qcd viscosity and bec-bcs crossover in effective field theory jiunn-wei chen ( 陳俊瑋 ) national...
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QCD viscosity and BEC-BCS crossover in effective field theory
Jiunn-Wei Chen (陳俊瑋 )
National Taiwan U.
Effect Field Theory
• Make use of scale separation to integrate out the high energy scales
• Low energy physics reproduced
Light-by-light Scattering
• QCD viscosity w/ Eiji Nakano, Yan-Han Lee, Yang-Fu Liu
• BEC-BCS Crossover w/ Eiji Nakano
QCD Viscosity
• Shear viscosity
.)(3
1
2
)()(
xV
xVxVT ij
ijjiij
y
x
)(yVx
Frictional force
Shear viscosity measures
how “perfect” a fluid is!
• Kovtun, Son, and Starinets (’05)
Conjecture: Shear viscosity / entropy density
• Motivated by AdS/CFT
• QGP (quark gluon plasma) almost saturates the bound @ just above Tc --- a perfect fluid
• What happens below Tc?
• Pion gas ChPT (chiral perturbation theory)
• Non-perturbative in coupling
Boltzman equation
JWC, Nakano
QCD Phase Diagram
The Landscape
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JWC, Lee, Liu, Nakano
The Landscape
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Cold Trapped Atoms
Source: C. Regal
Review: Scattering Length
Source: C. Regal
BEC-BCS Crossover
Source: C. Regal
Changing a at will: Technique of Feshbach Resonance
Epsilon Expansion (Nishida and Son)
• Computing in dim.
• Expanding in
• Setting
Why is 4d special?
has a singularity at
for
ground state a free Bose gas
Effective Potential Diagrams
BEC-BCS Crossover in NLO Epsilon Expansion JWC+ E. Nakano (cond-mat/0610011)
BEC-BCS Crossover in NLO Epsilon Expansion JWC+ E. Nakano (cond-mat/0610011)
Outlook
• viscosity/entropy: finite chemical potential, BEC-BCS crossover
• BEC-BCS crossover in epsilon exp.: NNLO