12 research outputs found
Twist-3 Distribute Amplitude of the Pion in QCD Sum Rules
We apply the background field method to calculate the moments of the pion
two-particles twist-3 distribution amplitude (DA) in QCD sum
rules. In this paper,we do not use the equation of motion for the quarks inside
the pion since they are not on shell and introduce a new parameter to
be determined. We get the parameter in this approach. If
assuming the expansion of in the series in Gegenbauer polynomials
, one can obtain its approximate expression which can be
determined by its first few moments.Comment: 12 pages, 3 figure
Direct Instantons in QCD Nucleon Sum Rules
We study the role of direct (i.e. small-scale) instantons in QCD correlation
functions for the nucleon. They generate sizeable, nonperturbative corrections
to the conventional operator product expansion, which improve the quality of
both QCD nucleon sum rules and cure the long-standing stability problem, in
particular, of the chirally odd sum-rule.Comment: 10 pages, UMD PP#93-17
Drell-Yan diffraction: breakdown of QCD factorisation
We consider the diffractive Drell-Yan process in proton-(anti)proton
collisions at high energies in the color dipole approach. The calculations are
performed at forward rapidities of the leptonic pair. Effect of eikonalization
of the universal "bare"dipole-target elastic amplitude in the saturation regime
takes into account the principal part of the gap survival probability. We
present predictions for the total and differential cross sections of the single
diffractive lepton pair production at RHIC and LHC energies. We analyze
implications of the QCD factorisation breakdown in the diffractive Drell-Yan
process, which is caused by a specific interplay of the soft and hard
interactions, and resulting in rather unusual properties of the corresponding
observables.Comment: 19 pages, 7 figure
The check of QCD based on the tau-decay data analysis in the complex q^2-plane
The thorough analysis of the ALEPH data on hadronic tau-decay is performed in
the framework of QCD. The perturbative calculations are performed in 3 and
4-loop approximations. The terms of the operator product expansion (OPE) are
accounted up to dimension D=8. The value of the QCD coupling constant
alpha_s(m_tau^2)=0.355 pm 0.025 was found from hadronic branching ratio R_tau.
The V+A and V spectral function are analyzed using analytical properties of
polarization operators in the whole complex q^2-plane. Borel sum rules in the
complex q^2 plane along the rays, starting from the origin, are used. It was
demonstrated that QCD with OPE terms is in agreement with the data for the
coupling constant close to the lower error edge alpha_s(m_tau^2)=0.330. The
restriction on the value of the gluonic condensate was found
=0.006 pm 0.012 GeV^2. The analytical perturbative QCD was
compared with the data. It is demonstrated to be in strong contradiction with
experiment. The restrictions on the renormalon contribution were found. The
instanton contributions to the polarization operator are analyzed in various
sum rules. In Borel transformation they appear to be small, but not in spectral
moments sum rules.Comment: 24 pages; 1 latex + 13 figure files. V2: misprints are corrected,
uncertainty in alpha_s is explained in more transparent way, acknowledgement
is adde
Vacuum condensates and the pion wave functions in the nonlocal chiral model
We use the simple instanton motivated Nambu Jona-Lasinio - type model to
calculate a twist 3 pseudoscalar pion light cone wave function. Using
normalisation condition for this wave function we calculate the quark
condensate and also the gluon condensate, which agree with the phenomenological
values for these quantities. Since we can compute also the k_T^2 dependence of
the light cone wave functions, we calculate k_T^2 moments of the pseudo-scalar
and axial-vector wave functions which are related to the mixed vacuum
condensates. This allows us to extract the condensates and compare them with
existing estimates.Comment: 12 pages, 7 figures; three new paragraphs added: one (in sec. IV)
discusses the relation between quark and gluon condensates, the other two (in
secs. I and VI) clarify the difference between the normalisation scale Q_0,
at which the condensates are evaluated, and the model parameter Lambda; new
references added; to be published in Phys. Rev.
The Chiral Magnetic Effect and Axial Anomalies
We give an elementary derivation of the chiral magnetic effect based on a
strong magnetic field lowest-Landau-level projection in conjunction with the
well-known axial anomalies in two- and four-dimensional space-time. The
argument is general, based on a Schur decomposition of the Dirac operator. In
the dimensionally reduced theory, the chiral magnetic effect is directly
related to the relativistic form of the Peierls instability, leading to a
spiral form of the condensate, the chiral magnetic spiral. We then discuss the
competition between spin projection, due to a strong magnetic field, and
chirality projection, due to an instanton, for light fermions in QCD and QED.
The resulting asymmetric distortion of the zero modes and near-zero modes is
another aspect of the chiral magnetic effect.Comment: 33 pages, 5 figures, to appear in Lect. Notes Phys. "Strongly
interacting matter in magnetic fields" (Springer), edited by D. Kharzeev, K.
Landsteiner, A. Schmitt, H.-U. Ye
Effects of mesoscale eddies in the active mixed layer: test of the parametrisation in eddy resolving simulations
In eddy resolving simulations, we test a mixed layer mesoscale parametrisation, developed recently by Canuto and Dubovikov [Ocean Model., 2011, 39, 200–207]. With no adjustable parameters, the parametrisation yields the horizontal and vertical mesoscale fluxes in terms of coarse-resolution fields and eddy kinetic energy (EKE). We compare terms of the parametrisation diagnosed from coarse-grained fields with the eddy mesoscale fluxes diagnosed directly from the high resolution model. An expression for the EKE in terms of mean fields has also been found to get a closed parametrisation in terms of the mean fields only. In 40 numerical experiments we simulated two types of flows: idealised flows driven by baroclinic instabilities only, and more realistic flows, driven by wind and surface fluxes as well as by inflow-outflow. The diagnosed quasi-instantaneous horizontal and vertical mesoscale buoyancy fluxes (averaged over – and 10 days) demonstrate a strong scatter typical for turbulent flows, however, the fluxes are positively correlated with the parametrisation with higher () correlations at the experiments with larger baroclinic radius Rossby. After being averaged over 3–4 months, diffusivities diagnosed from the eddy resolving simulations are consistent with the parametrisation for a broad range of parameters. Diagnosed vertical mesoscale fluxes restratify mixed layer and are in a good agreement with the parametrisation unless vertical turbulent mixing in the upper layer becomes strong enough in comparison with mesoscale advection. In the latter case, numerical simulations demonstrate that the deviation of the fluxes from the parametrisation is controlled by dimensionless parameter estimating the ratio of vertical turbulent mixing term to mesoscale advection. An analysis using a modified -equation reveals that the effects of the vertical mixing of vorticity is responsible for the two–three fold amplification of vertical mesoscale flux. Possible physical mechanisms, responsible for the amplification of vertical mesoscale flux are discussed