Saturday, 4 May 2013

Brookhaven Forum Day 3 Blog II

Final session of the conference.  Conference Website.

Talk 3: 10:50am: Lloyd Knox, "The Universe According to Planck"

With Planck having recently presented results, it is natural to have a review from a member of that collaboration.

The better experiments always have the funkiest animations.

Did he just say the released data is only 40% of what they took?  I thought almost all results were out.

Detection of gravitational lensing at the absurd 25 sigma.

The usual argument for the origin of the density fluctuations, seen in the CMB and seeding structure formation, but the slides are quite nice.

LambdaCDM fits the data with ridiculous non-trivial precision.  Things that are needed and have no free parameters:
  • Neutrinos
  • Neutrino cooling
  • Helium (for BBM consistency)
  • Non-equilibrium recombination
  • Gravitational lensing

Sound horizon at surface of last scattering:
  • Directly measured from CMB
  • Imprints itself in large scale structure, c.f. BOSS experiment.

Constraints on Non-Gaussianity.
  • Inflation, of course, predicts small non-gaussianity in almost all models.
  • Some non-Gaussianity inevitable from gravitational interactions, so measurements all relative to that.
Interesting statement; there is a small tension in the value of H0 measured at Planck and at other experiments, but this can be ameliorated with additional light (relativistic) degrees of freedom.  I must look into this in more detail.

So in summary, everything works.

Talk 4: 11:30 am: Juan Maldacena, "Recent Advances in Formal Theory"

So to end the conference we have the traditional big name to keep people's attention.  I've never heard Juan speak, so I don't know what to expect.  I do worry that this subject might be a bit too much for me after a late night drinking yesterday, though; we'll see.

  • QFT works; we haven't seen any violations at the LHC etc.
  • There nonetheless remain some theoretical problems, gaps in our understanding.
  • Computational techniques; we've seen some of that here already.
  • Strong couplings; strings?
  • Fixed points and renormalisation flows; I recall the recent kerfluffle over the a theorem.
  • No surprise that AdS/CFT is brought up!
The topology of this talk is multiply-connected.

  • The extra symmetry often makes the theories simpler; no surprise to see N=4 SYM brought up.
  • Work in N=2, N=1 and even N=0 :)
N = 4 SYM:
  • Maximally supersymetric U(Nc) QCD with coupling g
  • All fields lie in the adjoint representation
  • Planar limit: Nc to infinity, g^2 Nc fixed
Connection to strings: chain of gluons behaves like a string; closed strings are glueballs.  The string coupling goes like 1/Nc, hence the planar limit is the very weak coupling limit.

Discussion on loops in RGE flows; will we get enough details?  No, just a quote of the proof.

Some discussion on entanglement that seems to be related to the black hole entropy, and the way in which surfaces seem to describe the volumes they contain.  My head is dropping, though, and I didn't manage to follow the details.

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