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String/M Theory – what is it? Branes and brane world Holography

String/M Theory – what is it? Branes and brane world Holography

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Emergence from Confusion – 1960s Regge trajectories for mesons M vs J 2
Branes and brane world Holography The Landscape Nick Evans Strong Force Origins Superstrings Ten & eleven dimensions.
Paths to String Theory GUTs & SUSY Quantum gravity Strings Black holes QCD, CM
QCD String Theory Quarks Gluon mediated interactions SU(3) gauge invariance Confinement due to asymptotic freedom M ~ J 2 Fundamental strings Basic property is Tension
note this is a 2d field theory…..
Classical Solutions The solutions in flat space are not surprising: The CoM moves like a relativistic particle There are standing waves on the string The mass of the string depends on how many oscillations are excited Quantum Zero Point Energy After renormalization (trust us) this leads to a negative shift in the mass spectrum… Compute the Hamiltonian
Hints of a TOE String theory unifies gravity and other forces In D=26 the massless states are a photon (one excitation) and a graviton (one plus one)
Simplistic quantization of GR includes non-renormalizable interactions between gravitons – the theory becomes strongly coupled at the Planck Scale Quantum vacuum energies represent an enormous and unobserved dark energy component The strings length at 10 m would cut off the theory -34.
Supersymmetry is a symmetry that links fermions and bosons (unseen in nature as yet) photon (spin 1) photino (spin ½) electron (spin ½) selectron (spin 0) Amongst the constraints is one that scalar masses must be positive. GSO added fermions on the string world sheet and projected out a well behaved supersymmetric theory – first string revolution .
The d act as space time  matrices.. fermions in space time….
Conformal Field Theory in 2d conformal invariance Away from flat space we get interactions… In the quantum theory we get loops… and use dimensional regulation (d=2-  ) to control them…
A full picture of spacetime would explain how it emerges from the underlying degrees of freedom… String theory only watches one string in a classical background… Magically conformal invariance is only present with Einstein’s equations Maxwell’s equations D= In the full computations there are ghost fields as in QCD computations… the D=10 emerges because we are dialling the number of fermions to cancel a quantum anomaly Eg why is the right handed up quarks hyper charge = +4/3… because x (1/3 + 1/3 -2/3 + ) = 0.
Five Consistent String Theories There are five consistent anomaly free string theories Type IIA – closed strings in 10d Type IIB – closed strings in 10d but with an alternative choice of spin (LH vs RH) for the superpartner fermion Type I – open and closed strings in 10d Heterotic closed strings – left moving super-waves on the closed string live in 10d… right moving waves live in 26d… the extra dimensions can be compactified in two ways to give space time gauge groups SO(32) or E8 x E8 These theories match the possible 10d supersymmetric (but non-renormalizable) supergravity theories – they are the low energy actions of these string theories
A prediction…. But wrong!. Compactification We can imagine a space where directions are curled up Why are 6 dimensions compact… by what mechanism. UNKNOWN. There are a vast number of ways to compactify too – each generates a very different short distance theory….
As we shrink the circumference away E grows – eventually you can’t make the extra states… it’s gone. Standard string lore – E is 10 proton mass 19.
Wrapping Strings Closed strings can do something new in a compact space Wrapping modes have energies E’, 2E’, 3E’, 4E’, 5E’… As we shrink the circumference away these states are very low energy T Duality If we confuse winding modes and kinetic modes we can see a new dimension appear as another disappears!
Membranes Only closed strings see the new direction… not open strings… Electromagnetic particles live on a sub-space or brane Gravitons live in a higher dimension bulk Existence proof for such a world
Type I theory is just IIB with a space-filling 9-brane
There was always an 11d supergravity that could only include M2 and M5 branes… Witten proposed a 10+1 dimensional model of M2 and M5 branes that he showed compactifies to give all the string theories – but what is this theory. – Mystery…..
Holography General Relativity predicts there should be objects whose gravitational attraction is enough to stop even light escaping – BLACK HOLES ‘tHooft argued that any information dropped into a black hole must be lost to our Universe spread over the surface If the surface can contain all the information of the contents the real theory of the Universe must be dimensional!
Any strongly coupled gauge theory defines a string theory. We also are using this to better understand gauge theories (QCD ) * confinement (hadronization) * bound state spectra * mass generation * leading tool for heavy ion collision - quark gluon plasma * first applications( ) to condensed matter systems…..
2 R  U S The strength of gravity is determined by the number of spatial dimensions (gravitons spread out around mass) F = G M m r 2D=3+1 But…. we don’t know anything about gravity on length scales below 0.1mm… R could = 0.1mm… and we wouldn’t know it. If so we’ve miscalculated the strength of gravity (G) – it could become strong in our particle accelerators at any new energy!!.
BUT String theory does not solve the cosmological constant problem… the vacuum is now full of quantum strings… and ought to roll up into a ball… Roughly 120 orders of magnitude wrong!!!!.
Inflation &/or many worlds QM means they can all exist at once!.
Only these large, open Universes can support life… so any life will naturally see a small Cosmological Constant!.
A failed theory of mesons A renormalizable theory of quantum gravity A theory of everything A landscape multi-verse A point particle theory or membrane theory An 11 dimensional theory of membranes A rewriting of QCD-like theories An ideas factory for particle theory A fanciful dead end in theory space . Lot’s of fun!!.