26,015 research outputs found
Covariant four-dimensional scattering equations for the system
We derive a set of coupled four-dimensional integral equations for the
system using our modified version of the Taylor method of
classification-of-diagrams. These equations are covariant, obey two and
three-body unitarity and contain subtraction terms which eliminate the
double-counting present in some previous four-dimensional
equations. The equations are then recast into a from convenient for computation
by grouping the subtraction terms together and obtaining a set of two-fragment
scattering equations for the amplitudes of interest.Comment: Version accepted for publication in ``Annals of Physics''. New
section containing two new figures added. 58 pages, 20 figures. Uses RevTeX.
For copies of figures email [email protected]
R-matrix Approach to Quantum Superalgebras su_{q}(m|n)
Quantum superalgebras are studied in the framework of
-matrix formalism. Explicit parametrization of and
matrices in terms of generators are presented. We also show
that quantum deformation of nonsimple superalgebra requires its
extension to .Comment: 14 page
The classification of diagrams in perturbation theory
The derivation of scattering equations connecting the amplitudes obtained
from diagrammatic expansions is of interest in many branches of physics. One
method for deriving such equations is the classification-of-diagrams technique
of Taylor. However, as we shall explain in this paper, there are certain points
of Taylor's method which require clarification. Firstly, it is not clear
whether Taylor's original method is equivalent to the simpler
classification-of-diagrams scheme used by Thomas, Rinat, Afnan and Blankleider
(TRAB). Secondly, when the Taylor method is applied to certain problems in a
time-dependent perturbation theory it leads to the over-counting of some
diagrams. This paper first restates Taylor's method, in the process uncovering
reasons why certain diagrams might be double-counted in the Taylor method. It
then explores how far Taylor's method is equivalent to the simpler TRAB method.
Finally, it examines precisely why the double-counting occurs in Taylor's
method, and derives corrections which compensate for this double-counting.Comment: 50 pages, RevTeX. Major changes from original version. Thirty figures
available upon request to [email protected]. Accepted for
publication in Annals of Physic
The magnetic form factor of the deuteron in chiral effective field theory
We calculate the magnetic form factor of the deuteron up to O(eP^4) in the
chiral EFT expansion of the electromagnetic current operator. The two LECs
which enter the two-body part of the isoscalar NN three-current operator are
fit to experimental data, and the resulting values are of natural size. The
O(eP^4) description of G_M agrees with data for momentum transfers Q^2 < 0.35
GeV^2.Comment: 4 pages, 2 figure
A study of atom localization in an optical lattice by analysis of the scattered light
We present an experimental study of a four beam optical lattice using the
light scattered by the atoms in the lattice. We use both intensity correlations
and observations of the transient behavior of the scattering when the lattice
is suddenly switched on. We compare results for 3 different configurations of
the optical lattice. We create situations in which the Lamb-Dicke effect is
negligible and show that, in contrast to what has been stated in some of the
literature, the damping rate of the 'coherent' atomic oscillations can be much
smaller than the inelastic photon scattering rate.Comment: An old pape
Delta Effects in Pion-Nucleon Scattering and the Strength of the Two-Pion-Exchange Three-Nucleon Interaction
We consider the relationship between P-wave pi-N scattering and the strength
of the P-wave two-pion-exchange three-nucleon interaction (TPE3NI). We explain
why effective theories that do not contain the delta resonance as an explicit
degree of freedom tend to overestimate the strength of the TPE3NI. The
overestimation can be remedied by higher-order terms in these ``delta-less''
theories, but such terms are not yet included in state-of-the-art chiral EFT
calculations of the nuclear force. This suggests that these calculations can
only predict the strength of the TPE3NI to an accuracy of +/-25%.Comment: 13 pages, 2 figures, uses eps
Event structure semantics of (controlled) reversible CCS
CCSK is a reversible form of CCS which is causal, meaning that ac- tions can be reversed if and only if each action caused by them has already been reversed; there is no control on whether or when a computation reverses. We pro- pose an event structure semantics for CCSK. For this purpose we define a cat- egory of reversible bundle event structures, and use the causal subcategory to model CCSK. We then modify CCSK to control the reversibility with a rollback primitive, which reverses a specific action and all actions caused by it. To define the event structure semantics of rollback, we change our reversible bundle event structures by making the conflict relation asymmetric rather than symmetric, and we exploit their capacity for non-causal reversibility
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