421 research outputs found
An exact formula for the radiation of a moving quark in N=4 super Yang Mills
We derive an exact formula for the cusp anomalous dimension at small angles.
This is done by relating the latter to the computation of certain 1/8 BPS
Wilson loops which was performed by supersymmetric localization. This function
of the coupling also determines the power emitted by a moving quark in N=4
super Yang Mills, as well as the coefficient of the two point function of the
displacement operator on the Wilson loop. By a similar method we compute the
near BPS expansion of the generalized cusp anomalous dimension.Comment: 22 pages, 5 figures. v2: references added, typos correcte
Correlators of Wilson loops and local operators from multi-matrix models and strings in AdS
We study correlation functions of Wilson loops and local operators in a
subsector of N=4 SYM which preserves two supercharges. Localization arguments
allow to map the problem to a calculation in bosonic two-dimensional Yang-Mills
theory. In turn, this can be reduced to computing correlators in certain
Gaussian multi-matrix models. We focus on the correlation function of a Wilson
loop and two local operators, and solve the corresponding three-matrix model
exactly in the planar limit. We compare the strong coupling behavior to string
theory in AdS_5xS^5, finding precise agreement. We pay particular attention to
the case in which the local operators have large R-charge J \sim sqrt{lambda}
at strong coupling.Comment: 50 pages, 9 figures. v2: minor changes, references adde
Exact Results in ABJM Theory from Topological Strings
Recently, Kapustin, Willett and Yaakov have found, by using localization
techniques, that vacuum expectation values of Wilson loops in ABJM theory can
be calculated with a matrix model. We show that this matrix model is closely
related to Chern-Simons theory on a lens space with a gauge supergroup. This
theory has a topological string large N dual, and this makes possible to solve
the matrix model exactly in the large N expansion. In particular, we find the
exact expression for the vacuum expectation value of a 1/6 BPS Wilson loop in
the ABJM theory, as a function of the 't Hooft parameters, and in the planar
limit. This expression gives an exact interpolating function between the weak
and the strong coupling regimes. The behavior at strong coupling is in precise
agreement with the prediction of the AdS string dual. We also give explicit
results for the 1/2 BPS Wilson loop recently constructed by Drukker and
TrancanelliComment: 18 pages, two figures, small misprints corrected and references
added, final version to appear in JHE
Exact results for static and radiative fields of a quark in N=4 super Yang-Mills
In this work (which supersedes our previous preprint arXiv:1112.2345) we
determine the expectation value of the N=4$ SU(N) SYM Lagrangian density
operator in the presence of an infinitely heavy static particle in the
symmetric representation of SU(N), by means of a D3-brane probe computation.
The result that we obtain coincides with two previous computations of different
observables, up to kinematical factors. We argue that these agreements go
beyond the D-brane probe approximation, which leads us to propose an exact
formula for the expectation value of various operators. In particular, we
provide an expression for the total energy loss by radiation of a heavy
particle in the fundamental representation.Comment: 14 pages. This submission supersedes our previous preprint
arXiv:1112.2345. v2: numerical factors fixed, minor clarifications, added
reference
Can spacetime curvature induced corrections to Lamb shift be observable?
The Lamb shift results from the coupling of an atom to vacuum fluctuations of
quantum fields, so corrections are expected to arise when the spacetime is
curved since the vacuum fluctuations are modified by the presence of spacetime
curvature. Here, we calculate the curvature-induced correction to the Lamb
shift outside a spherically symmetric object and demonstrate that this
correction can be remarkably significant outside a compact massive
astrophysical body. For instance, for a neutron star or a stellar mass black
hole, the correction is 25% at a radial distance of ,
16% at and as large as 1.6% even at , where is
the mass of the object, the Newtonian constant, and the speed of light.
