Instruct: Identify the main and secondary category of Arxiv papers based on the titles and abstracts
Query: Brane versus shell cosmologies in Einstein and Einstein-Gauss-Bonnet
  theories   We first illustrate on a simple example how, in existing brane cosmological
models, the connection of a 'bulk' region to its mirror image creates matter on
the 'brane'. Next, we present a cosmological model with no $Z_2$ symmetry which
is a spherical symmetric 'shell' separating two metrically different
5-dimensional anti-de Sitter regions. We find that our model becomes
Friedmannian at late times, like present brane models, but that its early time
behaviour is very different: the scale factor grows from a non-zero value at
the big bang singularity. We then show how the Israel matching conditions
across the membrane (that is either a brane or a shell) have to be modified if
more general equations than Einstein's, including a Gauss-Bonnet correction,
hold in the bulk, as is likely to be the case in a low energy limit of string
theory. We find that the membrane can then no longer be treated in the thin
wall approximation. However its microphysics may, in some instances, be simply
hidden in a renormalization of Einstein's constant, in which cases Einstein and
Gauss-Bonnet membranes are identical.

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The categories of this paper are: cond-mat
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The categories of this paper are: funct-an
17
The categories of this paper are: q-fin
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The categories of this paper are: hep-ph
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The categories of this paper are: solv-int
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The categories of this paper are: acc-phys
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The categories of this paper are: supr-con
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The categories of this paper are: physics
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The categories of this paper are: cs
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The categories of this paper are: q-bio
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The categories of this paper are: math-ph
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The categories of this paper are: econ
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The categories of this paper are: adap-org
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The categories of this paper are: cmp-lg
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The categories of this paper are: plasm-ph
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The categories of this paper are: hep-lat