236 research outputs found
Numerical consistency check between two approaches to radiative corrections for neutrino masses and mixings
We briefly outline the two popular approaches on radiative corrections to
neutrino masses and mixing angles, and then carry out a detailed numerical
analysis for a consistency check between them in MSSM. We find that the two
approaches are nearly consistent with a small discrepancy of a factor of 13
percent in mass eigenvalues at low energy scale, but the predictions on mixing
angles are almost consistent. We check the stability of the three types of
neutrino models, i.e., hierarchical, inverted hierarchical and degenerate
models, under radiative corrections, using both approaches, and find consistent
conclusions. The neutrino mass models which are found to be stable under
radiative corrections in MSSM are the normal hierarchical model and the
inverted hierarchical model with opposite CP parity. We also carry out
numerical analysis on some important conjectures related to radiative
corrections in MSSM, viz., radiative magnification of solar and atmospheric
mixings in case of nearly degenerate model having same CP parity (MPR
conjecture) and radiative generation of solar mass scale in exactly two-fold
degenerate model with opposite CP parity and non-zero reactor angle (JM
conjecture). We observe certain exceptions to these conjectures. Finally the
effect of scale-dependent vacuum expectation value in neutrino mass
renormalisation is discussed.Comment: 26 pages, 5 figures,references added, typos corrected and text
modifie
Bottom-up approach and supersymmetry breaking
We present a bottom-up approach to the question of supersymmetry breaking in
the MSSM. Starting with the experimentally measurable low-energy supersymmetry
breaking parameters, which can take any values consistent with present
experimental constraints, we evolve them up to an arbitrary high energy scale.
Approximate analytical expressions for such an evolution, valid for low and
moderate values of , are presented. We then discuss qualitative
properties of the high-energy parameter space and, in particular, identify the
conditions on the low energy spectrum that are necessary for the parameters at
the high energy scale to satisfy simple regular pattern such as universality or
partial universality. As an illustrative example, we take low energy parameters
for which light sparticles, within the reach of the LEP2 collider, appear in
the spectrum, and which do not affect the Standard Model agreement with the
precision measurement data. Comparison between supersymmetry breaking at the
GUT scale and at a low energy scale is made.Comment: 33 pages (14 figures
High scale mixing unification and large neutrino mixing angles
Starting with the hypothesis that quark and lepton mixings are identical at
or near the GUT scale, we show that the large solar and atmospheric neutrino
mixing angles together with the small reactor angle can be understood
purely as a result of renormalization group evolution. The only requirements
are that the three neutrinos must be quasi degenerate in mass and have same CP
parity. It predicts that the common Majorana mass for the neutrinos must be
larger than 0.1 eV making the idea testable in the currently planned or ongoing
experiments searching for neutrinoless-double-beta decay.Comment: 10 pages, eight figure, two tables; new material added; results
remain unchange
Generation of large flavor mixing from radiative corrections
We provide a model independent criterion which would guarantee a large flavor
mixing of two quasi-degenerate Majorana neutrinos at the low scale,
irrespective of the mixing at the high scale. We also show that such a
situation is realizable for a phenomenologically interesting range of
parameters of the weak scale theory. We further show that for a similar
condition to be implementable for the three generation case, the CP parity of
one of the neutrinos needs to be opposite to that of the others.Comment: 14 pages RevTeX, 2 eps figures. Minor changes made, a few references
adde
Beyond MFV in family symmetry theories of fermion masses
Minimal Flavour Violation (MFV) postulates that the only source of flavour
changing neutral currents and CP violation, as in the Standard Model, is the
CKM matrix. However it does not address the origin of fermion masses and mixing
and models that do usually have a structure that goes well beyond the MFV
framework. In this paper we compare the MFV predictions with those obtained in
models based on spontaneously broken (horizontal) family symmetries, both
Abelian and non-Abelian. The generic suppression of flavour changing processes
in these models turns out to be weaker than in the MFV hypothesis. Despite
this, in the supersymmetric case, the suppression may still be consistent with
a solution to the hierarchy problem, with masses of superpartners below 1 TeV.
