Aspen Thursday

Morning:
attended Josh Davis and Eskos's session on string theory and QHE, Eskos work on QC conductivity in QH transition calculated by AdS/CFT very interesting, comapred to earlier CMP work:
Damle & Sachdev PRB 1997
Chen, Fisher and Wu 1993
Basically predicts "universal" shape of sigma(omega) as a function of omega/T, with a peak in the function.
string theory methods seem to give answers quicker and nicer.
I pointed out to Eskos that the peak of omega/T still need to be determined to guide experiments.
Also asked any sum rule (oscillation strengths for the function).
Semenoff pointed out that such phenomena should be best observed in graphene, esp. N=0 LL --- measure AC conductivity there!
Later called Zhigang on this and he will look into the data. So far IR spectroscopy he did not easy to extract pure AC conductivity, but possible.

Afternoon: Cheng-chin held an informal discussions on 2D BEC. Earlier Jason Ho, Cheng and I had this interesting discussions in our office --- Hall mark of 2D KT transition in superfluids is the jump of SF density at KT transition (predicted by Nelson et al, measured by John Reppy PRL) , would be nice if such (staitc SF density) jump can be observed directly in atoms, but audience suggested this would be almost round off in a finite system like trap.
Jason emphasized that holy grail: how to measure superfluid properties (esp. SF density) in cold atom clouds!! (also eg second sound...)
Cheng has loaded pancake BEC and some data on quasi-2D behavior.

This week's colloquium is by Daniel Bauman from Harvard on first 10^-10 seconds of universe,
cool points:
1) data so far suggest universe very flat, trivial topology; data also seen on "acausal correlation in density fluctuations in present universe" --- related to inflation that expands quantum fluctuations into density fluctuations beyond horizon
2) polarization CMB images can probe gravitation waves as only 400K years after bing Bang, much easier to probe than LIGO (gravitational waves at present), may prove inflational theory!
3) not addressing the 10^120 (ie where the cosmological constant is from) issue though