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Abstract |
Scalar-tensor theories serve models for inflation and dark energy. Many efforts have been made recently for
constructing the most general scalar-tensor theories with higher-order derivatives in their Lagrangian. 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 explain construction of healthy
degenerate theories with higher-order derivatives which circumvent Ostrogradsky ghost. The method also
allows us to construct ghost-free theories with derivatives higher than second order in Lagrangian.
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