Abstract
In their celebrated work, B. Andrews and J. Clutterbuck proved the fundamental gap (the difference between the first two eigenvalues) conjecture for convex domains in the Euclidean space [3] and conjectured similar results hold for spaces with constant sectional curvature. We prove the conjecture for the sphere. Namely when $D$, the diameter of a convex domain in the unit $\mathbb{S}^n$ sphere, is $\leq \frac{\pi}{2}$, the gap is greater than the gap of the corresponding 1-dim sphere model. We also prove the gap is $\geq 3 \frac{\pi^2}{D^2}$ when $n \geq 3$, giving a sharp bound. As in [3], the key is to prove a super log-concavity of the first eigenfunction.
Funding Statement
S. Shoo was partially supported by a Simons Travel Grant.
L. Wang was partially supported by CNSF Grant 11671141 and by the Geometry Center at ECNU.
G. Wei was partially supported by NSF DMS 1506393.
Citation
Shoo Seto. Lili Wang. Guofang Wei. "Sharp fundamental gap estimate on convex domains of sphere." J. Differential Geom. 112 (2) 347 - 389, June 2019. https://doi.org/10.4310/jdg/1559786428