2,687 research outputs found
Dynamical Supersymmetry Breaking and Low Energy Gauge Mediation
Dynamical breaking of supersymmetry was long thought to be an exceptional
phenomenon, but recent developments have altered this view. A question of great
interest in the current framework is the value of the underlying scale of
supersymmetry breaking. The "little hierarchy" problem suggests that
supersymmetry should be broken at low energies. Within one class of models, low
energy breaking be achieved as a consequence of symmetries, without requiring
odd coincidences. The low energy theories are distinguished by the presence or
absence of symmetries; in either case, and especially the latter one often
finds modifications of the minimal gauge-mediated spectrum which can further
ameliorate problems of fine tuning. Various natural mechanisms exist to solve
the problem in this framework.Comment: 20 pages (minor change in referencing
Phenomenological consequences of supersymmetry with anomaly-induced masses
In the supersymmetric standard model there exist pure gravity contributions
to the soft mass parameters which arise via the superconformal anomaly. We
consider the low-energy phenomenology with a mass spectrum dominated by the
anomaly-induced contributions. In a well-defined minimal model we calculate
electroweak symmetry breaking parameters, scalar masses, and the full one-loop
splitting of the degenerate Wino states. The most distinctive features are
gaugino masses proportional to the corresponding gauge coupling beta-functions,
the possibility of a Wino as the lightest supersymmetric particle, mass
degeneracy of sleptons, and a very massive gravitino. Unique signatures at
high-energy colliders include dilepton and single lepton final states,
accompanied by missing energy and displaced vertices. We also point out that
this scenario has the cosmological advantage of ameliorating the gravitino
problem. Finally, the primordial gravitino decay can produce a relic density of
Wino particles close to the critical value.Comment: 26 pages, 7 figures, LaTe
PeV-Scale Supersymmetry
Although supersymmetry has not been seen directly by experiment, there are
powerful physics reasons to suspect that it should be an ingredient of nature
and that superpartner masses should be somewhat near the weak scale. I present
an argument that if we dismiss our ordinary intuition of finetuning, and focus
entirely on more concrete physics issues, the PeV scale might be the best place
for supersymmetry. PeV-scale supersymmetry admits gauge coupling unification,
predicts a Higgs mass between 125 GeV and 155 GeV, and generally disallows
flavor changing neutral currents and CP violating effects in conflict with
current experiment. The PeV scale is motivated independently by dark matter and
neutrino mass considerations.Comment: 5 RevTex page
Probing Split Supersymmetry with Cosmic Rays
A striking aspect of the recently proposed split supersymmetry is the
existence of heavy gluinos which are metastable because of the very heavy
squarks which mediate their decay. In this paper we correlate the expected flux
of these particles with the accompanying neutrino flux produced in inelastic
collisions in distant astrophysical sources. We show that an event rate at
the Pierre Auger Observatory of approximately 1 yr for gluino masses of
about 500 GeV is consistent with existing limits on neutrino fluxes. The
extremely low inelasticity of the gluino-containing hadrons in their collisions
with the air molecules makes possible a distinct characterization of the
showers induced in the atmosphere. Should such anomalous events be observed, we
show that their cosmogenic origin, in concert with the requirement that they
reach the Earth before decay, leads to a lower bound on their proper lifetime
of the order of 100 years, and consequently, to a lower bound on the scale of
supersymmetry breaking, GeV. Obtaining
such a bound is not possible in collider experiments.Comment: Version to be published in Phys. Rev.
