That requires an optical dense medium. Such a medium has mass and the photon crossing it can't be clearly distinguished from this medium. It is a matter of definition where the photon ends and the medium begins. But no matter how you define it - if it has energy and moves with less than c, than it has mass.Example. In a region of space ##\varepsilon## and ##\mu## vary from one point to another
Light actually can have mass, but that's off-topic. We are talking about acceleration without mass.Light does not have ##m_o##, we know that. [...]
Newtonian physics is not valid for objects with m=0.[...] in Newtonian physics [...]
It's difficult to talk about acceleration if you don't even have a defined position.Is it also consistent with quantum theory?