Instruct: Identify the main and secondary category of Arxiv papers based on the titles and abstracts
Query: Comments on "Derivation of the Raychaudhuri Equation" by Dadhich   In a recent preprint, gr-qc/0511123, Dadhich has given a brief yet beautiful
exposition on some of the research works by Prof. A.K. Raychaudhuri. Here
Dadhich highlights the fact that the apparently ``self-evident'' assumption of
occurrence of ``trapped surfaces'' may not be realized atleast in some specific
cosmological models though no general proof for non-occurrence of trapped
surfaces exists in the cosmological context. However, Dadhich added, without
sufficient justification, that trapped surfaces should occur for collapse of
isolated bodies. We point out that actually trapped surfaces do not occur even
for collapse of spherically symmetric isolated bodies. Further unlike the
cosmological case, for isolated bodies, an exact proof for generic
non-occurrence of trapped surfaces is available. Thus for isolated bodies, the
above referred apparently ``self-evident'' assumption fails much more acutely
than in cosmology. Many recent astrophysical observations tend to corroborate
the fact trapped surfaces do not occur for isolated bodies. Two recent specific
papers (PRD) are cited to show that when radiative non-diispative collapse can
prevent formation of trapped surfaces.

25
The categories of this paper are: patt-sol
10
The categories of this paper are: q-bio
14
The categories of this paper are: math-ph
35
The categories of this paper are: mtrl-th
17
The categories of this paper are: q-fin
1
The categories of this paper are: cs
30
The categories of this paper are: q-alg
36
The categories of this paper are: cmp-lg
19
The categories of this paper are: eess
16
The categories of this paper are: stat
26
The categories of this paper are: bayes-an
13
The categories of this paper are: quant-ph
24
The categories of this paper are: dg-ga
8
The categories of this paper are: hep-ex
2
The categories of this paper are: math
15
The categories of this paper are: nucl-ex