12,533 research outputs found
Star formation in a diffuse high-altitude cloud?
A recent discovery of two stellar clusters associated with the diffuse
high-latitude cloud HRK 81.4-77.8 has important implications for star formation
in the Galactic halo. We derive a plausible distance estimate to HRK 81.4-77.8
primarily from its gaseous properties. We spatially correlate state-of-the-art
HI, far-infrared and soft X-ray data to analyze the diffuse gas in the cloud.
The absorption of the soft X-ray emission from the Galactic halo by HRK
81.4-77.8 is used to constrain the distance to the cloud. HRK 81.4-77.8 is most
likely located at an altitude of about 400 pc within the disk-halo interface of
the Milky Way Galaxy. The HI data discloses a disbalance in density and
pressure between the warm and cold gaseous phases. Apparently, the cold gas is
compressed by the warm medium. This disbalance might trigger the formation of
molecular gas high above the Galactic plane on pc to sub-pc scales.Comment: 6 pages, 4 figures, accepted for publication in Astronomy &
Astrophysic
Chiral Condensate and Short-Time Evolution of QCD(1+1) on the Light-Cone
Chiral condensates in the trivial light-cone vacuum emerge if defined as
short-time limits of fermion propagators. In gauge theories, the necessary
inclusion of a gauge string in combination with the characteristic light-cone
infrared singularities contain the relevant non-perturbative ingredients
responsible for formation of the condensate, as demonstrated for the 't Hooft
model.Comment: 4 pages, Revtex
Parsummable categories as a strictification of symmetric monoidal categories
We prove that the homotopy theory of parsummable categories (as defined by Schwede) with respect to the underlying equivalences of categories is equivalent to the usual homotopy theory of symmetric monoidal categories. In particular, this yields a model of symmetric monoidal categories in terms of categories equipped with a strictly commutative, associative, and unital (but only partially defined) operation
Polyakov Loop Dynamics in the Center Symmetric Phase
A study of the center symmetric phase of SU(2) Yang Mills theory is
presented. Realization of the center symmetry is shown to result from
non-perturbative gauge fixing. Dictated by the center symmetry, this phase
exhibits already at the perturbative level confinement like properties. The
analysis is performed by investigating the dynamics of the Polyakov loops. The
ultralocality of these degrees of freedom implies significant changes in the
vacuum structure of the theory. General properties of the confined phase and of
the transition to the deconfined phase are discussed. Perturbation theory built
upon the vacuum of ultralocal Polyakov loops is presented and used to
calculate, via the Polyakov loop correlator, the static quark-antiquark
potential.Comment: 45 pages, LaTeX, 8 figure
Color screening in a constituent quark model of hadronic matter
The effect of color screening on the formation of a heavy quark-antiquark
() bound state--such as the meson--is studied using a
constituent-quark model. The response of the nuclear medium to the addition of
two color charges is simulated directly in terms of its quark constituents via
a string-flip potential that allows for quark confinement within hadrons yet
enables the hadrons to separate without generating unphysical long-range
forces. Medium modifications to the properties of the heavy meson, such as its
energy and its mean-square radius, are extracted by solving Schr\"odinger's
equation for the pair in the presence of a (screened)
density-dependent potential. The density dependence of the heavy-quark
potential is in qualitative agreement with earlier studies of its temperature
dependence extracted from lattice calculations at finite temperature. In the
present model it is confirmed that abrupt changes in the properties of the
-meson in the hadronic medium ({\it plasma}), correlate strongly with
the deconfining phase transition.Comment: 7 pages, 3 figures, submitted to PRC for publication, uses revtex
The Path Integral for 1+1-dimensional QCD
We derive a path integral expression for the transition amplitude in
1+1-dimensional QCD starting from canonically quantized QCD. Gauge fixing after
quantization leads to a formulation in terms of gauge invariant but curvilinear
variables. Remainders of the curved space are Jacobians, an effective
potential, and sign factors just as for the problem of a particle in a box.
Based on this result we derive a Faddeev-Popov like expression for the
transition amplitude avoiding standard infinities that are caused by
integrations over gauge equivalent configurations.Comment: 16 pages, LaTeX, 3 PostScript figures, uses epsf.st
Requirements for contractility in disordered cytoskeletal bundles
Actomyosin contractility is essential for biological force generation, and is
well understood in highly organized structures such as striated muscle.
Additionally, actomyosin bundles devoid of this organization are known to
contract both in vivo and in vitro, which cannot be described by standard
muscle models. To narrow down the search for possible contraction mechanisms in
these systems, we investigate their microscopic symmetries. We show that
contractile behavior requires non-identical motors that generate large enough
forces to probe the nonlinear elastic behavior of F-actin. This suggests a role
for filament buckling in the contraction of these bundles, consistent with
recent experimental results on reconstituted actomyosin bundles.Comment: 10 pages, 6 figures; text shortene
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