Abstracts

Alexey Golovnev

Spin connections, local Lorentz transformations and cosmological perturbations in modified teleparallel theories of gravity

There used to be a lot of confusion in the literature regarding the properties of modified teleparallel gravity models such as f(T). The reason is that the local Lorentz rotations of a tetrad are realised as symmetries in TEGR only up to a surface term in the action. Of course, upon modification, they generically fail to be symmetries in any good sense, and new degree(s) of freedom do appear. These peculiarities must be properly taken into account even in most basic calculations of linear perturbation theory around the simplest cosmological backgrounds. In recent years there was considerable progress, and these topics got to be much better understood than before, though many important questions are yet unanswered. I will review both what we already know well, as well as give some speculations and personal opinions about the further development and perspectives of the field.