Detecting the cosmic acceleration with current data

TL;DR

This paper investigates the current state of cosmic acceleration using supernova and Hubble data, suggesting acceleration may slow down soon, but more data and methods are needed for a definitive conclusion.

Contribution

It introduces a non-parametric reconstruction method for the deceleration parameter that does not rely on specific cosmological models or assumptions.

Findings

Current data suggests acceleration might slow down in the near future.

Present decelerating expansion is excluded within 2σ error.

More precise data and methods are required for a definitive answer.

Abstract

The deceleration parameter q as the diagnostic of the cosmological accelerating expansion is investigated. By expanding the luminosity distance to the fourth order of redshift and the so-called y-redshift in two redshift bins and fitting the SNIa data (Union2), the marginalized likelihood distribution of the current deceleration parameter shows that the cosmic acceleration is still increasing, but there might be a tendency that the cosmic acceleration will slow down in the near future. We also fit the Hubble evolution data together with SNIa data by expanding the Hubble parameter to the third order, showing that the present decelerating expansion is excluded within $2\sigma$ error. Further exploration on this problem is also approached in a non-parametrization method by directly reconstructing the deceleration parameter from the distance modulus of SNIa, which depends neither on the validity of general relativity nor on the content of the universe or any assumption regarding cosmological parameters. More accurate observation datasets and more effective methods are still in need to make a clear answer on whether the cosmic acceleration will keep increasing or not.