29,284 research outputs found
Boundary conditions at the mobility edge
It is shown that the universal behavior of the spacing distribution of
nearest energy levels at the metal--insulator Anderson transition is indeed
dependent on the boundary conditions. The spectral rigidity also
depends on the boundary conditions but this dependence vanishes at high energy
. This implies that the multifractal exponent of the participation
ratio of wave functions in the bulk is not affected by the boundary conditions.Comment: 4 pages of revtex, new figures, new abstract, the text has been
changed: The large energy behavior of the number variance has been found to
be independent of the boundary condition
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.
Unitarity of the tree approximation to the Glauber AA amplitude for large A
The nucleus-nucleus Glauber amplitude in the tree approximation is studied
for heavy participant nuclei. It is shown that, contrary to previous published
results, it is not unitary for realistic values of nucleon-nucleon
cross-sections.Comment: 15 pages, 1 figure, 1 table. Submitted to Yad. Fi
Structural lubricity: Role of dimension and symmetry
When two chemically passivated solids are brought into contact, interfacial
interactions between the solids compete with intrabulk elastic forces. The
relative importance of these interactions, which are length-scale dependent,
will be estimated using scaling arguments. If elastic interactions dominate on
all length scales, solids will move as essentially rigid objects. This would
imply superlow kinetic friction in UHV, provided wear was absent. The results
of the scaling study depend on the symmetry of the surfaces and the
dimensionalities of interface and solids. Some examples are discussed
explicitly such as contacts between disordered three-dimensional solids and
linear bearings realized from multiwall carbon nanotubes.Comment: 7 pages, 1 figur
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
Fluctuations of the number of participants and binary collisions in AA interactions at fixed centrality in the Glauber approach
In the framework of the classical Glauber approach, the analytical
expressions for the variance of the number of wounded nucleons and binary
collisions in AA interactions at a given centrality are presented. Along with
the optical approximation term, they contain additional contact terms arising
only in the case of nucleus-nucleus collisions. The magnitude of the additional
contributions, e.g., for PbPb collisions at SPS energies, is larger than the
contribution of the optical approximation at some values of the impact
parameter. The sum of the additional contributions is in good agreement with
the results of independent Monte Carlo simulations of this process. Due to
these additional terms, the variance of the total number of participants for
peripheral PbPb collisions and the variance of the number of collisions at all
values of the impact parameter exceed several multiples of the Poisson
variances. The correlator between the numbers of participants in colliding
nuclei at fixed centrality is also analytically calculated.Comment: updated version; as published by Phys. Rev.
Decoherence in a system of many two--level atoms
I show that the decoherence in a system of degenerate two--level atoms
interacting with a bosonic heat bath is for any number of atoms 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
QCD sum rules in the effective heavy quark theory
We derive sum rules for the leptonic decay constant of a heavy-light meson in the effective heavy quark theory. We show that the summation of logarithms in the heavy quark mass by the renormalization group technique enhances considerably radiative corrections. Our result for the decay constant in the static limit agrees well with recent lattice calculations. Finite quark mass corrections are estimated
- …