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Speaker |
Tsujikawa, Shinji |
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| Talk Title |
Effective field theory approach to dark energy |
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Abstract |
The effective field theory (EFT) of cosmological perturbations is a useful framework to deal with the low-energy degrees of freedom present for inflation and dark energy. We review the EFT for modified gravitational theories by starting from the most general action in unitary gauge that involves the lapse function and the three-dimensional geometric scalar quantities appearing in the Arnowitt-Deser-Misner formalism. This analysis accommodates a wide range of modified gravitational theories such as Horndeski theories, Gleyzes-Langlois-Piazza-Vernizzi (GLPV) theories, and Horava-Lifshitz gravity. Expanding the action up to quadratic order in the perturbations and imposing conditions for the elimination of spatial derivatives higher than second order, we obtain the Lagrangian of curvature perturbations and gravitational waves with a single scalar degree of freedom. We apply our results to the evolution of matter density perturbations and the effective gravitational coupling in Horndeski and GLPV theories. In particular, we construct a dark energy model in which the gravitational interaction is weaker than that in General Relativity for the perturbations relevant to large-scale structures. |
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