698 research outputs found
Supersymmetry on Graphs and Networks
We show that graphs, networks and other related discrete model systems carry
a natural supersymmetric structure, which, apart from its conceptual importance
as to possible physical applications, allows to derive a series of spectral
properties for a class of graph operators which typically encode relevant graph
characteristics.Comment: 11 pages, Latex, no figures, remark 4.1 added, slight alterations in
lemma 5.3, a more detailed discussion at beginning of sect.6 (zero
eigenspace
On the solution of the initial value constraints for general relativity coupled to matter in terms of Ashtekar's variables
The method of solution of the initial value constraints for pure canonical
gravity in terms of Ashtekar's new canonical variables due to CDJ is further
developed in the present paper. There are 2 new main results : 1) We extend the
method of CDJ to arbitrary matter-coupling again for non-degenerate metrics :
the new feature is that the 'CDJ-matrix' adopts a nontrivial antisymmetric part
when solving the vector constraint and that the Klein-Gordon-field is used,
instead of the symmetric part of the CDJ-matrix, in order to satisfy the scalar
constraint. 2) The 2nd result is that one can solve the general initial value
constraints for arbitrary matter coupling by a method which is completely
independent of that of CDJ. It is shown how the Yang-Mills and gravitational
Gauss constraints can be solved explicitely for the corresponding electric
fields. The rest of the constraints can then be satisfied by using either
scalar or spinor field momenta. This new trick might be of interest also for
Yang-Mills theories on curved backgrounds.Comment: Latex, 15 pages, PITHA93-1, January 9
Tailoring the frictional properties of granular media
A method of modifying the roughness of soda-lime glass spheres is presented,
with the purpose of tuning inter-particle friction. The effect of chemical
etching on the surface topography and the bulk frictional properties of grains
is systematically investigated. The surface roughness of the grains is measured
using white light interferometry and characterised by the lateral and vertical
roughness length scales. The underwater angle of repose is measured to
characterise the bulk frictional behaviour. We observe that the co-efficient of
friction depends on the vertical roughness length scale. We also demonstrate a
bulk surface roughness measurement using a carbonated soft drink.Comment: 10 pages, 17 figures, submitted to Phys. Rev.
Renormalization of heavy-light currents in moving NRQCD
Heavy-light decays such as , and can be used to constrain the parameters of the Standard
Model and in indirect searches for new physics. While the precision of
experimental results has improved over the last years this has still to be
matched by equally precise theoretical predictions. The calculation of
heavy-light form factors is currently carried out in lattice QCD. Due to its
small Compton wavelength we discretize the heavy quark in an effective
non-relativistic theory. By formulating the theory in a moving frame of
reference discretization errors in the final state are reduced at large recoil.
Over the last years the formalism has been improved and tested extensively.
Systematic uncertainties are reduced by renormalizing the m(oving)NRQCD action
and heavy-light decay operators. The theory differs from QCD only for large
loop momenta at the order of the lattice cutoff and the calculation can be
carried out in perturbation theory as an expansion in the strong coupling
constant. In this paper we calculate the one loop corrections to the
heavy-light vector and tensor operator. Due to the complexity of the action the
generation of lattice Feynman rules is automated and loop integrals are solved
by the adaptive Monte Carlo integrator VEGAS. We discuss the infrared and
ultraviolet divergences in the loop integrals both in the continuum and on the
lattice. The light quarks are discretized in the ASQTad and highly improved
staggered quark (HISQ) action; the formalism is easily extended to other quark
actions.Comment: 24 pages, 11 figures. Published in Phys. Rev. D. Corrected a typo in
eqn. (51
Polar magneto-optical Kerr effect for low-symmetric ferromagnets
The polar magneto-optical Kerr effect (MOKE) for low-symmetric ferromagnetic
crystals is investigated theoretically based on first-principle calculations of
optical conductivities and a transfer matrix approach for the electrodynamics
part of the problem. Exact average magneto-optical properties of polycrystals
are described, taking into account realistic models for the distribution of
domain orientations. It is shown that for low-symmetric ferromagnetic single
crystals the MOKE is determined by an interplay of crystallographic
birefringence and magnetic effects. Calculations for single and bi-crystal of
hcp 11-20 Co and for a polycrystal of CrO_2 are performed, with results being
in good agreement with experimental data.Comment: 14 pages, 7 figures, accepted for publication in Phys. Rev.
Wigner Function Evolution of Quantum States in Presence of Self-Kerr Interaction
A Fokker-Planck equation for the Wigner function evolution in a noisy Kerr
medium ( non-linearity) is presented. We numerically solved this
equation taking a coherent state as an initial condition. The dissipation
effects are discussed. We provide examples of quantum interference, sub-Planck
phase space structures, and Gaussian versus non-Gaussian dynamical evolution of
the state. The results also apply to the description of a nanomechanical
resonator with an intrinsic Duffing nonlinearity.Comment: 10 pages, 11 figure
Evolution of cosmological constant in effective gravity
In contrast to the phenomenon of nullification of the cosmological constant
in the equilibrium vacuum, which is the general property of any quantum vacuum,
there are many options in modifying the Einstein equation to allow the
cosmological constant to evolve in a non-equilibrium vacuum. An attempt is made
to extend the Einstein equation in the direction suggested by the
condensed-matter analogy of the quantum vacuum. Different scenarios are found
depending on the behavior of and the relation between the relaxation parameters
involved, some of these scenarios having been discussed in the literature. One
of them reproduces the scenario in which the effective cosmological constant
emerges as a constant of integration. The second one describes the situation,
when after the cosmological phase transition the cosmological constant drops
from zero to the negative value; this scenario describes the relaxation from
this big negative value back to zero and then to a small positive value. In the
third example the relaxation time is not a constant but depends on matter; this
scenario demonstrates that the vacuum energy (or its fraction) can play the
role of the cold dark matter.Comment: LaTeX file, 5 pages, no figures, version submitted to JETP Letter
Progressive ataxia with oculo-palatal tremor and optic atrophy
The final publication is available at Springer via doi: 10.​1007/​s00415-013-7136-
Particle Counting Statistics of Time and Space Dependent Fields
The counting statistics give insight into the properties of quantum states of
light and other quantum states of matter such as ultracold atoms or electrons.
The theoretical description of photon counting was derived in the 1960s and was
extended to massive particles more recently. Typically, the interaction between
each particle and the detector is assumed to be limited to short time
intervals, and the probability of counting particles in one interval is
independent of the measurements in previous intervals. There has been some
effort to describe particle counting as a continuous measurement, where the
detector and the field to be counted interact continuously. However, no general
formula applicable to any time and space dependent field has been derived so
far. In our work, we derive a fully time and space dependent description of the
counting process for linear quantum many-body systems, taking into account the
back-action of the detector on the field. We apply our formalism to an
expanding Bose-Einstein condensate of ultracold atoms, and show that it
describes the process correctly, whereas the standard approach gives unphysical
results in some limits. The example illustrates that in certain situations, the
back-action of the detector cannot be neglected and has to be included in the
description
Superposition in nonlinear wave and evolution equations
Real and bounded elliptic solutions suitable for applying the Khare-Sukhatme
superposition procedure are presented and used to generate superposition
solutions of the generalized modified Kadomtsev-Petviashvili equation (gmKPE)
and the nonlinear cubic-quintic Schroedinger equation (NLCQSE).Comment: submitted to International Journal of Theoretical Physics, 23 pages,
2 figures, style change
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