60 research outputs found
Gluon condensate and c-quark mass in pseudoscalar sum rules at 3-loop order
Charmonium sum rules for pseudoscalar 0^{-+} state eta_c(1S) are analyzed
within perturbative QCD and Operator Product Expansion. The perturbative part
of the pseudoscalar correlator is considered at alpha_s^2 order and the
contribution of the gluon condensate is taken into account with alpha_s
correction. The OPE series includes the operators of dimension D=6,8 computed
both in the instanton and factorization model. The method of moments in MS-bar
scheme allows to establish acceptable values of the charm quark mass and gluon
condensate, using the experimental mass of eta_c. In result of the analisys the
charm quark mass is found to be m_c(m_c)=1.26+-0.02 GeV independently of the
condensate value. The sensitivity of the results to various approximations for
the massive 3-loop pseudoscalar correlator is discussed.Comment: 19 pages, 1 latex + 5 eps files. v2: Operators of dimension D=8
included; the condensate restriction relaxed; c-quark mass is found
m_c(m_c)=1.26+-0.02 GeV independently of other sum rules and condensate
value. To appear in JHE
Anomalous Charge Dynamics in the Superconducting State of Underdoped Cuprates
We present fermi liquid expressions for the low temperature behavior of the
superfluid stiffness, explain why they differ from those suggested recently by
Lee and Wen, and discuss their applicability to data on high-
superconductors. We find that a consistent description requires a strong,
doping dependent anisotropy, which affects states near the zone corners much
more strongly than those near the zone diagonals
Pion form factor and QCD sum rules: case of axial current
We present an analysis of QCD sum rules for pion form factor in
next-to-leading order of perturbation theory for the case of axial-vector pion
currents. The theoretical predictions for Q^2-dependence of pion form factor
are in good agreement with available experimental data. It is shown, that NLO
corrections are large in this case and should be taken into account in rigorous
theoretical analysis.Comment: LaTeX file, 10 pages, 5 figures, v2: added check of Ward identity
constrains at Q^2=0, the continuum thresholds are determined to satisfy
F_{\pi}(0)=1 condition with NLO accuracy, what led to \approx 10% reduction
of our numerical estimates, references adde
On the current correlators in QCD at finite temperature
Current correlators in QCD at a finite temperature are considered from
the viewpoint of operator product expansion. It is stressed that at low the
heat bath must be represented by hadronic, and not quark-gluon states. A
possibility to express the results in terms of -dependent resonance masses
is discussed. It is demonstrated that in order the masses do not move and
the only phenomenon which occurs is a parity and isospin mixing.Comment: 6 pages, TPI-MINN-92/64-
Next-to-leading-order temperature corrections to correlators in QCD
Corrections of order to vector and axial current correlators in QCD at
a finite temperature are obtained using dispersion relations for the
amplitudes of deep inelastic scattering on pions. Their relation with the
operator product expansion is presented. An interpretation of the results in
terms of -dependent meson masses is given: masses of and start
to move with temperature in order .Comment: 13 pages, no figures, CERN-TH.7215/94, BUTP-94/
Pion form factor and QCD sum rules: case of pseudoscalar current
We present an analysis of QCD sum rules for pion form factor in
next-to-leading order of perturbation theory for the case of pseudoscalar pion
currents. The essential instanton contribution is reanalysed with account for
present more accurate values of parameters entering Single Instanton
Approximation (SIA). The theoretical curve obtained for Q^2 dependence of pion
form factor is in a good agreement with existing experimental data. To
calculate NLO corrections for double spectral densities we developed an
effective computational technic. The details of the method together with the
results for pion form factor in a more theoretically clean case of axial
interpolating currents will be presented elsewhere.Comment: LaTeX file, 12 pages, 5 figures, uses axodraw.st
Spectral representation and QCD sum rules for nucleon at finite temperature
We examine the problem of constructing spectral representations for two point
correlation functions, needed to write down the QCD sum rules in the medium. We
suggest constructing them from the Feynman diagrams for the correlation
functions. As an example we use this procedure to write the QCD sum rules for
the nucleon current at finite temperature
The first dozen years of the history of ITEP Theoretical Physics Laboratory
The theoretical investigations at ITEP in the years 1945-1958 are reviewed.
There are exposed the most important theoretical results, obtained in the
following branches of physics: 1) the theory of nuclear reactors on thermal
neutrons; 2) the hydrogen bomb project ("Tube" in USSR and "Classical Super" in
USA); 3) radiation theory; ~4) low temperature physics; 5) quantum
electrodynamics and quantum field theories; 6) parity violation in weak
interactions, the theory of -decay and other weak processes; 7) strong
interaction and nuclear physics. To the review are added the English
translations of few papers, originally published in Russian, but unknown (or
almost unknown) to Western readers.Comment: 55 pages, 5 fig
Theoretical description of the ferromagnetic -junctions near the critical temperature
The theory of ferromagnetic Pi-junction near the critical temperature is
presented. It is demonstrated that in the dirty limit the modified Usadel
equation adequately describes the proximity effect in ferromagnets. To provide
the description of an experimentally relevant situation, oscillations of the
Josephson critical current are calculated as a function of ferromagnetic layer
thickness for different transparencies of the superconductor-ferromagnet
interfaces.Comment: 12 pages, 4 figures, submitted to Phys. Rev.
Strong compensation of the quantum fluctuation corrections in clean superconductor
The theory of fluctuation conductivity for an arbitrary impurity
concentration including ultra-clean limit is developed. It is demonstrated that
the formal divergency of the fluctuation density of states contribution
obtained previously for the clean case is removed by the correct treatment of
the non-local ballistic electron scattering. We show that in the ultra-clean
limit () the density-of-states quantum
corrections are canceled by the Maki-Thompson term and only quasi-classical
paraconductivity remains.Comment: 7 pages 2 figure
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