Seminario: Cosmological Constant and Renormalization Group Running in the IR

Lecturer: Ilya Shapiro (Universidade Federal de Juiz de Fora, Brazil on sabbatical leave at DFTUZ/UNIZAR).

Abstract: The Cosmological Constant (CC) Problem emerges in Quantum Field Theory (QFT) in curved space-time owing to the enormous magnitude of the induced vacuum energy. The CC Problem looks rather complicated, such that its solution from the first principles is not a realistic perspective, even in a far future. After reviewing the fundamental CC problem, we consider the possibility of a slightly variable CC because of the quantum effects of matter fields. There is no way to calculate relevant quantum contributions directly in the framework of available QFT methods. However, three different approaches converge to the unique form of the possible running of CC and the effective Newton constant G in the lowenergy limit. Assuming covariance, or the standard quadratic decoupling of massive fields at low energies, or using dimensional arguments, we arrive at the unique possible form of a running, which leads to the relatively simple cosmological model with potentially observable predictions. Much more recent result is that this possible running, with a single phenomenological parameter, may be useful in alleviating various tensions existing nowadays in cosmology.