45 research outputs found
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
Bremsstrahlung of a Quark Propagating through a Nucleus
The density of gluons produced in the central rapidity region of a heavy ion
collision is poorly known. We investigate the influence of the effects of
quantum coherence on the transverse momentum distribution of photons and gluons
radiated by a quark propagating through nuclear matter. We describe the case
that the radiation time substantially exceeds the nuclear radius (the relevant
case for RHIC and LHC energies), which is different from what is known as
Landau-Pomeranchuk-Migdal effect corresponding to an infinite medium. We find
suppression of the radiation spectrum at small transverse photon/gluon momentum
k_T, but enhancement for k_T>1GeV. Any nuclear effects vanish for k_T > 10GeV.
Our results allow also to calculate the k_T dependent nuclear effects in prompt
photon, light and heavy (Drell-Yan) dilepton and hadron production.Comment: Appendix A is extended compared to the version to be published in
Phys.Rev.
Low-temperature renormalization group study of uniformly frustrated models for type-II superconductors
We study phase transitions in uniformly frustrated SU(N)-symmetric
-dimensional lattice models describing type-II superconductors
near the upper critical magnetic field . The low-temperature
renormalization-group approach is employed for calculating the beta-function
with an arbitrary rational magnetic frustration. The
phase-boundary line is the ultraviolet-stable fixed point found
from the equation , the corresponding critical exponents being
identical to those of the non-frustrated continuum system. The critical
properties of the SU(N)-symmetric complex Ginzburg-Landau (GL) model are then
examined in dimensions. The possibility of a continuous phase
transition into the mixed state in such a model is suggested.Comment: REVTeX, 12 pages, to appear in the Phys.Rev.
Acoustic Signatures in the Primary Microwave Background Bispectrum
If the primordial fluctuations are non-Gaussian, then this non-Gaussianity
will be apparent in the cosmic microwave background (CMB) sky. With their
sensitive all-sky observation, MAP and Planck satellites should be able to
detect weak non-Gaussianity in the CMB sky. On large angular scale, there is a
simple relationship between the CMB temperature and the primordial curvature
perturbation. On smaller scales; however, the radiation transfer function
becomes more complex. In this paper, we present the angular bispectrum of the
primary CMB anisotropy that uses the full transfer function. We find that the
bispectrum has a series of acoustic peaks that change a sign, and a period of
acoustic oscillations is twice as long as that of the angular power spectrum.
Using a single non-linear coupling parameter to characterize the amplitude of
the bispectrum, we estimate the expected signal-to-noise ratio for COBE, MAP,
and Planck experiments. We find that the detection of the primary bispectrum by
any kind of experiments should be problematic for the simple slow-roll
inflationary scenarios. We compare the sensitivity of the primary bispectrum to
the primary skewness and conclude that when we can compute the predicted form
of the bispectrum, it becomes a ``matched filter'' for detecting the
non-Gaussianity in the data, and much more powerful tool than the skewness. We
also show that MAP and Planck can separate the primary bispectrum from various
secondary bispectra on the basis of the shape difference. The primary CMB
bispectrum is a test of the inflationary scenario, and also a probe of the
non-linear physics in the very early universe.Comment: Submitted to Physical Review D. (v1) letter version [4 pages, 3
figures]. (v2) full paper version including the primary skewness, secondary
bispectra, and the foreground separation [17 pages, 5 figures
Space, Time and Color in Hadron Production Via e+e- -> Z0 and e+e- -> W+W-
The time-evolution of jets in hadronic e+e- events at LEP is investigated in
both position- and momentum-space, with emphasis on effects due to color flow
and particle correlations. We address dynamical aspects of the four
simultanously-evolving, cross-talking parton cascades that appear in the
reaction e+e- -> gamma/Z0 -> W+W- -> q1 q~2 q3 q~4, and compare with the
familiar two-parton cascades in e+e- -> Z0 -> q1 q~2. We use a QCD statistical
transport approach, in which the multiparticle final state is treated as an
evolving mixture of partons and hadrons, whose proportions are controlled by
their local space-time geography via standard perturbative QCD parton shower
evolution and a phenomenological model for non-perturbative parton-cluster
formation followed by cluster decays into hadrons. Our numerical simulations
exhibit a characteristic `inside-outside' evolution simultanously in position
and momentum space. We compare three different model treatments of color flow,
and find large effects due to cluster formation by the combination of partons
from different W parents. In particular, we find in our preferred model a shift
of several hundred MeV in the apparent mass of the W, which is considerably
