3,535 research outputs found
Absolute conservation law for black holes
In all 2d theories of gravity a conservation law connects the (space-time
dependent) mass aspect function at all times and all radii with an integral of
the matter fields. It depends on an arbitrary constant which may be interpreted
as determining the initial value together with the initial values for the
matter field. We discuss this for spherically reduced Einstein-gravity in a
diagonal metric and in a Bondi-Sachs metric using the first order formulation
of spherically reduced gravity, which allows easy and direct fixations of any
type of gauge. The relation of our conserved quantity to the ADM and Bondi mass
is investigated. Further possible applications (ideal fluid, black holes in
higher dimensions or AdS spacetimes etc.) are straightforward generalizations.Comment: LaTex, 17 pages, final version, to appear in Phys. Rev.
On General Axial Gauges for QCD
General Axial Gauges within a perturbative approach to QCD are plagued by
'spurious' propagator singularities. Their regularisation has to face major
conceptual and technical problems. We show that this obstacle is naturally
absent within a Wilsonian or 'Exact' Renormalisation Group approach and explain
why this is so. The axial gauge turns out to be a fixed point under the flow,
and the universal 1-loop running of the gauge coupling is computed.Comment: 4 pages, latex, talk presented by DFL at QCD'98, Montpellier, July
2-8, 1998; to be published in Nucl. Phys. B (Proc. Suppl.
Universal conservation law and modified Noether symmetry in 2d models of gravity with matter
It is well-known that all 2d models of gravity---including theories with
nonvanishing torsion and dilaton theories---can be solved exactly, if matter
interactions are absent. An absolutely (in space and time) conserved quantity
determines the global classification of all (classical) solutions. For the
special case of spherically reduced Einstein gravity it coincides with the mass
in the Schwarzschild solution. The corresponding Noether symmetry has been
derived previously by P. Widerin and one of the authors (W.K.) for a specific
2d model with nonvanishing torsion. In the present paper this is generalized to
all covariant 2d theories, including interactions with matter. The related
Noether-like symmetry differs from the usual one. The parameters for the
symmetry transformation of the geometric part and those of the matterfields are
distinct. The total conservation law (a zero-form current) results from a two
stage argument which also involves a consistency condition expressed by the
conservation of a one-form matter ``current''. The black hole is treated as a
special case.Comment: 3
Caveolin-3 differentially orchestrates cholinergic and serotonergic constriction of murine airways
The mechanisms of controlling airway smooth muscle (ASM) tone are of utmost clinical importance as inappropriate constriction is a hallmark in asthma and chronic obstructive pulmonary disease. Receptors for acetylcholine and serotonin, two relevant mediators in this context, appear to be incorporated in specialized, cholesterol-rich domains of the plasma membrane, termed caveolae due to their invaginated shape. The structural protein caveolin-1 partly accounts for anchoring of these receptors. We here determined the role of the other major caveolar protein, caveolin-3 (cav-3), in orchestrating cholinergic and serotonergic ASM responses, utilizing newly generated cav-3 deficient mice. Cav-3 deficiency fully abrogated serotonin-induced constriction of extrapulmonary airways in organ baths while leaving intrapulmonary airways unaffected, as assessed in precision cut lung slices. The selective expression of cav-3 in tracheal, but not intrapulmonary bronchial epithelial cells, revealed by immunohistochemistry, might explain the differential effects of cav-3 deficiency on serotonergic ASM constriction. The cholinergic response of extrapulmonary airways was not altered, whereas a considerable increase was observed in cav-3â -/- intrapulmonary bronchi. Thus, cav-3 differentially organizes serotonergic and cholinergic signaling in ASM through mechanisms that are specific for airways of certain caliber and anatomical position. This may allow for selective and site-specific intervention in hyperreactive states
GdRhSi: An exemplary tetragonal system for antiferromagnetic order with weak in-plane anisotropy
The anisotropy of magnetic properties commonly is introduced in textbooks
using the case of an antiferromagnetic system with Ising type anisotropy. This
model presents huge anisotropic magnetization and a pronounced metamagnetic
transition and is well-known and well-documented both, in experiments and
theory. In contrast, the case of an antiferromagnetic - system with weak
in-plane anisotropy is only poorly documented. We studied the anisotropic
magnetization of the compound GdRhSi and found that it is a perfect
model system for such a weak-anisotropy setting because the Gd ions in
GdRhSi have a pure spin moment of S=7/2 which orders in a simple AFM
structure with . We observed experimentally in a
continuous spin-flop transition and domain effects for field applied along the
- and the -direction, respectively. We applied a mean field model
for the free energy to describe our data and combine it with an Ising chain
model to account for domain effects. Our calculations reproduce the
experimental data very well. In addition, we performed magnetic X-ray
scattering and X-ray magnetic circular dichroism measurements, which confirm
the AFM propagation vector to be and indicate the absence of
polarization on the rhodium atoms
Hawking Radiation for Non-minimally Coupled Matter from Generalized 2D Black Hole Models
It is well known that spherically symmetric reduction of General Relativity
(SSG) leads to non-minimally coupled scalar matter. We generalize (and correct)
recent results to Hawking radiation for a class of dilaton models which share
with the Schwarzschild black hole non-minimal coupling of scalar fields and the
basic global structure. An inherent ambiguity of such models (if they differ
from SSG) is discussed. However, for SSG we obtain the rather disquieting
result of a negative Hawking flux at infinity, if the usual recipe for such
calculations is applied.Comment: 8 page
Comment on: ``Trace anomaly of dilaton coupled scalars in two dimensions''
The trace anomaly for nonminimally coupled scalars in spherically reduced
gravity obtained by Bousso and Hawking (hep-th/9705236) is incorrect. We
explain the reasons for the deviations from our correct (published) result
which is supported by several other recent papers.Comment: 2 page
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