The roots of polynomial $ p(m) $ are:
$$ \begin{aligned}m_1 &= 0.5+0.866i\\[1 em]m_2 &= 0.5-0.866i\\[1 em]m_3 &= -0.5+0.866i\\[1 em]m_4 &= -0.5-0.866i \end{aligned} $$Polynomial $ m^4+m^2+1 $ has no rational roots that can be found using Rational Root Test, so the roots were found using quartic formulas.