4,213 research outputs found
A luminosity monitor for the A4 parity violation experiment at MAMI
A water Cherenkov luminosity monitor system with associated electronics has
been developed for the A4 parity violation experiment at MAMI. The detector
system measures the luminosity of the hydrogen target hit by the MAMI electron
beam and monitors the stability of the liquid hydrogen target. Both is required
for the precise study of the count rate asymmetries in the scattering of
longitudinally polarized electrons on unpolarized protons. Any helicity
correlated fluctuation of the target density leads to false asymmetries. The
performance of the luminosity monitor, investigated in about 2000 hours with
electron beam, and the results of its application in the A4 experiment are
presented.Comment: 22 pages, 12 figures, submitted to NIM
The No-Pole Condition in Landau gauge: Properties of the Gribov Ghost Form-Factor and a Constraint on the 2d Gluon Propagator
We study the Landau-gauge Gribov ghost form-factor sigma(p^2) for SU(N)
Yang-Mills theories in the d-dimensional case. We find a qualitatively
different behavior for d=3,4 w.r.t. d=2. In particular, considering any
(sufficiently regular) gluon propagator D(p^2) and the one-loop-corrected ghost
propagator G(p^2), we prove in the 2d case that sigma(p^2) blows up in the
infrared limit p -> 0 as -D(0)\ln(p^2). Thus, for d=2, the no-pole condition
\sigma(p^2) 0) can be satisfied only if D(0) = 0. On the
contrary, in d=3 and 4, sigma(p^2) is finite also if D(0) > 0. The same results
are obtained by evaluating G(p^2) explicitly at one loop, using fitting forms
for D(p^2) that describe well the numerical data of D(p^2) in d=2,3,4 in the
SU(2) case. These evaluations also show that, if one considers the coupling
constant g^2 as a free parameter, G(p^2) admits a one-parameter family of
behaviors (labelled by g^2), in agreement with Boucaud et al. In this case the
condition sigma(0) <= 1 implies g^2 <= g^2_c, where g^2_c is a 'critical'
value. Moreover, a free-like G(p^2) in the infrared limit is obtained for any
value of g^2 < g^2_c, while for g^2 = g^2_c one finds an infrared-enhanced
G(p^2). Finally, we analyze the Dyson-Schwinger equation (DSE) for sigma(p^2)
and show that, for infrared-finite ghost-gluon vertices, one can bound
sigma(p^2). Using these bounds we find again that only in the d=2 case does one
need to impose D(0) = 0 in order to satisfy the no-pole condition. The d=2
result is also supported by an analysis of the DSE using a spectral
representation for G(p^2). Thus, if the no-pole condition is imposed, solving
the d=2 DSE cannot lead to a massive behavior for D(p^2). These results apply
to any Gribov copy inside the so-called first Gribov horizon, i.e. the 2d
result D(0) = 0 is not affected by Gribov noise. These findings are also in
agreement with lattice data.Comment: 40 pages, 2 .eps figure
Color-superconductivity in the strong-coupling regime of Landau gauge QCD
The chirally unbroken and the superconducting 2SC and CFL phases are
investigated in the chiral limit within a Dyson-Schwinger approach for the
quark propagator in QCD. The hierarchy of Green's functions is truncated such
that at vanishing density known results for the vacuum and at asymptotically
high densities the corresponding weak-coupling expressions are recovered. The
anomalous dimensions of the gap functions are analytically calculated. Based on
the quark propagator the phase structure is studied, and results for the gap
functions, occupation numbers, coherence lengths and pressure differences are
given and compared with the corresponding expressions in the weak-coupling
regime. At moderate chemical potentials the quasiparticle pairing gaps are
several times larger than the extrapolated weak-coupling results.Comment: 14 pages, 9 figures; v2: one reference adde
Two infrared Yang-Mills solutions in stochastic quantization and in an effective action formalism
Three decades of work on the quantum field equations of pure Yang-Mills
theory have distilled two families of solutions in Landau gauge. Both coincide
for high (Euclidean) momentum with known perturbation theory, and both predict
an infrared suppressed transverse gluon propagator, but whereas the solution
known as "scaling" features an infrared power law for the gluon and ghost
propagators, the "massive" solution rather describes the gluon as a vector
boson that features a finite Debye screening mass.
In this work we examine the gauge dependence of these solutions by adopting
stochastic quantization. What we find, in four dimensions and in a rainbow
approximation, is that stochastic quantization supports both solutions in
Landau gauge but the scaling solution abruptly disappears when the parameter
controlling the drift force is separated from zero (soft gauge-fixing),
recovering only the perturbative propagators; the massive solution seems to
survive the extension outside Landau gauge. These results are consistent with
the scaling solution being related to the existence of a Gribov horizon, with
the massive one being more general.
