Decay of uniformly rotating particles

In this paper, we revisit the interpretation of the circular Unruh effect. To this aim, we rely on the principle of general covariance applied to the decay properties of non-inertial particles. Specifically, we show how the tree-level decay rate of an inverse-$\beta$ process involving scalar fields does not require the introduction of a thermal (or non-thermal) bath in the comoving frame to be a scalar under general coordinate transformations. Instead, we interpret any decay process as an emission of negative-energy quanta, whose existence is motivated by the absence of a global vacuum state for uniformly rotating observers. This implies that, in principle, no uniformly rotating particle can be regarded as stable.