In principle, we can look at the spectra from a distant compact super-massive
body to find such corrections. Therefore, our results suggest a possible way of
detecting fundamental quantum effects in astronomical observations.Comment: 13 pages, 3 figures, slight title change, clarifications and more
discussions added, version to be published in JHE
't Hooft Operators in Gauge Theory from Toda CFT
We construct loop operators in two dimensional Toda CFT and calculate with
them the exact expectation value of certain supersymmetric 't Hooft and dyonic
loop operators in four dimensional \Ncal=2 gauge theories with SU(N) gauge
group. Explicit formulae for 't Hooft and dyonic operators in \Ncal=2^* and
\Ncal=2 conformal SQCD with SU(N) gauge group are presented. We also briefly
speculate on the Toda CFT realization of arbitrary loop operators in these
gauge theories in terms of topological web operators in Toda CFT.Comment: 49 pages, LaTeX. Typos fixed, references adde
Comparison of inpatient vs. outpatient anterior cervical discectomy and fusion: a retrospective case series
<p>Abstract</p> <p>Background</p> <p>Spinal surgery is increasingly being done in the outpatient setting. We reviewed our experience with inpatient and outpatient single-level anterior cervical discectomy and fusion with plating (ACDF+P).</p> <p>Methods</p> <p>All patients undergoing single-level anterior cervical discectomy and fusion with plating between August 2005 and May 2007 by two surgeons (RPB or JAF) were retrospectively reviewed. All patients underwent anterior cervical microdiscectomy, arthrodesis using structural allograft, and titanium plating. A planned change from doing ACDF+P on an inpatient basis to doing ACDF+P on an outpatient basis was instituted at the midpoint of the study. There were no other changes in technique, patient selection, instrumentation, facility, or other factors. All procedures were done in full-service hospitals accommodating outpatient and inpatient care.</p> <p>Results</p> <p>64 patients underwent ACDF+P as inpatients, while 45 underwent ACDF+P as outpatients. When outpatient surgery was planned, 17 patients were treated as inpatients due to medical comorbidities (14), older age (1), and patient preference (2). At a mean follow-up of 62.4 days, 90 patients had an excellent outcome, 19 patients had a good outcome, and no patients had a fair or poor outcome. There was no significant difference in outcome between inpatients and outpatients. There were 4 complications, all occurring in inpatients: a hematoma one week post-operatively requiring drainage, a cerebrospinal fluid leak treated with lumbar drainage, syncope of unknown etiology, and moderate dysphagia.</p> <p>Conclusion</p> <p>In this series, outpatient ACDF+P was safe and was not associated with a significant difference in outcome compared with inpatient ACDF+P.</p
Differential Control of Yersinia pestis Biofilm Formation In Vitro and in the Flea Vector by Two c-di-GMP Diguanylate Cyclases
Yersinia pestis forms a biofilm in the foregut of its flea vector that promotes transmission by flea bite. As in many bacteria, biofilm formation in Y. pestis is controlled by intracellular levels of the bacterial second messenger c-di-GMP. Two Y. pestis diguanylate cyclase (DGC) enzymes, encoded by hmsT and y3730, and one phosphodiesterase (PDE), encoded by hmsP, have been shown to control biofilm production in vitro via their opposing c-di-GMP synthesis and degradation activities, respectively. In this study, we provide further evidence that hmsT, hmsP, and y3730 are the only three genes involved in c-di-GMP metabolism in Y. pestis and evaluated the two DGCs for their comparative roles in biofilm formation in vitro and in the flea vector. As with HmsT, the DGC activity of Y3730 depended on a catalytic GGDEF domain, but the relative contribution of the two enzymes to the biofilm phenotype was influenced strongly by the environmental niche. Deletion of y3730 had a very minor effect on in vitro biofilm formation, but resulted in greatly reduced biofilm formation in the flea. In contrast, the predominant effect of hmsT was on in vitro biofilm formation. DGC activity was also required for the Hms-independent autoaggregation phenotype of Y. pestis, but was not required for virulence in a mouse model of bubonic plague. Our results confirm that only one PDE (HmsP) and two DGCs (HmsT and Y3730) control c-di-GMP levels in Y. pestis, indicate that hmsT and y3730 are regulated post-transcriptionally to differentially control biofilm formation in vitro and in the flea vector, and identify a second c-di-GMP-regulated phenotype in Y. pestis
Localization of the four-dimensional N=4 SYM to a two-sphere and 1/8 BPS Wilson loops
We localize the four-dimensional N=4 super Yang-Mills theory on a four-sphere
to the two-dimensional constrained Hitchin/Higgs-Yang-Mills (cHYM) theory on a
two-sphere S^2. We show that expectation values of certain 1/8 BPS
supersymmetric Wilson loops on S^2 in the 4d N=4 SYM is captured by the 2d cHYM
theory. We further argue that expectation values of Wilson loops in the cHYM
theory agree with the prescription "two-dimensional bosonic Yang-Mills
excluding instanton contributions". Hence, we support the recent conjecture by
Drukker, Giombi, Ricci and Trancanelli on the 1/8 BPS Wilson loops on S^2 in
the 4d N=4 SYM.Comment: 49 pages; v3: typos correcte
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