Shot noise and Coulomb effects on non-local electron transport in normal-superconducting-normal heterostructures

We argue that Coulomb interaction can strongly influence non-local electron transport in normal-superconducting-normal structures and emphasize direct relation between Coulomb effects and non-local shot noise. In the tunneling limit non-local differential conductance is found to have an S-like shape and can turn negative at non-zero bias. At high transmissions crossed Andreev reflection yields positive noise cross-correlations and Coulomb anti-blockade of non-local electron transport.Comment: 8 pages, 2 figures. Published versio

Lipschitz gradients for global optimization in a one-point-based partitioning scheme

A global optimization problem is studied where the objective function $f(x)$ is a multidimensional black-box function and its gradient $f'(x)$ satisfies the Lipschitz condition over a hyperinterval with an unknown Lipschitz constant $K$. Different methods for solving this problem by using an a priori given estimate of $K$, its adaptive estimates, and adaptive estimates of local Lipschitz constants are known in the literature. Recently, the authors have proposed a one-dimensional algorithm working with multiple estimates of the Lipschitz constant for $f'(x)$ (the existence of such an algorithm was a challenge for 15 years). In this paper, a new multidimensional geometric method evolving the ideas of this one-dimensional scheme and using an efficient one-point-based partitioning strategy is proposed. Numerical experiments executed on 800 multidimensional test functions demonstrate quite a promising performance in comparison with popular DIRECT-based methods.Comment: 25 pages, 4 figures, 5 tables. arXiv admin note: text overlap with arXiv:1103.205

Odd-Parity Negative Modes of Einstein-Yang-Mills Black Holes and Sphalerons

An analytical proof of the existence of negative modes in the odd--parity perturbation sector is given for all known non-abelian Einstein--Yang--Mills black holes. The significance of the normalizability condition in the functional stability analysis is emphasized. The role of the odd--parity negative modes in the sphaleron interpretation of the Bartnik--McKinnon solutions is discussed.Comment: (minor typographical errors fixed, to appear in Phys.Lett.B

Correlation Functions of Sp(2n) Invariant Higher-Spin Systems

We study the general structure of correlation functions in an Sp(2n)-invariant formulation of systems of an infinite number of higher-spin fields. For n=4,8 and 16 these systems comprise the conformal higher-spin fields in space-time dimensions D=4,6 and 10, respectively, while when n=2, one deals with conventional D=3 conformal field theories of scalars and spinors. We show that for n>2 the Sp(2n) symmetry and current conservation makes the 3-point correlators of two (rank-one or rank-two) conserved currents with a scalar operator be that of free theory.This situation is analogous to the one in conventional conformal field theories, where conservation of higher-spin currents implies that the theories are free.Comment: 26 pages, some clarifications added, published versio

A hypothetical effect of the Maxwell-Proca electromagnetic stresses on galaxy rotation curves

The Maxwell-Proca electrodynamics corresponding to a finite photon mass causes a substantial change of the Maxwell stress tensor and, under certain circumstances, may cause the electromagnetic stresses to act effectively as "negative pressure." The paper describes a model where this negative pressure imitates gravitational pull and may produce forces comparable to gravity and even become dominant. The effect is associated with the random magnetic fields in the galactic disk with a scale exceeding the photon Compton wavelength. The presence of a weaker regular field does not affect the forces under consideration. The stresses act predominantly on the interstellar gas and cause an additional force pulling the gas towards the center and towards the galactic plane. The stars do not experience any significant direct force but get involved in this process via a "recycling loop" where rapidly evolving massive stars are formed from the gas undergoing galactic rotation and then lose their masses back to the gas within a time shorter than roughly 1/6 of the rotation period. This makes their dynamics inseparable from that of the rotating gas. The lighter, slowly evolving stars, as soon as they are formed, lose connection to the gas and are confined within the galaxy only gravitationally. Numerical examples based on the parameters of our galaxy reveal both opportunities and challenges of this model and motivate further analysis. The critical issue is the plausibility of formation of the irregular magnetic field that would be force free. Another challenge is developing a predictive model of the evolution of the gaseous and stellar population of the galaxy under the aforementioned scenario. It may be interesting to also explore possible broader cosmological implications of the negative-pressure model.Comment: 29 pages, 1 figur