280 research outputs found
Hidden gauge formalism for the radiative decays of axial-vector mesons
The radiative decay of the axial-vector resonances into a pseudoscalar meson
and a photon is studied using the vector meson Lagrangian obtained from the
hidden gauge symmetry (HGS) formalism. The formalism is well suited to study
this problem since it deals with pseudoscalar and vector mesons in a unified
way, respecting chiral invariance. We show explicitly the gauge invariance of
the set of diagrams that appear in the approach and evaluate the radiative
decay width of the a1(1260) and b1(1235) axial vector meson resonances into pi
gamma. We also include the contribution of loops involving anomalous couplings
and compare the results to those obtained previously within another formalism.Comment: 24 pages, 6 tables, 11 figure
Two-point correlation function with pion in QCD sum rules
Within the framework of the conventional QCD sum rules, we study the pion
two-point correlation function, , beyond the soft-pion limit. We construct sum rules from the
three distinct Dirac structures, i \gamma_5 \notp, i \gamma_5, \gamma_5
\sigma_{\mu \nu} {q^\mu p^\nu} and study the reliability of each sum rule. The
sum rule from the third structure is found to be insensitive to the continuum
threshold, , and contains relatively small contribution from the
undetermined single pole which we denote as . The sum rule from the structure is very different even though it contains similar
contributions from and as the ones coming from the structure. On the other hand, the sum rule from
the i \gamma_5 \notp structure has strong dependence on both and ,
which is clearly in constrast with the sum rule for . We identify the source of the sensitivity for each of the sum
rules by making specific models for higher resonance contributions and discuss
the implication.Comment: slightly revised. version accepted for publication in Physical Review
Effective Nucleon-Nucleon Interaction and Fermi Liquid Theory
We present two novel relations between the quasiparticle interaction in
nuclear matter and the unique low momentum nucleon-nucleon interaction in
vacuum. These relations provide two independent constraints on the Fermi liquid
parameters of nuclear matter. Moreover, the new constraints define two
combinations of Fermi liquid parameters, which are invariant under the
renormalization group flow in the particle-hole channels. Using empirical
values for the spin-independent Fermi liquid parameters, we are able to compute
the major spin-dependent ones by imposing the new constraints as well as the
Pauli principle sum rules.Comment: 4 pages, 5 figures, in Proc. 11th International Conference on Recent
Progress in Many-Body Theories, Manchester, UK, July 9-13, 200
Deconstructing 1S0 nucleon-nucleon scattering
A distorted-wave method is used to analyse nucleon-nucleon scattering in the
1S0 channel. Effects of one-pion exchange are removed from the empirical phase
shift to all orders by using a modified effective-range expansion. Two-pion
exchange is then subtracted in the distorted-wave Born approximation, with
matrix elements taken between scattering waves for the one-pion exchange
potential. The residual short-range interaction shows a very rapid energy
dependence for kinetic energies above about 100 MeV, suggesting that the
breakdown scale of the corresponding effective theory is only 270MeV. This may
signal the need to include the Delta resonance as an explicit degree of freedom
in order to describe scattering at these energies. An alternative strategy of
keeping the cutoff finite to reduce large, but finite, contributions from the
long-range forces is also discussed.Comment: 10 pages, 2 figures (introduction revised, references added; version
to appear in EPJA
Baryon structure in a quark-confining non-local NJL model
We study the nucleon and diquarks in a non-local Nambu-Jona-Lasinio model.
For certain parameters the model exhibits quark confinement, in the form of a
propagator without real poles. After truncation of the two-body channels to the
scalar and axial-vector diquarks, a relativistic Faddeev equation for nucleon
bound states is solved in the covariant diquark-quark picture. The dependence
of the nucleon mass on diquark masses is studied in detail. We find parameters
that lead to a simultaneous reasonable description of pions and nucleons. Both
the diquarks contribute attractively to the nucleon mass. Axial-vector diquark
correlations are seen to be important, especially in the confining phase of the
model. We study the possible implications of quark confinement for the
description of the diquarks and the nucleon. In particular, we find that it
leads to a more compact nucleon.Comment: 21 pages (RevTeX), 18 figures (eps
Pertinent Dirac structure for QCD sum rules of meson-baryon coupling constants
Using general baryon interpolating fields for
without derivative, we study QCD sum rules for meson-baryon couplings and their
dependence on Dirac structures for the two-point correlation function with a
meson i\int d^4x e^{iqx} \bra 0|{\rm T}[J_B(x)\bar{J}_B(0)] |{\cal M}(p)\ket.
Three distinct Dirac structures are compared: ,
i\gamma_5\fslash{p}, and structures.
From the dependence of the OPE on general baryon interpolating fields, we
propose criteria for choosing an appropriate Dirac structure for the coupling
sum rules. The sum rules satisfy the
criteria while the sum rules beyond the chiral limit do not. For
the i\gamma_5\fslash{p} sum rules, the large continuum contributions prohibit
reliable prediction for the couplings. Thus, the structure seems pertinent for realistic predictions. In the SU(3) limit,
we identify the OPE terms responsible for the ratio. We then study the
dependence of the ratio on the baryon interpolating fields. We conclude the
ratio for appropriate choice of the interpolating fields.Comment: To be published in Phys.Rev.C ; 21 pages,8 figures, revtex ;
references are adde
Scattering of unstable particles in a finite volume: The case of pi rho scattering and the a(1)(1260) resonance
We present a way to evaluate the scattering of unstable particles quantized in a finite volume with the aim of extracting physical observables for infinite volume from lattice data. We illustrate the method with the πρ scattering which generates dynamically the axial-vector a1(1260) resonance. Energy levels in a finite box are evaluated both considering the ρ as a stable and unstable resonance and we find significant differences between both cases. We discuss how to solve the problem to get the physical scattering amplitudes in the infinite volume, and hence phase shifts, from possible lattice results on energy levels quantized inside a finite box
Power counting and renormalization group invariance in the subtracted kernel method for the two-nucleon system
We apply the subtracted kernel method (SKM), a renormalization approach based
on recursive multiple subtractions performed in the kernel of the scattering
equation, to the chiral nucleon-nucleon (NN) interactions up to
next-to-next-to-leading-order (NNLO). We evaluate the phase-shifts in the 1S0
channel at each order in Weinberg's power counting scheme and in a modified
power counting scheme which yields a systematic power-law improvement. We also
explicitly demonstrate that the SKM procedure is renormalization group
invariant under the change of the subtraction scale through a non-relativistic
Callan-Symanzik flow equation for the evolution of the renormalized NN
interactions.Comment: Accepted for publication in Journal of Physics G: Nuclear and
Particle Physic
What does a change in the quark condensate say about restoration of chiral symmetry in matter?
The contribution of nucleons to the quark condensate in nuclear matter
includes a piece of first order in , arising from the contribution of
low-momentum virtual pions to the sigma commutator. Chiral symmetry
requires that no term of this order appears in the interaction. The mass
of a nucleon in matter thus cannot depend in any simple way on the quark
condensate alone. More generally, pieces of the quark condensate that arise
from low-momentum pions should not be associated with partial restoration of
chiral symmetry.Comment: 9 pages (RevTeX). Definition of effective mass changed; numerical
value of leading nonanalytic term corrected, along with various misprint
Response of nucleons to external probes in hedgehog models: II. General formalism
Linear response theory for SU(2) hedgehog soliton models is developed.Comment: 25 pages, DOE/ER/40322-163, U. of MD PP \#92-225, (ReVTeX
- …