1,049 research outputs found
Dark Matter in Gauge Mediation from Emergent Supersymmetry
We investigated the viability of neutralino dark matter in the gauge
mediation from emergent supersymmetry proposal. In this proposal, supersymmetry
is broken at Planck scale and consequently, the gravitino is superheavy and
completely decouples from the low energy theory. Squarks and sleptons obtain
their soft masses dominantly through gauge mediation with other mechanisms
highly suppressed. The lightest supersymmetric partner, in contrast to
traditional gauge mediation, is a neutralino which is also a dark matter
candidate. By explicit calculation of the low energy spectra, the parameter
space was constrained using the WMAP observed relic density of dark matter,
LEP2 Higgs mass bounds, collider bounds on supersymmetric partners and exotic
B-meson decays. We found that the model has intriguing hybrid features such as
a nearly gauge-mediated spectrum (the exception being the superheavy gravitino)
but with a dominant mSUGRA-like bino-stau coannihilation channel and at large
, A-resonance-like annihilation.Comment: 14 pages, 4 figure
Baryon magnetic moments in chiral perturbation theory
We consider the chiral expansion of the octet baryon magnetic moments in
heavy baryon chiral perturbation theory including all terms which are of order
. These terms are formally of quadratic order in the quark masses. We show
that despite the large non-analytic quark mass corrections to the
Coleman-Glashow relations at order , including all analytic and
non-analytic corrections at order , which in total are of moderate size,
allows for a fit to the measured magnetic moments due to the appearance of
counter terms with free coupling constants of natural size. In this scheme, the
transition moment is predicted to be .Comment: 20 pp, LaTeX file, 2 figures (uses epsf), corrected versio
Leptogenesis in the Light of Super-Kamiokande Data and a Realistic String Model
We discuss leptogenesis in the light of indications of neutrino masses and
mixings from Super-Kamiokande and other data on atmospheric neutrinos, as well
as the solar neutrino deficit. Neutrino masses and mixings consistent with
these data may produce in a natural and generic way a lepton asymmetry that is
suffient to provide the observed baryon asymmetry, after processing via
non-perturbative electroweak effects. We illustrate this discussion in the
framework of the string-derived flipped SU(5) model, using particle assignments
and choices of vacuum parameters that are known to give realistic masses to
quarks and charged leptons. We display one scenario for neutrino masses that
also accommodates leptogenesis.Comment: 18 pages, 1 figur
Partially composite 2-Higgs-doublet model
In the extra dimensional scenarios with gauge fields in the bulk, the
Kaluza-Klein (KK) gauge bosons can induce Nambu-Jona-Lasinio (NJL) type
attractive four-fermion interactions, which can break electroweak symmetry
dynamically with accompanying composite Higgs fields. We consider a possibility
that electroweak symmetry breaking (EWSB) is triggered by both a fundamental
Higgs and a composite Higgs arising in a dynamical symmetry breaking mechanism
induced by a new strong dynamics. The resulting Higgs sector is a partially
composite two-Higgs doublet model with specific boundary conditions on the
coupling and mass parameters originating at a compositeness scale .
