Biharmonic curves in Minkowski 3-space. Part II

This is a supplement to our previous research note [3]. In [3], we gave a characterization of biharmonic curves in Minkowski 3-space. More precisely, we pointed out that every biharmonic curves with nonnull principal normal in Minkowski 3-space is a helix, whose curvature κ and torsion τ satisfy κ2 = τ2. In the classification of biharmonic curves in Minkowski 3-space due to Chen and Ishikawa [1], there exist biharmonic spacelike curves with null principal normal. In this supplement, we give a characterization of biharmonic curves with null principal normal.