288 research outputs found
On the role of vortex stretching in energy optimal growth of three dimensional perturbations on plane parallel shear flows
The three dimensional optimal energy growth mechanism, in plane parallel
shear flows, is reexamined in terms of the role of vortex stretching and the
interplay between the span-wise vorticity and the planar divergent components.
For high Reynolds numbers the structure of the optimal perturbations in
Couette, Poiseuille, and mixing layer shear profiles is robust and resembles
localized plane-waves in regions where the background shear is large. The waves
are tilted with the shear when the span-wise vorticity and the planar
divergence fields are in (out of) phase when the background shear is positive
(negative). A minimal model is derived to explain how this configuration
enables simultaneous growth of the two fields, and how this mutual
amplification reflects on the optimal energy growth. This perspective provides
an understanding of the three dimensional growth solely from the two
dimensional dynamics on the shear plane
Color Superconductivity from Supersymmetry
A supersymmetric composite model of color superconductivity is proposed.
Quarks and diquarks are dynamically generated as composite fields by a newly
introduced strong gauge dynamics. It is shown that the condensation of the
scalar component of the diquark supermultiplet occurs when the chemical
potential becomes larger than some critical value. We believe that the model
well captures aspects of the diquark condensate behavior and helps our
understanding of the diquark dynamics in real QCD. The results obtained here
might be useful when we consider a theory composed of quarks and diquarks.Comment: 4 pages, 2 figures, An error in Eq.(10) correcte
Anomaly Mediation, Fayet-Iliopoulos D-terms and the Renormalisation Group
We address renormalisation group evolution issues that arise in the Anomaly
Mediated Supersymmetry Breaking scenario when the tachyonic slepton problem is
resolved by Fayet-Iliopoulos term contributions. We present typical sparticle
spectra both for the original formulation of this idea and an alternative using
Fayet-Iliopoulos terms for a U(1) compatible with a straightforward GUT
embedding.Comment: 20 pages, 2 figure
Purely Four-dimensional Viable Anomaly Mediation
Anomaly mediation of supersymmetry breaking solves the supersymmetric flavor
problem thanks to its ultraviolet-insensitivity. However, it suffers from two
problems: sleptons have negative masses-squared, and there are likely bulk
moduli that spoil the framework. Here, we present the first fully
ultraviolet-insensitive model of anomaly mediation with positive slepton
masses-squared in a purely four-dimensional framework. Our model is based on
the additional D-term contributions to the sparticle masses, and the conformal
sequestering mechanism.Comment: 7 pages, Uses RevTex4 (included). References modifie
Abelian D-terms and the superpartner spectrum of anomaly-mediated supersymmetry breaking
We address the tachyonic slepton problem of anomaly mediated supersymmetry
breaking using abelian D-terms. We demonstrate that the most general extra U(1)
symmetry that does not disrupt gauge coupling unification has a large set of
possible charges that solves the problem. It is shown that previous studies in
this direction that added both an extra hypercharge D-term and another D-term
induced by B-L symmetry (or similar) can be mapped into a single D-term of the
general ancillary U(1)_a. The U(1)_a formalism enables identifying the sign of
squark mass corrections which leads to an upper bound of the entire
superpartner spectrum given knowledge of just one superpartner mass.Comment: 10 pages, 2 figures, [v2] reference added, [v3] Eq. (9) corrected,
results unaffected, [v4] version to be published in Phys. Rev. D, expanded
parameter space for figures to match tex
Little Hierarchy, Little Higgses, and a Little Symmetry
Little Higgs theories are an attempt to address the little hierarchy problem,
i.e., the tension between the naturalness of the electroweak scale and the
precision measurements showing no evidence for new physics up to 5-10 TeV. In
little Higgs theories, the Higgs mass-squareds are protected to the one-loop
order from the quadratic divergence. This allows the cutoff to be raised up to
\~10 TeV, beyond the scales probed by the precision data. However, strong
constraints can still arise from the contributions of the new TeV scale
particles and hence re-introduces the fine-tuning problem. In this paper we
show that a new symmetry, denoted as T-parity, under which all heavy gauge
bosons and scalar triplets are odd, can remove all the tree-level contributions
to the electroweak observables and therefore makes the little Higgs theories
completely natural. The T-parity can be manifestly implemented in a majority of
little Higgs models by following the most general construction of the low
energy effective theory a la Callan, Coleman, Wess and Zumino. In particular,
we discuss in detail how to implement the T-parity in the littlest Higgs model
based on SU(5)/SO(5). The symmetry breaking scale f can be even lower than 500
GeV if the contributions from the unknown UV physics at the cutoff are somewhat
small. The existence of -parity has drastic impacts on the phenomenology of
the little Higgs theories. The T-odd particles need to be pair-produced and
will cascade down to the lightest T-odd particle (LTP) which is stable. A
neutral LTP gives rise to missing energy signals at the colliders which can
mimic supersymmetry. It can also serve as a good dark matter candidate.Comment: 20 pages, 2 figures, RevTeX; v2: Yukawa sector in the SU(5)/SO(5)
model slightly modified. Also added comments on the Dirac mass term for the
fermionic doublet partner; v3: clarifying comments on the modified Yukawa
sector. version to appear on JHE
Minimal Gaugomaly Mediation
Mixed anomaly and gauge mediation ("gaugomaly'' mediation) gives a natural
solution to the SUSY flavor problem with a conventional LSP dark matter
candidate. We present a minimal version of gaugomaly mediation where the
messenger masses arise directly from anomaly mediation, automatically
generating a messenger scale of order 50 TeV. We also describe a simple
relaxation mechanism that gives rise to realistic mu and B mu terms. B is
naturally dominated by the anomaly-mediated contribution from top loops, so the
mu/B mu sector only depends on a single new parameter. In the minimal version
of this scenario the full SUSY spectrum is determined by two continuous
parameters (the anomaly- and gauge-mediated SUSY breaking masses) and one
discrete parameter (the number of messengers). We show that these simple models
can give realistic spectra with viable dark matter.Comment: 18 pages, 4 figures; v2: corrected example generating non-holomorphic
Kahler term
Folded Supersymmetry and the LEP Paradox
We present a new class of models that stabilize the weak scale against
radiative corrections up to scales of order 5 TeV without large corrections to
precision electroweak observables. In these `folded supersymmetric' theories
the one loop quadratic divergences of the Standard Model Higgs field are
cancelled by opposite spin partners, but the gauge quantum numbers of these new
particles are in general different from those of the conventional
superpartners. This class of models is built around the correspondence that
exists in the large N limit between the correlation functions of supersymmetric
theories and those of their non-supersymmetric orbifold daughters. By
identifying the mechanism which underlies the cancellation of one loop
quadratic divergences in these theories, we are able to construct simple
extensions of the Standard Model which are radiatively stable at one loop.
Ultraviolet completions of these theories can be obtained by imposing suitable
boundary conditions on an appropriate supersymmetric higher dimensional theory
compactified down to four dimensions. We construct a specific model based on
these ideas which stabilizes the weak scale up to about 20 TeV and where the
states which cancel the top loop are scalars not charged under Standard Model
color. Its collider signatures are distinct from conventional supersymmetric
theories and include characteristic events with hard leptons and missing
energy.Comment: 18 pages, 5 figures, references correcte
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