135 research outputs found
Zeroes of the Neutrino Mass Matrix
We assume there to be precisely three left-handed neutrino states whose
Majorana masses are generated by an unspecified mechanism. Were CP conserved,
the symmetric neutrino mass matrix M would be real and all six of its distinct
entries could be experimentally determined. But CP is not conserved so that M
is likely to be complex. As a result, not all nine of its
convention-independent real parameters can be determined without an appeal to
theory. Thus we examine the possibility that a restricted class of neutrino
mass matrices may suffice to describe current data, namely those complex
symmetric matrices several of whose entries vanish. We find that there are
seven acceptable textures with two independent zeroes, and we explore their
contrasting phenomenological implications. Textures with more than two
independent zeroes appear to be excluded by experiment.Comment: Version to appear in PL
Can the Zee ansatz for neutrino masses be correct?
Working in the framework of three chiral neutrinos with Majorana masses, we
investigate a scenario first realized in an explicit model by Zee: that the
neutrino mass matrix is strictly off-diagonal in the flavor basis, with all its
diagonal entries precisely zero. This CP-conserving ansatz leads to two
relations among the three mixing angles and
two squared mass differences. We impose the constraint to conform with experiment, which requires the to
lie nearby one of four 1-parameter domains in -space. We exhibit the
implications for solar and atmospheric neutrino oscillations in each of these
cases. A unique version of the Zee {\it ansatz} survives confrontation with
experimental data, one which necessarily involves maximal just-so vacuum
oscillations of solar neutrinos.Comment: 7 pages, harvmac, typo corrected, ref. added, text modifie
Turnaround in Cyclic Cosmology
It is speculated how dark energy in a brane world can help reconcile an infinitely cyclic cosmology with the second law of thermodynamics. A cyclic cosmology is described, in which dark energy leads to a turnaround at a time, extremely shortly before the would-be Big Rip, at which both volume and entropy of our universe decrease by a gigantic factor, while very many independent similarly small contracting universes are spawned. The entropy of our universe decreases almost to zero at turnaround but increases for the remainder of the cycle by a vanishingly small amount during contraction, empty of matter and radiation, then by a very large factor during inflationary expansion
Production of doubly charged vector bilepton pairs at colliders
The production of pairs of doubly charged vector bileptons is studied at
future colliders. The unpolarized cross--section for the
subprocess is analytically calculated and
convoluted to predict the number of events in the complete process. The gauge or non--gauge character of the
vector bilepton is discussed. It is found that as a consequence
of its spectacular signature, as it decays dominantly into two identical
charged leptons, and also due to its charge contents, which significantly
enhance the cross--section, the detection of this class of particles with mass
in the sub--TeV region can be at the reach of these colliders. The
model--independent nature of our results is stressed.Comment: 9 pages, 7 figures, submitted to physical review
Chiral Fermions and Quadratic Divergences
In an approach towards naturalness without supersymmetry, renormalization
properties of nonsupersymmetric abelian quiver gauge theories are studied. In
the construction based on cyclic groups Z_p the gauge group is U(N)^p, the
fermions are all in bifundamentals and the construction allows scalars in
adjoints and bifundamentals. Only models without adjoint scalars, however,
exhibit both chiral fermions and the absence of one-loop quadratic divergences
in the scalar propagator.Comment: 11 page
Relic Neutrinos and Z-Resonance Mechanism for Highest-Energy Cosmic Rays
The origin of the highest-energy cosmic rays remains elusive. The decay of a
superheavy particle (X) into an ultra-energetic neutrino which scatters from a
relic (anti-)neutrino at the Z-resonance has attractive features. Given the
necessary X mass of GeV, the required lifetime,
y, renders model-building a serious challenge but three logical possibilities
are considered: (i) X is a Higgs scalar in SU(15) belonging to high-rank
representation, leading to {\it power}-enhanced lifetime; (ii) a global X
quantum number has {\it exponentially}-suppressed symmetry-breaking by
instantons; and (iii) with additional space dimension(s) localisation of X
within the real-world brane leads to {\it gaussian} decay suppression, the most
efficient of the suppression mechanisms considered.Comment: 10 page LaTeX and one postscript figure. References adde
Cabibbo Mixing and the Search for CP Violation
We examine certain extensions of the standard model in which violation
is spontaneous and the strong problem is resolved. In these models, the quark mixing matrix is neither real nor unitary. However, to a
precision of 0.1%, it is real and orthogonal. There are no readily observable
-violating effects besides those in the neutral kaon system.Comment: 6 pages, latex, no figure
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