# THEORY OF STRONG INTERACTIONS

**Academic Year 2021/2022**- 1° Year - Curriculum NUCLEAR AND PARTICLE PHYSICS and Curriculum THEORETICAL PHYSICS

**Teaching Staff:**

**Vincenzo GRECO**

**Credit Value:**6

**Scientific field:**FIS/02 - Theoretical physics, mathematical models and methods

**Taught classes:**35 hours

**Exercise:**15 hours

**Term / Semester:**2°

## Learning Objectives

The course aims to introduce the basic elements of quantum-relativistic field theory in order to provide the basis for the understanding of the modern theory of fundamental interactions. After a critical exposition of relativistic quantum mechanics, the main arguments concerning the formulation of a relativistic quantum field theory are exposed. The main objective is learning Quantum ElectroDynamics (QED), an abelian gauge theory, as a prototype of the modern description of a fundamental interaction, and then formulation and properties of non-abelian gauge theory for strong interaction: the QuantumChromoDynamics (QCD).

Upon completion of the course the student has to be able to calculate the cross section of the elemmentary processes in both QED and QCD. This will be achieved giving during the frontal lecture a very large space for explicit calculations with all students. Also several examples will be worked out with the explicit calculation of cross sections and decays in the classroom during the course itself.

## Course Structure

The Course is structured by meant of frontal lectures for both the theoretical part and for the exercises. There will be however also some exercise during the class held as practical tests to verify the understanding of some main part of the course. Should the circumstances require online or blended teaching, appropriate modifications to what is hereby stated may be introduced, in order to achieve the main objectives of the course.

## Detailed Course Content

**Introduction** - Dimensional analysis, senergy and time scale for process under the action of the foru fundamental forces. Primer on Lorentz group. Evoltuion from relativstic quantum mechanics to quantum field theroy. Lagrangian theory for classical fields and Eulero-Lagrange equation.Hamiltonian formulation. Symmetries: internal e space-time, discrete e continous, global an local gauge. Noether Theorem. Energy-Momentum Tensor. Example for a scalr, spinorial and electromagnetic field.

**Quantization of Fields **- Canonical quantization for scalar, spinors and elettromagnetic fields. Spin-Statistic theorem. Interacting fields. Propagators for bosons and fermions. Pertubation theory in quantum field theory. Normal and temporal products and Wick Theorem. Definitions of S , T and M matrice and their relation to cross sections and particle decay. Feymann digramas and primer on radiative corrections. Mandelstam variables and their use for the cross section: s-channel, t-channel ed u-channel. Crossing symmetry. Link of non-relativistic Bron approximation and leading order diagram in quantum field theory.

**Quantum ElecttroDynamics– QED** - Gauge field, minimal coupling and QED formualtion. Feynmann rules for QED. Coulomb Scattering for elettrons e positrons and non-relativistic reduction to Rutherford cross section; Electron scattering: Moeller cross section; Scattering elettron-positron: Babbha scattering; Scattering Compton and its Ultra-relativistic limit (production of energetic photons by laser).

**Quantum Chromodynamics- QCD** - Introduction to Stron Interactions and QCD lagragian; some proof for quarks and their flavor and color. on abelian gauge interaction in SU(2) e extension to SU(3). Non abelian bosonic tensor. Feynmann diaggrams in QED e QCD. Asymptotic freedom and Confinement. Chiral symmetry and transition from adronic matter to a plasma of quarks and gluons. Nuclear Interaction as meson exchange and Quantum HadroDinamics (QHD). Noon-perturbative phenomena of strong interactions. Deep-inelastic collisions and form factors and parton model. Derivation of Rosenbluth formula for hadronic scatterings: electric and magnetic form factors. Bjorken scaling and parton distribution functions. QCD diagrams at leading order (qq→qq, gg→gg, qg→qg …) and cross section evaluation for elementary processes at ultra-relativistic energies. Calcualtion of hadronic spectra proton-proton, proton-nucleus e nucleus-nucleus collisions at relativistic energy.

## Textbook Information

1) F. Mandl and G. Shaw, *Quantum Field Theory*, Ed. Wiley- 1993

2) M. Maggiore, *A Modern Introduction to Quantum Field Theory*, Ed. Oxford University Press-2005

3) F.Halzen and A.D.Martin, *Quarks and leptons: an introductory course in particle physics*, Ed. Wiley 1984

4) M.E. Peskin and D.V. Schroeder, *An Introduction to Quantum Field Theory*, Ed. Westview Press- 1995

5) F. Schwabl, Advanced Quantum Mechanics, Ed. Springer.

6) G. Sterman et al., “*Handbook of Perturbative QCD*”, Review of Modern Physics 67 (1995) 158.