2,282 research outputs found
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
Anomaly-free U(1) gauge symmetries in neutrino seesaw flavor models
Adding right-handed neutrino singlets and/or fermion triplets to the particle
content of the Standard Model allows for the implementation of the seesaw
mechanism to give mass to neutrinos and, simultaneously, for the construction
of anomaly-free gauge group extensions of the theory. We consider Abelian
extensions based on an extra U(1)_X gauge symmetry, where X is an arbitrary
linear combination of the baryon number B and the individual lepton numbers
L_{e,mu,tau}. By requiring cancellation of gauge anomalies, we perform a
detailed analysis in order to identify the charge assignments under the new
gauge symmetry that lead to neutrino phenomenology compatible with current
experiments. In particular, we study how the new symmetry can constrain the
flavor structure of the Majorana neutrino mass matrix, leading to two-zero
textures with a minimal extra fermion and scalar content. The possibility of
distinguishing different gauge symmetries and seesaw realizations at colliders
is also briefly discussed.Comment: 12 pages, 2 figures, 7 tables; comments and references added, a new
subsection with nonstandard interactions of neutrinos included; final version
to appear in Phys. Rev.
TOP-INDUCED ELECTROWEAK BREAKING IN THE MINIMAL SUPERSYMMETRIC STANDARD MODEL
Severe constraints on parameters of the minimal supersymmetric standard model
follow from a dynamical electroweak symmetry breaking mechanism dominated by
top and stop loops. In particular, the lightest Higgs boson mass is expected to
be smaller than 100 GeV.Comment: 10 pages, Latex, 6 Postcript Figure
Minimal anomaly-free chiral fermion sets and gauge coupling unification
We look for minimal chiral sets of fermions beyond the standard model that
are anomaly free and, simultaneously, vectorlike particles with respect to
colour SU(3) and electromagnetic U(1). We then study whether the addition of
such particles to the standard model particle content allows for the
unification of gauge couplings at a high energy scale, above GeV so as to be safely consistent with proton decay bounds. The
possibility to have unification at the string scale is also considered.
Inspired in grand unified theories, we also search for minimal chiral fermion
sets that belong to SU(5) multiplets. Restricting to representations up to
dimension 50, we show that some of these sets can lead to gauge unification at
the GUT and/or string scales.Comment: 13 pages, 5 figures, 8 tables; Comments and references added, final
version to appear in Phys. Rev.
Magnetized strange quark matter and magnetized strange quark stars
Strange quark matter could be found in the core of neutron stars or forming
strange quark stars. As is well known, these astrophysical objects are endowed
with strong magnetic fields which affect the microscopic properties of matter
and modify the macroscopic properties of the system. In this paper we study the
role of a strong magnetic field in the thermodynamical properties of a
magnetized degenerate strange quark gas, taking into account beta-equilibrium
and charge neutrality. Quarks and electrons interact with the magnetic field
via their electric charges and anomalous magnetic moments. In contrast to the
magnetic field value of 10^19 G, obtained when anomalous magnetic moments are
not taken into account, we find the upper bound B < 8.6 x 10^17 G, for the
stability of the system. A phase transition could be hidden for fields greater
than this value.Comment: 9 pages, 9 figure
The variation of the electromagnetic coupling and quintessence
The properties of quintessence are examined through the study of the
variation of the electromagnetic coupling. We consider two simple quintessence
models with a modified exponential potential and study the parameter space
constraints derived from the existing observational bounds on the variation of
the fine structure constant and the most recent Wilkinson Microwave Anisotropy
Probe observations.Comment: 7 pages, 7 figure
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