Evolving Newton’s constant, extended gravity theories, and SnIa data analysis

Abstract

If Newton's constant G evolves on cosmological timescales as predicted by extended gravity theories then Type Ia supernovae (SnIa) can not be treated as standard candles. The magnitude-redshift datasets however can still be useful. They can be used to simultaneously fit for both H(z) and G(z) (so that local G(z) constraints are also satisfied) in the context of appropriate parameterizations. Here we demonstrate how can this analysis be done by applying it to the Gold SnIa dataset. We compare the derived effective equation of state parameter w(z) at best fit with the corresponding result obtained by neglecting the evolution G(z). We show that even though the results clearly differ from each other, in both cases the best fit w(z) crosses the phantom divide w = −1. We then attempt to reconstruct a scalar tensor theory that predicts the derived best fit forms of H(z) and G(z). Since the best fit G(z) fixes the scalar tensor potential evolution F (z), there is no ambiguity in the reconstruction and the potential U (z) can be derived uniquely. The particular reconstructed scalar tensor theory however, involves a change of sign of the kinetic term Φ ′ (z) 2 as in the minimally coupled case.PACS numbers: 98.80. Es,98.65.Dx,98.62.Sb

Limits of extended quintessence

“…[36,38] The resulting χ 2 contours in the w 0 − w 1 space are shown in Fig. 5 (dashed lines) superposed with the corresponding contours constructed by neglecting the evolution of G (continuous lines).…”

“…[38]. In order to test the sensitivity of these contours with respect to the evolution of G we have repeated the χ 2 contour construction assuming a varying G according to the ansatz…”

“…We have considered the value of α = 0.2 (3.8) and repeated the SNLS data analysis taking into account the evolution of the SnIa absolute magnitude M due to the evolving G [38,40,41,42] as…”

Interacting modified holographic dark energy in Kaluza-Klein universe

“…Following this hypothesis, many efforts have been made through different aspects to obtain physical results about the universe. The idea of Brans-Dicke (BD) theory (Brans and Dicke 1961) and its generalization to other forms of scalartensor theories (Bergmann 1968;Wagoner 1970;Nordtvedt 1970) arose from variable-G theories in which gravitational constant is replaced by a scalar field coupling to gravity through a new parameter. Further, it was shown through different observations in favor of hypothesis that G could be varied as a function of time or equivalently of the scale factor (Umezu et al 2005;Nesseris and Perivolaropoulos 2006;Biesiada and Malec 2004).…”

Crossing the phantom divide: theoretical implications and observational status

“…The steps we followed for the minimization of (3.6) for the Gold and SNLS datasets are described in detail in Refs [96,101,109]. The form of H(z) used in (3.2), (3.7) is obtained by using the CPL parameterization (2.18) and leads to…”