2 research outputs found
Four Generations: SUSY and SUSY Breaking
We revisit four generations within the context of supersymmetry. We compute
the perturbativity limits for the fourth generation Yukawa couplings and show
that if the masses of the fourth generation lie within reasonable limits of
their present experimental lower bounds, it is possible to have perturbativity
only up to scales around 1000 TeV. Such low scales are ideally suited to
incorporate gauge mediated supersymmetry breaking, where the mediation scale
can be as low as 10-20 TeV. The minimal messenger model, however, is highly
constrained. While lack of electroweak symmetry breaking rules out a large part
of the parameter space, a small region exists, where the fourth generation stau
is tachyonic. General gauge mediation with its broader set of boundary
conditions is better suited to accommodate the fourth generation.Comment: 27 pages, 5 figure
Running of Radiative Neutrino Masses: The Scotogenic Model
We study the renormalization group equations of Ma's scotogenic model, which
generates an active neutrino mass at 1-loop level. In addition to other
benefits, the main advantage of the mechanism exploited in this model is to
lead to a natural loop-suppression of the neutrino mass, and therefore to an
explanation for its smallness. However, since the structure of the neutrino
mass matrix is altered compared to the ordinary type I seesaw case, the
corresponding running is altered as well. We have derived the full set of
renormalization group equations for the scotogenic model which, to our
knowledge, had not been presented previously in the literature. This set of
equations reflects some interesting structural properties of the model, and it
is an illustrative example for how the running of neutrino parameters in
radiative models is modified compared to models with tree-level mass
generation. We also study a simplified numerical example to illustrate some
general tendencies of the running. Interestingly, the structure of the RGEs can
be exploited such that a bimaximal leptonic mixing pattern at the high-energy
scale is translated into a valid mixing pattern at low energies, featuring a
large value of \theta_{13}. This suggests very interesting connections to
flavour symmetries.Comment: 35 pages, 10 figures, 2 table