Energy conditions bounds and their confrontation with supernovae data
Abstract
The energy conditions play an important role in the understanding of several properties of the Universe, including the current accelerating expansion phase and the possible existence of the so-called phantom fields. We show that the integrated bounds provided by the energy conditions on cosmological observables such as the distance modulus μ(z) and the lookback time tL(z) are not sufficient (nor necessary) to ensure the local fulfillment of the energy conditions, making explicit the limitation of these bounds in the confrontation with observational data. We recast the energy conditions as bounds on the deceleration and normalized Hubble parameters, obtaining new bounds which are necessary and sufficient for the local fulfillment of the energy conditions. A statistical confrontation, with 1σ-3σ confidence levels, between our bounds and supernovae data from the gold and combined samples is made for the recent past. Our analyses indicate, with 3σ confidence levels, the fulfillment of both the weak energy condition (WEC) and dominant energy condition (DEC) for z ≤ 1 and z 0.8, respectively. In addition, they suggest a possible recent violation of the null energy condition (NEC) with 3σ, i.e. a very recent phase of super-acceleration. Our analyses also show the possibility of violation of the strong energy condition (SEC) with 3σ in the recent past (z ≤ 1), but interestingly the q(z)-best-fit curve crosses the SEC-fulfillment divider at z 0.67, which is a value very close to the beginning of the epoch of cosmic acceleration predicted by the standard concordance flat scenario.