3,455 research outputs found
Consistent deformations of [p,p]-type gauge field theories
Using BRST-cohomological techniques, we analyze the consistent deformations
of theories describing free tensor gauge fields whose symmetries are
represented by Young tableaux made of two columns of equal length p, p>1. Under
the assumptions of locality and Poincare invariance, we find that there is no
consistent deformation of these theories that non-trivially modifies the gauge
algebra and/or the gauge transformations. Adding the requirement that the
deformation contains no more than two derivatives, the only possible
deformation is a cosmological-constant-like term.Comment: 17 pages, details of a proof added, accepted for publication in JHE
Polarization-selective excitation of N-V centers in diamond
The nitrogen-vacancy (N-V) center in diamond is promising as an electron spin
qubit due to its long-lived coherence and optical addressability. The ground
state is a spin triplet with two levels () degenerate at zero
magnetic field. Polarization-selective microwave excitation is an attractive
method to address the spin transitions independently, since this allows
operation down to zero magnetic field. Using a resonator designed to produce
circularly polarized microwaves, we have investigated the polarization
selection rules of the N-V center. We first apply this technique to N-V
ensembles in [100] and [111]-oriented samples. Next, we demonstrate an imaging
technique, based on optical polarization dependence, that allows rapid
identification of the orientations of many single N-V centers. Finally, we test
the microwave polarization selection rules of individual N-V centers of known
orientation
The WFCAM Multi-wavelength Variable Star Catalog
Stellar variability in the near-infrared (NIR) remains largely unexplored.
The exploitation of public science archives with data-mining methods offers a
perspective for the time-domain exploration of the NIR sky. We perform a
comprehensive search for stellar variability using the optical-NIR multi-band
photometric data in the public Calibration Database of the WFCAM Science
Archive (WSA), with the aim of contributing to the general census of variable
stars, and to extend the current scarce inventory of accurate NIR light curves
for a number of variable star classes. We introduce new variability indices
designed for multi-band data with correlated sampling, and apply them for
pre-selecting variable star candidates, i.e., light curves that are dominated
by correlated variations, from noise-dominated ones. Pre-selection criteria are
established by robust numerical tests for evaluating the response of
variability indices to colored noise characteristic to the data. We find 275
periodic variable stars and an additional 44 objects with suspected variability
with uncertain periods or apparently aperiodic variation. Only 44 of these
objects had been previously known, including 11 RR~Lyrae stars in the outskirts
of the globular cluster M3 (NGC~5272). We provide a preliminary classification
of the new variable stars that have well-measured light curves, but the
variability types of a large number of objects remain ambiguous. We classify
most of the new variables as contact binary stars, but we also find several
pulsating stars, among which 34 are probably new field RR~Lyrae and 3 are
likely Cepheids. We also identify 32 highly reddened variable objects close to
previously known dark nebulae, suggesting that these are embedded young stellar
objects. We publish our results and all light-curve data as the WFCAM Variable
Star Catalog.Comment: 21 pages, 11 figure
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Macular Pigment and Visual Function in Patients With Glaucoma: The San Diego Macular Pigment Study.
PurposeAlthough recent studies have shown that macular pigment (MP) is significantly lower in glaucoma patients, this relationship merits further investigation.MethodsThis cross-sectional study included 85 glaucoma patients and 22 controls. All subjects had standard automated perimetry (SAP) and retinal nerve fiber layer (RNFL) thickness measurements. Intake of lutein (L) and zeaxanthin (Z) was estimated using a novel dietary screener. The Heidelberg Spectralis dual-wavelength autofluorescence (AF) technology was employed to study the relationship between MP and glaucoma. The association between MP volume and glaucoma was investigated using linear regression models accounting for potential confounding factors.ResultsGlaucoma patients had significantly worse SAP mean deviation (MD) and lower RNFL thickness in the study eye compared to control subjects (P < 0.001 for both). MP (volume) was comparable between groups (P = 0.436). In the univariable model, diagnosis of glaucoma was not associated with MP volume (R2 = 1.22%; P = 0.257). Dietary intake of L and Z was positively and significantly related to MP in the univariable (P = 0.022) and multivariable (P = 0.020) models.ConclusionsThese results challenge previous studies that reported that glaucoma is associated with low MP. Dietary habits were found to be the main predictor of MP in this sample. Further research is merited to better understand the relationship between glaucoma, MP, and visual performance in these patients
On the nature of Lithium-rich giant stars: constraints from Beryllium abundances
We have derived beryllium abundances for 7 Li-rich giant (A(Li) > 1.5) stars
and 10 other Li-normal giants, with the aim of investigating the origin of the
Lithium in the Li-rich giants. In particular, we test the predictions of the
engulfment scenario proposed by Siess & Livio (1999), where the engulfment of a
brown dwarf or one or more giant planets would lead to a simultaneous
enrichment of 7Li and 9Be. We show that regardless their nature, none of the
stars studied in this paper were found to have detectable beryllium. Using
simple dilution arguments we show that the engulfment of an external object as
the sole source of Li enrichment is ruled out by the Li and Be abundance data.
The present results favor the idea that Li has been produced in the interior of
the stars by a Cameron-Fowler process and brought up to the surface by an extra
mixing mechanism.Comment: Accepted in A&
G2 Hitchin functionals at one loop
We consider the quantization of the effective target space description of
topological M-theory in terms of the Hitchin functional whose critical points
describe seven-manifolds with G2 structure. The one-loop partition function for
this theory is calculated and an extended version of it, that is related to
generalized G2 geometry, is compared with the topological G2 string. We relate
the reduction of the effective action for the extended G2 theory to the Hitchin
functional description of the topological string in six dimensions. The
dependence of the partition functions on the choice of background G2 metric is
also determined.Comment: 58 pages, LaTeX; v2: Acknowledgments adde
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