88 research outputs found
Hadamard Renormalisation of the Stress Energy Tensor on the Horizons of a Spherically Symmetric Black Hole Space-Time
We consider a quantum field which is in a Hartle-Hawking state propagating in
a general spherically symmetric black hole space-time. We make use of uniform
approximations to the radial equation to calculate the components of the stress
tensor, renormalized using the Hadamard form of the Green's function, on the
horizons of this space-time. We then specialize these results to the case of
the `lukewarm' Reissner-Nordstrom-de Sitter black hole and derive some
conditions on the stress tensor for the regularity of the Hartle-Hawking state.Comment: 18 pages, minor changes to introduction and conclusions, typos
correcte
Transport Equation Approach to Calculations of Hadamard Green functions and non-coincident DeWitt coefficients
Building on an insight due to Avramidi, we provide a system of transport
equations for determining key fundamental bi-tensors, including derivatives of
the world-function, \sigma(x,x'), the square root of the Van Vleck determinant,
\Delta^{1/2}(x,x'), and the tail-term, V(x,x'), appearing in the Hadamard form
of the Green function. These bi-tensors are central to a broad range of
problems from radiation reaction to quantum field theory in curved spacetime
and quantum gravity. Their transport equations may be used either in a
semi-recursive approach to determining their covariant Taylor series
expansions, or as the basis of numerical calculations. To illustrate the power
of the semi-recursive approach, we present an implementation in
\textsl{Mathematica} which computes very high order covariant series expansions
of these objects. Using this code, a moderate laptop can, for example,
calculate the coincidence limit a_7(x,x) and V(x,x') to order (\sigma^a)^{20}
in a matter of minutes. Results may be output in either a compact notation or
in xTensor form. In a second application of the approach, we present a scheme
for numerically integrating the transport equations as a system of coupled
ordinary differential equations. As an example application of the scheme, we
integrate along null geodesics to solve for V(x,x') in Nariai and Schwarzschild
spacetimes.Comment: 32 pages, 5 figures. Final published version with correction to Eq.
(3.24
Quantum field theory on the Bertotti-Robinson space-time
We consider the problem of quantum field theory on the Bertotti-Robinson
space-time, which arises naturally as the near horizon geometry of an extremal
Reissner-Nordstrom black hole but can also arise in certain near-horizon limits
of non-extremal Reissner Nordstrom space-time. The various vacuum states have
been considered in the context of black holes by Spradlin and
Strominger who showed that the Poincare vacuum, the Global vacuum and the
Hartle-Hawking vacuum are all equivalent, while the Boulware vacuum and the
Schwarzschild vacuum are equivalent. We verify this by explicitly computing the
Green's functions in closed form for a massless scalar field corresponding to
each of these vacua. Obtaining a closed form for the Green's function
corresponding to the Boulware vacuum is non-trivial, we present it here for the
first time by deriving a new summation formula for associated Legendre
functions that allows us to perform the mode-sum. Having obtained the
propagator for the Boulware vacuum, which is a zero-temperature Green's
function, we can then consider the case of a scalar field at an arbitrary
temperature by an infinite image imaginary-time sum, which yields the
Hartle-Hawking propagator upon setting the temperature to the Hawking
temperature. Finally, we compute the renormalized stress-energy tensor for a
massless scalar field in the various quantum vacua.Comment: 15 pages, to be published in PR
The renormalized stress tensor in Kerr space-time: general results
We derive constraints on the form of the renormalized stress tensor for
states on Kerr space-time based on general physical principles: symmetry, the
conservation equations, the trace anomaly and regularity on (sections of) the
event horizon. This is then applied to the physical vacua of interest. We
introduce the concept of past and future Boulware vacua and discuss the
non-existence of a state empty at both scri- and scri+. By calculating the
stress tensor for the Unruh vacuum at the event horizon and at infinity, we are
able to check our earlier conditions. We also discuss the difficulties of
defining a state equivalent to the Hartle-Hawking vacuum and comment on the
properties of two candidates for this state.Comment: 24 pages, no figures, revtex, minor changes to conclusion
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