395 research outputs found
Comment on SU(16) grand unification
In a recent paper on SU(16) grand unification, because of the presence of
intermediate-energy gauge groups containing products of U(1) factors which are
not orthogonal among themselves, the renormalization-group treatment has a few
small errors. I correct it. I emphasize that one should not switch gauge
couplings at the various thresholds. It is easier, and it avoids errors, to use
throughout the gauge couplings of the standard model, and compute at each
threshold, in the usual way, the extra contributions to the beta functions from
the extra non-decoupled fields. I also point out that the SU(16) grand
unification theory, due to the large number of scalars present in it, is not
asymptotically free. It becomes a strong-coupling theory at energies only
slightly larger than the unification scale.Comment: 5 latex pages, 2 tables, no figure
Constrained analytical interrelations in neutrino mixing
Hermitian squared mass matrices of charged leptons and light neutrinos in the
flavor basis are studied under general additive lowest order perturbations away
from the tribimaximal (TBM) limit in which a weak basis with mass diagonal
charged leptons is chosen. Simple analytical expressions are found for the
three measurable TBM-deviants in terms of perturbation parameters appearing in
the neutrino and charged lepton eigenstates in the flavor basis. Taking
unnatural cancellations to be absent and charged lepton perturbation parameters
to be small, interrelations are derived among masses, mixing angles and the
amount of CP-violation.Comment: To be published in the Springer Proceedings in the Physics Series
under the heading of the XXI DAE-BRNS Symposium (Guwahati, India
Asymmetric neutrino Yukawa matrices and neutrino mixing
We study leptonic CKM mixing matrices when the neutrino Yukawa matrices are
antisymmetric which gives rise to mass patterns suitable to explain solar,
atmospheric and LSND neutrino oscillation experiments. Taking diagonal leptonic
matrices which can give rise to hierarchical lepton masses, we compute the
leptonic CKM matrix.Comment: version to appear in Phys. Rev.
Proton Decay and Related Processes in Unified Models with Gauged Baryon Number:
In unification models based on SU(15) or SU(16), baryon number is part of the
gauge symmetry, broken spontaneously. In such models, we discuss various
scenarios of important baryon number violating processes like proton decay and
neutron-antineutron oscillation. Our analysis depends on the effective operator
method, and covers many variations of symmetry breaking, including different
intermediate groups and different Higgs boson content. We discuss processes
mediated by gauge bosons and Higgs bosons parallely. We show how accidental
global or discrete symmetries present in the full gauge invariant Lagrangian
restrict baryon number violating processes in these models. In all cases, we
find that baryon number violating interactions are sufficiently suppressed to
allow grand unification at energies much lower than the usual GeV.Comment: (32 pages LATEX) [DOE-ER\,40757-022, CPP-93-22] {Small changes made
and two references added. This version will appear in Phys. Rev. D
Left-Right Symmetry and Supersymmetric Unification
The existence of an SU(3) X SU(2)_L X SU(2)_R X U(1) gauge symmetry with g_L
= g_R at the TeV energy scale is shown to be consistent with supersymmetric
SO(10) grand unification at around 1O^{16} GeV if certain new particles are
assumed. The additional imposition of a discrete Z_2 symmetry leads to a
generalized definition of R parity as well as highly suppressed Majorana
neutrino masses. Another model based on SO(10) X SO(10) is also discussed.Comment: 11 pages, 2 figures not included, UCRHEP-T124, Apr 199
Infrared Quasi Fixed Point Structure in Extended Yukawa Sectors and Application to R-parity Violation
We investigate one-loop renormalization group evolutions of extended sectors
of Yukawa type couplings. It is shown that Landau Poles which usually provide
necessary low energy upper bounds that saturate quickly with increasing initial
value conditions, lead in some cases to the opposite behaviour: some of the low
energy couplings decrease and become vanishingly small for increasingly large
initial conditions. We write down the general criteria for this to happen in
typical situations, highlighting a concept of {\sl repulsive} quasi-fixed
points, and illustrate the case both within a two-Yukawa toy model as well as
in the minimal supersymmetric standard model with R-parity violation. In the
latter case we consider the theoretical upper bounds on the various couplings,
identifying regimes where are
dynamically suppressed due to the Landau Pole. We stress the importance of
considering a large number of couplings simultaneously. This leads altogether
to a phenomenologically interesting seesaw effect in the magnitudes of the
various R-parity violating couplings, complementing and in some cases improving
the existing limits.Comment: Latex, 33 pages, 6 figure
Effects of 126 dimensional Higgs scalar on Bottom-Tau unification and quasi-infrared fixed point
In the presence of Higgs multiplets in a SO(10)
theory, the fermion masses get contributions from an induced vacuum expectation
value (VEV) of a doublet residing in which differentiates
between quarks and leptons by a relative sign leading to a significant
correction to the prediction of the mass ratio of the bottom quark and the tau
lepton for ranges of the mass of this extra doublet. We perform a two-loop
renormalization group analysis of the minimal version of the one-step
supersymmetric SO(10) model to display this and re-calculate the corrections to
the top quark mass in the presence of such an induced VEV. We show that these
effects make the infra-red fixed point scenario consistent with experimental
results.Comment: revised version with same conclusions. To appear in Phys. Rev.
B-physics constraints on baryon number violating couplings: grand unification or R-parity violation
We investigate the role that baryon number violating interactions may play in
phenomenology. Present in various grand unified theories, supersymmetric
theories with R-parity violation and composite models, a diquark state could be
quite light. Using the data on B decays as well as mixing, we
find strong constraints on the couplings that such a light diquark state may
have with the Standard Model quarks.Comment: 19 pages, latex, no figures, 13 tables include
Infrared Fixed Point Structure in Minimal Supersymmetric Standard Model with Baryon and Lepton Number Violation
We study in detail the renomalization group evolution of Yukawa couplings and
soft supersymmetry breaking trilinear couplings in the minimal supersymmetric
standard model with baryon and lepton number violation. We obtain the exact
solutions of these equations in a closed form, and then depict the infrared
fixed point structure of the third generation Yukawa couplings and the highest
generation baryon and lepton number violating couplings. Approximate analytical
solutions for these Yukawa couplings and baryon and lepton number violating
couplings, and the soft supersymmetry breaking couplings are obtained in terms
of their initial values at the unification scale. We then numerically study the
infrared fixed surfaces of the model, and illustrate the approach to the fixed
points.Comment: 16 pages REVTeX, figures embedded as epsfigs, replaced with version
to appear in Physical Review D, minor typographical errors eliminated and
references reordered, figures correcte
Can the SO(10) Model with Two Higgs Doublets Reproduce the Observed Fermion Masses?
It is usually considered that the SO(10) model with one 10 and one 126 Higgs
scalars cannot reproduce the observed quark and charged lepton masses. Against
this conventional conjecture, we find solutions of the parameters which can
give the observed fermion mass spectra. The SO(10) model with one 10 and one
120 Higgs scalars is also discussed.Comment: 7 pages, 1 figure, REVTe
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