Quarks and Strings

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Quarks and Strings
On a remarkable connection between quark physics
string theory
Nick Evans
Theory Group
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The Rule of Three
Everything is made of just three things!

• Electrons
• Protons
• Neutrons

Previously
You have heard about electrons changing orbits
emitting or absorbing energy
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Quarks!
Protons and neutrons are made from up and down
quarks
The Strong Force
The strong force binds the quarks together then
the protons together.. Remarkably it gets
stronger with quark separation
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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 gtgt mass energy
The vacuum has lower energy if it fills itself
with quark anti-quark pairs!
Interaction energy provides proton mass
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Quantum Chromodynamics - QCD
There are three identical colours of each quark
and glue fields that allow them to probe each
others colour
The glue fields have properties of two quarks
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Computers needed!
Chris Jonathan
Gravitational Electrical Orbits are well behaved
QCD orbits are much harder to control
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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.
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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
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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
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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
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To get massless quarks the 7-brane 3-brane
should intersect
A simple (one page) calculation shows that the
branes repel they prefer to generate a
dynamical quark mass
Babington, Erdmenger, NE, Erlich, Zuralnik, 2003
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Health Warning

• Were still describing the basic features of QCD
  were using maths tricks which mean we are not
  yet calculating real QCD quantities.
• The new framework understandings are exciting
  though!