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Published October 11, 2017 | Submitted + Published
Journal Article Open

Priors on the effective dark energy equation of state in scalar-tensor theories

Abstract

Constraining the dark energy (DE) equation of state, w_(DE), is one of the primary science goals of ongoing and future cosmological surveys. In practice, with imperfect data and incomplete redshift coverage, this requires making assumptions about the evolution of w_(DE) with redshift z. These assumptions can be manifested in a choice of a specific parametric form, which can potentially bias the outcome, or else one can reconstruct w_(DE)(z) nonparametrically, by specifying a prior covariance matrix that correlates values of w_(DE) at different redshifts. In this work, we derive the theoretical prior covariance for the effective DE equation of state predicted by general scalar-tensor theories with second order equations of motion (Horndeski theories). This is achieved by generating a large ensemble of possible scalar-tensor theories using a Monte Carlo methodology, including the application of physical viability conditions. We also separately consider the special subcase of the minimally coupled scalar field, or quintessence. The prior shows a preference for tracking behaviors in the most general case. Given the covariance matrix, theoretical priors on parameters of any specific parametrization of w_(DE)(z) can also be readily derived by projection.

Additional Information

© 2017 American Physical Society. Received 25 March 2017; published 11 October 2017. We thank Wayne Hu and Gong-Bo Zhao for useful comments. MR is supported by U.S. Department of Energy Contract No. DE-FG02-13ER41958. PB is supported by an appointment to the NASA Postdoctoral Program at the Jet Propulsion Laboratory, California Institute of Technology, administered by Universities Space Research Association under contract with NASA. AS acknowledges support from the NWO and the Dutch Ministry of Education, Culture and Science (OCW), and also from the D-ITP consortium, a program of the NWO that is funded by the OCW. The work of LP is supported by the Natural Sciences and Engineering Research Council of Canada (NSERC).

Attached Files

Published - PhysRevD.96.083509.pdf

Submitted - 1703.05297.pdf

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August 19, 2023
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