text: where Π is evaluated by adding up the bubbles made 
  out of two normal and two anomalous Green’s functions. 
  Below 2∆, Π(Ω) is real (∼ Ω2/∆ for small Ω), and the 
  resonance emerges at Ω = ω0 at which Π(ω0) = ωsf . At 
  frequencies larger than 2∆, Π(Ω) has an imaginary part, 
  and this gives rise to a gaped continuum in χ(Ω). 
  
  (19) 
  
  where λn is the spin-fermion coupling constant, and ωsf 
  is a typical spin relaxation frequency of overdamped spin 
  collective excitations with a propagator 
  The imaginary part of the spin susceptibility around 
  
  the resonance frequency ω0 is31 
  
  χQ 
  1 − i Ω 
  ωsf 
  χ(q ∼ Q, Ω) =  (20) 
  
  πZoω0 
  2 
  
  ′′ 
  χ  (q, Ω) =  δ(Ω − ω0)  (22) 
  
  where χQ is the uniform static susceptibility. If we use 
  Ornstein-Zernike form of χ(q) and use either Eliashberg 
  45 or FLEX computational schemes48, we get rather sim- 
  ilar behavior of Σ as a function of frequency and rather 
  similar behavior of optical integrals. 