6,239 research outputs found
Solitonic supersymmetry restoration
Q-balls are a possible feature of any model with a conserved, global U(1)
symmetry and no massless, charged scalars. It is shown that for a broad class
of models of metastable supersymmetry breaking they are extremely influential
on the vacuum lifetime and make seemingly viable vacua catastrophically short
lived. A net charge asymmetry is not required as there is often a significant
range of parameter space where statistical fluctuations alone are sufficient.
This effect is examined for two supersymmetry breaking scenarios. It is found
that models of minimal gauge mediation (which necessarily have a messenger
number U(1)) undergo a rapid, supersymmetry restoring phase transition unless
the messenger mass is greater than 10^8 GeV. Similarly the ISS model, in the
context of direct mediation, quickly decays unless the perturbative
superpotential coupling is greater than the Standard Model gauge couplings.Comment: 17 pages, 3 figures, minor comments added, accepted for publication
in JHE
R-symmetry breaking, runaway directions and global symmetries in O'Raifeartaigh models
We discuss O'Raifeartaigh models with general R-charge assignments,
introduced by Shih to break R-symmetry spontaneously. We argue that most of
these models have runaway directions related to the R-symmetry. In addition, we
study the simplest model with a U(N) global symmetry and show that in a range
of parameters R-symmetry is spontaneously broken in a metastable vacuum.Comment: 16 pages, 1 figur
Meta-stable SUSY Breaking Model in Supergravity
We analyze a supersymmetry (SUSY) breaking model proposed by Intriligator,
Seiberg and Shih in a supergravity (SUGRA) framework. This is a simple and
natural setup which demands neither extra superpotential interactions nor an
additional gauge symmetry. In the SUGRA setup, the U(1)R symmetry is explicitly
broken by the constant term in the superpotential, and pseudo-moduli field
naturally takes non-zero vacuum expectation value through a vanishing
cosmological constant condition. Sfermions tend to be heavier than gauginos,
and the strong-coupling scale is determined once a ratio of sfermion to gaugino
masses is fixed.Comment: 13 page
X-ray Scattering Study of the spin-Peierls transition and soft phonon behavior in TiOCl
We have studied the S=1/2 quasi-one-dimensional antiferromagnet TiOCl using
single crystal x-ray diffraction and inelastic x-ray scattering techniques. The
Ti ions form staggered spin chains which dimerize below Tc1 = 66 K and have an
incommensurate lattice distortion between Tc1 and Tc2 = 92 K. Based on our
measurements of the intensities, wave vectors, and harmonics of the
incommensurate superlattice peaks, we construct a model for the incommensurate
modulation. The results are in good agreement with a soliton lattice model,
though some quantitative discrepancies exist near Tc2. The behavior of the
phonons has been studied using inelastic x-ray scattering with ~2 meV energy
resolution. For the first time, a zone boundary phonon which softens at the
spin-Peierls temperature Tsp has been observed. Our results show reasonably
good quantitative agreement with the Cross-Fisher theory for the phonon
dynamics at wave vectors near the zone boundary and temperatures near Tsp.
However, not all aspects of the data can be described, such as the strong
overdamping of the soft mode above Tsp. Overall, our results show that TiOCl is
a good realization of a spin-Peierls system, where the phonon softening allows
us to identify the transition temperature as Tsp=Tc2=92 KComment: 14 pages, 14 figure
Механические свойства композита на основе Al[2]O[3], армированного одностенными углеродными нанотрубками
Subject of this work is a dynamic simulation strategy for PCCI combustion that can be
used in closed-loop control development. A detailed multi-zone chemistry model for the
high-pressure part of the engine cycle is extended by a mean value model accounting for
the gas exchange losses. The resulting stationary model is capable of describing PCCI
combustion sufficiently well. It is at the same time very economic with respect to
computational costs. The model is further extended by identified system dynamics
influencing the stationary inputs. For this, a Wiener model is set up that uses the
stationary model as a nonlinear system representation. In this way, a dynamic nonlinear
model for the representation of the controlled plant Diesel engine is created. This paper
summarizes an important outcome of the the Collaborative Research Centre "SFB 686 -
Modellbasierte Regelung der homogenisierten Niedertemperatur-Verbrennung" at RWTH Aachen
University and Bielefeld University, Germany
Meta-Stable Brane Configuration with Orientifold 6 Plane
We present the intersecting brane configuration of type IIA string theory
corresponding to the meta-stable nonsupersymmetric vacua in four dimensional
N=1 supersymmetric SU(N_c) gauge theory with a symmetric flavor, a conjugate
symmetric flavor and fundamental flavors. By studying the previously known
