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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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