2,039 research outputs found
Topological Susceptibility of Yang-Mills Center Projection Vortices
The topological susceptibility induced by center projection vortices
extracted from SU(2) lattice Yang-Mills configurations via the maximal center
gauge is measured. Two different smoothing procedures, designed to eliminate
spurious ultraviolet fluctuations of these vortices before evaluating the
topological charge, are explored. They result in consistent estimates of the
topological susceptibility carried by the physical thick vortices
characterizing the Yang-Mills vacuum in the vortex picture. This susceptibility
is comparable to the one obtained from the full lattice Yang-Mills
configurations. The topological properties of the SU(2) Yang-Mills vacuum can
thus be accounted for in terms of its vortex content.Comment: 12 revtex pages, 6 ps figures included using eps
Photon-resolved Floquet theory in open quantum systems
Photon-resolved Floquet theory keeps track of the photon exchange of a
quantum system with a coherent driving field. It thus complements the standard
full-counting statistics that counts the number of photons exchanged with
incoherent photon modes giving rise to dissipation. In this paper, we introduce
a unifying framework describing both situations. We develop methods suitable
for an analytical evaluation of low-order cumulants of photonic probability
distributions. Within this framework we analyze the two-mode Jaynes-Cummings
model to demonstrate that the Photon-resolved Floquet theory and the standard
full-counting statistics make consistent statistical predictions.
Interestingly, we find that the photon-flux fluctuations diverge for vanishing
dissipation, which can be related to an entanglement effect between the driven
matter system and the driving field. To substantiate our results, we use our
framework to describe efficient photon up-conversion in an ac-driven lambda
system, that is characterized by a high signal-to-noise ratio. As the framework
is non-perturbative and predicts fluctuations, it paves the way towards
non-perturbative spectroscopy, which will assist to improve metrological
methods.Comment: 25 pages, 6 figures, 4 appendices. Comments are welcom
The band structure of BeTe - a combined experimental and theoretical study
Using angle-resolved synchrotron-radiation photoemission spectroscopy we have
determined the dispersion of the valence bands of BeTe(100) along ,
i.e. the [100] direction. The measurements are analyzed with the aid of a
first-principles calculation of the BeTe bulk band structure as well as of the
photoemission peaks as given by the momentum conserving bulk transitions.
Taking the calculated unoccupied bands as final states of the photoemission
process, we obtain an excellent agreement between experimental and calculated
spectra and a clear interpretation of almost all measured bands. In contrast,
the free electron approximation for the final states fails to describe the BeTe
bulk band structure along properly.Comment: 21 pages plus 4 figure
Nucleon Generalized Parton Distributions from Full Lattice QCD
We present a comprehensive study of the lowest moments of nucleon generalized
parton distributions in N_f=2+1 lattice QCD using domain wall valence quarks
and improved staggered sea quarks. Our investigation includes helicity
dependent and independent generalized parton distributions for pion masses as
low as 350 MeV and volumes as large as (3.5 fm)^3, for a lattice spacing of
0.124 fm. We use perturbative renormalization at one-loop level with an
improvement based on the non-perturbative renormalization factor for the axial
vector current, and only connected diagrams are included in the isosinglet
channel.Comment: 40 pages, 49 figures; Revised chiral extrapolations in sections A-K,
main conclusions unchange
Evidence for fine tuning of fermionic modes in lattice gluodynamics
We consider properties of zero and near-zero fermionic modes in lattice
gluodynamics. The modes are known to be sensitive to the topology of the
underlying gluonic fields in the quantum vacuum state of the gluodynamics. We
find evidence that these modes are fine tuned, that is exhibit sensitivity to
both physical (one can say, hadronic) scale and to the ultraviolet cutoff.
Namely, the density of the states is in physical units while the localization
volume of the modes tends to zero in physical units with the lattice spacing
tending to zero. We discuss briefly possible theoretical implications and also
include some general, review-type remarks.Comment: 7 pages, 7 eps figures, uses JETP Letters style (included);
substantial stylistic changes, discussions added, conclusions unchanged.
Supplementary materials and computer animations are available at
http://lattice.itep.ru/overla
Remarks on the Gribov Problem in Direct Maximal Center Gauge
We review the equivalence of maximal center gauge fixing to the problem of
finding the best fit, to a given lattice gauge field, by a thin vortex
configuration. This fit is necessarily worst at the location of P-plaquettes.
We then compare the fits achieved in Gribov copies generated by (i)
over-relaxation; (ii) over-relaxation after Landau gauge preconditioning; and
(iii) simulated annealing. Simulated annealing yields the best fit if all links
on the lattice are included, but the situation changes if we consider only the
lattice volume exterior to P-plaquettes. In this exterior region, the fit is
best for Gribov copies generated by over-relaxation, and worst for Gribov
copies generated after Landau gauge preconditioning. The two fitting criteria
(including or not including the P-plaquettes) yield string tensions differing
by -34% to +20% respectively, relative to the full string tension. Our usual
procedure (``quenched minimization'') seems to be a compromise between these
criteria, and yields string tensions at an intermediate value close to the full
string tension.Comment: 14 pages, 6 figure
Polyhedral units and network connectivity in calcium aluminosilicate glasses from high-energy x-ray diffraction
Structure factors for Cax/2AlxSi1-xO2 glasses (x=0,0.25,0.5,0.67) extended to
a wave vector of magnitude Q= 40 1/A have been obtained by high-energy x-ray
diffraction. For the first time, it is possible to resolve the contributions of
Si-O, Al-O and Ca-O coordination polyhedra to the experimental atomic pair
distribution functions (PDF). It has been found that both Si and Al are
four-fold coordinated and so participate in a continuous tetrahedral network at
low values of x. The number of network breaking defects in the form of
non-bridging oxygens (NBO's) increases slowly with x until x=0.5 (NBO's ~ 10%
at x=0.5). By x=0.67 the network breaking defects become significant as
evidenced by the significant drop in the average coordination number of Si. By
contrast, Al-O tetrahedra remain free of NBO's and fully integrated in the
Al/Si-O network for all values of x. Calcium maintains a rather uniform
coordination sphere of approximately 5 oxygen atoms for all values of x. The
results suggest that not only Si/Al-O tetrahedra but Ca-O polyhedra, too, play
a role in determining the glassy structure
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