“…For a free-energy functional depending only on one order parameter matrix q aρ,bλ , the corresponding eigenvalues are Λ 011 and Λ 122 given by formula (41) in ref. [10]. In our case, however, the free-energy depends on 2K matrices {Q l ,Q l } and the stability condition for each mode reads ∆(α, K) =Λ ( Λ + (K − 1)Λ ) − 1 K 2 < 0 wherê Λ, Λ, Λ are the eigenvalues computed for the fluctuations with respect toQ ℓQℓ , Q ℓ Q ℓ and Q ℓ Q m (ℓ = m) respectively [2,4].…”