Exorcising the Ostrogradsky ghost: Construction of healthy higher-derivative theories

June 26, 2017
3:00pm to 4:15pm

IFT Seminar Room/Red Room

Theoretical Physics, general interest
Hayato Motohashi
IFIC / CSIC-University of Valencia

IFT Seminar Room/Red Room


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.