107 research outputs found
An Improved Supersymmetric SU(5)
By supplementing minimal supersymmetric SU(5) (MSSU(5)) with a flavor symmetry and two pairs of `matter' supermultiplets, we
present an improved model which explains the charged fermion mass hierarchies
and the magnitudes of the CKM matrix elements, while avoiding the undesirable
asymptotic mass relations . The strong
coupling is predicted to be approximately 0.115, and the
proton lifetime is estimated to be about five times larger than the MSSU(5)
value. The atmospheric and solar neutrino puzzles are respectively resolved via
maximal and small mixing angle MSW
oscillations, where denotes a sterile neutrino. The
symmetry ensures not only a light but also automatic `matter' parity.Comment: 11 pp. LATEX. Version with minor addition accepted for publication in
Physics Letters
Neutrino Mixing and the Pattern of Supersymmetry Breaking
We study the implications of a large mixing angle on
lepton flavour violating radiative transitions in supersymmetric extensions of
the standard model. The transition rates are calculated to leading order in
, the parameter which characterizes the flavour mixing. The
uncertainty of the predicted rates is discussed in detail. For models with
modular invariance the branching ratio mostly exceeds
the experimental upper limit. In models with radiatively induced flavour mixing
the predicted range includes the upper limit, if the Yukawa couplings in the
lepton sector are large, as favoured by Yukawa coupling unification.Comment: 12 pages, 2 figures, used axodraw.sty, to be published in Physics
Letters
Reentrant violation of special relativity in the low-energy corner
In the effective relativistic quantum field theories the energy region, where
the special relativity holds, can be sandwiched from both the high and low
energies sides by domains where the special relativity is violated. An example
is provided by 3He-A where the relativistic quantum field theory emerges as the
effective theory. The reentrant violation of the special relativity in the
ultralow energy corner is accompanied by the redistribution of the
momentum-space topological charges between the fermionic flavors. At this
ultralow energy an exotic massless fermion with the topological charge
arises, whose energy spectrum mixes the classical and relativistic behavior.
This effect can lead to neutrino oscillations if neutrino flavors are still
massless at this energy scale.Comment: RevTeX file, 5 pages, one figure, submitted to JETP Let
Infrared Fixed Points and Fixed Lines in the Top-Bottom-Tau Sector in Supersymmetric Grand Unification
The two-loop ``top-down'' renormalization group flow for the top, bottom and
tau Yukawa couplings is explored in the framework of supersymmetric grand
unification; reproduction of the physical bottom and tau masses is required.
Instead of following the recent trend of implementing exact Yukawa coupling
unification i) a search for infrared (IR) fixed lines and fixed points in the
m(top)-tan(beta) plane is performed and ii) the extent to which these imply
approximate Yukawa unification is determined. Two IR fixed lines, intersecting
in an IR fixed point, are located. The more attractive fixed line has a branch
of almost constant top mass, 168-180 GeV, close to the experimental value, for
the large interval 2.5<tan(beta)<55; it realizes tau-bottom Yukawa unification
at MGUT approximately. The fixed point at m(top)= 170 GeV, tan(beta)=55
implements approximate top-bottom Yukawa unification at all scales. The fixed
point and lines are distinct from the much quoted effective IR fixed point
m(top)=O(200)GeV sin(beta).Comment: 12 pages, latex, epsfig, 3 figure
Bethe-Salpeter Approach for Meson-Meson Scattering in Chiral Perturbation Theory
The Bethe-Salpeter equation restores exact elastic unitarity in the s-
channel by summing up an infinite set of chiral loops. We use this equation to
show how a chiral expansion can be undertaken by successive approximations to
the potential which should be iterated. Renormalizability of the amplitudes in
a broad sense can be achieved by allowing for an infinite set of counter-terms
as it is the case in ordinary Chiral Perturbation Theory. Within this framework
we calculate the scattering amplitudes both for s- and p-waves at
lowest order in the proposed expansion where a successful description of the
low-lying resonances ( and ) and threshold parameters is
obtained. We also extract the SU(2) low energy parameters
from our amplitudes.Comment: 11 pages, final version submitted to PL
A Mechanism for Baryogenesis in Low Energy Supersymmetry Breaking Models
A generic prediction of models where supersymmetry is broken at scales within
a few orders of magnitude of the weak scale and is fed down to the observable
sector by gauge interactions is the existence of superconducting cosmic strings
which carry baryon number. In this paper we propose a novel mechanism for the
generation of the baryon asymmetry which takes place at temperatures much lower
than the weak scale. Superconducting strings act like ``bags'' containing the
baryon charge and protect it from sphaleron wash-out throughout the evolution
of the Universe, until baryon number violating processes become harmless. This
mechanism is efficient even if the electroweak phase transition in the MSSM is
of the second order and therefore does not impose any upper bound on the mass
of the Higgs boson. (13kb)Comment: LaTeX file, 17 pages. One ref. adde
Quark and Lepton Mass Patterns and the Absolute Neutrino Mass Scale
We investigate what could be learned about the absolute scale of neutrino
masses from comparisons among the patterns within quark and lepton mass
hierarchies. First, we observe that the existing information on neutrino masses
fits quite well to the unexplained, but apparently present regularities in the
quark and charged lepton sectors. Second, we discuss several possible mass
patterns, pointing out that this quite generally leads towards hierarchical
neutrino mass patterns especially disfavoring the vacuum solution.Comment: final version to be published in PRD, 5 pages, 2 figures, RevTe
Where to look for solving the gauge hierarchy problem?
A mass of the Higgs boson close to 126 GeV may give a hint that the standard
model of particle physics is valid up to the Planck scale. We discuss
perspectives for the solution of the gauge hierarchy problem at high scales.
Scenarios with an ultraviolet fixed point have predicted a Higgs boson mass
very close to 126 GeV if the fixed point value of the quartic scalar coupling
is small. In this case the top quark pole mass should be close to 172 GeV.Comment: additional references, somewhat extended discussion, 5 page
A Model for Neutrino Warm Dark Matter and Neutrino Oscillations
The muon- and tau-neutrinos with the mass in the keV range, which are allowed
in a low reheating temperature cosmology, can compose the warm dark matter of
the universe. A model of four light neutrinos including the keV scale
and is studied, which combines the seesaw mechanism and the Abelian
flavor symmetry. The atmospheric neutrino anomaly is due to the
oscillation. The solar neutrino problem is answered by the
oscillation into the light sterile neutrino, where the SMA, LMA, and LOW-QVO
solutions can be accommodated in our scenario.Comment: 11 pages, Final version to appear in PLB, References adde
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