5,599 research outputs found
Stress-energy tensor for a quantised bulk scalar field in the Randall-Sundrum brane model
We calculate the vacuum expectation value of the stress-energy tensor for a
quantised bulk scalar field in the Randall-Sundrum model, and discuss the
consequences of its local behaviour for the self-consistency of the model. We
find that, in general, the stress-energy tensor diverges in the vicinity of the
branes. Our main conclusion is that the stress-energy tensor is sufficiently
complicated that it has implications for the effective potential, or radion
stabilisation, methods that have so far been used.Comment: 16 pages, 3 figures. Minor changes made and references added. To
appear in Phys. Rev.
Wightman function and Casimir densities on AdS bulk with application to the Randall-Sundrum braneworld
Positive frequency Wightman function and vacuum expectation value of the
energy-momentum tensor are computed for a massive scalar field with general
curvature coupling parameter subject to Robin boundary conditions on two
parallel plates located on - dimensional AdS background. The general case
of different Robin coefficients on separate plates is considered. The mode
summation method is used with a combination of a variant of the generalized
Abel-Plana formula for the series over zeros of combinations of cylinder
functions. This allows us to extract manifestly the parts due to the AdS
spacetime without boundaries and boundary induced parts. The asymptotic
behavior of the vacuum densities near the plates and at large distances is
investigated. The vacuum forces acting on the boundaries are presented as a sum
of the self-action and interaction forces. The first one contains well-known
surface divergences and needs further regularization. The interaction forces
between the plates are attractive for Dirichlet scalar. We show that threre is
a region in the space of parameters defining the boundary conditions in which
the interaction forces are repulsive for small distances and attractive for
large distances. An application to the Randall-Sundrum braneworld with
arbitrary mass terms on the branes is discussed.Comment: 26 pages, 6 figures, discussions and figure labels added, accepted
for publication in Nuclear Physics
Casimir effect for scalar fields under Robin boundary conditions on plates
We study the Casimir effect for scalar fields with general curvature coupling
subject to mixed boundary conditions at on one () and two () parallel plates at a distance
from each other. Making use of the generalized Abel-Plana
formula previously established by one of the authors \cite{Sahrev}, the Casimir
energy densities are obtained as functions of and of
,,, respectively. In the case of two parallel plates,
a decomposition of the total Casimir energy into volumic and superficial
contributions is provided. The possibility of finding a vanishing energy for
particular parameter choices is shown, and the existence of a minimum to the
surface part is also observed. We show that there is a region in the space of
parameters defining the boundary conditions in which the Casimir forces are
repulsive for small distances and attractive for large distances. This yields
to an interesting possibility for stabilizing the distance between the plates
by using the vacuum forces.Comment: 21 pages, 8 figures, consideration of the contribution from complex
eigenmodes added, possibility for the stabilization of the distance between
the plates is discussed; accepted for publication in J. Phys.
On the energy-momentum tensor for a scalar field on manifolds with boundaries
We argue that already at classical level the energy-momentum tensor for a
scalar field on manifolds with boundaries in addition to the bulk part contains
a contribution located on the boundary. Using the standard variational
procedure for the action with the boundary term, the expression for the surface
energy-momentum tensor is derived for arbitrary bulk and boundary geometries.
Integral conservation laws are investigated. The corresponding conserved
charges are constructed and their relation to the proper densities is
discussed. Further we study the vacuum expectation value of the energy-momentum
tensor in the corresponding quantum field theory. It is shown that the surface
term in the energy-momentum tensor is essential to obtain the equality between
the vacuum energy, evaluated as the sum of the zero-point energies for each
normal mode of frequency, and the energy derived by the integration of the
corresponding vacuum energy density. As an application, by using the zeta
function technique, we evaluate the surface energy for a quantum scalar field
confined inside a spherical shell.Comment: 25 pages, 2 figures, section and appendix on the surface energy for a
spherical shell are added, references added, accepted for publication in
Phys. Rev.
Wightman function and scalar Casimir densities for a wedge with two cylindrical boundaries
Wightman function, the vacuum expectation values of the field square and the
energy-momentum tensor are investigated for a massive scalar field with general
curvature coupling parameter inside a wedge with two coaxial cylindrical
boundaries. It is assumed that the field obeys Dirichlet boundary condition on
bounding surfaces. The application of a variant of the generalized Abel-Plana
formula enables to extract from the expectation values the contribution
corresponding to the geometry of a wedge with a single shell and to present the
interference part in terms of exponentially convergent integrals. The local
properties of the vacuum are investigated in various asymptotic regions of the
parameters. The vacuum forces acting on the boundaries are presented as the sum
of self-action and interaction terms. It is shown that the interaction forces
between the separate parts of the boundary are always attractive. The
generalization to the case of a scalar field with Neumann boundary condition is
discussed.Comment: 19 pages, 3 figure
Calculating Casimir Energies in Renormalizable Quantum Field Theory
Quantum vacuum energy has been known to have observable consequences since
1948 when Casimir calculated the force of attraction between parallel uncharged
plates, a phenomenon confirmed experimentally with ever increasing precision.
