Stability switches in certain linear neutral differential equations

In this paper we study stability switches with respect to delay of the zero solution of certain neutral even order differential equations of the form y ^(2m)(t) + α y ^(2m)(t – π) = Σ^2m–1 _j=0 a _j y ^(j)(t) + Σ^2m–1 _j=0 b _j y ^(j)(t – π) where a _j , b_j , α ∈ (–1, 0) ∪ (0, 1) are constants, m ≥ 1, and π > 0 is a constant delay.