277 research outputs found
Self-force via a Green's function decomposition
The gravitational field of a particle of small mass \mu moving through curved
spacetime is naturally decomposed into two parts each of which satisfies the
perturbed Einstein equations through O(\mu). One part is an inhomogeneous field
which, near the particle, looks like the \mu/r field distorted by the local
Riemann tensor; it does not depend on the behavior of the source in either the
infinite past or future. The other part is a homogeneous field and includes the
``tail term''; it completely determines the self force effects of the particle
interacting with its own gravitational field, including radiation reaction.
Self force effects for scalar, electromagnetic and gravitational fields are all
described in this manner.Comment: PRD, in press. Enhanced emphasis on the equivalence principl
Perturbative Approach to an orbital evolution around a Supermassive black hole
A charge-free, point particle of infinitesimal mass orbiting a Kerr black
hole is known to move along a geodesic. When the particle has a finite mass or
charge, it emits radiation which carries away orbital energy and angular
momentum, and the orbit deviates from a geodesic.
In this paper we assume that the deviation is small and show that the
half-advanced minus half-retarded field surprisingly provides the correct
radiation reaction force, in a time-averaged sense, and determines the orbit of
the particle.Comment: accepted for publication in the Physical Revie
On the application of differences in intrinsic fluctuations of Cherenkov light images for separation of air showers
The sensitivity of ground-based imaging atmospheric Cherenkov gamma-ray
observatories depends critically on the primary particle identification methods
which are used to retain photon-initiated events and suppress the spurious
background produced by cosmic rays. We suggest a new discrimination technique
which utilizes differences in the fluctuations of the light intensity in the
images of showers initiated by photons and those initiated by protons or
heavier nuclei. The database of simulated events for the proposed VERITAS
observatory has been used to evaluate the efficiency of the new technique.
Analysis has been performed for both a single VERITAS imaging telescope, and a
system of these telescopes. We demonstrate that a discrimination efficiency of
> 1.5 - 2.0 can be achieved in addition to traditional background rejection
methods based on image shape parameters.Comment: 17 pages, 9 figures, accepted for publucation in Astropart. Phy
Gauge Problem in the Gravitational Self-Force II. First Post Newtonian Force under Regge-Wheeler Gauge
We discuss the gravitational self-force on a particle in a black hole
space-time. For a point particle, the full (bare) self-force diverges. It is
known that the metric perturbation induced by a particle can be divided into
two parts, the direct part (or the S part) and the tail part (or the R part),
in the harmonic gauge, and the regularized self-force is derived from the R
part which is regular and satisfies the source-free perturbed Einstein
equations. In this paper, we consider a gauge transformation from the harmonic
gauge to the Regge-Wheeler gauge in which the full metric perturbation can be
calculated, and present a method to derive the regularized self-force for a
particle in circular orbit around a Schwarzschild black hole in the
Regge-Wheeler gauge. As a first application of this method, we then calculate
the self-force to first post-Newtonian order. We find the correction to the
total mass of the system due to the presence of the particle is correctly
reproduced in the force at the Newtonian order.Comment: Revtex4, 43 pages, no figure. Version to be published in PR
Palaeozoic petroleum systems of the Irish Sea
This report synthesises the results of the 21CXRM Palaeozoic project in the Irish Sea to
describe the Palaeozoic petroleum systems of that area.
One hydrocarbon play system dominates the basin system: Namurian organic-rich marine
shales (Bowland Shale Formation) generated oil and gas with a peak during maximum burial
of the system in late Jurassic/early Cretaceous time. These hydrocarbons passed to reservoirs
in the Triassic Ormskirk Sandstone (Sherwood Sandstone Group) by way of structures
generated during the Variscan Orogeny and Cenozoic inversion, resulting in the Morecambe,
Hamilton and other gas and oil fields
The Palaeozoic study of the wider Irish Sea area has assessed the potential for more
widespread petroleum systems situated outside the well-known play, particularly within the
Carboniferous.
