1,318 research outputs found
Split extended supersymmetry from intersecting branes
We study string realizations of split extended supersymmetry, recently
proposed in hep-ph/0507192. Supersymmetry is broken by small ()
deformations of intersection angles of -branes giving tree-level masses of
order , where is the string scale, to localized
scalars. We show through an explicit one-loop string amplitude computation that
gauginos acquire hierarchically smaller Dirac masses . We also evaluate the one-loop Higgsino mass, , and show that,
in the absence of tree-level contributions, it behaves as . Finally we discuss an alternative suppression of scales using
large extra dimensions. The latter is illustrated, for the case where the gauge
bosons appear in N=4 representations, by an explicit string model with Standard
Model gauge group, three generations of quarks and leptons and gauge coupling
unification.Comment: 32 pages, 3 figure
The Higgs as a Portal to Plasmon-like Unparticle Excitations
A renormalizable coupling between the Higgs and a scalar unparticle operator
O_U of non-integer dimension d_U<2 triggers, after electroweak symmetry
breaking, an infrared divergent vacuum expectation value for O_U. Such IR
divergence should be tamed before any phenomenological implications of the
Higgs-unparticle interplay can be drawn. In this paper we present a novel
mechanism to cure that IR divergence through (scale-invariant) unparticle
self-interactions, which has properties qualitatively different from the
mechanism considered previously. Besides finding a mass gap in the unparticle
continuum we also find an unparticle pole reminiscent of a plasmon resonance.
Such unparticle features could be explored experimentally through their mixing
with the Higgs boson.Comment: 12 LaTeX pages, 2 figure
Some Cosmological Implications of Hidden Sectors
We discuss some cosmological implications of extensions of the Standard Model
with hidden sector scalars coupled to the Higgs boson. We put special emphasis
on the conformal case, in which the electroweak symmetry is broken radiatively
with a Higgs mass above the experimental limit. Our refined analysis of the
electroweak phase transition in this kind of models strengthens the prediction
of a strongly first-order phase transition as required by electroweak
baryogenesis. We further study gravitational wave production and the
possibility of low-scale inflation as well as a viable dark matter candidate.Comment: 23 pages, 8 figures; some comments added, published versio
The lightest Higgs mass in supersymmetric models with extra dimensions
In the four-dimensional supersymmetric standard model extended with gauge
singlets the lightest Higgs boson mass, , has an important contribution
proportional to the squared of the superpotential coupling of
singlets to Higgs fields, . The requirement of
perturbativity up to the unification scale yields an upper bound on GeV. In extensions to theories with (longitudinal) extra dimensions at the
TeV where such coupling exists and massive Kaluza-Klein states fall into N=2
representations, if either of the Higgs or singlet fields live in the bulk of
the extra dimensions, the -function of is suppressed due to
the absence of anomalous dimension of hypermultiplets to leading order. This
implies a slower running of and an enhancement of its low energy
value. The upper bound increases to values GeV.Comment: Latex2e, 11 pages, 1 figur
Inversion of the anomeric configuration of the transferred sugar during inactivation of the macrolide antibiotic oleandomycin catalyzed by a macrolide glycosyltransferase
AbstractMacrolides are a group of antibiotics structurally characterized by a macrocyclic lactone to which one or several deoxy-sugar moieties are attached. The sugar moieties are transferred to the different aglycones by glycosyltransferases (GTF). The OleI GTF of an oleandomycin producer, Streptomyces antibioticus, catalyzes the inactivation of this macrolide by glycosylation. The product of this reaction was isolated and its structure elucidated. The donor substrate of the reaction was UDP-α-D-glucose, but the reaction product showed a β-glycosidic linkage. The inversion of the anomeric configuration of the transferred sugar and other data about the kinetics of the reaction and primary structure analysis of several GTFs are compatible with a reaction mechanism involving a single nucleophilic substitution at the sugar anomeric carbon in the catalytic center of the enzyme
The MSSM from Scherk-Schwarz Supersymmetry Breaking
We present a five-dimensional model compactified on an interval where
supersymmetry is broken by the Scherk-Schwarz mechanism. The gauge sector
propagates in the bulk, two Higgs hypermultiplets are quasilocalized, and quark
and lepton multiplets localized, in one of the boundaries. The effective
four-dimensional theory is the MSSM with very heavy gauginos, heavy squarks and
light sleptons and Higgsinos. The soft tree-level squared masses of the Higgs
sector can be negative and they can (partially) cancel the positive one-loop
contributions from the gauge sector. Electroweak symmetry breaking can then
comfortably be triggered by two-loop radiative corrections from the top-stop
sector. The fine tuning required to obtain the electroweak scale is found to be
much smaller than in the MSSM, with essentially no fine-tuning for few TeV
gaugino masses. All bounds from direct Higgs searches at LEP and from
electroweak precision observables can be satisfied. The lightest supersymmetric
particle is a (Higgsino-like) neutralino that can accomodate the abundance of
Dark Matter consistently with recent WMAP observations.Comment: 23 pages, 3 figure
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