Instruct: Identify the main and secondary category of Arxiv papers based on the titles and abstracts
Query: Avoiding the dark energy coincidence problem with a cosmic vector   We show that vector theories on cosmological scales are excellent candidates
for dark energy. We consider two different examples, both are theories with no
dimensional parameters nor potential terms, with natural initial conditions in
the early universe and the same number of free parameters as LCDM. The first
one exhibits scaling behaviour during radiation and a strong phantom phase
today, ending in a "big-freeze" singularity. This model provides the best fit
to date for the SNIa Gold dataset. The second theory we consider is standard
electromagnetism. We show that a temporal electromagnetic field on cosmological
scales generates an effective cosmological constant and that primordial
electromagnetic quantum fluctuations produced during electroweak scale
inflation could naturally explain, not only the presence of this field, but
also the measured value of the dark energy density. The theory is compatible
with all the local gravity tests, and is free from classical or quantum
instabilities. Thus, not only the true nature of dark energy could be
established without resorting to new physics, but also the value of the
cosmological constant would find a natural explanation in the context of
standard inflationary cosmology.

19
The categories of this paper are: eess
25
The categories of this paper are: patt-sol
34
The categories of this paper are: chem-ph
12
The categories of this paper are: nucl-th
37
The categories of this paper are: supr-con
22
The categories of this paper are: chao-dyn
15
The categories of this paper are: nucl-ex
10
The categories of this paper are: q-bio
24
The categories of this paper are: dg-ga
7
The categories of this paper are: hep-th
2
The categories of this paper are: math
31
The categories of this paper are: ao-sci
4
The categories of this paper are: cond-mat
18
The categories of this paper are: econ
27
The categories of this paper are: comp-gas
13
The categories of this paper are: quant-ph