## Tesi etd-09252019-034550 |

Thesis type

Tesi di laurea magistrale

Author

CIAMBRIELLO, LUCA

URN

etd-09252019-034550

Title

Chiral Symmetry Breaking in Vector-like Gauge Theories

Struttura

FISICA

Corso di studi

FISICA

Supervisors

**relatore**Prof. Contino, Roberto

**relatore**Prof. D'Elia, Massimo

**commissario**Prof. Mannella, Riccardo

**commissario**Fidecaro, Francesco

**commissario**Prof. Forti, Francesco

**commissario**Prof. Guadagnini, Enore

**commissario**Prof. Leporini, Dino

**commissario**Prof. Roddaro, Stefano

**commissario**Prof. Shore, Steven Neil

Parole chiave

- symmetry breaking
- QCD
- gauge theories
- chiral symmetry
- anomaly matching
- strong interaction
- anomalies

Data inizio appello

16/10/2019;

Consultabilità

Secretata d'ufficio

Data di rilascio

16/10/2089

Riassunto analitico

The Standard Model is considered the best description of the fundamental interactions up to the highest energy scale in current experiments. Nonetheless, there are both theorethical and phenomenological reasons to extend it: e.g. the Hierarchy problem and the description of Dark Matter. The class of strongly interacting vector-like gauge theories is a valid candidate.

In this thesis we focus on QCD-like gauge theories with N colours and n flavours. The main question is whether the chiral flavour symmetry is spontaneously broken into its vectorial subgroup. In order to answer this question we use the method of 't Hooft anomaly matching and persistent mass conditions. These are constraints which can be put on the bound states spectrum in the hypothesis that the flavour symmetry is not broken and which lead to a linear system of equations in term of the number of bound states in each representation of the flavour group.

We find that the system has no acceptable solutions for n>N if the infrared spectrum contains only baryons, proving then the symmetry breaking.

We analyse in detail and with the help of numerical examples the case n<=N and the one in which the spectrum contains exotic bound states.

Finally we study vector-like theories in which the quarks belong to non-fundamental representations of the colour gague group.

In this thesis we focus on QCD-like gauge theories with N colours and n flavours. The main question is whether the chiral flavour symmetry is spontaneously broken into its vectorial subgroup. In order to answer this question we use the method of 't Hooft anomaly matching and persistent mass conditions. These are constraints which can be put on the bound states spectrum in the hypothesis that the flavour symmetry is not broken and which lead to a linear system of equations in term of the number of bound states in each representation of the flavour group.

We find that the system has no acceptable solutions for n>N if the infrared spectrum contains only baryons, proving then the symmetry breaking.

We analyse in detail and with the help of numerical examples the case n<=N and the one in which the spectrum contains exotic bound states.

Finally we study vector-like theories in which the quarks belong to non-fundamental representations of the colour gague group.

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