text: We now turn to a more microscopic model- the CB 
  model. The model describes fermions interacting by ex- 
  changing soft, overdamped collective bosons in a partic- 
  ular, near-critical, spin or charge channel31,44,45. This 
  interaction is responsible for the normal state self-energy 
  and also gives rise to a superconductivity. A peculiar 
  feature of the CB model is that the propagator of a col- 
  lective boson changes below Tc because this boson is not 
  an independent degree of freedom (as in EB model) but 
  is made out of low-energy fermions which are aﬀected by 
  superconductivity32. 
  
  0 
  
  FIG. 15: Top – σ(ω) in the NS and the SCS in the ‘corrected’ 
  MFLI model with the feedback from SC on the quasiparticle 
  √−ω2+∆2 . In the SCS σ 
  damping: iΓ term transforms into 
  now begins at Ω = 2∆. The parameters are same as in Fig. 
  10. Bottom – the behavior of Kubo sum with Γ. Observe 
  that W (ωc) in the NS is larger than in the SCS. 
  
  Γ 