28 research outputs found
Large Lepton Mixings from Continuous Symmetries
Within the broad context of quark-lepton unification, we investigate the
implications of broken continuous family symmetries which result from requiring
that in the limit of exact symmetry, the Dirac mass matrices yield hierarchical
masses for the quarks and charged leptons, but lead to degenerate light
neutrino masses as a consequence of the seesaw mechanism, without requiring
hierarchical right-handed neutrino mass terms. Quark mixing is then naturally
small and proportional to the size of the perturbation, but lepton mixing is
large as a result of degenerate perturbation theory, shifted from maximal
mixing by the size of the perturbation. Within this approach, we study an
illustrative two-family prototype model with an SO(2) family symmetry, and
discuss extensions to three-family models.Comment: 23 page
b -> s gamma in the left-right supersymmetric model
The rare decay is studied in the left-right supersymmetric
model. We give explicit expressions for all the amplitudes associated with the
supersymmetric contributions coming from gluinos, charginos and neutralinos in
the model to one-loop level. The branching ratio is enhanced significantly
compared to the standard model and minimal supersymmetric standard model values
by contributions from the right-handed gaugino and squark sector. We give
numerical results coming from the leading order contributions. If the only
source of flavor violation comes from the CKM matrix, we constrain the scalar
fermion-gaugino sector. If intergenerational mixings are allowed in the squark
mass matrix, we constrain such supersymmetric sources of flavor violation. The
decay sets constraints on the parameters of the model and
provides distinguishing signs from other supersymmetric scenarios.Comment: 12 figure
Leptogenesis and Neutrino Oscillations Within A Predictive G(224)/SO(10)-Framework
A framework based on an effective symmetry that is either G(224)= SU(2)_L x
SU(2)_R xSU(4)^c or SO(10) has been proposed (a few years ago) that
successfully describes the masses and mixings of all fermions including
neutrinos, with seven predictions, in good accord with the data. Baryogenesis
via leptogenesis is considered within this framework by allowing for natural
phases (~ 1/20-1/2) in the entries of the Dirac and Majorana mass-matrices. It
is shown that the framework leads quite naturally, for both thermal as well as
non-thermal leptogenesis, to the desired magnitude for the baryon asymmetry.
This result is obtained in full accord with the observed features of the
atmospheric and solar neutrino oscillations, as well as with those of the quark
and charged lepton masses and mixings, and the gravitino-constraint. Hereby one
obtains a unified description of fermion masses, neutrino oscillations and
baryogenesis (via leptogenesis) within a single predictive framework.Comment: Efficiency factor updated, some clarifications and new references
added. 19 page
SU(4)_c x SU(2)_L x SU(2)_R model from 5D SUSY SU(4)_c x SU(4)_{L+R}
We investigate supersymmetric theory in 5
dimensions whose compactification on a orbifold yields N=1
supersymmetric supplemented by a
\tl{U}(1) gauge symmetry. We discuss how the problem is resolved, a
realistic Yukawa sector achieved, and a stable proton realized. Neutrino masses
and oscillations are also briefly discussed.Comment: Version to appear in Physical Review
Physics Implications of Flat Directions in Free Fermionic Superstring Models I: Mass Spectrum and Couplings
From the "top-down" approach we investigate physics implications of the class
of D- and F- flat directions formed from non-Abelian singlets which are proven
flat to all orders in the nonrenormalizable superpotential, for a prototype
quasi-realistic free fermionic string model with the standard model gauge group
and three families (CHL5). These flat directions have at least an additional
U(1)' unbroken at the string scale. For each flat direction, the complete set
of effective mass terms and effective trilinear superpotential terms in the
observable sector are computed to all orders in the VEV's of the fields in the
flat direction. The "string selection-rules" disallow a large number of
couplings allowed by gauge invariance, resulting in a massless spectrum with a
large number of exotics, in most cases excluded by experiment, thus signifying
a generic flaw of these models. Nevertheless, the resulting trilinear couplings
of the massless spectrum possess a number of interesting features which we
analyse for two representative flat directions: for the fermion texture;
baryon- and lepton-number violating couplings; R-parity breaking; non-canonical
mu terms; and the possibility of electroweak and intermediate scale symmetry
breaking scenarios for U(1)'. The gauge coupling predictions are obtained in
the electroweak scale case. Fermion masses possess t-b and tau-mu universality,
with the string scale Yukawa couplings g and , respectively.
Fermion textures are present for certain flat directions, but only in the
down-quark sector. Baryon- and lepton- number violating couplings can trigger
proton-decay, oscillations, leptoquark interactions and R-parity
violation, leading to the absence of a stable LSP.Comment: 36 pages, 5 tables, 4 figures, RevTeX, minor change
Astrophysical input for gravitational wave searches
We describe several areas where the newly emerging field of gravitational wave astronomy would benefit from exploiting the expertise of the broader astrophysics community. We deal specifically with searches for long-lived gravitational wave signals from neutron stars, paying particular attention to the known radio pulsar population and supernova remnants