800 research outputs found
Heisenberg-limited eavesdropping on the continuous-variable quantum cryptographic protocol with no basis switching is impossible
The Gaussian quantum key distribution protocol based on coherent states and
heterodyne detection [Phys. Rev. Lett. 93, 170504 (2004)] has the advantage
that no active random basis switching is needed on the receiver's side. Its
security is, however, not very satisfyingly understood today because the bounds
on the secret key rate that have been derived from Heisenberg relations are not
attained by any known scheme. Here, we address the problem of the optimal
Gaussian individual attack against this protocol, and derive tight upper bounds
on the information accessible to an eavesdropper. The optical scheme achieving
this bound is also exhibited, which concludes the security analysis of this
protocol.Comment: 10 pages, 6 figure
Gluon distributions in nucleons and pions at a low resolution scale
In this paper we study the gluon distribution functions in nucleons and pions
at a low resolution scale. This is an important issue since parton
densities at low have always been taken as an external input which is
adjusted through DGLAP evolution to fit the experimental data at higher scales.
Here, in the framework of a model recently developed, it is shown that the
hypothetical cloud of {\it neutral} pions surrounding nucleons and pions
appears to be responsible for the characteristic valence-like gluon
distributions needed at the inital low scale. As an additional result, we get
the remarkable prediction that neutral and charged pions have different
intrinsic sea flavor contents.Comment: final version to appear in Phys. Rev. D. Discussion on several points
enlarge
Bargmann-Michel-Telegdi equation and one-particle relativistic approach
A reexamination of the semiclassical approach of the relativistic electron
indicates a possible variation of its helicity for electric and magnetic static
fields applied along its global motion due to zitterbewegung effects,
proportional to the anomalous part of the magnetic moment.Comment: 10 pages, LATEX2E, uses amsb
Longitudinal polarization in heavy ion collisions as a probe for QGP formation
We present an analysis of the longitudinal polarization in
ultra-relativistic heavy-ion collisions. The polarization of 's
coming from the decay chain exhibits a very
well differentiated behavior depending on the production region of the
primordial 's. This effect reflects the different values of the
ratio in the QGP region, where
nucleon-nucleon interactions take place in a hot and dense environment, and the
peripherical region, in which ordinary nucleon-nucleon interactions occur. An
increase in the longitudinal polarization signals a
strangeness enhancement which is thought as a property of the QGP phase.Comment: Latex file, 12 pages, 5 figures. To appear in Eur. Phys. J.
Results from the LHC Beam Dump Reliability Run
The LHC Beam Dumping System is one of the vital elements of the LHC Machine Protection System and has to operate reliably every time a beam dump request is made. Detailed dependability calculations have been made, resulting in expected rates for the different system failure modes. A 'reliability run' of the whole system, installed in its final configuration in the LHC, has been made to discover infant mortality problems and to compare the occurrence of the measured failure modes with their calculations
Asymptotic expansion for reversible A + B <-> C reaction-diffusion process
We study long-time properties of reversible reaction-diffusion systems of
type A + B C by means of perturbation expansion in powers of 1/t (inverse
of time). For the case of equal diffusion coefficients we present exact
formulas for the asymptotic forms of reactant concentrations and a complete,
recursive expression for an arbitrary term of the expansions. Taking an
appropriate limit we show that by studying reversible reactions one can obtain
"singular" solutions typical of irreversible reactions.Comment: 6 pages, no figures, to appear in PR
A common temperature dependence of nutritional demands in ectotherms
In light of ongoing climate change, it is increasingly important to know how nutritional requirements of ectotherms are affected by changing temperatures. Here, we analyse the wide thermal response of phosphorus (P) requirements via elemental gross growth efficiencies of Carbon (C) and P, and the Threshold Elemental Ratios in different aquatic invertebrate ectotherms: the freshwater model species Daphnia magna, the marine copepod Acartia tonsa, the marine heterotrophic dinoflagellate Oxyrrhis marina, and larvae of two populations of the marine crab Carcinus maenas. We show that they all share a non-linear cubic thermal response of nutrient requirements. Phosphorus requirements decrease from low to intermediate temperatures, increase at higher temperatures and decrease again when temperature is excessive. This common thermal response of nutrient requirements is of great importance if we aim to understand or even predict how ectotherm communities will react to global warming and nutrient-driven eutrophication
Formation of Liesegang patterns: A spinodal decomposition scenario
Spinodal decomposition in the presence of a moving particle source is
proposed as a mechanism for the formation of Liesegang bands. This mechanism
yields a sequence of band positions x_n that obeys the spacing law
x_n~Q(1+p)^n. The dependence of the parameters p and Q on the initial
concentration of the reagents is determined and we find that the functional
form of p is in agreement with the experimentally observed Matalon-Packter law.Comment: RevTex, 4 pages, 4 eps figure
- …