# Bernd Siebert

**Category: **Research Award Winners

**Affiliation: ** University of Hamburg

The 2016 Clay Research Award was made to Bernd Siebert and Mark Gross in recognition of their groundbreaking contributions to the understanding of mirror symmetry, in joint work generally known as the “Gross-Siebert Program.”

It has its origins in surprising predictions of non-perturbative dualities in string theory: that the properties of certain interesting geometries, notably Calabi-Yau manifolds, are reflected in counter-intuitive ways in partner geometries (‘mirror manifolds’).

The Gross-Siebert program builds on an earlier, differential-geometric, proposal of Strominger, Yau, and Zaslow, in which the Calabi-Yau manifold is fibred by special Lagrangian tori, and the mirror by dual tori. The program’s central idea is to translate this into an algebro-geometric construction in an appropriate limit, involving combinatorial data associated with a degenerating family of Calabi-Yau manifolds. It draws on many areas of geometry, analysis and combinatorics and has made a deep impact on fields such as tropical and non-archimedean geometry, logarithmic geometry, the calculation of Gromov-Witten invariants, the theory of cluster algebras and combinatorial representation theory. Remarkable results independent of mirror symmetry are now emerging, notably in the geometric compactification of moduli spaces of K3 surfaces, in the construction of theta functions on Fano and Calabi-Yau varieties, and in proofs of Looijenga’s conjecture on the smoothability of certain surface cusps and of the positivity of Laurent coefficients conjecture.