![Stable homology of braid groups with symplectic coefficients](/media/cache/video_light/uploads/video/2024-05-07_Petersen.mp4-02e4b37b08b4d31a5bc8706d66c76471-video-339dfc29f5d7136e6a7bcf8ea9ae0a67.jpg)
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Stable homology of braid groups with symplectic coefficients
By Dan Petersen
Appears in collection : COUNT - Computations and their Uses in Number Theory / Les calculs et leurs utilisations en théorie des nombres
An abelian surface defined over $\mathbb{Q}$ is said to be geometrically split if its base change to the complex numbers is isogenous to a product of elliptic curves. In this talk we will determine the algebras that arise as geometric endomorphism algebras of geometrically split abelian surfaces defined over $\mathbb{Q}$. In particular, we will show that there are 92 of them. A key step is determining the set of imaginary quadratic fields $M$ for which there exists an abelian surface over $\mathbb{Q}$ which is geometrically isogenous to the square of an elliptic curve with CM by $M$.
This is joint work with Francesc Fité.