Instruct: Identify the main and secondary category of Arxiv papers based on the titles and abstracts
Query: The cosmological constant in the brane world of string theory on
  $S^{1}/Z_{2}$   Orbifold branes in string theory are investigated, and the general field
equations on the branes are given explicitly for type II and heterotic string.
It is shown that the effective cosmological constant on each of the two branes
can be easily lowered to its current observational value, using large extra
dimensions. This is also true for type I string. The radion stability is
studied by using the Goldberger-Wise mechanism, and shown explicitly that it is
stable. Therefore, brane world of string theory provides a viable and built-in
mechanism for solving the long-standing cosmological constant problem. Applying
the formulas to cosmology, we obtain the generalized Friedmann equations on
each of the two branes.

3
The categories of this paper are: physics
13
The categories of this paper are: quant-ph
15
The categories of this paper are: nucl-ex
36
The categories of this paper are: cmp-lg
29
The categories of this paper are: funct-an
12
The categories of this paper are: nucl-th
28
The categories of this paper are: alg-geom
26
The categories of this paper are: bayes-an
9
The categories of this paper are: nlin
24
The categories of this paper are: dg-ga
16
The categories of this paper are: stat
21
The categories of this paper are: adap-org
10
The categories of this paper are: q-bio
32
The categories of this paper are: atom-ph
31
The categories of this paper are: ao-sci
34
The categories of this paper are: chem-ph