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Exorcising Ostrogradsky ghost: Construction of healthy higher-derivative theories

May. 25 - 14:30 - 2017

Speaker: Hayato Motohashi (IFIC, University of Valencia)

Abstract:

Scalar-tensor theories serve models for inflation and dark energy.  Many efforts have been made recently for constructing most general scalar-tensor theories with higher-order derivatives in their Lagrangian.  While the Horndeski theory has the most general second-order Euler-Lagrange equation, there exist more general healthy class of theories beyond Horndeski.  Since higher-derivative theories are typically associated with Ostrogradsky ghost which causes unbounded Hamiltonian, it is important to clarify how to evade it.  In this talk, I will discuss construction of healthy degenerate theories with higher derivatives which circumvent Ostrogradsky ghost.