Towards a realistic Standard Model from D-brane configurations
Effective low energy models arising in the context of D-brane configurations
with Standard Model (SM) gauge symmetry extended by several gauged abelian
factors are discussed. The models are classified according to their hypercharge
embeddings consistent with the SM spectrum hypercharge assignment. Particular
cases are analyzed according to their perspectives and viability as low energy
effective field theory candidates. The resulting string scale is determined by
means of a two-loop renormalization group calculation. Their implications in
Yukawa couplings, neutrinos and flavor changing processes are also presented.Comment: 22 pages, 12 EPS figures, some clarifications/references adde
Quark-antiquark pair production in space-time dependent fields
Fermion-antifermion pair-production in the presence of classical fields is
described based on the retarded and advanced fermion propagators. They are
obtained by solving the equation of motion for the Dirac Green's functions with
the respective boundary conditions to all orders in the field. Subsequently,
various approximation schemes fit for different field configurations are
explained. This includes longitudinally boost-invariant forms. Those occur
frequently in the description of ultrarelativistic heavy-ion collisions in the
semiclassical limit. As a next step, the gauge invariance of the expression for
the expectation value of the number of produced fermion-antifermion pairs as a
functional of said propagators is investigated in detail. Finally, the
calculations are carried out for a longitudinally boost-invariant model-field,
taking care of the last issue, especially.Comment: 32 pages, 8 figures, revised versio
Comparison of electric dipole moments and the Large Hadron Collider for probing CP violation in triple boson vertices
CP violation from physics beyond the Standard Model may reside in triple
boson vertices of the electroweak theory. We review the effective theory
description and discuss how CP violating contributions to these vertices might
be discerned by electric dipole moments (EDM) or diboson production at the
Large Hadron Collider (LHC). Despite triple boson CP violating interactions
entering EDMs only at the two-loop level, we find that EDM experiments are
generally more powerful than the diboson processes. To give example to these
general considerations we perform the comparison between EDMs and collider
observables within supersymmetric theories that have heavy sfermions, such that
substantive EDMs at the one-loop level are disallowed. EDMs generally remain
more powerful probes, and next-generation EDM experiments may surpass even the
most optimistic assumptions for LHC sensitivities.Comment: 26 pages, 14 figures, published version with more argument
Hierarchy from Baryogenesis
We study a recently proposed mechanism to solve the hierarchy problem in the
context of the landscape, where the solution of the hierarchy problem is
connected to the requirement of having baryons in our universe via Electroweak
Baryogenesis. The phase transition is triggered by the fermion condensation of
a new gauge sector which becomes strong at a scale Lambda determined by
dimensional transmutation, and it is mediated to the standard model by a new
singlet field. In a ``friendly'' neighborhood of the landscape, where only the
relevant operators are ``scanned'' among the vacua, baryogenesis is effective
only if the higgs mass m_h is comparable to this low scale Lambda, forcing m_h
to be of order Lambda, and solving the hierarchy problem. A new CP violating
phase is needed coupling the new singlet and the higgs field to new matter
fields. We study the constraints on this model given by baryogenesis and by the
electron electric dipole moment (EDM), and we briefly comment on gauge coupling
unification and on dark matter relic abundance. We find that next generation
experiments on the EDM will be sensitive to essentially the entire viable
region of the parameter space, so that absence of a signal would effectively
rule out the model.Comment: 28 pages, 4 figures. v2: Added comments and references. Corrected one
typo in eq.(81). Conclusions unaltere
Decaying neutralino dark matter in anomalous models
In supersymmetric models extended with an anomalous different
R-parity violating couplings can yield an unstable neutralino. We show that in
this context astrophysical and cosmological constraints on neutralino decaying
dark matter forbid bilinear R-parity breaking neutralino decays and lead to a
class of purely trilinear R-parity violating scenarios in which the neutralino
is stable on cosmological scales. We have found that among the resulting models
some of them become suitable to explain the observed anomalies in cosmic-ray
electron/positron fluxes.Comment: 19 pages, 3 figures. References added, typos corrected, accepted
version in Phys Rev
Late Reheating, Hadronic Jets and Baryogenesis
If inflaton couples very weakly to ordinary matter the reheating temperature
of the universe can be lower than the electroweak scale. In this letter we show
that the late reheating occurs in a highly non-uniform way, within narrow areas
along the jets produced by ordinary particles originated from inflaton decays.
Depending on inflaton mass and decay constant, the initial temperature inside
the lumps of the overheated plasma may be large enough to trigger the
unsuppressed sphaleron processes with baryon number non-conservation, allowing
for efficient local electroweak baryogenesis.Comment: 4 pages, 2 figures, revtex
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