1,400 research outputs found
Monopole Operators in Chern-Simons-Matter Theories
We study monopole operators at the infrared fixed points of
Chern-Simons-matter theories (QED, scalar QED, SQED,
and SQED) with matter flavors and Chern-Simons level
. We work in the limit where both and are taken to be large with
fixed. In this limit, we extract information about the low-lying
spectrum of monopole operators from evaluating the partition
function in the sector where the is threaded by magnetic flux .
At leading order in , we find a large number of monopole operators with
equal scaling dimensions and a wide range of spins and flavor symmetry
irreducible representations. In two simple cases, we deduce how the degeneracy
in the scaling dimensions is broken by the corrections. For QED at
, we provide conformal bootstrap evidence that this near-degeneracy
is in fact maintained to small values of . For SQED, we
find that the lowest dimension monopole operator is generically non-BPS.Comment: 52 pages plus appendices, 9 figures, v2: minor correction
Bootstrapping Vector Models with Four Supercharges in
We analyze the conformal bootstrap constraints in theories with four
supercharges and a global flavor symmetry in dimensions. In particular, we consider the 4-point function of
-fundamental chiral operators that have no chiral primary in the
-singlet sector of their OPE. We find features in our numerical bounds
that nearly coincide with the theory of chiral super-fields with
superpotential , as well as general bounds on SCFTs
where vanishes in the chiral ring.Comment: 25 pages, 8 figure
Accidental Symmetries and the Conformal Bootstrap
We study an supersymmetric generalization of the
three-dimensional critical vector model that is described by
chiral superfields with superpotential . By
combining the tools of the conformal bootstrap with results obtained through
supersymmetric localization, we argue that this model exhibits a symmetry
enhancement at the infrared superconformal fixed point due to flowing to
zero. This example is special in that the existence of an infrared fixed point
with , which does not exhibit symmetry enhancement, does not
generally lead to any obvious unitarity violations or other inconsistencies. We
do show, however, that the -theorem excludes the models with
for . The conformal bootstrap provides a stronger constraint and excludes
such models for . We provide evidence that the models, which have
the enhanced symmetry, come close to saturating the bootstrap
bounds. We extend our analysis to fractional dimensions where we can motivate
the nonexistence of the models by studying them perturbatively
in the expansion.Comment: 26 pages, 5 figure
Optical Geolocation for Small Unmanned Aerial Systems
This paper presents an airborne optical geolocation system using four optical targets to provide position and attitude estimation for a sUAS supporting the NASA Acoustic Research Mission (ARM), where the goal is to reduce nuisance airframe noise during approach and landing. A large precision positioned microphone array captures the airframe noise for multiple passes of a Gulfstream III aircraft. For health monitoring of the microphone array, the Acoustic Calibration Vehicle (ACV) sUAS completes daily flights with an onboard speaker emitting tones at frequencies optimized for determining microphone functionality. An accurate position estimate of the ACV relative to the array is needed for microphone health monitoring. To this end, an optical geolocation system using a downward facing camera mounted to the ACV was developed. The 3D positioning of the ACV is computed using the pinhole camera model. A novel optical geolocation algorithm first detects the targets, then a recursive algorithm tightens the localization of the targets. Finally, the position of the sUAS is computed using the image coordinates of the targets, the 3D world coordinates of the targets, and the camera matrix. A Real-Time Kinematic GPS system is used to compare the optical geolocation system
Bose-Einstein Condensation in a Harmonic Potential
We examine several features of Bose-Einstein condensation (BEC) in an
external harmonic potential well. In the thermodynamic limit, there is a phase
transition to a spatial Bose-Einstein condensed state for dimension D greater
than or equal to 2. The thermodynamic limit requires maintaining constant
average density by weakening the potential while increasing the particle number
N to infinity, while of course in real experiments the potential is fixed and N
stays finite. For such finite ideal harmonic systems we show that a BEC still
occurs, although without a true phase transition, below a certain
``pseudo-critical'' temperature, even for D=1. We study the momentum-space
condensate fraction and find that it vanishes as 1/N^(1/2) in any number of
dimensions in the thermodynamic limit. In D less than or equal to 2 the lack of
a momentum condensation is in accord with the Hohenberg theorem, but must be
reconciled with the existence of a spatial BEC in D=2. For finite systems we
derive the N-dependence of the spatial and momentum condensate fractions and
the transition temperatures, features that may be experimentally testable. We
show that the N-dependence of the 2D ideal-gas transition temperature for a
finite system cannot persist in the interacting case because it violates a
theorem due to Chester, Penrose, and Onsager.Comment: 34 pages, LaTeX, 6 Postscript figures, Submitted to Jour. Low Temp.
Phy
Swift observations of the SFXT SAX J1818.6-1703 in outburst
We present the Swift observations of the supergiant fast X-ray transient
(SFXT) SAX J1818.6-1703 collected during the most recent outburst, which
occurred on May 6 2009. In particular, we present broad-band spectroscopic and
timing analysis as well as a Swift/XRT light curve that spans more than two
weeks of observations. The broad-band spectral models and length of the
outburst resemble those of the prototype of the SFXT class, XTE J1739-302,
further confirming SAX J1818.6-1703 as a member of this class.Comment: Proceedings of 'X-Ray Astronomy 2009, Present Status, multiwavelength
approach and future perspectives', September 7 - 11, 2009, Bologna, Ital
Uniform approximation for the overlap caustic of a quantum state with its translations
The semiclassical Wigner function for a Bohr-quantized energy eigenstate is
known to have a caustic along the corresponding classical closed phase space
curve in the case of a single degree of freedom. Its Fourier transform, the
semiclassical chord function, also has a caustic along the conjugate curve
defined as the locus of diameters, i.e. the maximal chords of the original
curve. If the latter is convex, so is its conjugate, resulting in a simple fold
caustic. The uniform approximation through this caustic, that is here derived,
describes the transition undergone by the overlap of the state with its
translation, from an oscillatory regime for small chords, to evanescent
overlaps, rising to a maximum near the caustic. The diameter-caustic for the
Wigner function is also treated.Comment: 14 pages, 9 figure
A Wave Function Describing Superfluidity in a Perfect Crystal
We propose a many-body wave function that exhibits both diagonal and
off-diagonal long-range order. Incorporating short-range correlations due to
interatomic repulsion, this wave function is shown to allow condensation of
zero-point lattice vibrations and phase rigidity. In the presence of an
external velocity field, such a perfect crystal will develop non-classical
rotational inertia, exhibiting the supersolid behavior. In a sample calculation
we show that the superfluid fraction in this state can be as large as of order
0.01 in a reasonable range of microscopic parameters. The relevance to the
recent experimental evidence of a supersolid state by Chan and Kim is
discussed.Comment: final version to be published in Journal of Statistical Mechanics:
Theory and Experimen
Superconducting-coil--resistor circuit with electric field quadratic in the current
It is shown for the first time that the observed [Phys. Lett. A 162 (1992)
105] potential difference Phi_t between the resistor and the screen surrounding
the circuit is caused by polarization of the resistor because of the kinetic
energy of the electrons of the superconducting coil. The proportionality of
Phi_t to the square of the current and to the length of the superconducting
wire is explained. It is pointed out that measuring Phi_t makes it possible to
determine the Fermi quasimomentum of the electrons of a metal resistor.Comment: 2 pages, 1 figur
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