113 research outputs found
Conformal Scalar Propagation on the Schwarzschild Black-Hole Geometry
The vacuum activity generated by the curvature of the Schwarzschild
black-hole geometry close to the event horizon is studied for the case of a
massless, conformal scalar field. The associated approximation to the unknown,
exact propagator in the Hartle-Hawking vacuum state for small values of the
radial coordinate above results in an analytic expression which
manifestly features its dependence on the background space-time geometry. This
approximation to the Hartle-Hawking scalar propagator on the Schwarzschild
black-hole geometry is, for that matter, distinct from all other. It is shown
that the stated approximation is valid for physical distances which range from
the event horizon to values which are orders of magnitude above the scale
within which quantum and backreaction effects are comparatively pronounced. An
expression is obtained for the renormalised in the
Hartle-Hawking vacuum state which reproduces the established results on the
event horizon and in that segment of the exterior geometry within which the
approximation is valid. In contrast to previous results the stated expression
has the superior feature of being entirely analytic. The effect of the
manifold's causal structure to scalar propagation is also studied.Comment: 34 pages, 2 figures. Published on line on October 16, 2009 and due to
appear in print in Gen.Rel.Gra
Vacuum polarization in two-dimensional static spacetimes and dimensional reduction
We obtain an analytic approximation for the effective action of a quantum
scalar field in a general static two-dimensional spacetime. We apply this to
the dilaton gravity model resulting from the spherical reduction of a massive,
non-minimally coupled scalar field in the four-dimensional Schwarzschild
geometry. Careful analysis near the event horizon shows the resulting
two-dimensional system to be regular in the Hartle-Hawking state for general
values of the field mass, coupling, and angular momentum, while at spatial
infinity it reduces to a thermal gas at the black-hole temperature.Comment: REVTeX 4, 23 pages. Accepted by PRD. Minor modifications from
original versio
Fluctuations of an evaporating black hole from back reaction of its Hawking radiation: Questioning a premise in earlier work
This paper delineates the first steps in a systematic quantitative study of
the spacetime fluctuations induced by quantum fields in an evaporating black
hole. We explain how the stochastic gravity formalism can be a useful tool for
that purpose within a low-energy effective field theory approach to quantum
gravity. As an explicit example we apply it to the study of the
spherically-symmetric sector of metric perturbations around an evaporating
black hole background geometry. For macroscopic black holes we find that those
fluctuations grow and eventually become important when considering sufficiently
long periods of time (of the order of the evaporation time), but well before
the Planckian regime is reached. In addition, the assumption of a simple
correlation between the fluctuations of the energy flux crossing the horizon
and far from it, which was made in earlier work on spherically-symmetric
induced fluctuations, is carefully analyzed and found to be invalid. Our
analysis suggests the existence of an infinite amplitude for the fluctuations
of the horizon as a three-dimensional hypersurface. We emphasize the need for
understanding and designing operational ways of probing quantum metric
fluctuations near the horizon and extracting physically meaningful information.Comment: 10 pages, REVTeX; minor changes, a few references added and a brief
discussion of their relevance included. To appear in the proceedings of the
10th Peyresq meeting. Dedicated to Rafael Sorkin on the occasion of his 60th
birthda
Analytical approximation of the stress-energy tensor of a quantized scalar field in static spherically symmetric spacetimes
Analytical approximations for and of a
quantized scalar field in static spherically symmetric spacetimes are obtained.
The field is assumed to be both massive and massless, with an arbitrary
coupling to the scalar curvature, and in a zero temperature vacuum state.
The expressions for and are divided into
low- and high-frequency parts. The contributions of the high-frequency modes to
these quantities are calculated for an arbitrary quantum state. As an example,
the low-frequency contributions to and are
calculated in asymptotically flat spacetimes in a quantum state corresponding
to the Minkowski vacuum (Boulware quantum state). The limits of the
applicability of these approximations are discussed.Comment: revtex4, 17 pages; v2: three references adde
Some general properties of the renormalized stress-energy tensor for static quantum states on (n+1)-dimensional spherically symmetric black holes
We study the renormalized stress-energy tensor (RSET) for static quantum
states on (n+1)-dimensional, static, spherically symmetric black holes. By
solving the conservation equations, we are able to write the stress-energy
tensor in terms of a single unknown function of the radial co-ordinate, plus
two arbitrary constants. Conditions for the stress-energy tensor to be regular
at event horizons (including the extremal and ``ultra-extremal'' cases) are
then derived using generalized Kruskal-like co-ordinates. These results should
be useful for future calculations of the RSET for static quantum states on
spherically symmetric black hole geometries in any number of space-time
dimensions.Comment: 9 pages, no figures, RevTeX4, references added, accepted for
publication in General Relativity and Gravitatio
Method to compute the stress-energy tensor for the massless spin 1/2 field in a general static spherically symmetric spacetime
A method for computing the stress-energy tensor for the quantized, massless,
spin 1/2 field in a general static spherically symmetric spacetime is
presented. The field can be in a zero temperature state or a non-zero
temperature thermal state. An expression for the full renormalized
stress-energy tensor is derived. It consists of a sum of two tensors both of
which are conserved. One tensor is written in terms of the modes of the
quantized field and has zero trace. In most cases it must be computed
numerically. The other tensor does not explicitly depend on the modes and has a
trace equal to the trace anomaly. It can be used as an analytic approximation
for the stress-energy tensor and is equivalent to other approximations that
have been made for the stress-energy tensor of the massless spin 1/2 field in
static spherically symmetric spacetimes.Comment: 34 pages, no figure
Collider and Dark Matter Searches in Models with Mixed Modulus-Anomaly Mediated SUSY Breaking
We investigate the phenomenology of supersymmetric models where moduli fields
and the Weyl anomaly make comparable contributions to SUSY breaking effects in
the observable sector of fields. This mixed modulus-anomaly mediated
supersymmetry breaking (MM-AMSB) scenario is inspired by models of string
compactification with fluxes, which have been shown to yield a de Sitter vacuum
(as in the recent construction by Kachru {\it et al}). The phenomenology
depends on the so-called modular weights which, in turn, depend on the location
of various fields in the extra dimensions. We find that the model with zero
modular weights gives mass spectra characterized by very light top squarks
and/or tau sleptons, or where M_1\sim -M_2 so that the bino and wino are
approximately degenerate. The top squark mass can be in the range required by
successful electroweak baryogenesis. The measured relic density of cold dark
matter can be obtained via top squark co-annihilation at low \tan\beta, tau
slepton co-annihilation at large \tan\beta or via bino-wino coannihilation.
