In this talk, we will introduce the 3-dimensional Noether inequality and completely classify the canonical threefolds on the Noether line with $p_g \ge 5$ by studying their moduli spaces. For every such moduli space, we establish an explicit stratification, estimate the number of its irreducible components and prove the dimension formula. A new and unexpected phenomenon is that the number of irreducible components grows linearly with the geometric genus, while the moduli space of canonical surfaces on the Noether line with any prescribed geometric genus has at most two irreducible components of the same dimension. This is a joint work with S.Coughlan, R.Pignatelli and T.Zhang.
Yong Hu, Noether Inequality for Irregular Threefolds of General Type
Let X be a smooth irregular 3-fold of general type. In this talk, we will prove that the optimal Noether inequality vol(X) ≥ (4/3) pg(X) holds if pg(X) ≥ 16 or if X has a Gorenstein minimal model. Moreover, when X attains the equality and pg(X) ≥ 16, its canonical model will be explicitly described. This is a joint work with Tong Zhang.
Yong Hu, Noether-Severi Inequality and Equality for Irregular Threefolds of General Type
For complex smooth irregular 3-folds of general type, I will introduce the optimal Noether-Severi inequality. This answers an open question of Zhi Jiang in dimension three. Moreover, I will also completely describe the canonical models of irregular 3-folds attaining the Noether-Severi equality. This is a joint work with Tong Zhang.