Matrix models and the gravitational interaction
  The large-N reduced models have been proposed as the nonperturbative formulation of the superstring theory. One of the most promising candidates is the IIB matrix model. While there have been a lot of interesting discoveries of the IIB matrix model in relation to the gravity, we have a lot of problems to surmount, if a large-N reduced model is to be an eligible framework to unify the gravitational interaction. Firstly, it is still an enigma how we can realize the local Lorentz invariant matrix model. In addition, we need to understand how we can describe the curved spacetime more manifestly, in terms of a large-N reduced model.   This thesis discusses several attempts to address these issues concerning the gravitational interaction. This thesis is based on the following author's works hep-th/0102168, hep-th/0204078, hep-th/0209057 and hep-th/0401038. 
Takehiro Azuma