The phenomenology of this model is discussed including the collider
phenomenology at LHC and ILC.Comment: To appear in the proceeding of LCWS06, Bangalore, Indi
Phase Transition in a One-Dimensional Extended Peierls-Hubbard Model with a Pulse of Oscillating Electric Field: III. Interference Caused by a Double Pulse
In order to study consequences of the differences between the
ionic-to-neutral and neutral-to-ionic transitions in the one-dimensional
extended Peierls-Hubbard model with alternating potentials for the TTF-CA
complex, we introduce a double pulse of oscillating electric field in the
time-dependent Schr\"odinger equation and vary the interval between the two
pulses as well as their strengths. When the dimerized ionic phase is
photoexcited, the interference effect is clearly observed owing to the
coherence of charge density and lattice displacements. Namely, the two pulses
constructively interfere with each other if the interval is a multiple of the
period of the optical lattice vibration, while they destructively interfere if
the interval is a half-odd integer times the period, in the processes toward
the neutral phase. The interference is strong especially when the pulse is
strong and short because the coherence is also strong. Meanwhile, when the
neutral phase is photoexcited, the interference effect is almost invisible or
weakly observed when the pulse is weak. The photoinduced lattice oscillations
are incoherent due to random phases. The strength of the interference caused by
a double pulse is a key quantity to distinguish the two transitions and to
evaluate the coherence of charge density and lattice displacements.Comment: 16 pages, 8 figure
Partially Composite Higgs in Supersymmetry
We propose a framework for natural breaking of electroweak symmetry in
supersymmetric models, where elementary Higgs fields are semi-perturbatively
coupled to a strong superconformal sector. The Higgs VEVs break conformal
symmetry in the strong sector at the TeV scale, and the strong sector in turn
gives important contributions to the Higgs potential, giving rise to a kind of
Higgs bootstrap. A Higgs with mass 125\GeV can be accommodated without any
fine tuning. A Higgsino mass of order the Higgs mass is also dynamically
generated in these models. The masses in the strong sector generically violate
custodial symmetry, and a good precision electroweak fit requires tuning of
order . The strong sector has an approximately supersymmetric
spectrum of hadrons at the TeV scale that can be observed by looking for a peak
in the invariant mass distribution, as well as final states containing
multiple , , and Higgs bosons. The models also generically predict large
corrections (either enhancement or suppression) to the h \to \ga\ga width.Comment: 31 page
Anomaly Mediated Supersymmetry Breaking in Four Dimensions, Naturally
We present a simple four-dimensional model in which anomaly mediated
supersymmetry breaking naturally dominates. The central ingredient is that the
hidden sector is near a strongly-coupled infrared fixed-point for several
decades of energy below the Planck scale. Strong renormalization effects then
sequester the hidden sector from the visible sector. Supersymmetry is broken
dynamically and requires no small input parameters. The model provides a
natural and economical explanation of the hierarchy between the
supersymmetry-breaking scale and the Planck scale, while allowing anomaly
mediation to address the phenomenological challenges posed by weak scale
supersymmetry. In particular, flavor-changing neutral currents are naturally
near their experimental limits.Comment: 14 pages, Late
Visible Effects of the Hidden Sector
The renormalization of operators responsible for soft supersymmetry breaking
is usually calculated by starting at some high scale and including only visible
sector interactions in the evolution equations, while ignoring hidden sector
interactions. Here we explain why this is correct only for the most trivial
structures in the hidden sector, and discuss possible implications. This
investigation was prompted by the idea of conformal sequestering. In that
framework hidden sector renormalizations by nearly conformal dynamics are
critical. In the original models of conformal sequestering it was necessary to
impose hidden sector flavor symmetries to achieve the sequestered form. We
present models which can evade this requirement and lead to no-scale or anomaly
mediated boundary conditions; but the necessary structures do not seem generic.
More generally, the ratios of scalar masses to gaugino masses, the -term,
the -term, -terms, and the gravitino mass can be significantly
affected.Comment: 23 pages, no figure
Improved Single Sector Supersymmetry Breaking
Building on recent work by N. Arkani-Hamed and the present authors, we
construct realistic models that break supersymmetry dynamically and give rise
to composite quarks and leptons, all in a single strongly-coupled sector. The
most important improvement compared to earlier models is that the
second-generation composite states correspond to dimension-2 "meson" operators
in the ultraviolet. This leads to a higher scale for flavor physics, and gives
a completely natural suppression of flavor-changing neutral currents. We also
construct models in which the hierarchy of Yukawa couplings is explained by the
dimensionality of composite states. These models provide an interesting and
viable alternative to gravity- and gauge-mediated models. The generic
signatures are unification of scalar masses with different quantum numbers at
the compositeness scale, and lighter gaugino, Higgsino, and third-generation
squark and slepton masses. We also analyze large classes of models that give
rise to both compositeness and supersymmetry breaking, based on gauge theories
with confining, fixed-point, or free-magnetic dynamics.Comment: 34 pages, LaTeX2
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