Quarks and Strings Nick Evans “On a remarkable connection between quark physics & string theory…” Theory Group

The Rule of Three Electrons Protons Neutrons Previously You have heard about electrons changing orbits & emitting or absorbing energy Everything is made of just three things!

Quarks! The strong force binds the quarks together & then the protons together.. Remarkably it gets stronger with quark separation Protons and neutrons are made from up and down quarks The Strong Force

Confinement You can never pull hard enough to liberate a quark from a proton… The Vacuum The attractive force between quarks is so strong that binding energy >> mass energy The vacuum has lower energy if it fills itself with quark anti- quark pairs! Interaction energy provides proton mass

Quantum Chromodynamics - QCD There are three identical colours of each quark… and “glue” fields that allow them to probe each other’s colour The glue fields have properties of two quarks…

Computers needed! Gravitational & Electrical Orbits are well behaved QCD orbits are much harder to control Chris & Jonathan

String Theory A quark pair can look like a string BUT String theory lives in 9 spatial dimensions Short strings have the charge of two quarks so are glue fields Closed strings describe gravity fields This is not QCD (surely?) but an interesting possible theory of everything….

The Cat is Out! Membranes too… and 3-branes… and… In string theory branes emerge as areas of space where strings have their ends tied

String Dual of QCD The open strings tied to a 3-brane make up a theory of QCD glue fields in 3 spatial dimensions Maldacena conjectured that the remaining strings in 9 dimensions provide an alternative description of QCD

Quarks Too To have quarks as well we need to anchor one end of the strings somewhere else eg on a 7-brane The mass of the quark is given by the minimum length of the string energy = length x tension

To get massless quarks the 7-brane & 3-brane should intersect Babington, Erdmenger, NE, Erlich, Zuralnik, 2003 A simple (one page) calculation shows that the branes repel – they prefer to generate a dynamical quark mass

Health Warning We’re still describing the basic features of QCD… we’re using maths tricks which mean we are not yet calculating real QCD quantities…. The new framework & understandings are exciting though!