773 research outputs found

### A pair potential supporting a mixed mean-field / BCS- phase

We construct a Hamiltonian which in a scaling limit becomes equivalent to one
that can be diagonalized by a Bogoliubov transformation. There may appear
simultaneously a mean-field and a superconducting phase. They influence each
other in a complicated way. For instance, an attractive mean field may
stimulate the superconducting phase and a repulsive one may destroy it.Comment: 11 pages, 5 figures, LaTe

### Analysis of the exactness of mean-field theory in long-range interacting systems

Relationships between general long-range interacting classical systems on a
lattice and the corresponding mean-field models (infinitely long-range
interacting models) are investigated. We study systems in arbitrary dimension d
for periodic boundary conditions and focus on the free energy for fixed value
of the total magnetization. As a result, it is shown that the equilibrium free
energy of the long-range interacting systems are exactly the same as that of
the corresponding mean-field models (exactness of the mean-field theory).
Moreover, the mean-field metastable states can be also preserved in general
long-range interacting systems. It is found that in the case that the
magnetization is conserved, the mean-field theory does not give correct
property in some parameter region.Comment: 4 pages, 5 figures; clarifications and discussion about boundary
effects is added; the title is change

### Do anyons solve Heisenberg's Urgleichung in one dimension

We construct solutions to the chiral Thirring model in the framework of
algebraic quantum field theory. We find that for all positive temperatures
there are fermionic solutions only if the coupling constant is $\lambda =
\sqrt{2(2n + 1)\pi}, n \in \bf N$.Comment: 19 pages LaTeX, to appear in Eur. Phys. J.

### Noncommutative Manifolds from the Higgs Sector of Coincident D-Branes

The Higgs sector of the low-energy physics of n of coincident D-branes
contains the necessary elements for constructing noncommutative manifolds. The
coordinates orthogonal to the coincident branes, as well as their conjugate
momenta, take values in the Lie algebra of the gauge group living inside the
brane stack. In the limit when n=\infty (and in the absence of orientifolds),
this is the unitary Lie algebra u(\infty). Placing a smooth manifold K
orthogonally to the stack of coincident D-branes one can construct a
noncommutative C*-algebra that provides a natural definition of a
noncommutative partner for the manifold K.Comment: 10 page

### Validity and failure of some entropy inequalities for CAR systems

Basic properties of von Neumann entropy such as the triangle inequality and
what we call MONO-SSA are studied for CAR systems.
We show that both inequalities hold for any even state. We construct a
certain class of noneven states giving counter examples of those inequalities.
It is not always possible to extend a set of prepared states on disjoint
regions to some joint state on the whole region for CAR systems.
However, for every even state, we have its `symmetric purification' by which
the validity of those inequalities is shown.
Some (realized) noneven states have peculiar state correlations among
subsystems and induce the failure of those inequalities.Comment: 14 pages, latex, to appear in JMP. Some typos are correcte

### The Einstein-Hilbert Lagrangian Density in a 2-dimensional Spacetime is an Exact Differential

Recently Kiriushcheva and Kuzmin claimed to have shown that the
Einstein-Hilbert Lagrangian cannot be written in any coordinate gauge as an
exact differential in a 2-dimensional spacetime. Since this is contrary to
other statements on the subject found in the literature, as e.g., by Deser and
Jackiw, Jackiw, Grumiller, Kummer and Vassilevich it is necessary to do decide
who has reason. This is done in this paper in a very simply way using the
Clifford bundle formalism. In this version we added Section 18 which discusses
a recent comment on our paper just posted by Kiriushcheva and Kuzmin.Comment: 11 pages, Misprints in some equations have been corrected; four new
references have been added, Section 18 adde

### A microscopic model for Josephson currents

A microscopic model of a Josephson junction between two superconducting
plates is proposed and analysed. For this model, the nonequilibrium steady
state of the total system is explicitly constructed and its properties are
analysed. In particular, the Josephson current is rigorously computed as a
function of the phase difference of the two plates and the typical properties
of the Josephson current are recovered

### Statistics and Quantum Chaos

We use multi-time correlation functions of quantum systems to construct
random variables with statistical properties that reflect the degree of
complexity of the underlying quantum dynamics.Comment: 12 pages, LateX, no figures, restructured versio

- âŠ