Instruct: Identify the main and secondary category of Arxiv papers based on the titles and abstracts
Query: Cosmological constant problems and their solutions   There are now two cosmological constant problems: (i) why the vacuum energy
is so small and (ii) why it comes to dominate at about the epoch of galaxy
formation. Anthropic selection appears to be the only approach that can
naturally resolve both problems. The challenge presented by this approach is
that it requires scalar fields with extremely flat potentials or four-form
fields coupled to branes with an extremely small charge. Some recent
suggestions are reviewed on how such features can arise in particle physics
models.

29
The categories of this paper are: funct-an
27
The categories of this paper are: comp-gas
8
The categories of this paper are: hep-ex
15
The categories of this paper are: nucl-ex
17
The categories of this paper are: q-fin
26
The categories of this paper are: bayes-an
4
The categories of this paper are: cond-mat
9
The categories of this paper are: nlin
22
The categories of this paper are: chao-dyn
31
The categories of this paper are: ao-sci
36
The categories of this paper are: cmp-lg
16
The categories of this paper are: stat
10
The categories of this paper are: q-bio
25
The categories of this paper are: patt-sol
33
The categories of this paper are: plasm-ph
21
The categories of this paper are: adap-org