833 research outputs found
The light Higgs in supersymmetric models with Higgs triplets
In supersymmetric models the presence of Higgs triplets introduce new quartic
interactions for the doublets that may raise the mass of the lightest CP-even
field up to 205 GeV. We show that the complete effect of the triplets can be
understood by decoupling them from the minimal sector and then analyzing the
vacuum and the spectrum of the two-Higgs doublet model that results. We find
that the maximum value of m_h is only achieved in a very definite region of the
parameter space. In this region, however, radiative corrections decrease the
bound to 190 GeV.Comment: 10 pages, 1 figur
Higgsino dark matter in partly supersymmetric models
Models where supersymmetry (SUSY) is manifest only in a sector of the
low-energy spectrum have been recently proposed as an alternative to the MSSM.
In these models the electroweak scale is explained by a fine-tuning between
different Higgs mass contributions (split-SUSY models), or by the localization
of the Higgs sector in a point of an extra dimension where all the mass
parameters are suppressed by the metric (partly-SUSY models). Therefore, the
presence of a good dark matter candidate becomes the main motivation for
(partial) low-energy SUSY. We study this issue in minimal frameworks where the
higgsinos are the only light supersymmetric particles. Whereas in split-SUSY
models the higgsino should have a mass around 1 TeV, we show that in
partly-SUSY models the lightest higgsino could also be found below MW.Comment: 12 pages, 3 figures, version to appear in Phys. Rev.
Probing TeV gravity at neutrino telescopes
Models with extra dimensions and the fundamental scale at the TeV could imply
sign als in large neutrino telescopes due to gravitational scattering of
cosmogenic neu trinos in the detection volume. Apart from the production of
microscopic black hol es, extensively studied in the literature, we present
gravity-mediated interactions at larger distances, that can be calculated in
the e ikonal approximation. In these elastic processes the neutrino loses a
small fracti on of energy to a hadronic shower and keeps going. The event rate
of these events is higher than that of black hole formation and the signal is
distinct: no charged leptons and possibly multiple-bang events.Comment: 5 pages; to appear in the proceedings of the Workshop on Exotic
Physics with Neutrino Telesocpes, Uppsala 20-22 September 200
Ultraviolet dependence of Kaluza-Klein effects on electroweak observables
In extensions of the standard model (SM) with d extra dimensions at the TeV
scale the virtual exchange of Kaluza-Klein (KK) excitations of the gauge bosons
gives contributions that change the SM relations between electroweak
observables. These corrections are finite only for d=1; for d\ge 2 the infinite
tower of KK modes gives a divergent contribution that has to be regularized
introducing a cutoff (the string scale). However, the ultraviolet dependence of
the KK effects is completely different if the running of the couplings with the
scale is taken into account. We find that for larger d the number of
excitations at each KK level increases, but their larger number is compensated
by the smaller value of the gauge coupling at that scale. As a result, for any
number of extra dimensions the exchange of the complete KK tower always gives a
finite contribution. We show that (i) for d=1 the running of the gauge coupling
decreases an 14% the effect of the KK modes on electroweak observables; (ii) in
all cases more than 90% of the total effect comes from the excitations in the
seven lowest KK levels and is then independent of ultraviolet physics.Comment: 8 pages, to appear in Phys. Rev.
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