Abstract:
A surface XX is called unirational if there exists a dominant rational map P2⇢XP2⇢X.
For algebraically closed fields of characteristic zero any unirational surface is rational by
Castelnuovo’s rationality criterion. But if the ground field kk is an arbitrary algebraically
non-closed field then this does not hold. For example, any del Pezzo surface of degree 44, 33,
or 22 (having a point defined over kk in sufficiently general position) is unirational over kk, but
some of these surfaces are not rational over kk.
A particular case of unirational surfaces is Galois unirational surfaces, that are surfaces
birationally equivalent to quotients of rational surfaces. In the talk I will give a complete classification of Galois unirational surfaces over algebraically non-closed fields of characteristic
zero, and discuss some related questions.