335 research outputs found
The pion mass dependence of the nucleon form-factors of the energy momentum tensor in the chiral quark-soliton model
The nucleon form factors of the energy-momentum tensor are studied in the
large-Nc limit in the framework of the chiral quark-soliton model for model
parameters that simulate physical situations in which pions are heavy. This
allows for a direct comparison to lattice QCD results.Comment: 17 pages, 12 figure
Collective coordinates of the Skyrme model coupled with fermions
The problem of construction of fiber bundle over the moduli space of the
Skyrme model is considered. We analyse an extension of the original Skyrme
model which includes the minimal interaction with fermions. An analogy with
modili space of the fermion-monopole system is used to construct a fiber bundle
structure over the skyrmion moduli space. The possibility of the non-trivial
holonomy appearance is considered. It is shown that the effect of the fermion
interaction turns the -skyrmion moduli space into a real vector bundle with
natural connection.Comment: 10 page
QCD Instantons in Vacuum and Matter
The singlet coupling to the topological charge density in the instanton
vacuum, causes the instantons and antiinstantons to be screened over distances
of the order of 1/2 fm. Dilute instanton systems behave as a free gas, while
dense instanton systems behave as a plasma. The free gas behaviour is favored
by a density of 1 fm. Owing to the Higgs mechanism, the ' mass is
heavy (1100 MeV). The vacuum topological susceptibility is small (0.07
fm) and consistent with the QCD Ward identity. In the chiral limit, the
singlet screening vanishes, leading to a four dimensional plasma state with a
temperature given by the nonet decay constant (90 MeV). The phase is Debye
screened. In the presence of matter, the screening is quenched, and a
Kosterlitz-Thouless transition may occur signaling the restoration of the
symmetry. We suggest to use the spatial asymptotics of the static
topological charge correlator together with the topological susceptibility to
probe the interplay between the restoration and the chiral restoration
in finite temperature QCD. The relevance of these results to the bulk
thermodynamics in the instanton vacuum is discussed.Comment: 18 Page
The Neutron Electric Dipole Moment in the Instanton Vacuum: Quenched Versus Unquenched Simulations
We investigate the role played by the fermionic determinant in the evaluation
of the CP-violating neutron electric dipole moment (EDM) adopting the Instanton
Liquid Model. Significant differences between quenched and unquenched
calculations are found. In the case of unquenched simulations the neutron EDM
decreases linearly with the quark mass and is expected to vanish in the chiral
limit. On the contrary, within the quenched approximation, the neutron EDM
increases as the quark mass decreases and is expected to diverge as (1/m)**Nf
in the chiral limit. We argue that such a qualitatively different behavior is a
parameter-free, semi-classical prediction and occurs because the neutron EDM is
sensitive to the topological structure of the vacuum. The present analysis
suggests that quenched and unquenched lattice QCD simulations of the neutron
EDM as well as of other observables governed by topology might show up
important differences in the quark mass dependence, for mq < Lambda(QCD).Comment: 8 pages, 3 figures, 2 table
Extraction of radiative decay width for the non-strange partner of Theta^+
Using the results of the GRAAL collaboration on the \eta photoproduction from
the neutron target, we attempt to extract the partial radiative width of the
possible new nucleon resonance N^*(1675). The obtained estimates support this
resonance to be a very attractive candidate for the non-strange member of the
exotic antidecuplet of baryons -- a partner of the \Theta^+ pentaquark. Our
phenomenological value for the transition magnetic moment \mu(n^* n), appears
to be in good agreement with predictions of the Chiral Quark Soliton Model.Comment: 4 pages, v2 corresponds to the journal publicatio
Scattering Through QCD Sphalerons
Diffractive parton-parton scattering in the soft pomeron regime can be
explained by the production of a QCD sphaleron. Sphaleron production results
into the emission of gluons and quarks. At RHIC we expect many
sphalerons to be released thereby affecting most prompt processes.Comment: Contribution to quark matter 200
Trying to understand confinement in the Schroedinger picture
We study the gauge-invariant gaussian ansatz for the vacuum wave functional
and show that it potentially possesses many desirable features of the
Yang--Mills theory, like asymptotic freedom, mass generation through the
transmutation of dimensions and a linear potential between static quarks. We
point out that these (and other) features can be studied in a systematic way by
combining perturbative and 1/n expansions. Contrary to the euclidean approach,
confinement can be easily formulated and easily built in, if not derived, in
the variational Schroedinger approach.Comment: 21 pages, 1 figure. Lecture given at the 4th St.Petersburg Winter
School in Theoretical Physics, Feb. 22-28, 199
Spin-dependent twist-4 matrix elements from the instanton vacuum: Flavor-singlet and nonsinglet
We estimate the twist-4 spin-1 nucleon matrix element f_2 in an
instanton-based description of the QCD vacuum. In addition to the
flavor-nonsinglet we compute also the flavor-singlet matrix element, which
appears in next-to-leading order of the (1/N_c)-expansion. The corresponding
twist-3 spin-2 matrix elements d_2 are suppressed in the packing fraction of
the instanton medium, (\bar \rho)/(\bar R) << 1. We use our results to estimate
the leading (1/Q^2) power corrections to the first moment of the proton and
neutron spin structure functions G_1, as well as the intrinsic charm
contribution to the nucleon spin.Comment: 17 pages, 4 eps figures include
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