Something Anomalies can tell about SM and Gravity

Abstract

This ia a review/research paper on anomalies applied to a bottom-up approach to standard model and gravity. It is divided in two parts. The first consists in a review proper of anomalies in quantum field theories. Anomalies are analyzed according to three different methods: a perturbative one based on Feynman diagram, a non-perturbative one relying on the Schwinger-DeWitt approach and, third, the one hinging on the Atiyah-Singer family's index theorem. The three methods are applied both to chiral gauge anomalies and trace anomalies. The fundamental distinction that our presentation leads to is between obstructive (O) and non-obstructive (NO) anomalies. The former are tied to the non-existence of fermion propagators, which fatally maim the corresponding theory. In the second part we apply this analysis to the SM and various of its extensions immersed in a gravitational background, and find that they all are plagued by a residual chiral trace anomaly. To completely eliminate all kind of dangerous anomalies in SM-like theories we propose a somewhat unconventional scheme, and exemplify it by means of an explicit model. The latter is a left-right symmetric model. We embed it in a Weyl geometry to render it conformal invariant. We then deal with some of its quantum aspects, in particular its even (NO) trace anomalies and the means to preserve its confomal invariance at the quantum level. We briefly review renormalization and unitarity in the framework of similar models discussed in the existing literature. Finally we present a possible (conjectural) application of the model to describe the junction between cosmology and quantum field theory.