Continuous and Discrete Asymptotic Behaviours of the J-function of a Fano Manifold
ChunYin Hau
TL;DR
The paper introduces the asymptotically Mittag-Leffler (aML) condition for cohomology-valued J-functions of Fano manifolds and proves that, when $t^{\frac{1}{2}\dim X} J(t)$ is $(T,\theta,A)$-scaled aML, the J-function admits the exponential growth $J(t) = \frac{1}{r} t^{-\frac{1}{2}\dim X} e^{T t} (A + o(1))$ as $t\to+\infty$, enabling computation of the principal asymptotic class from $J$-function coefficients. The authors establish that the aML property is preserved under products and under taking hypersurfaces (via quantum Lefschetz), and they verify the projective space case explicitly, showing the framework aligns with known Gamma conjecture I predictions. They further develop a calculus for aML series, including a Riemann-Liouville extension to cohomology and a product rule that yields aML behavior for products of manifolds, thereby enabling the construction of aML $J$-functions for a broad class of Fano manifolds. Overall, the work provides a practical, coefficient-based method to extract principal asymptotic data from the $J$-function, with implications for understanding the Gamma class and its conjectural equality (Gamma conjecture I) in various geometric settings.
Abstract
In this paper, we propose a condition on the coefficients of a cohomology-valued power series, which we call ``asymptotically Mittag-Leffler''. We show that if the $J$-function of a Fano manifold is asymptotically Mittag-Leffler, then it has the exponential growth as $t\to +\infty$. This provides an alternative method to compute the principal asymptotic class of a Fano manifold using the coefficients of $J$-function. We also verify that the $J$-function of the projective space is asymptotically Mittag-Leffler, and the property of having an asymptotically Mittag-Leffler $J$-function is preserved when taking product and hypersurface.
