2,798 research outputs found
Operator Formulation of q-Deformed Dual String Model
We present an operator formulation of the q-deformed dual string model
amplitude using an infinite set of q-harmonic oscillators. The formalism
attains the crossing symmetry and factorization and allows to express the
general n-point function as a factorized product of vertices and propagators.Comment: 6pages, Late
An Example of Poincare Symmetry with a Central Charge
We discuss a simple system which has a central charge in its Poincare
algebra. We show that this system is exactly solvable after quantization and
that the algebra holds without anomalies.Comment: 11 pages, Revte
Effective potential approach to quantum dissipation in condensed matter systems
The effects of dissipation on the thermodynamic properties of nonlinear
quantum systems are approached by the path-integral method in order to
construct approximate classical-like formulas for evaluating thermal averages
of thermodynamic quantities. Explicit calculations are presented for
one-particle and many-body systems. The effects of the dissipation mechanism on
the phase diagram of two-dimensional Josephson arrays is discussed.Comment: 7 pages, 5 figures, to appear in the Proceedings of Nonlinearity,
Integrability And All That 20 Years After Needs 7
The Fubini-Furlan-Rossetti Sum Rule Revisited
The Fubini-Furlan-Rossetti sum rule for pion photoproduction on the nucleon
is evaluated by dispersion relations at constant t, and the corrections to the
sum rule due to the finite pion mass are calculated. Near threshold these
corrections turn out to be large due to pion-loop effects, whereas the sum rule
value is closely approached if the dispersion integrals are evaluated for
sub-threshold kinematics. This extension to the unphysical region provides a
unique framework to determine the low-energy constants of chiral perturbation
theory by global properties of the excitation spectrum.Comment: 12 pages, 7 postscript figures, EPJ style files include
Entanglement and factorized ground states in two-dimensional quantum antiferromagnets
Making use of exact results and quantum Monte Carlo data for the entanglement
of formation, we show that the ground state of anisotropic two-dimensional
S=1/2 antiferromagnets in a uniform field takes the classical-like form of a
product state for a particular value and orientation of the field, at which the
purely quantum correlations due to entanglement disappear. Analytical
expressions for the energy and the form of such states are given, and a novel
type of exactly solvable two-dimensional quantum models is therefore singled
out. Moreover, we show that the field-induced quantum phase transition present
in the models is unambiguously characterized by a cusp minimum in the
pairwise-to-global entanglement ratio R, marking the quantum-critical
enhancement of \emph{multipartite} entanglement. A detailed discussion is
provided on the universality of the cusp in R as a signature of quantum
critical behavior entirely based on entanglement.Comment: 4 pages, 3 figure
Staggered magnetization and entanglement enhancement by magnetic impurities in spin chain
We study the effects of a magnetic impurity on the behavior of a spin
chain. At T=0, both with and without an applied uniform magnetic field, an
oscillating magnetization appears, whose decay with the distance from the
impurity is ruled by a power law. As a consequence, pairwise entanglement is
either enhanced or quenched, depending on the distance of the spin pair with
respect to the impurity and on the values of the magnetic field and the
intensity of the impurity itself. This leads us to suggest that acting on such
control parameters, an adiabatic manipulation of the entanglement distribution
can be performed. The robustness of our results against temperature is checked,
and suggestions about possible experimental applications are put forward.Comment: 4 pages, 8 figure
New Phenomenon of Nonlinear Regge Trajectory and Quantum Dual String Theory
The relation between the spin and the mass of an infinite number of particles
in a -deformed dual string theory is studied. For the deformation parameter
a root of unity, in addition to the relation of such values of with the
rational conformal field theory, the Fock space of each oscillator mode in the
Fubini-Veneziano operator formulation becomes truncated. Thus, based on general
physical grounds, the resulting spin-(mass) relation is expected to be
below the usual linear trajectory. For such specific values of , we find
that the linear Regge trajectory turns into a square-root trajectory as the
mass increases.Comment: 12 pages, Latex, HU-SEFT R 1994-0
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