6,377 research outputs found
N=2 Supersymmetric Sigma Models and D-branes
We study D-branes of N=2 supersymmetric sigma models. Supersymmetric
nonlinear sigma models with 2-dimensional target space have D0,D1,D2-branes,
which are realized as A-,B-type supersymmetric boundary conditions on the
worldsheet. When we embed the models in the string theory, the Kahler potential
is restricted and leads to a 2-dim black hole metric with a dilaton background.
The D-branes in this model are susy cycles and consistent with the analysis of
conjugacy classes. The generalized metrics with U(n) isometry is proposed and
dynamics on them are realized by linear sigma models. We investigate D-branes
of the linear sigma models and compare the results with those in the nonlinear
sigma models.Comment: 23 pages, 5 figure
A Bilocal Field Theory in Four Dimensions
A bilocal field theory having M\"{o}bius gauge invariance is proposed. In
four dimensions there exists a zero momentum state of the first quantized
model, which belongs to a non-trivial BRS cohomology class. A field theory
lagrangian having a gauge invariance only in four dimensions is constructed.Comment: 13 pages, TEP-9R, LaTe
Strings on pp-waves and massive two dimensional field theories
We find a general class of pp-wave solutions of type IIB string theory such
that the light cone gauge worldsheet lagrangian is that of an interacting
massive field theory. When the light cone Lagrangian has (2,2) supersymmetry we
can find backgrounds that lead to arbitrary superpotentials on the worldsheet.
We consider situations with both flat and curved transverse spaces. We describe
in some detail the background giving rise to the N=2 sine Gordon theory on the
worldsheet. Massive mirror symmetry relates it to the deformed model (or
sausage model) which seems to elude a purely supergravity target space
interpretation.Comment: harvmac, 26 pages, v2,3: references added, typos correcte
Orientifolds and Mirror Symmetry
We study parity symmetries and crosscap states in classes of N=2
supersymmetric quantum field theories in 1+1 dimensions, including non-linear
sigma models, gauged WZW models, Landau-Ginzburg models, and linear sigma
models. The parity anomaly and its cancellation play important roles in many of
them. The case of the N=2 minimal model are studied in complete detail, from
all three realizations -- gauged WZW model, abstract RCFT, and LG models. We
also identify mirror pairs of orientifolds, extending the correspondence
between symplectic geometry and algebraic geometry by including unorientable
worldsheets. Through the analysis in various models and comparison in the
overlapping regimes, we obtain a global picture of orientifolds and D-branes.Comment: 137 page
Half-Twisted Correlators from the Coulomb Branch
We compute correlators of chiral operators in half-twisted (0,2)
supersymmetric gauged linear sigma models. Our results give simple algebraic
formulas for a (0,2) generalization of genus zero Gromov-Witten invariants of
compact toric varieties. We derive compact expressions for deformed quantum
cohomology relations and apply our general method to several examples.Comment: 21 pages, LaTex; typos corrected; some discussion adde
Orientifolds of Gepner Models
We systematically construct and study Type II Orientifolds based on Gepner
models which have N=1 supersymmetry in 3+1 dimensions. We classify the parity
symmetries and construct the crosscap states. We write down the conditions that
a configuration of rational branes must satisfy for consistency (tadpole
cancellation and rank constraints) and spacetime supersymmetry. For certain
cases, including Type IIB orientifolds of the quintic and a two parameter
model, one can find all solutions in this class. Depending on the parity, the
number of vacua can be large, of the order of 10^{10}-10^{13}. For other
models, it is hard to find all solutions but special solutions can be found --
some of them are chiral. We also make comparison with the large volume regime
and obtain a perfect match. Through this study, we find a number of new
features of Type II orientifolds, including the structure of moduli space and
the change in the type of O-planes under navigation through non-geometric
phases.Comment: 142 page
D-brane Categories for Orientifolds -- The Landau-Ginzburg Case
We construct and classify categories of D-branes in orientifolds based on
Landau-Ginzburg models and their orbifolds. Consistency of the worldsheet
parity action on the matrix factorizations plays the key role. This provides
all the requisite data for an orientifold construction after embedding in
string theory. One of our main results is a computation of topological field
theory correlators on unoriented worldsheets, generalizing the formulas of Vafa
and Kapustin-Li for oriented worldsheets, as well as the extension of these
results to orbifolds. We also find a doubling of Knoerrer periodicity in the
orientifold context.Comment: 45 pages, 6 figure
Dynamic Response to Global Oscillation of Propulsion Systems with Cavitating Pumps
A time-domain model was developed to evaluate the dynamic response of pumping systems in the accelerating
environment of rockets with a focus on cavitation. The model was first verified by comparing the results with
measurements in ground-based tests of an LE-7A rocket engine. In these tests, various resonances occurred and
levels of pump cavitation or incorporation of an accumulator altered them. The model results simulated the test data well, matching both the frequency and the amplitude. The test and model results also demonstrated the stability of the LE-7A propulsion system within nonaccelerating environments. Then, the model was used to examine the response of the propulsion system in accelerating frames; sinusoidal vehicle oscillations over a range of frequencies were explored. Under noncavitating conditions, the pressure amplitudes within the propulsion system did not substantially exceed the quasi-static acceleration head response Ïah. However, under cavitating conditions (Ï = 0.02), the same accelerations produced violent responses with pressure and flow amplitudes about 2 orders of magnitude greater than in noncavitating conditions. The obvious conclusion is that vehicle oscillations can cause substantial pressure and flow amplitudes, particularly when the pump is cavitating, even if the ground-based tests and the calculations in static frames indicate stable and well-behaved responses
Preliminary Results from Recent Measurements of the Antiprotonic Helium Hyperfine Structure
We report on preliminary results from a systematic study of the hyperfine
(HF) structure of antiprotonic helium. This precise measurement which was
commenced in 2006, has now been completed. Our initial analysis shows no
apparent density or power dependence and therefore the results can be averaged.
The statistical error of the observable M1 transitions is a factor of 60
smaller than that of three body quantum electrodynamic (QED) calculations,
while their difference has been resolved to a precision comparable to theory (a
factor of 10 better than our first measurement). This difference is sensitive
to the antiproton magnetic moment and agreement between theory and experiment
would lead to an increased precision of this parameter, thus providing a test
of CPT invariance.Comment: 6 pages, 4 figure
Stretching short biopolymers by fields and forces
We study the mechanical properties of semiflexible polymers when the contour
length of the polymer is comparable to its persistence length. We compute the
exact average end-to-end distance and shape of the polymer for different
boundary conditions, and show that boundary effects can lead to significant
deviations from the well-known long-polymer results. We also consider the case
of stretching a uniformly charged biopolymer by an electric field, for which we
compute the average extension and the average shape, which is shown to be
trumpetlike. Our results also apply to long biopolymers when thermal
fluctuations have been smoothed out by a large applied field or force.Comment: 10 pages, 7 figure
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