TY - JOUR T1 - On semistable principal bundles over a complex projective manifold JF - Int. Math. Res. Not. vol. 2008, article ID rnn035 Y1 - 2008 A1 - Indranil Biswas A1 - Ugo Bruzzo AB - Let G be a simple linear algebraic group defined over the complex numbers. Fix a proper parabolic subgroup P of G and a nontrivial antidominant character \\\\chi of P. We prove that a holomorphic principal G-bundle E over a connected complex projective manifold M is semistable and the second Chern class of its adjoint bundle vanishes in rational cohomology if and only if the line bundle over E/P defined by \\\\chi is numerically effective. Similar results remain valid for principal bundles with a reductive linear algebraic group as the structure group. These generalize an earlier work of Y. Miyaoka where he gave a characterization of semistable vector bundles over a smooth projective curve. Using these characterizations one can also produce similar criteria for the semistability of parabolic principal bundles over a compact Riemann surface. PB - Oxford University Press UR - http://hdl.handle.net/1963/3418 U1 - 917 U2 - Mathematics U3 - Mathematical Physics ER -