Current constraints on the epoch of cosmic acceleration

Abstract

The cosmographic expansion history of the universe is investigated by using the 557 type Ia supernovae from the Union2 Compilation set along with the current estimates involving the product of the CMB acoustic scale ℓA and the BAO peak at two different redshifts. Using a well-behaved parameterization for the deceleration parameter, q(z) = q0 +q1z/(1+z), we estimate the accelerating redshift zacc = −q0/(q0 + q1) (at which the universe switches from deceleration to acceleration) and investigate the influence of a non-vanishing spatial curvature on these estimates. We also use the asymptotic value of q(z) at high-z to place more restrictive bounds on the model parameters q0 and q1, which results in a more precise determination of the epoch of cosmic acceleration.PACS numbers: 95.36.+x, 98.80.Es

On the luminosity distance and the epoch of acceleration

“…7; as expected, negative q0 is required at very high significance. (This agrees well with a similar figure in Santos et al (2011)). The figure also shows lines bounding the regions of no past deceleration q0 + qa < 0, and the region zacc < 2 equivalent to q0 + 2qa/3 > 0; the wedge between these lines corresponds to a transition redshift zacc > 2.…”

“…This model has been used before by various authors (e.g. Cunha & Lima 2008, Santos et al 2011, since it is simple, fairly flexible and can produce a fairly good approximation to the behaviour of many dark energy models at z < ∼ 2. We have fitted this parameter pair to the Union 2.1 SN data, with best-fit values at (−0.62, +1.40) and the resulting likelihood contours shown in Fig.…”

Small-Bang versus Big-Bang Cosmology

“…At the present time [15] we have the approximate value q ≈ -0.5, which implies Ω cp ≈ -2. The present creation pressure is then pretty high.…”

“…The present estimates [15] of the numerical values of the deceleration parameter q are: for very high red shift, close to the initial stages of the universe, q ≈ 0.5 which implies Ω cp ≈ 0. The initial creation pressure is very small, corresponding to a small dark energy component, if any.…”

“…It means that given the measured values of q [15] one can approach its time variation by the linear relationship:…”