Within the Main Graben system of the East Irish Sea Basin, Coal Measures strata were
partially removed following Variscan inversion and early Permian uplift. They are not rich in
coals, and not inferred to be a significant source rock. There is some potential in the
Millstone Grit and Yoredale sequences, as some shales (particularly those associated with
marine bands) are known to have high Total Organic Contents. The source rock potential of
shales within the Carboniferous Limestone sequence is poorly constrained by data. A
Devonian source rock is unproven and considered unlikely.
Potential Namurian source rocks, such as the Yoredale Group, have been largely eroded in
the Peel and North Channel basins, considerably reducing their prospectivity, although
terrestrial sequences of equivalent age in the Solway Basin may offer better potential.
The variable seismic data quality at Carboniferous levels and sparsity of deep well control
have led to challenges in interpretation, particularly of the deeper picks. The interpretation of
the surfaces contains a strong model-driven element, evidenced by the onshore relationships
and areas where seismic picks can be made with the greatest confidence. Based upon the
integration of regional seismic mapping with a limited well, source rock and reservoir
property dataset, the most prospective parts of the region, outside the Ormskirk conventional
gas play, are considered to be:
The thick Westphalian sequences preserved in the Eubonia Tilt-Block in Quadrant
109, outside the main Permian-Mesozoic graben system and unaffected by Cenozoic
inversion. The presence and quality of seals form a major risk as the Cumbrian Coast
Group seal is thin or absent and Carboniferous intraformational seals are required but
untested. Based on the limited dataset available in adjacent basins, reservoir quality is
also a significant risk.
A belt of Variscan inversion structures correlated with structures on the Formby
Platform, and Ribbledale Foldbelt onshore, from which hydrocarbons have leaked
into the overlying, Ormskirk-hosted Hamilton fields. The biggest risk here is whether
reservoirs remain unbreached at the Pre-Permian level, and retain good poroperm
characteristics at depths of about 2500 m.
A more speculative play lies in the extensive carbonate platform in Quadrant 109 and
surrounding the Isle of Man, in reefal facies with enhanced secondary porosity. Here,
source rock presence and migration pathways, reservoir properties and seal quality are
major risks
Mass loss by a scalar charge in an expanding universe
We study the phenomenon of mass loss by a scalar charge -- a point particle
that acts a source for a noninteracting scalar field -- in an expanding
universe. The charge is placed on comoving world lines of two cosmological
spacetimes: a de Sitter universe, and a spatially-flat, matter-dominated
universe. In both cases, we find that the particle's rest mass is not a
constant, but that it changes in response to the emission of monopole scalar
radiation by the particle. In de Sitter spacetime, the particle radiates all of
its mass within a finite proper time. In the matter-dominated cosmology, this
happens only if the charge of the particle is sufficiently large; for smaller
charges the particle first loses some of its mass, but then regains it all
eventually.Comment: 11 pages, RevTeX4, Accepted for Phys. Rev.
Seismic interpretation and generation of depth surfaces for Late Palaeozoic strata in the Irish Sea Region
This report describes the methodology and results of a regional seismic interpretation of the
basins of the Irish Sea. It does not review the basins of the Celtic Sea. The aim of the
interpretation was to map the distribution of Palaeozoic basins and highs, interpreting the key
Devonian-Carboniferous surfaces and main structural elements of the area. About 40,000 km
of 2D seismic reflection data have been interpreted and tied to key released wells in the
project area. The seismic and well data were augmented by donated reports from sponsor
companies.
