Dr Angnis SCHMIDT-MAY (ETH Zürich)
The recent development of ghost-free nonlinear massive gravity and its generalization to bimetric theory has created an exciting new research area within theoretical cosmology. Bimetric theory can be viewed as a deformation of general relativity by the presence of a massive spin-2 field. It is usually formulated in terms of two metrics with individual Einstein-Hilbert terms as well as an interaction potential whose structure is severely constrained by consistency. In particular, the interactions contain a matrix square-root which may not always be well-defined and unfortunately complicates many computations. In this talk, I will provide the conditions under which the square-root matrix is well-defined and discuss their relation to the vierbein formulation of bimetric theory. Moreover, I will suggest a method of dealing with the linear variation of the square root which can simplify the treatment of perturbation theory around curved backgrounds.