larger than in previous model calculations. This suggests that the
determination of the W mass at LEP2 may turn out to be a sensitive probe of
spatial correlations and hadronization dynamics.Comment: 52 pages, latex, 18 figures as uu-encoded postscript fil
Purification of molybdenum oxide, growth and characterization of medium size zinc molybdate crystals for the LUMINEU program
The LUMINEU program aims at performing a pilot experiment on neutrinoless
double beta decay of 100Mo using radiopure ZnMoO4 crystals operated as
scintillating bolometers. Growth of high quality radiopure crystals is a
complex task, since there are no commercially available molybdenum compounds
with the required levels of purity and radioactive contamination. This paper
discusses approaches to purify molybdenum and synthesize compound for high
quality radiopure ZnMoO4 crystal growth. A combination of a double sublimation
(with addition of zinc molybdate) with subsequent recrystallization in aqueous
solutions (using zinc molybdate as a collector) was used. Zinc molybdate
crystals up to 1.5 kg were grown by the low-thermal-gradient Czochralski
technique, their optical, luminescent, diamagnetic, thermal and bolometric
properties were tested.Comment: Contribution to Proc. of Int. Workshop on Radiopure Scintillators
RPSCINT 2013, 17-20 September 2013, Kyiv, Ukraine; to be published in EPJ Web
of Conferences; expected to be online in January 2014; 6 pages, 6 figures,
and 3 table
Polarization Signal of Distant Clusters and Reconstruction of Primordial Potential Fluctuations
We examine the polarization signal of the cosmic microwave background
radiation associated with distant clusters.
The polarization is induced by the Thomson scattering of microwave photons
with ionized gas of clusters and contains information of quadrupole temperature
anisotropies observed at the clusters. The three-dimensional map of the signal
are expressed in terms of the spin-weighted harmonics for its angular
dependence. Its radial dependence is expanded perturbatively with respect to
the distances (equivalently redshifts) to the clusters.
The independent information that we can extract out from the map is clarified
explicitly.Comment: 14 pages, 4 figures, to appear in Phys.Rev.
Phase transitions in quantum chromodynamics
The current understanding of finite temperature phase transitions in QCD is
reviewed. A critical discussion of refined phase transition criteria in
numerical lattice simulations and of analytical tools going beyond the
mean-field level in effective continuum models for QCD is presented.
Theoretical predictions about the order of the transitions are compared with
possible experimental manifestations in heavy-ion collisions. Various places in
phenomenological descriptions are pointed out, where more reliable data for
QCD's equation of state would help in selecting the most realistic scenario
among those proposed. Unanswered questions are raised about the relevance of
calculations which assume thermodynamic equilibrium. Promising new approaches
to implement nonequilibrium aspects in the thermodynamics of heavy-ion
collisions are described.Comment: 156 pages, RevTex. Tables II,VIII,IX and Fig.s 1-38 are not included
as postscript files. I would like to ask the requestors to copy the missing
tables and figures from the corresponding journal-referenc
QCD and strongly coupled gauge theories : challenges and perspectives
We highlight the progress, current status, and open challenges of QCD-driven physics, in theory and in experiment. We discuss how the strong interaction is intimately connected to a broad sweep of physical problems, in settings ranging from astrophysics and cosmology to strongly coupled, complex systems in particle and condensed-matter physics, as well as to searches for physics beyond the Standard Model. We also discuss how success in describing the strong interaction impacts other fields, and, in turn, how such subjects can impact studies of the strong interaction. In the course of the work we offer a perspective on the many research streams which flow into and out of QCD, as well as a vision for future developments.Peer reviewe
Existence Result and Approximation of an Optimal Control Problem for the Perona-Malik Equation
We discuss some optimal control problem for the evolutionary Perona-Malik equations with the Neumann boundary condition. The control variable v is taken as a distributed control. The optimal control problem is to minimize the discrepancy between a given distribution u_d in L^2(Omega) and the current system state. Since we cannot expect to have a solution of the original boundary value problem for each admissible control, we make use of a variant of its approximation using the model with fictitious control in coefficients of the principle elliptic operator. We introduce a special family of regularized optimization problems for linear parabolic equations and show that each of these problems is consistent, well-posed, and their solutions allow to attain (in the limit) an optimal solution of the original problem as the parameter of regularization tends to zero