1,307 research outputs found
Integrals over Products of Distributions and Coordinate Independence of Zero-Temperature Path Integrals
In perturbative calculations of quantum-statistical zero-temperature path
integrals in curvilinear coordinates one encounters Feynman diagrams involving
multiple temporal integrals over products of distributions, which are
mathematically undefined. In addition, there are terms proportional to powers
of Dirac delta-functions at the origin coming from the measure of path
integration. We give simple rules for integrating products of distributions in
such a way that the results ensure coordinate independence of the path
integrals. The rules are derived by using equations of motion and partial
integration, while keeping track of certain minimal features originating in the
unique definition of all singular integrals in dimensions. Our
rules yield the same results as the much more cumbersome calculations in 1-
epsilon dimensions where the limit epsilon --> 0 is taken at the end. They also
agree with the rules found in an independent treatment on a finite time
interval.Comment: Author Information under
http://www.physik.fu-berlin.de/~kleinert/institution.html . Latest update of
paper (including all PS fonts) at
http://www.physik.fu-berlin.de/~kleinert/33
Coordinate Independence of of Quantum-Mechanical Path Integrals
We develop simple rules for performing integrals over products of
distributions in coordinate space. Such products occur in perturbation
expansions of path integrals in curvilinear coordinates, where the interactions
contain terms of the form dot q^2 q^n, which give rise to highly singular
Feynman integrals. The new rules ensure the invariance of perturbatively
defined path integrals under coordinate transformations.Comment: Author Information under
http://www.physik.fu-berlin.de/~kleinert/institution.html . Latest update of
paper also at http://www.physik.fu-berlin.de/~kleinert/305
Universality Principle for Orbital Angular Momentum and Spin in Gravity with Torsion
We argue that compatibility with elementary particle physics requires
gravitational theories with torsion to be unable to distinguish between orbital
angular momentum and spin. An important consequence of this principle is that
spinless particles must move along autoparallel trajectories, not along
geodesics.Comment: Author Information under
http://www.physik.fu-berlin.de/~kleinert/institution.html . Latest update of
paper also at http://www.physik.fu-berlin.de/~kleinert/kleiner_re27
Covariant Effective Action for Quantum Particle with Coordinate-Dependent Mass
Using a covariant background field method we calculate the one-loop quantum
effective action for a particle with coordinate-dependent mass moving slowly
through a one-dimensional configuration space. The procedure can easily be
extended to any desired loop order.Comment: Author Information under
http://www.physik.fu-berlin.de/~kleinert/institution.html . Latest update of
paper (including all PS fonts) at
http://www.physik.fu-berlin.de/~kleinert/31
Critical dynamics, duality, and the exact dynamic exponent in extreme type II superconductors
The critical dynamics of superconductors is studied using renormalization
group and duality arguments. We show that in extreme type II superconductors
the dynamic critical exponent is given exactly by . This result does not
rely on the widely used models of critical dynamics. Instead, it is shown that
follows from the duality between the extreme type II superconductor and
a model with a critically fluctuating gauge field. Our result is in agreement
with Monte Carlo simulations.Comment: 7 pages, no figures; version accepted for publication in PR
Observing Quantum Tunneling in Perturbation Series
We apply Borel resummation method to the conventional perturbation series of
ground state energy in a metastable potential, . We observe
numerically that the discontinuity of Borel transform reproduces the imaginary
part of energy eigenvalue, i.e., total decay width due to the quantum
tunneling. The agreement with the exact numerical value is remarkable in the
whole tunneling regime 0.Comment: 12 pages, 2 figures. Phyzzx, Tables.tex, The final version to appear
in Phys. Lett.
Variational Perturbation Theory for Markov Processes
We develop a convergent variational perturbation theory for conditional
probability densities of Markov processes. The power of the theory is
illustrated by applying it to the diffusion of a particle in an anharmonic
potential.Comment: Author Information under
http://www.physik.fu-berlin.de/~kleinert/institution.html Latest update of
paper also at http://www.physik.fu-berlin.de/~kleinert/33
Nonholonomic Mapping Principle for Classical Mechanics in Spaces with Curvature and Torsion. New Covariant Conservation Law for Energy-Momentum Tensor
The lecture explains the geometric basis for the recently-discovered
nonholonomic mapping principle which specifies certain laws of nature in
spacetimes with curvature and torsion from those in flat spacetime, thus
replacing and extending Einstein's equivalence principle. An important
consequence is a new action principle for determining the equation of motion of
a free spinless point particle in such spacetimes. Surprisingly, this equation
contains a torsion force, although the action involves only the metric. This
force changes geodesic into autoparallel trajectories, which are a direct
manifestation of inertia. The geometric origin of the torsion force is a
closure failure of parallelograms. The torsion force changes the covariant
conservation law of the energy-momentum tensor whose new form is derived.Comment: Corrected typos. Author Information under
http://www.physik.fu-berlin.de/~kleinert/institution.html . Paper also at
http://www.physik.fu-berlin.de/~kleinert/kleiner_re261/preprint.htm
Towards a Simulation of Quantum Computers by Classical Systems
We present a two-dimensional classical stochastic differential equation for a
displacement field of a point particle in two dimensions and show that its
components define real and imaginary parts of a complex field satisfying the
Schroedinger equation of a harmonic oscillator. In this way we derive the
discrete oscillator spectrum from classical dynamics. The model is then
generalized to an arbitrary potential. This opens up the possibility of
efficiently simulating quantum computers with the help of classical systems.Comment: Author Information under
http://www.physik.fu-berlin.de/~kleinert/institution.html . Latest update of
paper (including all PS fonts) at
http://www.physik.fu-berlin.de/~kleinert/kleiner_re324/preprint.htm
Superconducting transition in disordered granular superconductors in magnetic fields
Motivated by a recent argument that the superconducting (SC) transition field
of three-dimensional (3D) disordered superconductors with granular structure in
a nonzero magnetic field should lie above in low limit, the
glass transition (or, in 2D, crossover) curve of disordered quantum
Josephson junction arrays is examined by incorporating SC fluctuations. It is
found that the glass transition or crossover in the granular materials can be
described on the same footing as the vortex-glass (VG) transition in
amorphous-like (i.e., nongranular) materials. In most of 3D granular systems,
the vanishing of resistivity upon cooling should occur even above ,
while the corresponding sharp drop of the resistivity in 2D case may appear
only below as a result of an enhanced quantum fluctuation.Comment: Accepted for publication in Phys. Rev. B. The content of sec.3 in v.2
was removed from here and presented more extensively in a separate paper
(cond-mat/0606522) where the argument of nonsuperconducting vortex-glass in
cond-mat/0512432 is shown to be fals
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