458 research outputs found
New and old N=8 superconformal field theories in three dimensions
We show that an infinite family of N=6 d=3 superconformal Chern-Simons-matter
theories has hidden N=8 superconformal symmetry and hidden parity on the
quantum level. This family of theories is different from the one found by
Aharony, Bergman, Jafferis and Maldacena, as well as from the theories
constructed by Bagger and Lambert, and Gustavsson. We also test several
conjectural dualities between BLG theories and ABJ theories by comparing
superconformal indices of these theories.Comment: 16 pages, late
Index for Three Dimensional Superconformal Field Theories and Its Applications
We review aspects of superconformal indices in three dimension. Three
dimensional superconformal indices can be exactly computed by using
localization method including monopole contribution, and can be applied to
provide evidences for mirror duality, AdS_4/CFT_3 correspondence and global
symmetry enhancement of strongly coupled gauge theories. After reviewing, we
discuss the possibility of global symmetry enhancement in a finite rank of
gauge group.Comment: 14 pages, Proceedings of the Seventh International Conference Quantum
Theory and Symmetries (QTS-7) in Prague, Czech Republic, August, 2011; v2:
minor modifications, discussion of supersymmetry enhancement of abelian ABJM
theory by using an index were adde
Supersymmetry enhancement by monopole operators
We describe a method which allows one to study hidden symmetries in a large
class of strongly coupled supersymmetric gauge theories in three dimensions. We
apply this method to the ABJM theory and to the infrared limit of N=4 SQCD with
adjoint and fundamental matter. We show that the U(N) ABJM model with
Chern-Simons level k=1 or k=2 has hidden N=8 supersymmetry. Hidden
supersymmetry is also shown to occur in N=4 d=3 SQCD with one fundamental and
one adjoint hypermultiplet. The latter theory, as well as the U(N) ABJM theory
at k=1, are shown to have a decoupled free sector. This provides evidence that
both models are dual to the infrared limit of N=8 U(N) super-Yang-Mills theory.Comment: 29 pages, late
Results from a Prototype Proton-CT Head Scanner
We are exploring low-dose proton radiography and computed tomography (pCT) as
techniques to improve the accuracy of proton treatment planning and to provide
artifact-free images for verification and adaptive therapy at the time of
treatment. Here we report on comprehensive beam test results with our prototype
pCT head scanner. The detector system and data acquisition attain a sustained
rate of more than a million protons individually measured per second, allowing
a full CT scan to be completed in six minutes or less of beam time. In order to
assess the performance of the scanner for proton radiography as well as
computed tomography, we have performed numerous scans of phantoms at the
Northwestern Medicine Chicago Proton Center including a custom phantom designed
to assess the spatial resolution, a phantom to assess the measurement of
relative stopping power, and a dosimetry phantom. Some images, performance, and
dosimetry results from those phantom scans are presented together with a
description of the instrument, the data acquisition system, and the calibration
methods.Comment: Conference on the Application of Accelerators in Research and
Industry, CAARI 2016, 30 October to 4 November 2016, Ft. Worth, TX, US
Dynamic constriction and fission of endoplasmic reticulum membranes by reticulon
The endoplasmic reticulum (ER) is a continuous cell-wide membrane network. Network formation has been associated with proteins producing membrane curvature and fusion, such as reticulons and atlastin. Regulated network fragmentation, occurring in different physiological contexts, is less understood. Here we find that the ER has an embedded fragmentation mechanism based upon the ability of reticulon to produce fission of elongating network branches. In Drosophila, Rtnl1-facilitated fission is counterbalanced by atlastin-driven fusion, with the prevalence of Rtnl1 leading to ER fragmentation. Ectopic expression of Drosophila reticulon in COS-7 cells reveals individual fission events in dynamic ER tubules. Consistently, in vitro analyses show that reticulon produces velocity-dependent constriction of lipid nanotubes leading to stochastic fission via a hemifission mechanism. Fission occurs at elongation rates and pulling force ranges intrinsic to the ER, thus suggesting a principle whereby the dynamic balance between fusion and fission controlling organelle morphology depends on membrane motility
Superconformal indices of three-dimensional theories related by mirror symmetry
Recently, Kim and Imamura and Yokoyama derived an exact formula for
superconformal indices in three-dimensional field theories. Using their
results, we prove analytically the equality of superconformal indices in some
U(1)-gauge group theories related by the mirror symmetry. The proofs are based
on the well known identities of the theory of -special functions. We also
suggest the general index formula taking into account the global
symmetry present for abelian theories.Comment: 17 pages; minor change
Prediction of image noise contributions in proton computed tomography and comparison to measurements
We present a method to accurately predict image noise in proton computed tomography (pCT) using data generated from a Monte Carlo simulation and a patient or object model that may be generated from a prior x-ray CT image. This enables noise prediction for arbitrary beam fluence settings and, therefore, the application of fluence-modulated pCT (FMpCT), which can achieve prescribed noise targets and may significantly reduce the integral patient dose.
We extended an existing Monte Carlo simulation of a prototype pCT scanner to include effects of quenching in the energy detector scintillators and constructed a beam model from experimental tracking data. Simulated noise predictions were compared to experimental data both in the projection domain and in the reconstructed image. Noise prediction agreement between simulated and experimental data in terms of the root-mean-square (RMS) error was better than 7% for a homogeneous water phantom and a sensitometry phantom with tubular inserts. For an anthropomorphic head phantom, modeling the anatomy of a five-year-old child, the RMS error was better than 9% in three evaluated slices. We were able to reproduce subtle noise features near heterogeneities. To demonstrate the feasibility of Monte Carlo simulated noise maps for fluence modulation, we calculated a fluence profile that yields a homogeneous noise level in the image. Unlike for bow-tie filters in x-ray CT this does not require constant fluence at the detector and the shape of the fluence profile is fundamentally different.
Using an improved Monte Carlo simulation, we demonstrated the feasibility of using simulated data for accurate image noise prediction for pCT. We believe that the agreement with experimental data is sufficient to enable the future optimization of FMpCT fluence plans to achieve prescribed noise targets in a fluence-modulated acquisition
Measurement of inclusive D*+- and associated dijet cross sections in photoproduction at HERA
Inclusive photoproduction of D*+- mesons has been measured for photon-proton
centre-of-mass energies in the range 130 < W < 280 GeV and a photon virtuality
Q^2 < 1 GeV^2. The data sample used corresponds to an integrated luminosity of
37 pb^-1. Total and differential cross sections as functions of the D*
transverse momentum and pseudorapidity are presented in restricted kinematical
regions and the data are compared with next-to-leading order (NLO) perturbative
QCD calculations using the "massive charm" and "massless charm" schemes. The
measured cross sections are generally above the NLO calculations, in particular
in the forward (proton) direction. The large data sample also allows the study
of dijet production associated with charm. A significant resolved as well as a
direct photon component contribute to the cross section. Leading order QCD
Monte Carlo calculations indicate that the resolved contribution arises from a
significant charm component in the photon. A massive charm NLO parton level
calculation yields lower cross sections compared to the measured results in a
kinematic region where the resolved photon contribution is significant.Comment: 32 pages including 6 figure
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