128,091 research outputs found
Quantum Zeno tomography
We show that the resolution "per absorbed particle" of standard absorption
tomography can be outperformed by a simple interferometric setup, provided that
the different levels of "gray" in the sample are not uniformly distributed. The
technique hinges upon the quantum Zeno effect and has been tested in numerical
simulations. The scheme we propose could be implemented in experiments with
UV-light, neutrons or X-rays.Comment: 8 pages, 5 figure
Reflection and Transmission in a Neutron-Spin Test of the Quantum Zeno Effect
The dynamics of a quantum system undergoing frequent "measurements", leading
to the so-called quantum Zeno effect, is examined on the basis of a
neutron-spin experiment recently proposed for its demonstration. When the
spatial degrees of freedom are duely taken into account, neutron-reflection
effects become very important and may lead to an evolution which is totally
different from the ideal case.Comment: 26 pages, 6 figure
Quantum Squeezing and Cosmological Entropy Production
The entropy growth in a cosmological process of pair production is completely
determined by the associated squeezing parameter, and is insensitive to the
number of particles in the initial state. The total produced entropy may
represent a significant fraction of the entropy stored today in the cosmic
black-body radiation, provided pair production originates from a change in the
background metric at a curvature scale of the Planck order.Comment: 7 pages, plain TEX, to appear in Class.Quantum Grav., CERN-TH.6954/9
London Penetration Length and String Tension in SU(2) Lattice Gauge Theory
We study the distribution of the color fields due to a static quark-antiquark
pair in SU(2) lattice gauge theory. We find evidence of dual Meissner effect.
We put out a simple relation between the penetration length and the string
tension.Comment: uuencoded compressed Postscript file (text+figures
Dual Superconductor Mechanism of Confinement on the Lattice
We investigate the dual superconductor mechanism of confinement for pure
SU(2) lattice gauge theory in the maximally abelian gauge. We focus on the the
dual Meissner effect. We find that the transverse distribution of the
longitudinal chromoelectric field due to a static quark-antiquark pair
satisfies the dual London equation. Moreover we show that the size of the flux
tube scales according to asymptotic freedom.Comment: LaTeX, 9 pages, 6 figures available as a PostScript file from L.
Cosmai, BARI - TH 110/9
Gravitational waves in non-singular string cosmologies
We study the evolution of tensor metric fluctuations in a class of
non-singular models based on the string effective action, by including in the
perturbation equation the higher-derivative and loop corrections needed to
regularise the background solutions. We discuss the effects of such
higher-order corrections on the final graviton spectrum, and we compare the
results of analytical and numerical computations.Comment: 24 pages, 7 figure
Selfdecomposability and selfsimilarity: a concise primer
We summarize the relations among three classes of laws: infinitely divisible,
selfdecomposable and stable. First we look at them as the solutions of the
Central Limit Problem; then their role is scrutinized in relation to the Levy
and the additive processes with an emphasis on stationarity and selfsimilarity.
Finally we analyze the Ornstein-Uhlenbeck processes driven by Levy noises and
their selfdecomposable stationary distributions, and we end with a few
particular examples.Comment: 24 pages, 3 figures; corrected misprint in the title; redactional
modifications required by the referee; added references from [16] to [28];.
Accepted and in press on Physica
Hints of theta_13>0 from global neutrino data analysis
Nailing down the unknown neutrino mixing angle theta_13 is one of the most
important goals in current lepton physics. In this context, we perform a global
analysis of neutrino oscillation data, focusing on theta_13, and including
recent results [Neutrino 2008, Proceedings of the XXIII International
Conference on Neutrino Physics and Astrophysics, Christchurch, New Zealand,
2008 (unpublished)]. We discuss two converging hints of theta_13>0, each at the
level of ~1sigma: an older one coming from atmospheric neutrino data, and a
newer one coming from the combination of solar and long-baseline reactor
neutrino data. Their combination provides the global estimate sin^2(theta_13) =
0.016 +- 0.010 (1sigma), implying a preference for \theta_13>0 with
non-negligible statistical significance (~90% C.L.). We discuss possible
refinements of the experimental data analyses, which might sharpen such
intriguing indication.Comment: Minor changes in the text. Matches published version in PR
Maxwell-Kosteleck\'y Electromagnetism and Cosmic Magnetization
The Lorentz violating term in the photon sector of Standard Model Extension,
\mathcal{L}_K = -{\frac14} (k_F)_{\alpha \beta \mu \nu} F^{\alpha \beta}
F^{\mu \nu} (here referred to as the Kosteleck\'{y} term), breaks conformal
invariance of electromagnetism and enables a superadiabatic amplification of
magnetic vacuum fluctuations during inflation. For a wide range of values of
parameters defining Lorentz symmetry violation and inflation, the present-day
magnetic field can have an intensity of order of nanogauss on megaparsec scales
and then could explain the large-scale magnetization of the universe.Comment: 10 pages, 1 figure, minor revisions; accepted for publication in
Physics Letters
Testing the Isotropy of the Universe with Type Ia Supernovae
We analyze the magnitude-redshift data of type Ia supernovae included in the
Union and Union2 compilations in the framework of an anisotropic Bianchi type I
cosmological model and in the presence of a dark energy fluid with anisotropic
equation of state. We find that the amount of deviation from isotropy of the
equation of state of dark energy, the skewness \delta, and the present level of
anisotropy of the large-scale geometry of the Universe, the actual shear
\Sigma_0, are constrained in the ranges -0.16 < \delta < 0.12 and -0.012 <
\Sigma_0 < 0.012 (1\sigma C.L.) by Union2 data. Supernova data are then
compatible with a standard isotropic universe (\delta = \Sigma_0 = 0), but a
large level of anisotropy, both in the geometry of the Universe and in the
equation of state of dark energy, is allowed.Comment: 12 pages, 7 figures, 2 tables. Union2 analysis added. New references
added. To appear in Phys. Rev.
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