14 research outputs found
Unification with Enlarged Kaluza-Klein Dimensions
In minimal theories with extra spatial dimensions at scales mu_0 much lower
than the conventional GUT scale, unification can give too-large predictions for
alpha_3(M_Z) given alpha_1(M_Z) and alpha_2(M_Z) as empirical input. We
systematically study the effects of adding extra states above the
compactification scale on running of the gauge couplings and find several
simple examples that give unification where all alpha_i(M_Z) are consistent
with low-energy data. We study both the supersymmetric and nonsupersymmetric
unification.Comment: 18 pages, LaTeX, analysis for the susy case takes into account that
extra hypermultiplets come in conjugate pairs, minor changes in text and
references, to be published in Phys. Lett.
Seeking Gauge Bileptons in Linear Colliders
A promising direction to find physics beyond the standard model is to look
for violation of conservation. In particular the process with the exchange of a gauge bilepton has a striking
signal without background and is predicted in the most economical model to have
a cross-section an order of magnitude higher than previous estimates.Comment: 4 pages LaTeX and 5 postscript figure
Flavor changing interactions mediated by scalars at the weak scale
The quark and lepton mass matrices possess approximate flavor symmetries.
Several results follow if the interactions of new scalars possess these
approximate symmetries. Present experimental bounds allow these exotic scalars
to have a weak scale mass. The Glashow-Weinberg criterion is rendered
unnecessary. Finally, rare leptonic B meson decays provide powerful probes of
these scalars, especially if they are leptoquarks.Comment: 13 pages, report LBL-3234
CP violation in multi-Higgs supersymmetric models
We consider supersymmetric extensions of the standard model with two pairs of
Higgs doublets. We study the possibility of spontaneous violation in these
scenarios and present a model where the origin of violation is soft, with
all the complex phases in the Lagrangian derived from complex masses and vacuum
expectation values (VEVs) of the Higgs fields. The main ingredient of the model
is an approximate global symmetry, which determines the order of magnitude of
Yukawa couplings and scalar VEVs. We assume that the terms violating this
symmetry are suppressed by powers of the small parameter
. The tree-level flavor changing interactions are
small due to a combination of this global symmetry and a flavor symmetry, but
they can be the dominant source of violation. All -violating effects
occur at order as the result of exchange of {\it
almost}-decoupled extra Higgs bosons and/or through the usual mechanisms with
an {\it almost}-real CKM matrix. On dimensional grounds, the model gives
and predicts for the neutron electric
dipole moment (and possibly also for ) a suppression of order
with respect to the values obtained in standard and minimal
supersymmetric scenarios. The predicted asymmetries in decays are
generically too small to be seen in the near future. The mass of the lightest
neutral scalar, the strong problem, and possible contributions to the
decay into quarks (the puzzle) are also briefly addressed in the
framework of this model.Comment: Latex, 31 pages including 6 figures which are a part of the Latex
fil
See-saw and Supersymmetry or Exact R-parity
We show how the renormalizable see-saw mechanism in the context of
supersymmetry and spontaneously broken B-L symmetry implies exact R-parity at
all energies. We argue that supersymmetry plays an important role in providing
a "canonical" form for the see-saw, in particular in grand unified theories
that solve the doublet-triplet splitting problem via the Dimopoulos-Wilczek
mechanism.Comment: 4 pages, 1 figure. Minor changes and 2 references added, one
correcte
SO(10) theory of R-parity and neutrino mass
We study the Higgs sector of a SO(10) grand unified theory which predicts
exact conservation of R-parity at all scales and incorporates the see-saw
mechanism. We find possible intermediate scales and light states compatible
with the constraints coming from the running of the gauge couplings. Such a
pattern could lower the SO(10) breaking scale, allowing the d=6 proton decay
operators to be comparable in magnitude to the d=5 ones.Comment: 22 pages, 4 figure
Approximate Flavor Symmetries in the Lepton Sector
Approximate flavor symmetries in the quark sector have been used as a handle
on physics beyond the Standard Model. Due to the great interest in neutrino
masses and mixings and the wealth of existing and proposed neutrino experiments
it is important to extend this analysis to the leptonic sector. We show that in
the see-saw mechanism, the neutrino masses and mixing angles do not depend on
the details of the right-handed neutrino flavor symmetry breaking, and are
related by a simple formula. We propose several ans\"{a}tze which relate
different flavor symmetry breaking parameters and find that the MSW solution to
the solar neutrino problem is always easily fit. Further, the oscillation is unlikely to solve the atmospheric neutrino problem
and, if we fix the neutrino mass scale by the MSW solution, the neutrino masses
are found to be too small to close the Universe.Comment: 12 pages (no figures), LBL-3459
Hierarchical Quark Mass Matrices
I define a set of conditions that the most general hierarchical Yukawa mass
matrices have to satisfy so that the leading rotations in the diagonalization
matrix are a pair of (2,3) and (1,2) rotations. In addition to Fritzsch
structures, examples of such hierarchical structures include also matrices with
(1,3) elements of the same order or even much larger than the (1,2) elements.
Such matrices can be obtained in the framework of a flavor theory. To leading
order, the values of the angle in the (2,3) plane (s_{23}) and the angle in the
(1,2) plane (s_{12}) do not depend on the order in which they are taken when
diagonalizing. We find that any of the Cabbibo-Kobayashi-Maskawa matrix
parametrizations that consists of at least one (1,2) and one (2,3) rotation may
be suitable. In the particular case when the s_{13} diagonalization angles are
sufficiently small compared to the product s_{12}s_{23}, two special CKM
parametrizations emerge: the R_{12}R_{23}R_{12} parametrization follows with
s_{23} taken before the s_{12} rotation, and vice versa for the
R_{23}R_{12}R_{23} parametrization.Comment: LaTeX, 19 pages. References added, minor changes in text. Version
published in Phys. Rev.
Simple supersymmetric solution to the strong CP problem
It is shown that the minimal supersymmetric left-right model can provide a
natural solution to the strong {\it CP} problem without the need for an axion,
nor any additional symmetries beyond supersymmetry and parity.Comment: Plain Latex. 10 pages, including two figures which are part of the
Latex file. Shortened version, to appear in Phys. Rev. Lett. 7
Hypercharge and the Cosmological Baryon Asymmetry
Stringent bounds on baryon and lepton number violating interactions have been
derived from the requirement that such interactions, together with electroweak
instantons, do not destroy a cosmological baryon asymmetry produced at an
extremely high temperature in the big bang. While these bounds apply in
specific models, we find that they are generically evaded. In particular, the
only requirement for a theory to avoid these bounds is that it contain charged
particles which, during a certain cosmological epoch, carry a non-zero
hypercharge asymmetry. Hypercharge neutrality of the universe then dictates
that the remaining particles must carry a compensating hypercharge density,
which is necessarily shared amongst them so as to give a baryon asymmetry.
Hence the generation of a hypercharge density in a sector of the theory forces
the universe to have a baryon asymmetry.Comment: 12 pages plus 1 Postscript figure available upon request. LBL 3482