L=200;​​Ω=1;​​σ=5;​​λ=0.1;​​​​t[τ_]:=1/aSinh[aτ]​​x[τ_]:=1/a(Cosh[aτ]-1)​​​​(*Ensuremisnumerictoavoidsymbolicevaluations*)​​η0[a_]:=λNSum[NIntegrate[Exp[-τ^2/(2σ^2)]Exp[IΩτ+(2IPi)/L(Abs[m]t[τ]-mx[τ])]1/Sqrt[4PiAbs[m]],{τ,-100,100}],{m,1,100}]​​​​η1[a_]:=λNSum[NIntegrate[Exp[-τ^2/(2σ^2)]Exp[IΩτ-(2IPi)/L(Abs[m]t[τ]-mx[τ])]1/Sqrt[4PiAbs[m]],{τ,-100,100}],{m,1,100}]​​​​F[a_]:=-(η0[a]^2/(1+η0[a]^2))+1/(1+η1[a]^2)​​​​η0[0.21]​​​​
0.1NSumNIntegrate
Exp-
2
τ
2
2
σ
ExpΩτ+
(2π)(Abs[m]t[τ]-mx[τ])
L

4πAbs[m]
,{τ,-100,100},{m,1,100}
​