914 research outputs found
Erratum: Dirichlet Forms and Dirichlet Operators for Infinite Particle Systems: Essential Self-adjointness
We reprove the essential self-adjointness of the Dirichlet operators of
Dirchlet forms for infinite particle systems with superstable and
sub-exponentially decreasing interactions.Comment: This is an erratum to the work appeared in J. Math. Phys. 39(12),
6509-6536 (1998
Phase transitions and quantum effects in anharmonic crystals
The most important recent results in the theory of phase transitions and
quantum effects in quantum anharmonic crystals are presented and discussed. In
particular, necessary and sufficient conditions for a phase transition to occur
at some temperature are given in the form of simple inequalities involving the
interaction strength and the parameters describing a single oscillator. The
main characteristic feature of the theory is that both mentioned phenomena are
described in one and the same setting, in which thermodynamic phases of the
model appear as probability measures on path spaces. Then the possibility of a
phase transition to occur is related to the existence of multiple phases at the
same values of the relevant parameters. Other definitions of phase transitions,
based on the non-differentiability of the free energy density and on the
appearance of ordering, are also discussed
An explicitly solvable model of the spontaneous PT-symmetry breaking
We contemplate the pair of the purely imaginary delta-function potentials on
a finite interval with Dirichlet boundary conditions. The two parameter model
exhibits nicely the expected quantitative features of the unavoided level
crossing and of a "phase-transition" complexification of the energies.
Combining analytic and numerical techniques we investigate strength- and
position-dependence of its spectrum.Comment: presented in the int. conference "Pseudo-Hermitian Hamiltonians in
Quantum Physics III" (Instanbul, Koc University, June 20 - 22, 2005).
accepted in Czechoslovak J. Phy
Boundary Conditions for Singular Perturbations of Self-Adjoint Operators
Let A:D(A)\subseteq\H\to\H be an injective self-adjoint operator and let
\tau:D(A)\to\X, X a Banach space, be a surjective linear map such that
\|\tau\phi\|_\X\le c \|A\phi\|_\H. Supposing that \text{\rm Range}
(\tau')\cap\H' =\{0\}, we define a family of self-adjoint
operators which are extensions of the symmetric operator .
Any in the operator domain is characterized by a sort
of boundary conditions on its univocally defined regular component \phireg,
which belongs to the completion of D(A) w.r.t. the norm \|A\phi\|_\H. These
boundary conditions are written in terms of the map , playing the role of
a trace (restriction) operator, as \tau\phireg=\Theta Q_\phi, the extension
parameter being a self-adjoint operator from X' to X. The self-adjoint
extension is then simply defined by A^\tau_\Theta\phi:=A \phireg. The case in
which is a convolution operator on LD, T a distribution with
compact support, is studied in detail.Comment: Revised version. To appear in Operator Theory: Advances and
Applications, vol. 13
Non Commutative Arens Algebras and their Derivations
Given a von Neumann algebra with a faithful normal semi-finite trace
we consider the non commutative Arens algebra and the related algebras
and
which are proved to be complete metrizable locally
convex *-algebras. The main purpose of the present paper is to prove that any
derivation of the algebra is inner and all
derivations of the algebras and
are spatial and implemented by elements of Comment: 19 pages. Submitted to Journal of Functional analysi
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