Pomeron Vertices in Perturbative QCD in Diffractive Scattering

We analyse the momentum space triple Pomeron vertex in perturbative QCD. In addition to the standard form of this vertex which is used in the context of total cross-sections at high energies and in the QCD reggeon field theory, there exists an alternative form which has to be used in the study of high-mass diffraction. We review and analyse the relation between these two versions. We discuss some implications for the BK-equation. In the second part of our paper we extend this analysis to the Pomeron-Odderon-Odderon vertex.Comment: 23 pages, 5 figures, Late

Decoherence in a system of many two--level atoms

I show that the decoherence in a system of $N$ degenerate two--level atoms interacting with a bosonic heat bath is for any number of atoms $N$ governed by a generalized Hamming distance (called ``decoherence metric'') between the superposed quantum states, with a time--dependent metric tensor that is specific for the heat bath.The decoherence metric allows for the complete characterization of the decoherence of all possible superpositions of many-particle states, and can be applied to minimize the over-all decoherence in a quantum memory. For qubits which are far apart, the decoherence is given by a function describing single-qubit decoherence times the standard Hamming distance. I apply the theory to cold atoms in an optical lattice interacting with black body radiation.Comment: replaced with published versio

On Free Quotients of Complete Intersection Calabi-Yau Manifolds

In order to find novel examples of non-simply connected Calabi-Yau threefolds, free quotients of complete intersections in products of projective spaces are classified by means of a computer search. More precisely, all automorphisms of the product of projective spaces that descend to a free action on the Calabi-Yau manifold are identified.Comment: 39 pages, 3 tables, LaTe

Drift velocity and gain in argon- and xenon-based mixtures

We present measurements of drift velocities and gains in gas mixtures based on Ar and Xe, with CO2, CH4, and N2 as quenchers, and compare them with calculations. In particular, we show the dependence of Ar- and Xe-CO2 drift velocities and gains on the amount of nitrogen contamination in the gas, which in real experiments may build up through leaks. A quantification of the Penning mechanism which contributes to the Townsend coefficients of a given gas mixture is proposed.Comment: 11 pages, 7 figures, accepted for publication in Nucl.Instrum.Meth. A. Data files available at http://www-alice.gsi.de/tr

Solitonic-exchange mechanism of surface~diffusion

We study surface diffusion in the framework of a generalized Frenkel-Kontorova model with a nonconvex transverse degree of freedom. The model describes a lattice of atoms with a given concentration interacting by Morse-type forces, the lattice being subjected to a two-dimensional substrate potential which is periodic in one direction and nonconvex (Morse) in the transverse direction. The results are used to describe the complicated exchange-mediated diffusion mechanism recently observed in MD simulations [J.E. Black and Zeng-Ju Tian, Phys. Rev. Lett. {\bf 71}, 2445-2448(1993)].Comment: 22 Revtex pages, 9 figures to appear in Phys. Rev.

Spin exchange interaction with tunable range between graphene quantum dots

We study the spin exchange between two electrons localized in separate quantum dots in graphene. The electronic states in the conduction band are coupled indirectly by tunneling to a common continuum of delocalized states in the valence band. As a model, we use a two-impurity Anderson Hamiltonian which we subsequently transform into an effective spin Hamiltonian by way of a two-stage Schrieffer-Wolff transformation. We then compare our result to that from a Coqblin-Schrieffer approach as well as to fourth order perturbation theory.Comment: 8 pages, 3 figure

Centrality dependence of global variables in relativistic heavy ion collisions: Final pTp_{T} data analysis in the framework of a statistical model

The global variables like the transverse energy at midrapidity, the charged particle multiplicity at midrapidity and the total multiplicity of charged particles are evaluated in the single-freeze-out statistical model for different centrality bins at RHIC at $\sqrt{s_{NN}}=130$ and 200 GeV. Full description of decays of hadron resonances is applied in these estimations. The geometric parameters of the model are obtained from the fit to the final data on the $p_{T}$ spectra. The predicted values of the global variables agree qualitatively well with the experimental data. The centrality independence of the total number of charged particles per participant pair has been also reproduced.Comment: Revtex, 12 figures (included), 16 pages. This is the revised final version accepted for publication in Physical Review C. The main difference with the first version is that the geometric parameters of the model have been fitted again with the use of the newer estimates of the statistical parameters reported in Refs. [20,21] for the case of $\sqrt{s_{NN}}=200$ GeV. Also because of the editorial reasons the title has been slightly change