6,329 research outputs found
Metastable Vacua in Superconformal SQCD-like Theories
We study dynamical supersymmetry breaking in vector-like superconformal N=1
gauge theories. We find appropriate deformations of the superpotential to
overcome the problem of the instability of the non supersymmetric vacuum. The
request for long lifetime translates into constraints on the physical couplings
which in this regime can be controlled through efficient RG analysis.Comment: 17 pages, 7 figures, JHEP3.cl
PORTABLE CAMERA AIDED SIMULATOR (PORTCAS) FOR MINIMALLY INVASIVE SURGICAL TRAINING
The present disclosure is directed to a system and method for surgical training with low cost, reusable materials and a highly customizable virtual environment for skill-building. According to various embodiments, a surgical training tool is usable in conjunction with a support structure configured to at least partially constrain the tool movement. Meanwhile, the tool is tracked in real-time with off-tool detectors to generate a tool path driving a virtual rendering of the surgical training tool in an operative environment. The virtual rendering may be visually observable via a display device and may include a customizable and/or selectable operative environment with one or more structures that can be operated on by the virtual surgical training tool. By tracking the virtual tool interaction with the virtual structures, a task path may be established for documenting and/or objectively assessing the performance of one or more operative tasks
How two-dimensional brick layer J-aggregates differ from linear ones: Excitonic properties and line broadening mechanisms
We study the excitonic coupling and homogeneous spectral line width of brick layer J-aggregate films. We begin by analysing the structural information revealed by the two-exciton states probed in two-dimensional spectra. Our first main result is that the relation between the excitonic couplings and the spectral shift in a two-dimensional structure is different (larger shift for the same nearest neighbour coupling) from that in a one-dimensional structure, which leads to an estimation of dipolar coupling in two-dimensional lattices. We next investigate the mechanisms of homogeneous broadening - population relaxation and pure dephasing - and evaluate their relative importance in linear and two-dimensional aggregates. Our second main result is that pure dephasing dominates the line width in two-dimensional systems up to a crossover temperature, which explains the linear temperature dependence of the homogeneous line width. This is directly related to the decreased density of states at the band edge when compared with linear aggregates, thus reducing the contribution of population relaxation to dephasing. Pump-probe experiments are suggested to directly measure the lifetime of the bright state and can therefore support the proposed model
Decays of metastable vacua in SQCD
The decay rates of metastable SQCD vacua in ISS-type models, both towards
supersymmetric vacua as well as towards other nonsupersymmetric configurations
arising in theories with elementary spectators, are estimated numerically in
the semiclassical approximation by computing the corresponding multifield
bounce configurations. The scaling of the bounce action with respect to the
most relevant dimensionless couplings and ratios of scales is analyzed. In the
case of the decays towards the susy vacua generated by nonperturbative effects,
the results confirm previous analytical estimations of this scaling, obtained
by assuming a triangular potential barrier. The decay rates towards susy vacua
generated by R-symmetry breaking interactions turn out to be more than
sufficiently suppressed for the phenomenologically relevant parameter range,
and their behavior in this regime differs from analytic estimations valid for
parametrically small scale ratios. It is also shown that in models with
spectator fields, even though the decays towards vacua involving nonzero
spectator VEVs don't have a strong parametric dependence on the scale ratios,
the ISS vacuum can still be made long-lived in the presence of R-symmetry
breaking interactions.Comment: 22 pages, 7 figure
Superconformal Flavor Simplified
A simple explanation of the flavor hierarchies can arise if matter fields
interact with a conformal sector and different generations have different
anomalous dimensions under the CFT. However, in the original study by Nelson
and Strassler many supersymmetric models of this type were considered to be
'incalculable' because the R-charges were not sufficiently constrained by the
superpotential. We point out that nearly all such models are calculable with
the use of a-maximization. Utilizing this, we construct the simplest
vector-like flavor models and discuss their viability. A significant constraint
on these models comes from requiring that the visible gauge couplings remain
perturbative throughout the conformal window needed to generate the
hierarchies. However, we find that there is a small class of simple flavor
models that can evade this bound.Comment: 43 pages, 1 figure; V3: small corrections and clarifications,
references adde
Dynamical completions of generalized O'Raifeartaigh models
We present gauge theory completions of Wess-Zumino models admitting
supersymmetry breaking vacua with spontaneously broken R-symmetry. Our models
are simple deformations of generalized ITIY models, a supersymmetric theory
with gauge group Sp(N), N+1 flavors plus singlets, with a modified tree level
superpotential which explicitly breaks (part of) the global symmetry. Depending
on the nature of the deformation, we obtain effective O'Raifeartaigh-like
models whose pseudomoduli space is locally stable in a neighborhood of the
origin of field space, or in a region not including it. Hence, once embedded in
direct gauge mediation scenarios, our models can give low energy spectra with
either suppressed or unsuppressed gaugino mass.Comment: 21 pages, 1 figure; v3: reference adde
Terahertz Kerr effect
We have observed optical birefringence in liquids induced by single-cycle terahertz pulses with field strengths exceeding 100 kV/cm. The induced change in polarization is proportional to the square of the terahertz electric field. The time-dependent terahertz Kerr signal is composed of a fast electronic response that follows the individual cycles of the electric field and a slow exponential response associated with molecular orientation.United States. Office of Naval Research (ONR Grant. No. N00014â06â1â0459
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