An Old Universe in K-Essence Cosmology

Abstract EN

Models in which the Lagrangian contains only a kinetic factor and does not depend explicitly on the field itself in k-essence cosmology are considered.

In the case of a constant potential, we obtain an exact analytic solution of k-essence, wk=−(3α−2)/3α, under a simple hypothesis, a=a0(t/t0)α, but without any assumption about the form of F(X).

In purely kinetic k-essence model, the acceleration can only be induced after the matter-dominated epoch; the Universe is about 33.5−3.4+4.2 Gyr old now and about 3.1 Gyr old at z=3.9 which is consistent with the fact of quasar observation, while this observation contradicts with the prediction of ΛCDM model, and the year where a transition from deceleration to acceleration expansion is about from 18.43 Gyr to 25.2 Gyr after the beginning of the Universe.

These results may offer clues to test observationally the k-essence scenario in the future.