Fermions from Cold Atoms to Neutron Stars: Benchmarking the Many-Body Problem (INT-11-1)March 14 - May 20, 2011Michael McNeil Forbes, Aurel Bulgac, Alexandros Gezerlis, Gora V. Shlyapnikov, Tin-Lun (Jason) Ho, Martin W. Zwierlein

Pairing in low density fermion systems: Open problems

Symmetric (unpolarized) systems

- What is the size of the Cooper pair?

Nature 454, 739-743 (2008)

- Is there a pseudo-gap phase? What is the best way to put it in evidence experimentally?

- Response of a paired system to a weak external field, RF spectroscopy.

Asymmetric (polarized/imbalanced) systems

Son and Stephanov, 2005 Bulgac, Forbes, Schwenk, 2006

Gapless superfluid

LOFF

normal

Bulgac and Yoon, 2009

Going beyond the naïve BCS approximation (P-wave pairing)Going beyond the naïve BCS approximation (P-wave pairing)

BCS approx. (black)BCS approx. (black)

Eliashberg approx. (blue)Eliashberg approx. (blue)

Full momentum and frequency dependence of the self-Full momentum and frequency dependence of the self-consistent equations (red)consistent equations (red)

nb/nf = 2, 1, 0.5(from upper to lower panel)

5/32 2/3 23 (6 )

( , ) 5 2

ba b a

a

nE n n n g

m n

Bulgac, Forbes, 2008

LOFF at unitarity

5/23/2

2 2

2 2[ , ]

30b

a b aa

mP h

Next Frontier - Time-dependent probes