246 research outputs found
Classification of spacetimes according to conformal Killing vectors
Conformal Killing vectors (CKVs) preserve the spacetime metric up to a
factor. Homothetic vectors and Killing vectors are special cases of CKVs.
Classification of some classes of spacetimes on the basis of CKVs give
interesting results showing how homothetic and Killing vectors which form
subsets of the set of CKVs can be recovered as a result of the above
classification.Comment: 4 page
On the definition of matter collineations
It is shown that when the stress-energy tensor of a spacetime is diagonal and
is written in the mixed form, its collineations admit infinite dimensional Lie
algebras except possibly in the case when the tensor depends on all the
spacetime coordinates. The result can be extended for more general second rank
tensors
Greybody factor of scalar fields from black strings
The greybody factor of massless, uncharged scalar fields is studied in the
background of cylindrically symmetric spacetimes, in the low-energy
approximation. We discuss two cases. In the first case we derive analytical
expression for the absorption probability when the spacetime is kinetically
coupled with the Einstein tensor. In the second case we do the analysis in the
absence of the coupling constant. For this purpose we analyze the wave equation
which is obtained from Klein-Gordon equation. The radial part of the wave
equation is solved in the form of the hypergeometric function in the near
horizon region, whereas in the far region the solution is of the form of
Bessel's function. Finally, considering continuity of the wave function we
smoothly match the two solutions in the low energy approximation to get the
formula for the absorption probability
Greybody factor of scalar field from Reissner-Nordstrom-de Sitter black hole
In this work we derive a general expression for the greybody factor of
non-minimally coupled scalar fields in Reissner-Nordstr\"om-de Sitter spacetime
in low frequency approximation. In particular case of zero momentum, greybody
factor tends to zero in low frequency limit as frequency squared goes to zero
for non-vanishing coupling. We also elaborate the significance of the results
by giving formulae of differential energy rate and general absorption cross
section. The greybody factor gives insight into the spectrum of Hawking
radiations
Comments on matter collineations of plane symmetric, cylindrically symmetric and spherically symmetric spacetimes
Comments are made on some recently published papers on matter collineations
of plane symmetric, cylindrically symmetric and spherically symmetric
spacetimes
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