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[en] We consider the effect of quantum interactions on Pauli-Fierz massive gravity. With generic graviton cubic interactions, we observe that the 1-loop counterterms do not conform to the tree level structure of Pauli-Fierz action, resulting in the reappearance of the sixth mode ghost. Then to explore the quantum effects to the full extent, we calculate the resummed graviton propagator with an arbitrary interaction and analyze its complete structure, from which a minimal condition for the absence of the ghost is obtained.

[en] If gaugino condensations occur in the early universe, domain walls are produced as a result of the spontaneous breaking of a discrete R symmetry. Those domain walls eventually annihilate with one another, producing the gravitational waves. We show that the gravitational waves can be a probe for measuring the gravitino mass, if the constant term in the superpotential is the relevant source of the discrete R symmetry breaking

[en] We consider the Palatini formalism of the Born–Infeld gravity. In the Palatini formalism, the propagating mode is only graviton, whose situation is different from that in the metric formalism. We discuss the FRW cosmology by using an effective potential. Especially we consider the condition that the bouncing could occur. We also give some speculations about the black hole formation

[en] Theoretical studies on more than three spatial dimensions are currently showing a distinct shift toward the 'brane world' picture, in which ordinary matter (with the possible exceptions of gravitons and hypothetical particles interacting very weakly with matter) is within a three-dimensional submanifold - brane - embedded in a multi-dimensional space. The extra dimensions may be large and indeed infinite and may show up directly in current or future experiments. In the present paper the basic ideas of the brane theory are presented in an accessible way using simple field-theoretical models. (reviews of topical problems)