210 research outputs found
Laplacian modes probing gauge fields
We show that low-lying eigenmodes of the Laplace operator are suitable to
represent properties of the underlying SU(2) lattice configurations. We study
this for the case of finite temperature background fields, yet in the
confinement phase. For calorons as classical solutions put on the lattice, the
lowest mode localizes one of the constituent monopoles by a maximum and the
other one by a minimum, respectively. We introduce adjustable phase boundary
conditions in the time direction, under which the role of the monopoles in the
mode localization is interchanged. Similar hopping phenomena are observed for
thermalized configurations. We also investigate periodic and antiperiodic modes
of the adjoint Laplacian for comparison.
In the second part we introduce a new Fourier-like low-pass filter method. It
provides link variables by truncating a sum involving the Laplacian eigenmodes.
The filter not only reproduces classical structures, but also preserves the
confining potential for thermalized ensembles. We give a first characterization
of the structures emerging from this procedure.Comment: 43 pages, 26 figure
Modelling photometric reverberation data -- a disk-like broad-line region and a potentially larger black hole mass for 3C120
We consider photometric reverberation mapping, where the nuclear continuum
variations are monitored via a broad-band filter and the echo of emission line
clouds of the broad line region (BLR) is measured with a suitable narrow-band
(NB) filter. We investigate how an incomplete emission-line coverage by the NB
filter influences the BLR size determination. This includes two basic cases: 1)
a symmetric cut of the blue and red part of the line wings, and 2) the filter
positioned asymmetrically to the line centre so that essentially a complete
half of the emission line is contained in the NB filter. Under the assumption
that the BLR size is dominated by circular Keplerian orbits, we find that
symmetric cutting of line wings may lead to overestimating the BLR size by less
than 5%. The case of asymmetric half-line coverage, similar as for our data of
the Seyfert 1 galaxy 3C120, yields the BLR size with a bias of less than 1%.
Our results suggest that any BLR size bias due to narrow-band line cut in
photometric reverberation mapping is small and in most cases negligible. We
used well sampled photometric reverberation mapping light curves with sharp
variation features in both the continuum and the Hbeta light curves to
determine the geometry type of the Hbeta BLR for 3C120. Modelling of the light
curve, under the assumption that the BLR is essentially virialised, argues
against a spherical geometry and favours a nearly face-on disk-like geometry
with inclination i = 10 +/- 4 deg and extension from 22 to 28 light days. The
low inclination may lead to a larger black hole mass than the derived when
using the average geometry scaling factor f=5.5. We discuss deviations of
Seyfert 1 galaxies from the M_BH - sigma relation.Comment: 9 pages, 11 figures, accepted for publication in Astronomy and
Astrophysic
Probing for Instanton Quarks with epsilon-Cooling
We use epsilon-cooling, adjusting at will the order a^2 corrections to the
lattice action, to study the parameter space of instantons in the background of
non-trivial holonomy and to determine the presence and nature of constituents
with fractional topological charge at finite and zero temperature for SU(2). As
an additional tool, zero temperature configurations were generated from those
at finite temperature with well-separated constituents. This is achieved by
"adiabatically" adjusting the anisotropic coupling used to implement finite
temperature on a symmetric lattice. The action and topological charge density,
as well as the Polyakov loop and chiral zero-modes are used to analyse these
configurations. We also show how cooling histories themselves can reveal the
presence of constituents with fractional topological charge. We comment on the
interpretation of recent fermion zero-mode studies for thermalized ensembles at
small temperatures.Comment: 26 pages, 14 figures in 33 part
Monopole and vortex content of a meron pair
We investigate the monopole and vortex content of a meron pair by calculating
the points at which the transformation to the Laplacian Center Gauge is
ill-defined and by studying the behavior of Wilson loops. These techniques
reveal complementary aspects of the vortex and monopole structure, including
the presence of closed monopole lines and closed vortex surfaces joining the
two merons, and evidence for intersecting vortex surfaces at each meron.Comment: 14 pages, 5 figures. v2, minor changes, references added, to appear
in PL
Adjoint quarks and fermionic boundary conditions
We study quenched SU(2) lattice gauge theory with adjoint fermions in a wide
range of temperatures. We focus on spectral quantities of the Dirac operator
and use the temporal fermionic boundary conditions as a tool to probe the
system. We determine the deconfinement temperature through the Polyakov loop,
and the chiral symmetry restoration temperature for adjoint fermions through
the gap in the Dirac spectrum. This chiral transition temperature is about four
times larger than the deconfinement temperature. In between the two transitions
we find that the system is characterized by a non-vanishing chiral condensate
which differs for periodic and anti-periodic fermion boundary conditions. Only
for the latter (physical) boundary conditions, the condensate vanishes at the
chiral transition. The behavior between the two transitions suggests that
deconfinement manifests itself as the onset of a dependence of spectral
quantities of the Dirac operator on boundary conditions. This picture is
supported further by our results for the dual chiral condensate.Comment: Minor changes; final version to appear in JHE
The history of Shtokman field development
Let's twist again! The first highly enantioselective asymmetric reaction in which a chiral reaction medium is the sole source of chirality is presented. The azaâBaylisâHillman reaction in an ionic liquid with a chiral anion, whose design is based on mechanistic insights, gave products with up to 84â% ee
Numerical properties of staggered quarks with a taste-dependent mass term
The numerical properties of staggered Dirac operators with a taste-dependent
mass term proposed by Adams [1,2] and by Hoelbling [3] are compared with those
of ordinary staggered and Wilson Dirac operators. In the free limit and on
(quenched) interacting configurations, we consider their topological
properties, their spectrum, and the resulting pion mass. Although we also
consider the spectral structure, topological properties, locality, and
computational cost of an overlap operator with a staggered kernel, we call
attention to the possibility of using the Adams and Hoelbling operators without
the overlap construction. In particular, the Hoelbling operator could be used
to simulate two degenerate flavors without additive mass renormalization, and
thus without fine-tuning in the chiral limit.Comment: 14 pages, 9 figures. V2: published version; important note added
regarding Hoelbling fermions, otherwise minor change
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
Confinement, Chiral Symmetry Breaking, and Axial Anomaly from Domain Formation at Intermediate Resolution
Based on general renormalization group arguments, Polyakov's loop-space
formalism, and recent analytical lattice arguments, suggesting, after Abelian
gauge fixing, a description of pure gluodynamics by means of a Georgi-Glashow
like model, the corresponding vacuum fields are defined in a non-local way.
Using lattice information on the gauge invariant field strength correlator in
full QCD, the resolution scale \La_b, at which these fields become relevant
in the vacuum, is determined. For SU(3) gauge theory it is found that
\La_b\sim 2.4 GeV, 3.1 GeV, and 4.2 GeV for ( MeV), ( MeV), and pure gluodynamics, repectively. Implications for the operator
product expansion of physical correlators are discussed. It is argued that the
emergence of magnetic (anti)monopoles in the vacuum at resolution \La_b is a
direct consequence of the randomness in the formation of a low entropy Higgs
condensate. This implies a breaking of chiral symmetry and a proliferation of
the axial U(1) anomaly at this scale already. Justifying Abelian projection, a
decoupling of non-Abelian gauge field fluctuations from the dynamics occurs.
The condensation of (anti)monopoles at \La_c<\La_b follows from the demand
that vacuum fields ought to have vanishing action at any resolution. As
monopoles condense they are reduced to their cores, and hence they become
massless. Apparently broken gauge symmetries at resolutions \La_c<\La\le\La_b
are restored in this process.Comment: 11 pages, 3 figure
- âŠ