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Abstract.
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 ΛCDM. The ï¬rst one exhibits scaling behaviour during radiation and a strong phantom phase today, ending in a "big-freeze" singularity. This model provides the best ï¬t to date for the SNIa Gold dataset. The second theory we consider is standard electromagnetism. We show that a temporal electromagnetic ï¬eld 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 ï¬eld, 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 ï¬nd a natural explanation in the context of standard inflationary cosmology
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CONCLUSIONS
We have shown that vector theories offer a simple and accurate description of dark en-
ergy in which the coincidence problem could be easily avoided. In our ï¬rst example, the
scaling behaviour during radiation and the natural initial conditions for the vector ï¬eld
offer a neat way around the problem. Moreover, in our second example, the presence
of a cosmological electromagnetic ï¬eld generated during inflation provides a natural
explanation for the cosmic acceleration. This result not only offers a solution to the
problem of establishing the true nature of dark energy, but also explains the value of
the cosmological constant without resorting to new physics. In this scenario the fact that
matter and dark energy densities coincide today is just a consequence of inflation taking
place at the electroweak scale. Present and forthcoming astrophysical and cosmologi-
cal observations will be able to discriminate these proposals from the standard ΛCDM
cosmology.
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 ΛCDM. The ï¬rst one exhibits scaling behaviour during radiation and a strong phantom phase today, ending in a "big-freeze" singularity. This model provides the best ï¬t to date for the SNIa Gold dataset. The second theory we consider is standard electromagnetism. We show that a temporal electromagnetic ï¬eld 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 ï¬eld, 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 ï¬nd a natural explanation in the context of standard inflationary cosmology
>
>
CONCLUSIONS
We have shown that vector theories offer a simple and accurate description of dark en-
ergy in which the coincidence problem could be easily avoided. In our ï¬rst example, the
scaling behaviour during radiation and the natural initial conditions for the vector ï¬eld
offer a neat way around the problem. Moreover, in our second example, the presence
of a cosmological electromagnetic ï¬eld generated during inflation provides a natural
explanation for the cosmic acceleration. This result not only offers a solution to the
problem of establishing the true nature of dark energy, but also explains the value of
the cosmological constant without resorting to new physics. In this scenario the fact that
matter and dark energy densities coincide today is just a consequence of inflation taking
place at the electroweak scale. Present and forthcoming astrophysical and cosmologi-
cal observations will be able to discriminate these proposals from the standard ΛCDM
cosmology.