6 papers
Topological groupoids with involution and real algebraic stacks
Emiliano Ambrosi, Olivier de Gaay Fortman
To a topological groupoid endowed with an involution, we associate a topological groupoid of fixed points, generalizing the fixed-point subspace of a topological space with involut…
Wild Brauer classes via prismatic cohomology
Emiliano Ambrosi, Rachel Newton, Margherita Pagano
Let be a finite extension of and a smooth proper -variety with good reduction. Under a mild assumption on the behaviour of Hodge numbers under reduction m…
On the topology of real algebraic stacks
Emiliano Ambrosi, Olivier de Gaay Fortman
Motivated by questions arising in the theory of moduli spaces in real algebraic geometry, we develop a range of methods to study the topology of the real locus of a Deligne-Mumford…
Geometrically simple counterexamples to a local-global principle for quadratic twists
Emiliano Ambrosi, Nirvana Coppola, Francesc Fité
Two abelian varieties and over a number field are said to be strongly locally quadratic twists if they are quadratic twists at every completion of . While it was kno…
An Artin--Mumford criterion for conic bundles in characteristic two
Emiliano Ambrosi, Giuseppe Ancona
We prove a characteristic two version of the famous criterion of Artin and Mumford for irrationality of conic bundles. On the one hand, combined with the pathological behaviour of…
Reduction modulo of the Noether problem
Emiliano Ambrosi, Domenico Valloni
Let be a complete valuation ring of mixed characteristic with algebraically closed fraction field and residue field . Let be a smooth projective morphism.…