A set of 8 depth structure maps of key horizons have been produced for the pre-Permian
succession. These maps provide a key dataset to aid assessment of the petroleum systems of
the Palaeozoic strata within the study area. The surfaces, supplied digitally at a grid spacing
of 5000 m, give a regional view of the topography of the horizons, and comprise:
âUVARâ (Variscan Unconformity) beneath Permian and Triassic strata
Base Warwickshire Group (late Westphalian - ?Stephanian)
Top Namurian (Base Pennine Coal Measures Group)
Top Intra-Namurian (Top Bowland Shale in south, Base Millstone Grit elsewhere)
Top Visean (Lower Carboniferous)
Intra-Visean (amalgamated with Top Middle Border Group in north)
Base Carboniferous (amalgamated with Base Clyde Plateau lavas in the North
Channel to South-West Arran Sub-Basin)
âUCALâ Acadian (Caledonian) Unconformity)
It is important to note that the variable data quality and sparsity of deep wells leads to a
seismic interpretation which is strongly driven by regional geological models, themselves
heavily dependent on inference from the onshore area. This is particularly the case with the
deeper Carboniferous horizons which are not penetrated by any well and which may be only
weakly reflective. In such cases, picks from better quality data may be interpolated through
areas with poor quality data, as a modelled surface, to ensure a continuous surface for
gridding.
The well dataset has been re-interpreted (Wakefield et al., 2016) before integration with the
seismic interpretation.
The following general observations are made:
The present study has confirmed the Permian-Mesozoic structural framework for the region
established by Jackson and Mulholland (1993) and Jackson et al. (1995, 1996, 1997).
The basin recognised in Quadrant 109 by Jackson and co-workers (op. cit.) is
reinterpreted as a major Carboniferous half-graben structure controlled by a
syndepositional fault on its NW side. It continues beneath thin Permo-Triassic cover
into the Eubonia Basin and Ogham Platform, preserving a thick Westphalian
succession, including inferred Warwickshire Group strata. It is inferred to have
continued eastward into the Lagman Basin prior to its tectonic dissection by a
combination of Variscan inversion and Permo-Mesozoic graben development along
the Keys Fault.
A belt of Variscan fold/thrust inversion structures on the Godred Croven Platform is
correlated with structures on the Formby Platform and Ribblesdale Foldbelt onshore.
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The area of Carboniferous (undivided) subcrop depicted on mapping by BGS (1994)
to north and west of the Isle of Man has been reclassified into Visean and Namurian
elements.
The presence of significant thicknesses of Carboniferous strata in the southern part of
the North Channel is regarded as doubtful, but farther north, in the Larne, Rathlin and
South-West Arran Sub-basins, greater thicknesses may be present.
A detailed description of tectono-stratigraphic development based on the seismic
interpretation is given in Pharaoh et al. (2016b), integrated with the petroleum system
analysis
Massive-Field Approach to the Scalar Self Force in Curved Spacetime
We derive a new regularization method for the calculation of the (massless)
scalar self force in curved spacetime. In this method, the scalar self force is
expressed in terms of the difference between two retarded scalar fields: the
massless scalar field, and an auxiliary massive scalar field. This field
difference combined with a certain limiting process gives the expression for
the scalar self-force. This expression provides a new self force calculation
method.Comment: 23 pages, few modification
Extragalactic Sources of TeV Gamma Rays: A Summary
The development of techniques whereby gamma rays of energy 100 GeV and above
can be studied from the ground, using indirect, but sensitive, techniques has
opened up a new area of high energy photon astronomy. The most exciting result
that has come from these is the detection of highly variable fluxes of TeV
gamma rays from the relativistic jets in nearby AGN. The recent detection of
signals from a starburst galaxy and from a radio galaxy opens the possibility
that the extragalactic emission of TeV gamma rays is a ubiquitous phenomenon.
Here we attempt to summarize the properties of the sources detected so far.Comment: 13 pages, 2 figures, New Astronomy Reviews; Summary Talk at the "2nd
VERITAS Symposium on TeV Astrohysics of Extragalactic Sources", April 24-26,
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Cosmic Censorship, Area Theorem, and Self-Energy of Particles
The (zeroth-order) energy of a particle in the background of a black hole is
given by Carter's integrals. However, exact calculations of a particle's {\it
self-energy} (first-order corrections) are still beyond our present reach in
many situations. In this paper we use Hawking's area theorem in order to derive
bounds on the self-energy of a particle in the vicinity of a black hole.
Furthermore, we show that self-energy corrections {\it must} be taken into
account in order to guarantee the validity of Penrose cosmic censorship
conjecture.Comment: 11 page
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