405 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]
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
Model Dependence of the 2H Electric Dipole Moment
Background: Direct measurement of the electric dipole moment (EDM) of the
neutron lies in the future; measurement of a nuclear EDM may well come first.
The deuteron is one nucleus for which exact model calculations are feasible.
Purpose: We explore the model dependence of deuteron EDM calculations. Methods:
Using a separable potential formulation of the Hamiltonian, we examine the
sensitivity of the deuteron EDM to variation in the nucleon-nucleon
interaction. We write the EDM as the sum of two terms, the first depending on
the target wave function with plane-wave intermediate states, and the second
depending on intermediate multiple scattering in the 3P1 channel, the latter
being sensitive to the off-shell behavior of the 3P1 amplitude. Results: We
compare the full calculation with the plane-wave approximation result, examine
the tensor force contribution to the model results, and explore the effect of
short range repulsion found in realistic, contemporary potential models of the
deuteron. Conclusions: Because one-pion exchange dominates the EDM calculation,
separable potential model calculations will provide an adequate description of
the 2H EDM until such time as a better than 10% measurement is obtained.Comment: 21 pages, 2 figures, submitted to Physical Review
The energy dependence of the amplitude and the three-nucleon interaction
By calculating the contribution of the three-body force to the
three-nucleon binding energy in terms of the amplitude using
perturbation theory, we are able to determine the importance of the energy
dependence and the contribution of the different partial waves of the
amplitude to the three-nucleon force. A separable representation of the
non-pole amplitude allows us to write the three-nucleon force in terms
of the amplitude for , propagation of the system,
and the amplitude for , with being the
quasi-particle amplitude in a given state. The division of the
amplitude into a pole and non-pole gives a procedure for the determination of
the form factor within the model. The total contribution of the
three-body force to the binding energy of the triton for the separable
approximation to the Paris nucleon-nucleon potential (PEST) is found to be very
small mainly as a result of the energy dependence of the amplitude, the
cancellation between the - and -wave amplitudes, and the soft
form factor.Comment: RevTex file, 36 pages, 10 figures available from authors:
[email protected]
Importance of Baryon-Baryon Coupling in Hypernuclei
The coupling in --hypernuclei and coupling in --hypernuclei produce novel
physics not observed in the conventional, nonstrange sector. Effects of
conversion in H are reviewed.
The role of coupling suppression in the
--hypernuclei due to Pauli blocking is highlighted, and the
implications for the structure of B are explored.
Suppression of conversion in He is hypothesized as the reason that the
matrix element is small. Measurement of H is
proposed to investigate the full interaction. The
implication for analog states is discussed.Comment: 17 pages LATEX, 1 figure uuencoded postscrip
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