14,444 research outputs found
Essential self-adjointness in one-loop quantum cosmology
The quantization of closed cosmologies makes it necessary to study squared
Dirac operators on closed intervals and the corresponding quantum amplitudes.
This paper proves self-adjointness of these second-order elliptic operators.Comment: 14 pages, plain Tex. An Erratum has been added to the end, which
corrects section
Non-Local Boundary Conditions in Euclidean Quantum Gravity
Non-local boundary conditions for Euclidean quantum gravity are proposed,
consisting of an integro-differential boundary operator acting on metric
perturbations. In this case, the operator P on metric perturbations is of
Laplace type, subject to non-local boundary conditions; by contrast, its
adjoint is the sum of a Laplacian and of a singular Green operator, subject to
local boundary conditions. Self-adjointness of the boundary-value problem is
correctly formulated by looking at Dirichlet-type and Neumann-type realizations
of the operator P, following recent results in the literature. The set of
non-local boundary conditions for perturbative modes of the gravitational field
is written in general form on the Euclidean four-ball. For a particular choice
of the non-local boundary operator, explicit formulae for the boundary-value
problem are obtained in terms of a finite number of unknown functions, but
subject to some consistency conditions. Among the related issues, the problem
arises of whether non-local symmetries exist in Euclidean quantum gravity.Comment: 23 pages, plain Tex. The revised version is much longer, and new
original calculations are presented in section
One-Loop Effective Action for Euclidean Maxwell Theory on Manifolds with Boundary
This paper studies the one-loop effective action for Euclidean Maxwell theory
about flat four-space bounded by one three-sphere, or two concentric
three-spheres. The analysis relies on Faddeev-Popov formalism and
-function regularization, and the Lorentz gauge-averaging term is used
with magnetic boundary conditions. The contributions of transverse,
longitudinal and normal modes of the electromagnetic potential, jointly with
ghost modes, are derived in detail. The most difficult part of the analysis
consists in the eigenvalue condition given by the determinant of a
or matrix for longitudinal and normal modes. It is shown that the
former splits into a sum of Dirichlet and Robin contributions, plus a simpler
term. This is the quantum cosmological case. In the latter case, however, when
magnetic boundary conditions are imposed on two bounding three-spheres, the
determinant is more involved. Nevertheless, it is evaluated explicitly as well.
The whole analysis provides the building block for studying the one-loop
effective action in covariant gauges, on manifolds with boundary. The final
result differs from the value obtained when only transverse modes are
quantized, or when noncovariant gauges are used.Comment: 25 pages, Revte
One-Loop Divergences in Simple Supergravity: Boundary Effects
This paper studies the semiclassical approximation of simple supergravity in
Riemannian four-manifolds with boundary, within the framework of
-function regularization. The massless nature of gravitinos, jointly
with the presence of a boundary and a local description in terms of potentials
for spin , force the background to be totally flat. First, nonlocal
boundary conditions of the spectral type are imposed on spin-
potentials, jointly with boundary conditions on metric perturbations which are
completely invariant under infinitesimal diffeomorphisms. The axial
gauge-averaging functional is used, which is then sufficient to ensure
self-adjointness. One thus finds that the contributions of ghost and gauge
modes vanish separately. Hence the contributions to the one-loop wave function
of the universe reduce to those values resulting from physical modes
only. Another set of mixed boundary conditions, motivated instead by local
supersymmetry and first proposed by Luckock, Moss and Poletti, is also
analyzed. In this case the contributions of gauge and ghost modes do not cancel
each other. Both sets of boundary conditions lead to a nonvanishing
value, and spectral boundary conditions are also studied when two concentric
three-sphere boundaries occur. These results seem to point out that simple
supergravity is not even one-loop finite in the presence of boundaries.Comment: 37 pages, Revtex. Equations (5.2), (5.3), (5.5), (5.7), (5.8) and
(5.13) have been amended, jointly with a few misprint
Single electron transistor strongly coupled to vibrations: Counting Statistics and Fluctuation Theorem
Using a simple quantum master equation approach, we calculate the Full
Counting Statistics of a single electron transistor strongly coupled to
vibrations. The Full Counting Statistics contains both the statistics of
integrated particle and energy currents associated to the transferred electrons
and phonons. A universal as well as an effective fluctuation theorem are
derived for the general case where the various reservoir temperatures and
chemical potentials are different. The first relates to the entropy production
generated in the junction while the second reveals internal information of the
system. The model recovers Franck-Condon blockade and potential applications to
non-invasive molecular spectroscopy are discussed.Comment: extended discussion, to appear in NJ
Modeling Self-Subtraction in Angular Differential Imaging: Application to the HD 32297 Debris Disk
We present a new technique for forward-modeling self-subtraction of spatially
extended emission in observations processed with angular differential imaging
(ADI) algorithms. High-contrast direct imaging of circumstellar disks is
limited by quasi-static speckle noise and ADI is commonly used to suppress
those speckles. However, the application of ADI can result in self-subtraction
of the disk signal due to the disk's finite spatial extent. This signal
attenuation varies with radial separation and biases measurements of the disk's
surface brightness, thereby compromising inferences regarding the physical
processes responsible for the dust distribution. To compensate for this
attenuation, we forward-model the disk structure and compute the form of the
self-subtraction function at each separation. As a proof of concept, we apply
our method to 1.6 and 2.2 micron Keck AO NIRC2 scattered-light observations of
the HD 32297 debris disk reduced using a variant of the "locally optimized
combination of images" (LOCI) algorithm. We are able to recover disk surface
brightness that was otherwise lost to self-subtraction and produce simplified
models of the brightness distribution as it appears with and without
self-subtraction. From the latter models, we extract radial profiles for the
disk's brightness, width, midplane position, and color that are unbiased by
self-subtraction. Our analysis of these measurements indicates a break in the
brightness profile power law at r~110 AU and a disk width that increases with
separation from the star. We also verify disk curvature that displaces the
midplane by up to 30 AU towards the northwest relative to a straight fiducial
midplane.Comment: Accepted for publication in ApJ, 20 pages, 10 figures, 1 tabl
- …