68 research outputs found
Nucleon QCD sum rules in nuclear matter including four-quark condensates
We calculate the nucleon parameters in nuclear matter using the QCD sum rules
approach in Fermi gas approximation. Terms up to 1/q^2 in the operator product
expansion (OPE) are taken into account. The higher moments of the nucleon
structure functions are included. The complete set of the nucleon expectation
values of the four-quark operators is employed. Earlier the lack of information
on these values has been the main obstacle for the further development of the
approach. We show that the four-quark condensates provide the corrections of
the order 20% to the results obtained in the leading orders of the OPE. This is
consistent with the assumption about the convergence of the OPE. The nucleon
vector self-energy \Sigma_v and the nucleon effective mass m^* are expressed in
terms of the in-medium values of QCD condensates. The numerical results for
these parameters at the saturation value of the density agree with those
obtained by the methods of nuclear physics.Comment: 38 pages, 5 figure
QCD Sum Rules Description of Nucleons in Asymmetric Nuclear Matter
We calculate the nucleon parameters in isospin asymmetric nuclear matter
using the QCD sum rules. The nucleon self-energies are expressed in terms of
the in-medium values of QCD condensates. The simple approximate expressions for
the self-energies are obtained in terms of these condensates. Relation between
successive inclusion of the condensates and the meson-exchange picture of the
nucleon interaction with medium is analyzed. The values of the self-energies
and of the symmetry energy agree with those obtained by the methods of nuclear
physics.Comment: 40 pages, 6 figure
A new approach to axial coupling constants in the QCD sum rule
We derive new QCD sum rules for the axial coupling constants by considering
two-point correlation functions of the axial-vector currents in a one nucleon
state. The QCD sum rules tell us that the axial coupling constants are
expressed by nucleon matrix elements of quark and gluon operators which are
related to the sigma terms and the moments of parton distribution functions.
The results for the iso-vector axial coupling constants and the 8th component
of the SU(3) octet are in good agreement with experiment.Comment: 10 pages, 1 figure include
QCD Sum Rules for Hyperons in Nuclear Matter
Within finite-density QCD sum-rule approach we investigate the self-energies
of hyperons propagating in nuclear matter from a correlator of
interpolating fields evaluated in the nuclear matter ground state. We
find that the Lorentz vector self-energy of the is similar to the
nucleon vector self-energy. The magnitude of Lorentz scalar self-energy of the
is also close to the corresponding value for nucleon; however, this
prediction is sensitive to the strangeness content of the nucleon and to the
assumed density dependence of certain four-quark condensate. The scalar and
vector self-energies tend to cancel, but not completely. The implications for
the couplings of to the scalar and vector mesons in nuclear matter and
for the spin-orbit force in a finite nucleus are discussed.Comment: 20 pages in revtex, 6 figures available under request as ps files,
UMD preprint #94--11
Analysis of the doubly heavy baryons in the nuclear matter with the QCD sum rules
In this article, we study the doubly heavy baryon states ,
, and in the nuclear matter using the QCD
sum rules, and derive three coupled QCD sum rules for the masses, vector
self-energies and pole residues. The predictions for the mass-shifts in the
nuclear matter , , and
can be confronted with the
experimental data in the future.Comment: 10 pages, 4 figure
Chiral symmetry and quantum hadro-dynamics
Using the linear sigma model, we study the evolutions of the quark condensate
and of the nucleon mass in the nuclear medium. Our formulation of the model
allows the inclusion of both pion and scalar-isoscalar degrees of freedom. It
guarantees that the low energy theorems and the constrains of chiral
perturbation theory are respected. We show how this formalism incorporates
quantum hadro-dynamics improved by the pion loops effects.Comment: 24 pages, 2 figure
Sigma-term physics in the perturbative chiral quark model
We apply the perturbative chiral quark model (PCQM) at one loop to analyse
meson-baryon sigma-terms. Analytic expressions for these quantities are
obtained in terms of fundamental parameters of low-energy pion-nucleon physics
(weak pion decay constant, axial nucleon coupling, strong pion-nucleon form
factor) and of only one model parameter (radius of the nucleonic three-quark
core). Our result for the piN sigma term of about 45 MeV is in good agreement
with the value deduced by Gasser, Leutwyler and Sainio using
dispersion-relation techniques and exploiting the chiral symmetry constraints.Comment: 19 pages, LaTeX-file, 2 Figure
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
Spectral asymmetries in nucleon sum rules at finite density
Apparent inconsistencies between different formulations of nucleon sum rules
at finite density are resolved through a proper accounting of asymmetries in
the spectral functions between positive- and negative-energy states.Comment: 10 pages in RevTeX, OSU-090
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