  We derive the generalized magneto-absorption spectra for curved graphene
nanorib- bons and carbon nanotubes by using the Peierls tight-binding model.
The main spectral characteristics and the optical selection rules result from
the cooperative or competitive relationships between the geometric structure
and a magnetic field. In curved ribbons, the dominant selection rule remains
unchanged during the variation of the curvature. When the arc angle increases,
the prominent peaks are split, with some even vanishing as the angle exceeds a
critical value. In carbon nanotubes, the angular-momentum coupling induces
extra selection rules, of which more are revealed due to the increase of either
(both) of the factors: tube diameter and field strength. Particularly once the
two factors exceed certain critical values, the optical spectra could reflect
the quasi-Landau-level structures. The identifying features of the spec- tra
provide insight into optical excitations for curved systems with either open or
closed boundary condition.
