Modified gravity theories with applications to cosmology
Shinji Tsujikawa
Waseda University, Tóquio, Japão

We review the basics of modified gravity theories, paying parcular aenon to scalar-tensor theories with second-order field equaons of moon. In such theories we derive the perturbaon equaons without fixing gauges and apply them to the physics of inflaon and dark energy. Our general formulaon of cosmological perturbaons can be used to disnguish between the models from the observaons of CMB etc. In parcular, we show that there exist dark energy models in scalar-tensor theories showing the beer fit to the data in comparison to the $\Lambda$CDM model.