Exploring cosmological expansion parametrizations with the gold SnIa data set

We use the SnIa gold data set to compare LCDM (lambda cold dark matter) with ten representative parametrizations of the recent Hubble expansion history H(z). For the comparison we use two statistical tests: the usual X-min(2) and a statistical test that we call the p-test which depends on both the value of X-min(2) and the number n of parametrization parameters. The p-test measures the confidence level to which the parameter values corresponding to LCDM are excluded from the viewpoint of the parametrization tested. For example, for a linear equation of state parametrization w(z) = w(0) + w(1)z, the LCDM parameter values (w(0) = -1, w(1) = 0) are excluded at the 75% confidence level. We use a. at prior and Omega(0)m = 0.3. All parametrizations tested are consistent with the gold data set at their best fit. According to both statistical tests, the worst fits among the ten parametrizations correspond to the Chaplygin gas, the brane world and the Cardassian parametrizations. The best fit is achieved by oscillating parametrizations which can exclude the parameter values corresponding to LCDM at the 85% confidence level. Even though this level of significance does not provide a statistically significant exclusion of LCDM ( it is less than 2 sigma) and does not by itself constitute conclusive evidence for oscillations in the cosmological expansion, when combined with similar independent recent evidence for oscillations coming from the cosmic microwave background and matter power spectra, it becomes an issue worthy of further investigation.