31 research outputs found
Neutrino Masses and Mixing Angles in SUSY-GUT Theories with explicit R-Parity Breaking
In minimal SUSY GUT models the -parity breaking terms are severely
constrained by SU(5) gauge invariance. We consider the particular case where
the explicit -parity breaking occurs only via dimension 2 terms of the
superpotential. This model possesses only three R-parity breaking parameters.
We have studied the predictions of this model for the neutrino masses and
mixing angles at the one-loop level within the framework of a radiatively
broken unified supergravity model. We find that this model naturally yields
masses and mixing angles that can explain the solar and atmospheric neutrino
problems. In addition, there are regions in parameter space where the solution
to the solar neutrino puzzle is compatible with either the LSND result or the
existence of significant hot dark matter neutrinos.Comment: Revised version as published in Nucl. Phys. B; several typos
correcte
On the fine-tuning problem in minimal SO(10) SUSY-GUT
In grand unified theories (GUT) based on SO(10) all fermions of one
generation are embedded in a single representation. As a result, the top quark,
the bottom quark, and the lepton have a universal Yukawa coupling at the
GUT scale. This implies a very large ratio of Higgs vacuum expectation values,
\tanb \simeq m_t/m_b. We analyze the naturalness of such a scenario
quantitatively including all the relevant radiative corrections and find that
in minimal unified supergravity models with universal soft supersymmetry
breaking parameters at the GUT scale, the necessary amount of fine-tuning
needed is excessive. GUT threshold correction to the universal Higgs mass
parameter can significantly reduce the fine-tuning required for such large
values of \tanb. We also point out that the top quark mass can play a crucial
role in explaining the hierarchy between the SUSY breaking scale and the
electro-weak scale and, hence, the naturalness of large values of \tanb.Comment: 20 pages, 10 figs, uses PHYZZX version to be published in Phys Rev.
Approximating the radiatively corrected Higgs mass in the Minimal Supersymmetric Model
To obtain the most accurate predictions for the Higgs masses in the minimal
supersymmetric model (MSSM), one should compute the full set of one-loop
radiative corrections, resum the large logarithms to all orders, and add the
dominant two-loop effects. A complete computation following this procedure
yields a complex set of formulae which must be analyzed numerically. We discuss
a very simple approximation scheme which includes the most important terms from
each of the three components mentioned above. We estimate that the Higgs masses
computed using our scheme lie within 2 GeV of their theoretically predicted
values over a very large fraction of MSSM parameter space.Comment: 31 pages, 10 embedded figures, latex with psfig.sty the complete
postscript file of this preprint, including figures, is available via
anonymous ftp at ftp://www-ttp.physik.uni-karlsruhe.de/ttp95-09/ttp95-09.ps
or via www at http://www-ttp.physik.uni-karlsruhe.de/cgi-bin/preprints
Can the Supersymmetric parameter be generated dynamically without a light Singlet?
It is generally assumed that the dynamical generation of the Higgs mass
parameter of the superpotential, , implies the existence of a light
singlet at or below the supersymmetry breaking scale, \msusy. We present a
counter-example in which the singlet field can receive an arbitrarily heavy
mass (\eg, of the order of the Planck scale, M_{\rm P}\approx 10^{19}~\gev).
In this example, a non-zero value of is generated through soft
supersymmetry breaking parameters and is thus naturally of the order of
\msusy.Comment: 6 pages, phyzzx, DESY 94-06