456 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
Approximate k-state solutions to the Dirac-Yukawa problem based on the spin and pseudospin symmetry
Using an approximation scheme to deal with the centrifugal
(pseudo-centrifugal) term, we solve the Dirac equation with the screened
Coulomb (Yukawa) potential for any arbitrary spin-orbit quantum number
{\kappa}. Based on the spin and pseudospin symmetry, analytic bound state
energy spectrum formulas and their corresponding upper- and lower-spinor
components of two Dirac particles are obtained using a shortcut of the
Nikiforov-Uvarov method. We find a wide range of permissible values for the
spin symmetry constant C_{s} from the valence energy spectrum of particle and
also for pseudospin symmetry constant C_{ps} from the hole energy spectrum of
antiparticle. Further, we show that the present potential interaction becomes
less (more) attractive for a long (short) range screening parameter {\alpha}.
To remove the degeneracies in energy levels we consider the spin and pseudospin
solution of Dirac equation for Yukawa potential plus a centrifugal-like term. A
few special cases such as the exact spin (pseudospin) symmetry Dirac-Yukawa,
the Yukawa plus centrifugal-like potentials, the limit when {\alpha} becomes
zero (Coulomb potential field) and the non-relativistic limit of our solution
are studied. The nonrelativistic solutions are compared with those obtained by
other methods.Comment: 21 pages, 6 figure
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
Approximate relativistic bound state solutions of the Tietz-Hua rotating oscillator for any -state
Approximate analytic solutions of the Dirac equation with Tietz-Hua (TH)
potential are obtained for arbitrary spin-orbit quantum number using the
Pekeris approximation scheme to deal with the spin-orbit coupling terms In the
presence of exact spin and pseudo-spin (pspin) symmetric limitation, the bound
state energy eigenvalues and associated two-component wave functions of the
Dirac particle moving in the field of attractive and repulsive TH potential are
obtained using the parametric generalization of the Nikiforov-Uvarov (NU)
method. The cases of the Morse potential, the generalized Morse potential and
non-relativistic limits are studied.Comment: 19 pages; 7 figures; Few-Body Systems (2012) (at press
Out of equilibrium: understanding cosmological evolution to lower-entropy states
Despite the importance of the Second Law of Thermodynamics, it is not
absolute. Statistical mechanics implies that, given sufficient time, systems
near equilibrium will spontaneously fluctuate into lower-entropy states,
locally reversing the thermodynamic arrow of time. We study the time
development of such fluctuations, especially the very large fluctuations
relevant to cosmology. Under fairly general assumptions, the most likely
history of a fluctuation out of equilibrium is simply the CPT conjugate of the
most likely way a system relaxes back to equilibrium. We use this idea to
elucidate the spacetime structure of various fluctuations in (stable and
metastable) de Sitter space and thermal anti-de Sitter space.Comment: 27 pages, 11 figure
The Vacuole Model: New Terms in the Second Order Deflection of Light
The present paper is an extension of a recent work (Bhattacharya et al. 2010)
to the Einstein-Strauss vacuole model with a cosmological constant, where we
work out the light deflection by considering perturbations up to order M^3 and
confirm the light bending obtained previously in their vacuole model by Ishak
et al. (2008). We also obtain another local coupling term
-((5{\pi}M^2{\Lambda})/8) related to {\Lambda}, in addition to the one obtained
by Sereno (2008, 2009). We argue that the vacuole method for light deflection
is exclusively suited to cases where the cosmological constant {\Lambda}
disappears from the path equation. However, the original Rindler-Ishak method
(2007) still applies even if a certain parameter {\gamma} of Weyl gravity does
not disappear. Here, using an alternative prescription, we obtain the known
term -(({\gamma}R)/2), as well as another new local term ((3{\pi}{\gamma}M)/2)
between M and {\gamma}. Physical implications are compared, where we argue that
the repulsive term -(({\gamma}R)/2) can be masked by the Schwarzschild term
((2M)/R) in the halo regime supporting attractive property of the dark matter.Comment: 15 page
Comment on: “Peatland carbon stocks and burn history: Blanket bog peat core evidence highlights charcoal impacts on peat physical properties and long-term carbon storage”, by A. Heinemeyer, Q. Asena, W.L. Burn and A.L. Jones (Geo: Geography and Environment. 2018; e00063)
A recent paper by Heinemeyer et al. (2018) in this journal has suggested that the use of prescribed fire may enhance carbon accumulation in UK upland blanket bogs. We challenge this finding based on a number of concerns with the original manuscript including the lack of an unburned control, insufficient replication, unrecognised potential confounding factors, and potentially large inaccuracies in the core dating approach used to calculate carbon accumulation rates. We argue that burn‐management of peatlands is more likely to lead to carbon loss than carbon gain
More than canons: teacher knowledge and the literary domain of the secondary English curriculum
The construction of masculinities and femininities in the Church of England:the case of the male clergy spouse
The ordination of women to the priesthood in the Church of England in 1994 signified great change. The impact of the new priests was well documented, and their integration became the focus of much research in the following years. One important area of change was the altered dynamics of gender identity. New roles had opened up for women, but new identities had also emerged for men. While women priests were a new historical emergence, so too were clergy husbands. This paper will consider the historical construction of masculinities and femininities within the church and will go on to look at this in the context of clergy spouses, specifically focusing on men occupying this role. Some provisional findings, acting as work in progress, will be considered
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
- …