We also examine the effective action in Faddeev-Popov quantization that
generates the rainbow and we find, for a bare vertex approximation, that the
the massive-type solutions minimise the quantum effective action.Comment: 13 pages, 7 figures. Change of title to reflect version accepted for
publicatio
Інтеграція радіоастрономії України в європейську радіоастрономічну науку
Виступ академіка НАН України О.О. Коноваленка
More on Gribov copies and propagators in Landau-gauge Yang-Mills theory
Fixing a gauge in the non-perturbative domain of Yang-Mills theory is a
non-trivial problem due to the presence of Gribov copies. In particular, there
are different gauges in the non-perturbative regime which all correspond to the
same definition of a gauge in the perturbative domain. Gauge-dependent
correlation functions may differ in these gauges. Two such gauges are the
minimal and absolute Landau gauge, both corresponding to the perturbative
Landau gauge. These, and their numerical implementation, are described and
presented in detail. Other choices will also be discussed.
This investigation is performed, using numerical lattice gauge theory
calculations, by comparing the propagators of gluons and ghosts for the minimal
Landau gauge and the absolute Landau gauge in SU(2) Yang-Mills theory. It is
found that the propagators are different in the far infrared and even at energy
scales of the order of half a GeV. In particular, also the finite-volume
effects are modified. This is observed in two and three dimensions. Some
remarks on the four-dimensional case are provided as well.Comment: 23 pages, 16 figures, 6 tables; various changes throughout most of
the paper; extended discussion on different possibilities to define the
Landau gauge and connection to existing scenarios; in v3: Minor changes,
error in eq. (3) & (4) corrected, version to appear in PR
Gluons at finite temperature in Landau gauge Yang--Mills theory
The infrared behavior of Yang-Mills theory at finite temperature provides
access to the role of confinement. In this review recent results on this topic
from lattice calculations and especially Dyson-Schwinger studies are discussed.
These indicate persistence of a residual confinement even in the
high-temperature phase. The confinement mechanism is very similar to the one in
the vacuum for the chromomagnetic sector. In the chromoelectric sector
screening occurs at the soft scale g^2T, although not leading to a perturbative
behavior.Comment: 15 pages, 4 figures, invited brief review for MPL
Pengaruh Pupuk Majemuk NPK + Zn terhadap Pertumbuhan, Produksi dan Serapan Zn Padi Sawah di Vertisol, Sragen
Vertisol is a soil that has neutral to slightly alkaline pH. Zinc availability decreases with increasing pH. The existence of symptoms micronutrients scarcity, especially zinc, also caused by the use of highly yielding seeds with unbalanced fertilization. In addition, Zn uptake by plants is sustainability process which resulted in a decrease in nutrient levels of Zn in the root zone. The aim of the research was to determine the optimum Zn formula that can be added to the NPK compound fertilizer and to determine the effectiveness of the fertilizer on the growth and yield of rice. The experiment was arranged by completely randomized block design with 10 treatments and 3 replicates of each treatment. NPK compound fertilizer dose was given 300kg / ha. The result of this study showed that the compound fertilizer NPK + Zn had no effect on plant height, number of tillers and weight of the plant. The additional dose compound of 2% Zn to the dose of compound fertilizer NPK + Zn did not increase the yield. There was a tendency NPK treatment +0.75% Zn deliver the highest results. NPK compound fertilizer application + Zn significantly increased the uptake of Zn
Nontrivial ghost-gluon vertex and the match of RGZ, DSE and lattice Yang-Mills propagators
Either by solving the ghost propagator DSE or through a one-loop computation
in the RGZ (Refined Gribov-Zwanziger) formalism, we show that a non-trivial
ghost-gluon vertex is anyhow required to obtain a ghost propagator prediction
compatible with the available corresponding lattice data in the SU(3) case. For
the necessary gluon propagator input, we present RGZ tree level fits which
account well for the gluon lattice data. Interestingly, this propagator can be
rewritten in terms of a running gluon mass. A comparison of both DSE and RGZ
results for the ghost propagator is furthermore provided. We also briefly
discuss the connection between the RGZ and the OPE gluon condensate.Comment: 21 pages, 3 figure
Chiral and deconfinement transition from correlation functions: SU(2) vs. SU(3)
We study a gauge invariant order parameter for deconfinement and the chiral
condensate in SU(2) and SU(3) Yang-Mills theory in the vicinity of the
deconfinement phase transition using the Landau gauge quark and gluon
propagators. We determine the gluon propagator from lattice calculations and
the quark propagator from its Dyson-Schwinger equation, using the gluon
propagator as input. The critical temperature and a deconfinement order
parameter are extracted from the gluon propagator and from the dependency of
the quark propagator on the temporal boundary conditions. The chiral transition
is determined using the quark condensate as order parameter. We investigate
whether and how a difference in the chiral and deconfinement transition between
SU(2) and SU(3) is manifest.Comment: 15 pages, 9 figures. For clarification one paragraph and two
references added in the introduction and two sentences at the end of the
first and last paragraph of the summary. Appeared in EPJ
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