Astronomy and Astrophysics – Astrophysics – Cosmology and Extragalactic Astrophysics
Scientific paper
2010-09-23
Astronomy and Astrophysics
Astrophysics
Cosmology and Extragalactic Astrophysics
7 pages, 4 figures
Scientific paper
In the standard Friedmann-Lemaitre-Robertson-Walker (FLRW) cosmological model, the energy conditions provides model-independent bounds on the behavior of the distance modulus. However, this method can not provide us the detailed information about the violation between the energy conditions and the observation. In this paper, we present an extended analysis of the energy conditions based upon the entropy density of the universe. On the one hand, we find that these conditions imply that entropy density $s$ depends on Hubble parameter H(z). On the other hand, we compare the theoretical entropy density from the conservation law of energy-momentum tensor with that from the energy conditions using the observational Hubble parameter. We find that the two kinds of entropy density are in agreement, only when the present-day entropy density satisfies 0.0222 <= s_0 <= 0.7888. We also obtain that the strong energy condition (SEC) accords with the first law of thermodynamics in the redshift range z < 2.7, the null energy condition (NEC) at z<3.2, and the dominant energy condition (DEC) at z > 2.6. In addition, the energy conditions gives the deceleration parameter 0 <= q(z) <= 2, which is in a predicament of the accelerated expansion of the universe. In particular, the NEC suggests q(z) >= 5/3.
Ma Cong
Zhang Ming-Jian
Zhang Tong-Jie
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