18 research outputs found
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
P, C and Strong CP in Left-Right Supersymmetric Models
We systematically study the connection between P, C and strong CP in the
context of both non-supersymmetric and supersymmetric left-right theories. We
find that the solution to the strong CP problem requires both supersymmetry and
parity breaking scales to be around the weak scale.Comment: 5 pages, RevTex, no figures. Some minor changes, final version as
published in Phys. Rev. Lett. 79, 4744 (1997
Minimal Supersymmetric Scenarios for Spontaneous CP Violation
We study the possibility of spontaneous CP violation (SCPV) at the tree level
in models with an extended Higgs sector. We show that the minimum equations for
the complex phases of the vacuum expectation values (VEVs) have always a
geometrical interpretation in terms of triangles. To illustrate our method we
analyze the minimal supersymmetric (SUSY) model with R-parity violating
couplings and sneutrino VEVs, where there is no SCPV. Then we study SUSY models
with extra Higgs doublets and/or gauge singlets, and find that the simplest
scenario with SCPV must include at least two singlet fields.Comment: LaTeX, 19 pages, 4 figure
Supersymmetry and Large Scale Left-Right Symmetry
We show that the low energy limit of the minimal supersymmetric Left-Right
models is the supersymmetric standard model with an exact R-parity. The theory
predicts a number of light Higgs scalars and fermions with masses much below
the and breaking scales. The non-renormalizable version of the
theory has a striking prediction of light doubly charged supermultiplets which
may be accessible to experiment. Whereas in the renormalizable case the scale
of parity breaking is undetermined, in the non-renormalizable one it must be
bigger than about GeV. The precise nature of the see-saw
mechanism differs in the two versions, and has important implications for
neutrino masses.Comment: LaTeX, 30 pages. Minor changes. Some references adde
Large Top Quark Yukawa Coupling and Horizontal Symmetries
We consider the maximal U(3) horizontal scheme as a handle on fermion masses
and mixings. In particular, we attempt to explain the large top Yukawa coupling
and the masses and mixing in the two heaviest generations. A simple model is
constructed by enlarging the matter content of the Standard Model with that of
a pair of SU(5). The third generation particles get their masses
when U(3) is broken to U(2). Top quark mass is naturally of order one. Bottom
and tau masses are suppressed because of a hierarchy in the effective Yukawa
couplings and not from the hierarchy in the Higgs doublet vacuum expectation
values. The hierarchy is a consequence of the fact that the particle spectrum
contains an incomplete vector-like generation and can come from hierarchies
between scales of breaking of different grand unified groups. Hierarchies and
mixings between the second and third generation are obtained by introducing a
single parameter epsilon' representing the breaking U(2) -> U(1). As a
consequence, we show that the successful (and previosuly obtained) relations
V_{cb} \approx (m_s / m_b) \approx \sqrt (m_c / m_t) easily follow from our
scheme.Comment: 23 pages, LaTe