Speaker
Description
Usual calculations of the (Euclidean) effective action in quantum gravity, performed within the heat-kernel formalism, give rise to quartic and quadratic UV-sensitive contributions (Planck scale) to the vacuum energy. The comparison of this result to the observed value of the vacuum energy unveils a severe naturalness problem, the strongest facet of the long-standing “cosmological constant problem”. In this talk, I will show that the appearance of these UV-sensitive terms in usual calculations is due to an improper treatment of the path integral measure and of the UV physical cutoff of the theory. When the diffeomorphism invariant measure proposed by Fradkin and Vilkovisky is used, and the UV physical cutoff properly introduced, the radiative correction to the vacuum energy turns out to be only logarithmically sensitive to the UV scale. In this respect, the Fradkin-Vilkovisky measure is sometimes claimed not to be diffeomorphism invariant due to the presence in it of non-covariant $g^{00}$ factors of the time-time component of the inverse metric. I will show that such a claim is incorrect, and that, on the contrary, these $g^{00}$ factors turn out to be crucial to ensure the diffeomorphism invariance of the path integral measure.
