Physics 8.323 Quantum Field Theory I Section 1: Course Logistics and February 2012 c 2012 W. Taylor 8.323 Section 1: Logistics + intro 1 / 1
Course info: http://web.mit.edu/8.323/www Lecturer: Washington (Wati) Taylor, wati@mit.edu Office hours: Tuesday, 1:30-2:30, Room 6-317 Lectures: Tuesday, Thursday, 11-12:30, room 4-231 Recitations: Friday, 4-5, room 4-145 TA: Koushik Balasubramanian, koushikb@mit.edu Office hours: Monday, 3:00-4:00 p.m., Room 6-312 Main text: Peskin and Schroeder: An to Quantum Field Theory (also useful: Brown, Ryder, Srednicki, Weinberg, Zee) Homework: Generally due Tuesday, 5:00 pm in homework box You may work with others but the final writeup should be your own. Grade: Based on homework, lowest homework grade dropped. c 2012 W. Taylor 8.323 Section 1: Logistics + intro 2 / 1
Physics 8.323, Quantum Field Theory I: First week: homework and reading Week 1 reading: Lecture notes, Sections 1 and 2 Peskin and Schroeder, Chapter 1, 9.1 Homework 1: due Tuesday, 2/21 c 2012 W. Taylor 8.323 Section 1: Logistics + intro 3 / 1
1. Motivating Remarks What is Quantum Field Theory (QFT)? QFT = Quantum Mechanics + Special Relativity Arises from imposing relativistic Lorentz symmetry on Quantum Mechanics Conceptual framework & set of tools for describing particles and their interactions (Perturbative) L = 1 2 µφ µ φ 1 2 m2 φ 2 + 1 24 λφ4 (Nonperturbative) Technically complex but conceptually simple: QM of many DOF # DOF of any physical system finite, in QFT idealization # DOF Appropriate framework for any relativistic theory of (non-gravitational) particles c 2012 W. Taylor 8.323 Section 1: Logistics + intro 4 / 1
Successes of QFT: Pinnacle of physical theory to date. Developed in 1920 s-70 s best known fundamental framework for predicting observable physics Can be used to describe systems from stars to protons primary tool for particle physicists, useful to CM, astro,... Standard Model is a QFT describes all terrestrial experiments (without gravity effects) to high precision Will probably describe new phenomena seen at LHC: extension of SM QFT is a principal tool in studying quantum gravity/string theory (still lacking complete framework for QG/ST; dualities : in some cases QG = QFT) c 2012 W. Taylor 8.323 Section 1: Logistics + intro 5 / 1
Limitations of QFT: Not completely well-defined mathematically (but pretty close, well-defined for finite DOF, can take limit) Contains divergences ( s) related to incompleteness of theory at short distances (but relevant physics independent of short-distance details) NOT a fundamental theory Doesn t include gravity (at least not directly) More fundamental theory must exist at short distances Doesn t predict particles, symmetries, just describes them at low energies (sub-planck) (but particles/symmetries may not be uniquely fixed may be point in landscape ) Non-perturbative physics can be very difficult to calculate e.g. mass of proton in QCD analogous to turbulence, etc. c 2012 W. Taylor 8.323 Section 1: Logistics + intro 6 / 1
Large Hadron Collider (LHC): Geneva, Switzerland/France Construction: 1998-2008; First collisions: 2010 Cost: $4 10 9 ; Size: 27 km circumference May discover new particles: Higgs particle? Supersymmetry? Dark matter? Z? Or may discover more radical phenomena: Extra dimensions? May be news in March 2012! Basic tool in analyzing data from the LHC: Perturbative QFT c 2012 W. Taylor 8.323 Section 1: Logistics + intro 7 / 1
What you ll learn this semester Theory and practice of perturbative QFT: QED + + e e scattering Perturbative QFT: expansion in coupling strength between field and particles QED: α = e2 e2 1 (fine structure constant, units = c = 1) 4π c 4π 137 perturbative expansion good QCD (quantum chromodynamics): α s 1/3 perturbative expansion generally not good c 2012 W. Taylor 8.323 Section 1: Logistics + intro 8 / 1
Covered in 8.324, 8.325: Systematics of loop diagrams, regularization and renormalization Nonabelian gauge groups (strong, weak nuclear forces) Standard model of particle physics (and possible extensions) Nonperturbative methods and structures (e.g. lattice QCD, instantons, etc.) c 2012 W. Taylor 8.323 Section 1: Logistics + intro 9 / 1