General Relativity tells us that the paths of parallel photons propagating in free space should be unaffected by each other, while the paths of anti-parallel photons should bend towards each other. I'm using an already answered question as a reference:
I would like to extend this question to further consider the spin angular momentum of a system of two photons.
Consider the following two scenarios for anti-parallel (moving towards each other) propagating photons $A$ and $B$.
The photon spins are parallel (e.g. helicity of $A$ is 1, helicity of $B$ is -1).
The photon spins are anti-parallel (e.g. helicity of $A$ is 1, helicity of $B$ is also 1).
My question is: Since general relativity and QFT don't predict a difference in the paths taken by the pair between 1 and 2, how do candidate theories for quantum gravity approach this? Do they produce specific predictions for the paths of the photons accounting for their spin alignment?