23 research outputs found
Derivation of the Effective Pion-Nucleon Lagrangian within Heavy Baryon Chiral Perturbation Theory
We develop a method for constructing the Heavy Baryon Chiral Perturbation
Theory Lagrangian (L_{HBChPT}), to a given chiral order, within HBChPT. We work
within SU(2) theory, with only the pion field interacting with the nucleon. The
main difficulties, which are solved, are to develop techniques for implementing
charge conjugation invariance, and for taking the nucleon on shell, both within
the nonrelativistic formalism. We obtain complete lists of independent terms in
L_{HBChPT} through O(q^3) for off- shell nucleons. Then, eliminating
equation-of-motion (eom) terms at the relativistic and nonrelativistic level
(both within HBChPT), we obtain L_{HBCHPT} for on-shell nucleons, through
O(q^3). The extension of the method (to obtain on-shell L_{HBChPT} within
HBChPT) to higher orders is also discussed.Comment: 31 pages, LaTex; original version shortened; 2 new tables and new
material on extending on-shell reduction method within HBChPT to arbitrary
chiral orders, include
Comment on "Role of heavy meson exchange in near threshold N N --> d pi"
In a recent paper by C. J. Horowitz (Phys. Rev. C {\bf 48}, 2920 (1993)) a
heavy meson exchange is incorporated into threshold NN --> d pi to enhance the
grossly underestimated cross section. However, that calculation uses an
unjustified assumption on the initial and final momenta, which causes an
overestimate of this effect by a factor of 3--4. I point out that the inclusion
of the Delta(1232) isobar increases the cross section significantly even at
threshold.Comment: 7 pages, figures by fax or mail from [email protected]
Improved lower bounds for the ground-state energy of many-body systems
New lower bounds for the binding energy of a quantum-mechanical system of
interacting particles are presented. The new bounds are expressed in terms of
two-particle quantities and improve the conventional bounds of the Hall-Post
type. They are constructed by considering not only the energy in the
two-particle system, but also the structure of the pair wave function. We apply
the formal results to various numerical examples, and show that in some cases
dramatic improvement over the existing bounds is reached.Comment: 29 pages, 5 figures, to be published in Phys. Rev.
Self-consistent Green's function approaches
We present the fundamental techniques and working equations of many-body
Green's function theory for calculating ground state properties and the
spectral strength. Green's function methods closely relate to other polynomial
scaling approaches discussed in chapters 8 and 10. However, here we aim
directly at a global view of the many-fermion structure. We derive the working
equations for calculating many-body propagators, using both the Algebraic
Diagrammatic Construction technique and the self-consistent formalism at finite
temperature. Their implementation is discussed, as well as the inclusion of
three-nucleon interactions. The self-consistency feature is essential to
guarantee thermodynamic consistency. The pairing and neutron matter models
introduced in previous chapters are solved and compared with the other methods
in this book.Comment: 58 pages, 14 figures, Submitted to Lect. Notes Phys., "An advanced
course in computational nuclear physics: Bridging the scales from quarks to
neutron stars", M. Hjorth-Jensen, M. P. Lombardo, U. van Kolck, Editor
Chiral perturbation theory calculation for pn -> dpipi at threshold
We investigate the reaction pn -> dpipi in the framework of Chiral
Perturbation Theory. For the first time a complete calculation of the leading
order contributions is presented. We identify various diagrams that are of
equal importance as compared to those recognized in earlier works. The diagrams
at leading order behave as expected by the power counting. Also for the first
time the nucleon-nucleon interaction in the initial, intermediate and final
state is included consistently and found to be very important. This study
provides a theoretical basis for a controlled evaluation of the non-resonant
contributions in two-pion production reactions in nucleon-nucleon collisions.Comment: 24 pages, 3 figures, 3 table
Realistic Model of the Nucleon Spectral Function in Few- and Many- Nucleon Systems
By analysing the high momentum features of the nucleon momentum distribution
in light and complex nuclei, it is argued that the basic two-nucleon
configurations generating the structure of the nucleon Spectral Function at
high values of the nucleon momentum and removal energy, can be properly
described by a factorised ansatz for the nuclear wave function, which leads to
a nucleon Spectral Function in the form of a convolution integral involving the
momentum distributions describing the relative and center-of-mass motion of a
correlated nucleon-nucleon pair embedded in the medium. The Spectral Functions
of and infinite nuclear matter resulting from the convolution formula
and from many-body calculations are compared, and a very good agreement in a
wide range of values of nucleon momentum and removal energy is found.
Applications of the model to the analysis of inclusive and exclusive processes
are presented, illustrating those features of the cross section which are
sensitive to that part of the Spectral Function which is governed by
short-range and tensor nucleon-nucleon correlations.Comment: 40 pages Latex , 16 ps figures available from the above e-mail
address or from [email protected]
Nuclear structure theory. Annual technical progress report, October 1, 1976--September 30, 1977. [Research progress at the University of Rochester]
This report summarizes progress during the past year in the following areas of nuclear structure and reaction theory: (1) statistical spectroscopy, including giant resonances for beta and electromagnetic excitation and sum rules (including inverse-energy-weighted sum rules), statistical methods of truncating shell model spaces and renormalization of operators, study of state labelling and ''chains'' of groups, evaluation of fluctuation measures, technical aspects of operator averaging; (2) meson interactions with nuclei, including scattering and absorption of mesons by nuclei (general methods), models for absorption, single- and double-charge exchange of pions, role of rho mesons