Then, we typically find low rates for direct and indirect detection of
neutralino dark matter. However, essentially all the WMAP-allowed parameter
space can be probed by experiments at the CERN LHC, while significant portions
may also be explored at an e^+e^- collider with \sqrt{s}=0.5--1 TeV. We also
investigate a case with non-zero modular weights. In this case,
co-annihilation, A-funnel annihilation and bulk annihilation of neutralinos are
all allowed. Results for future colliders are qualitatively similar, but
prospects for indirect dark matter searches via gamma rays and anti-particles
are somewhat better.Comment: 38 pages including 22 EPS figures; latest version posted to conform
with published versio
Reach of the Fermilab Tevatron for minimal supergravity in the region of large scalar masses
The reach of the Fermilab Tevatron for supersymmetric matter has been
calculated in the framework of the minimal supergravity model in the clean
trilepton channel. Previous analyses of this channel were restricted to scalar
masses m_0<= 1 TeV. We extend the analysis to large values of scalar masses
m_0\sim 3.5 TeV. This includes the compelling hyperbolic branch/focus point
(HB/FP) region, where the superpotential \mu parameter becomes small. In this
region, assuming a 5\sigma (3\sigma) signal with 10 (25) fb^{-1} of integrated
luminosity, the Tevatron reach in the trilepton channel extends up to
m_{1/2}\sim 190 (270) GeV independent of \tan\beta . This corresponds to a
reach in terms of the gluino mass of m_{\tg}\sim 575 (750) GeV.Comment: 11 page latex file including 6 EPS figures; several typos corrected
and references adde
4pi Models of CMEs and ICMEs
Coronal mass ejections (CMEs), which dynamically connect the solar surface to
the far reaches of interplanetary space, represent a major anifestation of
solar activity. They are not only of principal interest but also play a pivotal
role in the context of space weather predictions. The steady improvement of
both numerical methods and computational resources during recent years has
allowed for the creation of increasingly realistic models of interplanetary
CMEs (ICMEs), which can now be compared to high-quality observational data from
various space-bound missions. This review discusses existing models of CMEs,
characterizing them by scientific aim and scope, CME initiation method, and
physical effects included, thereby stressing the importance of fully 3-D
('4pi') spatial coverage.Comment: 14 pages plus references. Comments welcome. Accepted for publication
in Solar Physics (SUN-360 topical issue
Life path analysis: scaling indicates priming effects of social and habitat factors on dispersal distances
1. Movements of many animals along a life-path can be separated into repetitive ones within home ranges and transitions between home ranges. We sought relationships of social and environmental factors with initiation and distance of transition movements in 114 buzzards Buteo buteo that were marked as nestlings with long-life radio tags.
2. Ex-natal dispersal movements of 51 buzzards in autumn were longer than for 30 later in their first year and than 35 extra-natal movements between home ranges after leaving nest areas. In the second and third springs, distances moved from winter focal points by birds that paired were the same or less than for unpaired birds. No post-nuptial movement exceeded 2 km.
3. Initiation of early ex-natal dispersal was enhanced by presence of many sibs, but also by lack of worm-rich loam soils. Distances travelled were greatest for birds from small broods and with relatively little short grass-feeding habitat near the nest. Later movements were generally enhanced by the absence of loam soils and short grassland, especially with abundance of other buzzards and probable poor feeding habitats (heathland, long grass).
4. Buzzards tended to persist in their first autumn where arable land was abundant, but subsequently showed a strong tendency to move from this habitat.
5. Factors that acted most strongly in ½-km buffers round nests, or round subsequent focal points, usually promoted movement compared with factors acting at a larger scale. Strong relationships between movement distances and environmental characteristics in ½-km buffers, especially during early ex-natal dispersal, suggested that buzzards became primed by these factors to travel far.
6. Movements were also farthest for buzzards that had already moved far from their natal nests, perhaps reflecting genetic predisposition, long-term priming or poor habitat beyond the study area
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