Lines on surfaces, how to count them

par Victor Chachay (IMB)

mardi 30 sept. 2025, 16:00 → 17:00 Europe/Paris

318

Since algebraic varieties are defined by polynomial equations, the properties of the variety may change depending on the field of definition (an equation may have solutions over C but not R). We will study the example of a cubic equation to observe some of these facts. To recover an invariant that was lost if not over C will be the excuse to introduce some motivic theory tools, mainly Euler classes and degree in the Milnor-Witt K-theory.