The Unruh Effect and the Cosmological Constant Problem

In this work, I show that the vacuum energy arising from zero-point fluctuations and symmetry breakings vanishes when the acceleration exceeds the critical value as observed by an accelerating observer taking into account the Unruh effect. By requiring that the cosmological constant is a small constant independent of the observer, it would however probably be a mistake to construct the vacuum stress-energy tensor using vacuum energy derived from quantum fluctuations and symmetry breakings. The fact that the zero-point energy density of the vacuum is proportional to the fourth power of the particle mass implies that only the covariant part of the self-energy of particles contributes to the cosmological constant, resulting in a significantly reduced theoretical value. It turns out that a correct calculation of the cosmological constant may rely on a hypothetical covariant theory of quantum gravity.