A comparison of FCNC and CP violation in processes involving a variety of
different family quantum numbers should be able to distinguish between various
family symmetry models and models satisfying the MFV hypothesis.Comment: 34 pages, no figure
Neutrino Unification
Present neutrino data are consistent with neutrino masses arising from a
common seed at some ``neutrino unification'' scale . Such a simple
theoretical ansatz naturally leads to quasi-degenerate neutrinos that could lie
in the electron-volt range with neutrino mass splittings induced by
renormalization effects associated with supersymmetric thresholds. In such a
scheme the leptonic analogue of the Cabibbo angle describing
solar neutrino oscillations is nearly maximal. Its exact value is correlated
with the smallness of . These features agree both with latest
data on the solar neutrino spectra and with the reactor neutrino data. The two
leading mass-eigenstate neutrinos present in \ne form a pseudo-Dirac neutrino,
avoiding conflict with neutrinoless double beta decay.Comment: RevTex format, 2 figures, 4 pages, a few new references, no other
important change, figures unchanged, version to be published in PR
Improved full one-loop corrections to A^0 -> \sf_1 \sf_2 and \sf_2 -> \sf_1 A^0
We calculate the full electroweak one-loop corrections to the decay of the
CP-odd Higgs boson A^0 into scalar fermions in the minimal supersymmetric
extension of the Standard Model. For this purpose many parameters of the MSSM
have to be properly renormalized in the on-shell renormalization scheme. We
have also included the SUSY-QCD corrections. For the decay into bottom squarks
and tau sleptons, especially for large \tan\b, the corrections can be very
large making the perturbation expansion unreliable. We solve this problem by an
appropriate definition of the tree-level coupling in terms of running fermion
masses and running trilinear couplings A_f. We also discuss the decay of heavy
scalar fermions into light scalar fermions and A^0. We find that the
corrections can be sizeable and therefore cannot be neglected.Comment: 42 pages, 20 figures (23 eps-files
Revisiting Leptogenesis in a SUSY SU(5) x T' Model of Flavour
We investigate the generation of the baryon asymmetry of the Universe within
a SUSY SU(5) x T' model of flavour, which gives rise to realistic masses and
mixing patterns for quarks and leptons. The model employs the see-saw mechanism
for generation of the light neutrino masses and the baryon asymmetry is
produced via leptogenesis. We perform detailed calculations of both the CP
violating lepton asymmetries, originating from the decays of the heavy Majorana
neutrinos operative in the see-saw mechanism, and of the efficiency factors
which account for the lepton asymmetry wash-out processes in the Early
Universe. The latter are calculated by solving numerically the system of
Boltzmann equations describing the generation and the evolution of the lepton
asymmetries. The baryon asymmetry in the model considered is proportional to
the J_{CP} factor, which determines the magnitude of CP violation effects in
the oscillations of flavour neutrinos. The leptogenesis scale can be
sufficiently low, allowing to avoid the potential gravitino problem.Comment: 14 pages, 1 figure; published versio
Constraints on the Charged Higgs Sector from the Tevatron Collider Data on Top Quark Decay
The top quark data in the lepton plus channel offers a viable probe
for the charged Higgs boson signal. We analyse the recent Tevatron collider
data in this channel to obtain a significant limit on the mass in the
large region.Comment: 8 pages, LaTeX file; 2 figures included (PS files
Z\rightarrow A^0 A^0\nu\bar\nue^+e^-\rightarrow A^0 A^0 Z$ in Two Higgs Doublet Models
In LEP searches for the neutral CP-odd scalar of a multi-Higgs doublet
model, experimenters have searched for (where is
the lightest CP-even scalar). No model-independent limit on the mass can
be deduced from present data if . In this paper, we compute the
rates for and .
Assuming that no light CP-even neutral scalars exist, the branching ratio for
is found to be less than .
At higher center-of-mass energies, peaks at ~fb. A comparison with other direct searches for the is
briefly considered.Comment: 16 pages, PHYZZX forma
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