Einstein gravity and beyond
Gravity still remains the least known interaction at the fundamental level, though much impressive progress has been made during the past few decades. In this presentation, we will describe the essential aspects of the universe with gravity and cosmology. Then we move on to the possible candidate theories beyond the Einstein gravity theory. We will focus on the Gauss-Bonnet term, which is one of the simplest extensions with the higher curvature. The properties of this theory will be explained by looking at black holes, which show some characteristic differences compared with those of the Einstein gravity. One property is that it may be unstable under the fragmentation. Also, there exists the minimum mass below which the black hole cannot be formed. In other words, the Gauss-Bonnet term makes gravity less attractive. We also briefly mention the implication to cosmology.