62,251 research outputs found
Spin and occupation number entanglement of Dirac fields for non-inertial observers
We investigate the Unruh effect on entanglement taking into account the spin
degree of freedom of the Dirac field. We analyze spin Bell states in this
setting, obtaining their entanglement dependance on the acceleration of one of
the partners. Then, we consider simple analogs to the occupation number
entangled state |00>+|11>, but with spin quantum numbers for |11> showing that,
despite their apparent similitude, while the spinless case is always qubit x
qubit, for the spin case acceleration produces a qubit x qu4it state. We also
introduce a procedure to consistently erase the spin information from our
setting preserving occupation numbers. We show how the maximally entangled
state for occupation number emerges from our setting, we also analyze its
entanglement dependance on acceleration, obtaining a greater entanglement
degradation than in the spinless case.Comment: RevTex, 11 pages, 3 figures. The replacement is due to some minor
misprints correction
Nonlinear dynamic analysis of shells of revolution by matrix displacement method
Nonlinear dynamic analysis of shells of revolution by matrix displacement metho
Geometrical estimators as a test of Gaussianity in the CMB
We investigate the power of geometrical estimators on detecting
non-Gaussianity in the cosmic microwave background. In particular the number,
eccentricity and Gaussian curvature of excursion sets above (and below) a
threshold are studied. We compare their different performance when applied to
non-Gaussian simulated maps of small patches of the sky, which take into
account the angular resolution and instrumental noise of the Planck satellite.
These non-Gaussian simulations are obtained as perturbations of a Gaussian
field in two different ways which introduce a small level of skewness or
kurtosis in the distribution. A comparison with a classical estimator, the
genus, is also shown. We find that the Gaussian curvature is the best of our
estimators in all the considered cases. Therefore we propose the use of this
quantity as a particularly useful test to look for non-Gaussianity in the CMB.Comment: 9 pages, 6 postscript figures, submitted to MNRA
Quasar-galaxy associations revisited
Gravitational lensing predicts an enhancement of the density of bright,
distant QSOs around foreground galaxies. We measure this QSO-galaxy correlation
w_qg for two complete samples of radio-loud quasars, the southern 1Jy and
Half-Jansky samples. The existence of a positive correlation between z~1
quasars and z~0.15 galaxies is confirmed at a p=99.0% significance level
(>99.9%) if previous measurements on the northern hemisphere are included). A
comparison with the results obtained for incomplete quasar catalogs (e.g. the
Veron-Cetty and Veron compilation) suggests the existence of an `identification
bias', which spuriously increases the estimated amplitude of the quasar-galaxy
correlation for incomplete samples. This effect may explain many of the
surprisingly strong quasar-galaxy associations found in the literature.
Nevertheless, the value of w_qg that we measure in our complete catalogs is
still considerably higher than the predictions from weak lensing. We consider
two effects which could help to explain this discrepancy: galactic dust
extinction and strong lensing.Comment: 9 pages, 6 figures, MNRAS accepte
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