Dario Scovacricchi, Silvio A. Bonometto, Marino Mezzetti, Giuseppe La Vacca
We assume a DE state equation w(a) = w_0+w_a(a_p-a), and study the dependence of the constraints on w_0 and w_a coefficients on the pivoting redshift 1+z_p=1/a_p. The main findings of our analysis are specific differences between the cases when neutrino mass is allowed or disregarded. The set of data used include WMAP7, SNIa (Union 2.1), BAO's (including WiggleZ and SDSS results) and H_0 constraints. The fitting algorithm is CosmoMC. More in detail: (i)we confirm that the inclination of the likelihood ellipse on the w_0-w_a plane depends on z_p. (ii) When we assume massless neutrinos, the constraints on w_0 and w_a are then independent only around z_p~0.35. (iii) On the contrary, when we consider massive neutrinos, the ellipse axes become parallel to the coordinate axes at a lower z_p~0.25. (iv) When we neglect neutrino mass and we marginalize over all other parameters, the expected range of w_0 values gradually increases when greater z_p values are considered; as expected, it becomes narrowest at z_p~0.35, being then (-1.19,-0.93) at 2 sigma; on the contrary, when neutrino mass is allowed, w_0 decreases when z_p increases and it narrowest 2 sigma range, at z_p~0.25 is (-1.31,-0.97).
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http://arxiv.org/abs/1211.7315
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