowledge about low-energy
neutrino parameters and the matter-antimatter asymmetry observed in the
Universe. In this framework, we find that leptogenesis favors a hierarchical
light neutrino mass spectrum, while for quasi-degenerate and inverted
hierarchical neutrino masses there is a very narrow allowed window. The
absolute neutrino mass scale turns out to be m < 0.1 eV.Comment: 10 pages, 3 figure
Neutrino masses and mixing in A4 models with three Higgs doublets
We study neutrino masses and mixing in the context of flavor models with A4
symmetry, three scalar doublets in the triplet representation, and three lepton
families. We show that there is no representation assignment that yields a
dimension-five mass operator consistent with experiment. We then consider a
type-I seesaw with three heavy right-handed neutrinos, explaining in detail why
it fails, and showing with a numerical example that agreement with the present
neutrino oscillation data can be recovered with the inclusion of
dimension-three heavy neutrino mass terms that break softly the A4 symmetry.Comment: 10 pages, RevTex, 3 figures. v2: much expanded section on softly
broken A4; refs adde
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.Comment: 11 pages, REVTeX, typos and a few equations corrected, a comment
added to the conclusions, acknowledgments adde
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 , the
equations of motion do not predict any deviation from the standard Lorentz
force, while for an additional force, which corresponds to the
magnetic dipole force, is obtained.Comment: Latex file, 11 page
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