1,403 research outputs found
Lattice Theories with Nonlinearly Realized Chiral Symmetry
We present the lattice formulation of effective Lagrangians in which chiral
symmetry is realized nonlinearly on the fermion fields. In this framework both
the Wilson term removing unphysical doubler fermions and the fermion mass term
do not break chiral symmetry. Our lattice formulation allows us to address
non-perturbative questions in effective theories of baryons interacting with
pions and in models involving constitutent quarks interacting with pions and
gluons. With the presented methods, a system containing a non-zero density of
static baryons interacting with pions can be studied on the lattice without
encountering a complex action problem. This might lead to new insights into the
phase diagram of strongly interacting matter at non-zero chemical potential.Comment: 3 pages, Lattice2003(chiral
Aspects of Nucleon Chiral Perturbation Theory
I review recent progress made in the calculation of nucleon properties in the
framework of heavy baryon CHPT. Topics include: Compton scattering,
scattering, the anatomy of a low-energy constant and the induced pseudoscalar
form factor.Comment: plain TeX (macro included), 12pp, lecture delivered at the workshop
on "Chiral Dynamics: Theory and Experiments", MIT, July 25-29, 199
The pion-nucleon scattering lengths from pionic deuterium
We use the framework of effective field theories to discuss the determination
of the S-wave \pi N scattering lengths from the recent high-precision
measurements of pionic deuterium observables. The theoretical analysis proceeds
in several steps. Initially, the precise value of the pion-deuteron scattering
length a_{\pi d} is extracted from the data. Next, a_{\pi d} is related to the
S-wave \pi N scattering lengths a_+ and a_-. We discuss the use of this
information for constraining the values of these scattering lengths in the full
analysis, which also includes the input from the pionic hydrogen energy shift
and width measurements, and throughly investigate the accuracy limits for this
procedure. In this paper, we also give a detailed comparison to other effective
field theory approaches, as well as with the earlier work on the subject,
carried out within the potential model and multiple scattering framework.Comment: The replacement includes an erratum, which is published in Eur. Phys.
J.
Aspects of Chiral Dynamics
I discuss several topics in chiral perturbation theory - in particular, I
recall pecularities of the chiral expansion in the baryon sector.Comment: 14 pages, Latex with lamuphys.sty, 3 figures embedded with
epsfig.sty. To appear in Proc. of Workshop on Chiral Dynamics 1997, Mainz,
Germany, Sept. 199
Chiral condensate thermal evolution at finite baryon chemical potential within Chiral Perturbation Theory
We present a model independent study of the chiral condensate evolution in a
hadronic gas, in terms of temperature and baryon chemical potential. The
meson-meson interactions are described within Chiral Perturbation Theory and
the pion-nucleon interaction by means of Heavy Baryon Chiral Perturbation
Theory, both at one loop, and nucleon-nucleon interactions can be safely
neglected within our hadronic gas domain of validity. Together with the virial
expansion, this provides a systematic expansion at low temperatures and
chemical potentials, which includes the physical quark masses. This can serve
as a guideline for further studies on the lattice. We also obtain estimates of
the critical line of temperature and chemical potential where the chiral
condensate melts, which systematically lie somewhat higher than recent lattice
calculations but are consistent with several hadronic models. We have also
estimated uncertainties due to chiral parameters, heavier hadrons and higher
orders through unitarized Chiral Perturbation Theory.Comment: 15 pages, 15 figures, 3 tables, ReVTeX. Version to appear in Phys.
Rev. D. References added. More conservative estimate of applicability domain,
with new figure. More detailed explanation of final results with two more
figures. Results unchange
Aspects of Nucleon Compton Scattering
We consider the spin-averaged nucleon forward Compton scattering amplitude in
heavy baryon chiral perturbation theory including all terms to order . The chiral prediction for the spin-averaged forward Compton scattering
amplitude is in good agreement with the data for photon energies MeV. We also evaluate the nucleon electric and magnetic Compton
polarizabilities to this order and discuss the uncertainties of the various
counter terms entering the chiral expansion of these quantities.Comment: 17 pp, TeX, 7 figures available from the authors, preprint CRN-93/5
A Novel Method of Extraction of Blend Component Structure from SANS Measurements of Homopolymer Bimodal Blends
A new method is presented for the extraction of single-chain form factors and interchain interference functions from a range of small-angle neutron scattering (SANS) experiments on bimodal homopolymer blends. The method requires a minimum of three blends, made up of hydrogenated and deuterated components with matched degree of polymerization at two different chain lengths, but with carefully varying deuteration levels. The method is validated through an experimental study on polystyrene homopolymer bimodal blends with inline image. By fitting Debye functions to the structure factors, it is shown that there is good agreement between the molar mass of the components obtained from SANS and from chromatography. The extraction method also enables, for the first time, interchain scattering functions to be produced for scattering between chains of different lengths
Virtual Compton Scattering off the Pseudoscalar Meson Octet
We present a calculation of the virtual Compton scattering amplitude for the
pseudoscalar meson octet in the framework of chiral perturbation theory at
. We calculate the electromagnetic generalized polarizabilities
and compare the results in the real Compton scattering limit to available
experimental values. Finally, we give predictions for the differential cross
section of electron-meson bremsstrahlung.Comment: 9 pages, Latex, uses cjp3.sty (included), 4 eps figures, to be
published in the proceedings of the 13th Indian-Summer School "Understanding
the Structure of Hadrons," August 28 - September 1, 2000, Prague, Czech
Republi
Neutron-proton mass difference in nuclear matter
Isospin-breaking effects in nuclear matter are studied in the framework of a
medium-modified Skyrme model. The proposed effective Lagrangian incorporates
both the medium influence of the surrounding nuclear environment on the single
nucleon properties and an explicit isospin-breaking effect in the mesonic
sector. The approach predicts that the neutron-proton mass difference decreases
in isospin-symmetric nuclear matter but by a very small amount only.Comment: 8 pages, 4 figures, revised versio
Bethe-Salpeter Approach for the Elastic Pion-Nucleon Scattering in Heavy Baryon Chiral Perturbation Theory
Heavy Baryon Chiral Perturbation Theory (HBChPT) to leading order provides a
kernel to solve the Bethe-Salpeter equation for the
(-channel) system, in the infinite nucleon mass limit.
Crossed Born terms include, when iterated within the Bethe-Salpeter equation,
both {\it all} one- and {\it some} two-pion intermediate states, hence
preserving elastic unitarity below the two-pion production threshold. This
suggests searching for a solution with the help of dispersion relations and
suitable subtraction constants, when all in-elasticities are explicitly
neglected. The solution allows for a successful description of the experimental
phase shift from threshold up to MeV in terms of four
subtraction constants. Next-to-leading order HBChPT calculations are also used
to estimate the unknown subtraction constants which appear in the solution.
Large discrepancies are encountered which can be traced to the slow convergence
rate of HBChPT.Comment: 11 pages, 3 figure
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