Aspects of Conformal Field Theory

TL;DR

This thesis explores three aspects of Conformal Field Theories: descendant correlation functions, trace anomalies in Weyl fermions, and holographic descriptions involving irrelevant operators, providing new computational tools and confirming theoretical predictions.

Contribution

It introduces a recursive formula and computer implementation for descendant correlation functions, clarifies the absence of Pontryagin density in Weyl fermion anomalies, and extends holographic models to include irrelevant operators with modified trace anomalies.

Findings

Recursive formula enables calculation of descendant correlators.

Pontryagin density is absent in Weyl fermion trace anomalies.

Holographic models with irrelevant operators show modified trace anomalies.

Abstract

In this thesis we analyse three aspects of Conformal Field Theories (CFTs). First, we consider correlation functions of descendant states in two-dimensional CFTs. We discuss a recursive formula to calculate them and provide a computer implementation of it. This allows us to obtain any correlation function of vacuum descendants, and for non-vacuum descendants to express the correlator as a differential operator acting on the respective primary correlator. With this code, we study some entanglement and distinguishability measures between descendant states, i.e. the R\'enyi entropy, trace square distance and sandwiched R\'enyi divergence. With our results we can test the R\'enyi Quantum Null Energy Condition and provide new tools to analyse the holographic description of descendant states. Second, we study four-dimensional Weyl fermions on different backgrounds. Our interest is in their trace anomaly, where the Pontryagin density has been claimed to appear. To ascertain this possibility, we compute the anomalies of Dirac fermions coupled to vector and axial non-abelian gauge fields and then in a metric-axial-tensor background. Appropriate limits of the backgrounds allow to recover the anomalies of Weyl fermions coupled to non-abelian gauge fields and in a curved spacetime. In both cases we confirm the absence of the Pontryagin density in the trace anomalies. Third, we provide the holographic description of a four-dimensional CFT with an irrelevant operator. When the operator has integer conformal dimension, its presence in the CFT modifies the Weyl transformation of the metric, which in turns modifies the trace anomaly. Exploiting the equivalence between bulk diffeomorphisms and boundary Weyl transformations, we compute these modifications from the dual gravity theory. Our results represent an additional test of the AdS/CFT conjecture.