Instruct: Identify the main and secondary category of Arxiv papers based on the titles and abstracts
Query: Why do we live in 3+1 dimensions?   In the context of string theory we argue that higher dimensional Dp-branes
unwind and evaporate so that we are left with D3-branes embedded in a
(9+1)-dimensional bulk. One of these D3-branes plays the role of our Universe.
Within this picture, the evaporation of the higher dimensional Dp-branes
provides the entropy of our Universe.

30
The categories of this paper are: q-alg
36
The categories of this paper are: cmp-lg
28
The categories of this paper are: alg-geom
14
The categories of this paper are: math-ph
13
The categories of this paper are: quant-ph
10
The categories of this paper are: q-bio
17
The categories of this paper are: q-fin
11
The categories of this paper are: hep-lat
22
The categories of this paper are: chao-dyn
1
The categories of this paper are: cs
31
The categories of this paper are: ao-sci
18
The categories of this paper are: econ
12
The categories of this paper are: nucl-th
35
The categories of this paper are: mtrl-th
33
The categories of this paper are: plasm-ph
21
The categories of this paper are: adap-org