Casimir himself suggested that a similar attractive self-stress existed for a
conducting spherical shell, but Boyer obtained a repulsive stress. Other
geometries and higher dimensions have been considered over the years. Local
effects, and divergences associated with surfaces and edges have been studied
by several authors. Quite recently, Graham et al. have re-examined such
calculations, using conventional techniques of perturbative quantum field
theory to remove divergences, and have suggested that previous self-stress
results may be suspect. Here we show that the examples considered in their work
are misleading; in particular, it is well-known that in two dimensions a
circular boundary has a divergence in the Casimir energy for massless fields,
while for general dimension not equal to an even integer the corresponding
Casimir energy arising from massless fields interior and exterior to a
hyperspherical shell is finite. It has also long been recognized that the
Casimir energy for massive fields is divergent for . These conclusions
are reinforced by a calculation of the relevant leading Feynman diagram in
and three dimensions. There is therefore no doubt of the validity of the
conventional finite Casimir calculations.Comment: 25 pages, REVTeX4, 1 ps figure. Revision includes new subsection 4B
and Appendix, and other minor correction
Local and Global Casimir Energies: Divergences, Renormalization, and the Coupling to Gravity
From the beginning of the subject, calculations of quantum vacuum energies or
Casimir energies have been plagued with two types of divergences: The total
energy, which may be thought of as some sort of regularization of the
zero-point energy, , seems manifestly divergent. And
local energy densities, obtained from the vacuum expectation value of the
energy-momentum tensor, , typically diverge near
boundaries. The energy of interaction between distinct rigid bodies of whatever
type is finite, corresponding to observable forces and torques between the
bodies, which can be unambiguously calculated. The self-energy of a body is
less well-defined, and suffers divergences which may or may not be removable.
Some examples where a unique total self-stress may be evaluated include the
perfectly conducting spherical shell first considered by Boyer, a perfectly
conducting cylindrical shell, and dilute dielectric balls and cylinders. In
these cases the finite part is unique, yet there are divergent contributions
which may be subsumed in some sort of renormalization of physical parameters.
The divergences that occur in the local energy-momentum tensor near surfaces
are distinct from the divergences in the total energy, which are often
associated with energy located exactly on the surfaces. However, the local
energy-momentum tensor couples to gravity, so what is the significance of
infinite quantities here? For the classic situation of parallel plates there
are indications that the divergences in the local energy density are consistent
with divergences in Einstein's equations; correspondingly, it has been shown
that divergences in the total Casimir energy serve to precisely renormalize the
masses of the plates, in accordance with the equivalence principle.Comment: 53 pages, 1 figure, invited review paper to Lecture Notes in Physics
volume in Casimir physics edited by Diego Dalvit, Peter Milonni, David
Roberts, and Felipe da Ros
Systematics of the Relationship between Vacuum Energy Calculations and Heat Kernel Coefficients
Casimir energy is a nonlocal effect; its magnitude cannot be deduced from
heat kernel expansions, even those including the integrated boundary terms. On
the other hand, it is known that the divergent terms in the regularized (but
not yet renormalized) total vacuum energy are associated with the heat kernel
coefficients. Here a recent study of the relations among the eigenvalue
density, the heat kernel, and the integral kernel of the operator
is exploited to characterize this association completely.
Various previously isolated observations about the structure of the regularized
energy emerge naturally. For over 20 years controversies have persisted
stemming from the fact that certain (presumably physically meaningful) terms in
the renormalized vacuum energy density in the interior of a cavity become
singular at the boundary and correlate to certain divergent terms in the
regularized total energy. The point of view of the present paper promises to
help resolve these issues.Comment: 19 pages, RevTeX; Discussion section rewritten in response to
referees' comments, references added, minor typos correcte
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p90 ribosomal S6 kinases play a significant role in early gene regulation in the cardiomyocyte response to Gq protein-coupled receptor stimuli, endothelin-1 and α1-adrenergic receptor agonists
Extracellular signal-regulated kinases 1/2 (ERK1/2) and their substrates, p90 ribosomal S6 kinases (RSKs), phosphorylate different transcription factors, contributing differentially to transcriptomic profiles. In cardiomyocytes, ERK1/2 are required for >70% of the transcriptomic response to endothelin-1. Here, we investigated the role of RSKs in the transcriptomic responses to Gq protein-coupled receptor agonists, endothelin-1, phenylephrine (generic α1-adrenergic receptor agonist) and A61603 (α1A-adrenergic receptor selective). Phospho-ERK1/2 and phospho-RSKs appeared in cardiomyocyte nuclei within 2-3 min of stimulation (endothelin-1>a61603≈phenylephrine). All agonists increased nuclear RSK2, but only endothelin-1 increased nuclear RSK1 content. PD184352 (inhibits ERK1/2 activation) and BI-D1870 (inhibits RSKs) were used to dissect the contribution of RSKs to the endothelin-1-responsive transcriptome. Of 213 RNAs upregulated at 1 h, 51% required RSKs for upregulation whereas 29% required ERK1/2 but not RSKs. The transcriptomic response to phenylephrine overlapped with, but was not identical to, endothelin-1. As with endothelin-1, PD184352 inhibited upregulation of most phenylephrine-responsive transcripts, but the greater variation in effects of BI-D1870 suggests that differential RSK signalling influences global gene expression. A61603 induced similar changes in RNA expression in cardiomyocytes as phenylephrine, indicating that the signal was mediated largely through α1A-adrenergic receptors. A61603 also increased expression of immediate early genes in perfused adult rat hearts and, as in cardiomyocytes, upregulation of the majority of genes was inhibited by PD184352. PD184352 or BI-D1870 prevented the increased surface area induced by endothelin-1 in cardiomyocytes. Thus, RSKs play a significant role in regulating cardiomyocyte gene expression and hypertrophy in response to Gq protein-coupled receptor stimulation
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