Remarks on the consistency of minimal deviations from general relativity

We study the consequences of some possible modifications of the phase space structure of general relativity imposed by breaking, in the simplest manner, the full diffeomorphism invariance but retaining the time foliation preserving diffeomorphisms. We examine the different sectors in phase space that satisfy the new structure of constraints. For some sectors we find an infinite tower of constraints. In spite of that, we also show that these sectors allow for solutions, among them some well-known families of black hole and cosmologies which fulfill all the constraints. We raise some physical concerns on the consequences of an absolute Galilean time, on the thermodynamical pathologies of such models, and on their unusual vacuum structure.

Figure 1

Pictorial representation of the vacuum solutions in the $(\Lambda ,1-3\lambda )$ plane. The horizontal (red) axis represents the critical case $\lambda =\frac{1}{3}$. $N$ stands for $N=\frac{|1-3\lambda |}{2}$ and $\frac{1}{{\alpha }^2}≔\frac{1}{3}N|\Lambda |$.