16 research outputs found
Quark induced excitations of the instanton liquid
The selfconsistent approach to the quark interactions in the instanton liquid
is developed within the tadpole approximation calculating the basic functional
integral. The effective Lagrangian obtained includes colourless scalar field
interacting with quarks. The origin of this dynamical field as an interaction
carrier in soft momentum region is discussed.Comment: 17 pages, 1 figure ps.file. Slightly revised improved versio
Instanton vacuum at finite density of quark matter
We study light quark interactions in the instanton liquid at finite
quark/baryon number density analyzing chiral and diquark condensates and
investigate the behaviors of quark dynamical mass and both condensates together
with instanton liquid density as a function of quark chemical potential. We
conclude the quark impact (estimated in the tadpole approximation) on the
instanton liquid could shift color superconducting phase transition to higher
values of the chemical potential bringing critical quark matter density to the
values essentially higher than conventional nuclear one.Comment: Lattice 2001 (Non-zero temperature and density), 3 pages, 4 figure
Chiral Lagrangian with confinement from the QCD Lagrangian
An effective Lagrangian for the light quark in the field of a static source
is derived systematically using the exact field correlator expansion. The
lowest Gaussian term is bosonized using nonlocal colorless bosonic fields and a
general structure of effective chiral Lagrangian is obtained containing all set
of fields. The new and crucial result is that the condensation of scalar
isoscalar field which is a usual onset of chiral symmetry breaking and is
constant in space-time, assumes here the form of the confining string and
contributes to the confining potential, while the rest bosonic fields describe
mesons with the q\bar q quark structure and pseudoscalars play the role of
Nambu-Goldstone fields. Using derivative expansion the effective chiral
Lagrangian is deduced containing both confinement and chiral effects for
heavy-light mesons. The pseudovector quark coupling constant is computed to be
exactly unity in the local limit,in agreement with earlier large N_c arguments.Comment: LaTeX2e, 17 page
High-frequency hopping conductivity in the quantum Hall effect regime: Acoustical studies
The high-frequency conductivity of Si delta-doped GaAs/AlGaAs
heterostructures is studied in the integer quantum Hall effect (QHE) regime,
using acoustic methods. Both the real and the imaginary parts of the complex
conductivity are determined from the experimentally observed magnetic field and
temperature dependences of the velocity and the attenuation of a surface
acoustic wave. It is demonstrated that in the structures studied the mechanism
of low-temperature conductance near the QHE plateau centers is hopping. It is
also shown that at magnetic fields corresponding to filling factors 2 and 4,
the doped Si delta- layer efficiently shunts the conductance in the
two-dimensional electron gas (2DEG) channel. A method to separate the two
contributions to the real part of the conductivity is developed, and the
localization length in the 2DEG channel is estimated.Comment: 8pages, 9 figure
Skewed and double distributions in pion and nucleon
We study the non-forward matrix elements of twist-2 QCD light-ray operators
and their representations in terms of skewed and double distributions,
considering the pion as well as the nucleon. We point out the importance of
explicitly including all twist-2 structures in the double distribution
representation, which naturally leads to a ``two-component'' structure of the
skewed distribution, with different contributions in the regions |X| > xi/2 and
|X| < \xi/2. We compute the skewed and double quark distributions in the pion
at a low normalization point in the effective chiral theory based on the
instanton vacuum. Also, we derive the crossing relations expressing the skewed
quark distribution in the pion through the distribution amplitude for two--pion
production. Measurement of the latter in two-pion production in gamma^* gamma
and gamma^* N reactions could provide direct information about the skewed as
well as the usual quark/antiquark-distribution in the pion.Comment: 37 pages, LaTeX. 5 figures included using eps
Search for the radiative decay in the SND experiment at VEPP-2M
The decay was investigated by the SND detector
at VEPP-2M collider in the reaction .
Here we present the results and some details of this study. We report an upper
limit (90% c.l.) as our
final result. Our upper limit does not contradict the earlier measurement by
GAMS spectrometer. To facilitate future studies a rather detailed review of the
problem is also given.Comment: 24 pages, 6 figures, LaTex. To be published in Nucl. Phys.
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.
Transversity Form Factors and Generalized Parton Distributions of the pion in chiral quark models
The transversity Generalized Parton Distributions (tGPDs) and related
transversity form factors of the pion are evaluated in chiral quark models,
both local (Nambu--Jona-Lasinio) and nonlocal, involving a momentum-dependent
quark mass. The obtained tGPDs satisfy all a priori formal requirements, such
as the proper support, normalization, and polynomiality. We evaluate
generalized transversity form factors accessible from the recent lattice QCD
calculations. These form factors, after the necessary QCD evolution, agree very
well with the lattice data, confirming the fact that the spontaneously broken
chiral symmetry governs the structure of the pion also in the case of the
transversity observables.Comment: 6 pages, 3 figures, presented by WB at LIGHTCONE 2011, 23 - 27 May,
2011, Dalla
Deconfining Phase Transition as a Matrix Model of Renormalized Polyakov Loops
We discuss how to extract renormalized from bare Polyakov loops in SU(N)
lattice gauge theories at nonzero temperature in four spacetime dimensions.
Single loops in an irreducible representation are multiplicatively renormalized
without mixing, through a renormalization constant which depends upon both
representation and temperature. The values of renormalized loops in the four
lowest representations of SU(3) were measured numerically on small, coarse
lattices. We find that in magnitude, condensates for the sextet and octet loops
are approximately the square of the triplet loop. This agrees with a large
expansion, where factorization implies that the expectation values of loops in
adjoint and higher representations are just powers of fundamental and
anti-fundamental loops. For three colors, numerically the corrections to the
large relations are greatest for the sextet loop, ; these
represent corrections of for N=3. The values of the renormalized
triplet loop can be described by an SU(3) matrix model, with an effective
action dominated by the triplet loop. In several ways, the deconfining phase
transition for N=3 appears to be like that in the matrix model of
Gross and Witten.Comment: 24 pages, 7 figures; v2, 27 pages, 12 figures, extended discussion
for clarity, results unchange