14,024 research outputs found
Conformal Gravity with Electrodynamics for Fermion Fields and their Symmetry Breaking Mechanism
In this paper we consider an axial torsion to build metric-compatible
connections in conformal gravity, with gauge potentials; the geometric
background is filled with Dirac spinors: scalar fields with suitable potentials
are added eventually. The system of field equations is worked out to have
torsional effects converted into spinorial self-interactions: the massless
spinors display self-interactions of a specific form that gives them the
features they have in the non-conformal theory but with the additional
character of renormalizability, and the mechanisms of generation of mass and
cosmological constants become dynamical. As a final step we will address the
cosmological constant and coincidence problems.Comment: 13 page
Static quantum corrections to the Schwarzschild spacetime
We study static quantum corrections of the Schwarzschild metric in the
Boulware vacuum state. Due to the absence of a complete analytic expression for
the full semiclassical Einstein equations we approach the problem by
considering the s-wave approximation and solve numerically the associated
backreaction equations. The solution, including quantum effects due to pure
vacuum polarization, is similar to the classical Schwarzschild solution up to
the vicinity of the classical horizon. However, the radial function has a
minimum at a time-like surface close to the location of the classical event
horizon. There the g_{00} component of the metric reaches a very small but
non-zero value. The analysis unravels how a curvature singularity emerges
beyond this bouncing point. We briefly discuss the physical consequences of
these results by extrapolating them to a dynamical collapsing scenario.Comment: 10 pages; Talk given at QG05, Cala Gonone (Italy), September 200
Can conformal Transformations change the fate of 2D black holes?
By using a classical Liouville-type model of two dimensional dilaton gravity
we show that the one-loop theory implies that the fate of a black hole depends
on the conformal frame. There is one frame for which the evaporation process
never stops and another one leading to a complete disappearance of the black
hole. This can be seen as a consequence of the fact that thermodynamic
variables are not conformally invariant. In the second case the evaporation
always produces the same static and regular end-point geometry, irrespective of
the initial state.Comment: Some typos corrected. A few comments and two references added.
Accepted for publication in PLB. Latex, 11 pages, no figure
Low-energy scattering of extremal black holes by neutral matter
We investigate the decay of a spherically symmetric near-extremal charged
black hole, including back-reaction effects, in the near-horizon region. The
non-locality of the effective action controlling this process allows and also
forces us to introduce a complementary set of boundary conditions which permit
to determine the asymptotic late time Hawking flux. The evaporation rate goes
down exponentially and admits an infinite series expansion in Planck's
constant. At leading order it is proportional to the total mass and the higher
order terms involve higher order momenta of the classical stress-tensor.
Moreover we use this late time behaviour to go beyond the near-horizon
approximation and comment on the implications for the information loss paradox.Comment: LaTeX file, 14 pages. Expanded version replacing earlier
hep-th/001201
Labour market performance of immigrants in the UK labour market
From executive summary:
This document is a report commissioned by the Home Office to analyse the performance of immigrants in the UK labour market. It attempts to draw a comprehensive picture of
the labour market performance of immigrants, and the process of adaptation relative to the UK-born white population. Four indicators of economic performance are investigated: (i) employment, (ii) labour force participation, (iii) self-employment, and (iv) wages. The
analysis distinguishes between males and females, and between groups of different origin. The effects of specific variables on these outcomes are investigated in detail. The report also considers labour market outcomes of ethnic minority individuals who are born in the UK, and compares their outcomes with those of UK-born white individuals, and of ethnic minority individuals who are foreign-born
Semiclassical zero-temperature corrections to Schwarzschild spacetime and holography
Motivated by the quest for black holes in AdS braneworlds, and in particular
by the holographic conjecture relating 5D classical bulk solutions with 4D
quantum corrected ones, we numerically solve the semiclassical Einstein
equations (backreaction equations) with matter fields in the (zero temperature)
Boulware vacuum state. In the absence of an exact analytical expression for
in four dimensions we work within the s-wave approximation. Our
results show that the quantum corrected solution is very similar to
Schwarzschild till very close to the horizon, but then a bouncing surface for
the radial function appears which prevents the formation of an event horizon.
We also analyze the behavior of the geometry beyond the bounce, where a
curvature singularity arises. In the dual theory, this indicates that the
corresponding 5D static classical braneworld solution is not a black hole but
rather a naked singularity.Comment: 26 pages, 4 figures; revised version (title changed, conclusions
shortened), published as Phys. Rev. D73, 104023 (2006
The Holographic Interpretation of Hawking Radiation
Holography gives us a tool to view the Hawking effect from a new, classical
perspective. In the context of Randall-Sundrum braneworld models, we show that
the basic features of four-dimensional evaporating solutions are nicely
translated into classical five-dimensional language. This includes the dual
bulk description of particles tunneling through the horizon.Comment: 10 pages, 1 figure, Honorable Mention in the Gravity Research
Foundation Essay Competition 200
- …