Modifying General Relativity with boundary terms

Abstract: In this talk I present an outline of our recent work [2103.15906 gr-qc] which looks at yet another modification of General Relativity (GR) of the form f(something). Here it’s based on a generalisation of the first-order Einstein or Gamma-squared action, which differs from the Einstein-Hilbert action by a boundary term. The underlying geometry is the usual Riemannian structure of GR (with vanishing torsion and nonmetricity). However, I look at some of the equivalences with the other popular geometric theories f(T) and f(Q) gravity, set in different non-Riemannian geometries. In the talk, I focus on the importance of breaking the diffeomorphism invariance of the gravitational action and field equations, and how this differs from many current theories. The similarities with the Lorentz non-invariance of modified teleparallel f(T) gravity are also highlighted. Lastly, new boundary terms which differentiate between the gravitational actions of this theory and f(T) and f(Q) gravity are identified, and I look at how they can be used in a unified approach to modelling these apparently distinct theories.

astrophysicscondensed mattergeneral relativity and quantum cosmologyhigh energy physicsmathematical physicsclassical physicsgeneral physics

Audience: researchers in the topic

Theoretical physics seminar @ Tartu