Almost Hilbertian Fields *

This paper is devoted to some variants of the Hilbert specialization property. For example, the RG-hilbertian property (for a field K), which arose in connection with the Inverse Galois Problem, requires that the specialization property holds solely for extensions of K(T ) that are Galois and regular over K. We show that fields inductively obtained from a real hilbertian field by adjoining real p-th roots (p odd prime) are RG-hilbertian; some of these fields are not hilbertian. There are other variants of interest: the R-hilbertian property is obtained from the RG-hilbertian property by dropping the condition “Galois”, the mordellian property is that every non-trivial extension of K(T ) has infinitely many non-trivial specializations, etc. We investigate the connections existing between these properties. In the case of PAC fields we obtain pure Galois-theoretic characterizations. We use them to show that “mordellian” does not imply “hilbertian” and that every PAC R-hilbertian field is hilbertian.