supersymmetric M5-brane curve, the M-theory lift for this type IIA brane
configuration, which consists of NS5-branes, D4-branes, D6-branes and an
orientifold 6-plane, is analyzed.Comment: 21 pp, 3 colored figures; stability arguments added in page 11 and
12, a typo in figure 3 corrected, and to appear in JHE
Fermion Masses and Mixing in Four and More Dimensions
We give an overview of recent progress in the study of fermion mass and
flavor mixing phenomena. Mass matrix ansatze are considered within the SM and
SUSY GUTs where some predictive frameworks based on SU(5) and SO(10) are
reviewed. We describe a variety of schemes to construct quark mass matrices in
extra dimensions focusing on four major classes: models with the SM residing on
3-brane, models with universal extra dimensions, models with split fermions and
models with warped extra dimensions. We outline how realistic patterns of quark
mass matrices could be derived from orbifold models in heterotic superstring
theory. Finally, we address the fermion mass problem in intersecting D-branes
scenarios, and present models with D6-branes able to give a good quantitatively
description of quark masses and mixing. The role of flavor/CP violation problem
as a probe of new physics is emphasized.Comment: a review based on seminars presented by S.K. in different places, 34
pages, late
Role of the Bcl-2 gene family in prostate cancer progression and its implications for therapeutic intervention.
Prostate cancer (PC) is an escalating health burden in the western world. A large number of patients still present with extraprostatic (i.e., T3/T4, N0, M0/M1 or any T category and M1 disease or involved lymph nodes) and therefore incurable disease. Since the work of Huggins in 1940, there have been no major therapeutic advances and androgen ablation remains the best treatment option for extraprostatic androgen-responsive PC. Eighty to ninety percent of PC patients respond well to this form of treatment initially. After a median time of approximately 2 years, however, relapse to an androgen-independent (AI) state occurs, followed by death after a further median 6 months. Androgen ablation is rarely curative. The major molecular defect in extraprostatic and AI PC is the inability of PC cells to initiate apoptosis in response to a variety of stimuli, including different forms of androgen ablation and cytotoxic agents. The balance between cellular proliferation and cell death is regulated by multiple genes or families of genes through the cell cycle. The exact mechanisms governing this intricate and complex process are as yet not fully understood. One family of genes involved in cell survival/death control is the Bcl-2 gene family, which consists of homologous proteins that function to regulate distal and crucial commitment steps of the apoptotic pathway. The Bcl-2 family constitutes both agonists and antagonists of apoptosis that function at least in part through protein-protein interactions between various members of the family. The final outcome depends on the relative ratio of death agonists and antagonists. Bcl-2 expression has been closely associated with the AI phenotype of PC. Cytotoxic chemotherapy may be used as palliative therapy in AI PC but has not been found effective. Most chemotherapeutic cytotoxic agents induce apoptosis in cancer cells by direct and indirect action on the cell cycle. In vitro and in vivo studies have established that Bcl-2 expression confers an antiapoptotic activity against androgen withdrawal and cytotoxic chemotherapy. It thus offers a tempting potential target for therapeutic manipulations of PC
An Extension for Direct Gauge Mediation of Metastable Supersymmetry Breaking
We study the direct mediation of metastable supersymmetry breaking by a
\Phi^2-deformation to the ISS model and extend it by splitting both Tr\Phi and
Tr\Phi^2 terms in the superpotential and gauging the flavor symmetry. We find
that with such an extension the enough long-lived metastable vacua can be
obtained and the proper gaugino masses can be generated. Also, this allows for
constructing a kind of models which can avoid the Landau pole problem.
Especially, in our metastable vacua there exist a large region for the
parameter m_3 which can satisfy the phenomenology requirements and allow for a
low SUSY breaking scale (\sim 100 TeV).Comment: version in Europhys. Let
R-symmetric Gauge Mediation and the MRSSM
This is an invited summary of a seminar talk given at various institutions in
the United States and Canada. After a brief introduction, a review of the
minimal R-symmetric supersymmetric standard model is given, and the benefits to
the flavor sector are discussed. R-symmetric gauge mediation is an attempt to
realize this model using metastable supersymmetry breaking techniques. Sample
low energy spectra are presented and tuning is discussed. Various other
phenomenological results are summarized.Comment: 14 pages, invited Brief Review, submitted to Modern Physics Letters
A; v2: replaced Figure 1, updated acknowledgments, fixed typo
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