
arXiv: 2203.06453
The ellipsoidal capacity function of a symplectic four manifold X measures how much the form on X must be dilated in order for it to admit an embedded ellipsoid of eccentricity z . In most cases there are just finitely many obstructions to such an embedding besides the volume. If there are infinitely many obstructions, X is said to have a staircase. This paper gives an almost complete description of the staircases in the ellipsoidal capacity functions of the family of symplectic Hirzebruch surfaces H_{b} formed by blowing up the projective plane with weight b . We describe an interweaving, recursively defined, family of obstructions to symplectic embeddings of ellipsoids that show there is an open dense set of shape parameters b that are blocked, i.e. have no staircase, and an uncountable number of other values of b that do admit staircases. The remaining b -values form a countable sequence of special rational numbers that are closely related to the symmetries discussed in Magill–McDuff (arXiv:2106.09143). We show that none of them admit ascending staircases. Conjecturally, none admit descending staircases. Finally, we show that, as long as b is not one of these special rational values, any staircase in H_{b} has irrational accumulation point. A crucial ingredient of our proofs is the new, more indirect approach to using almost toric fibrations in the analysis of staircases by Magill (arXiv:2204.12460). In particular, the structure of the relevant mutations of the set of almost toric fibrations on H_{b} is echoed in the structure of the set of blocked b -intervals.
Mathematics - Number Theory, ellipsoidal capacity functions, continued fractions, Symplectic manifolds (general theory), symplectic embeddings, Mathematics - Symplectic Geometry, 53D05, 11Y99, FOS: Mathematics, Symplectic Geometry (math.SG), Number Theory (math.NT), symplectic staircases, Symplectic structures in 4 dimensions, almost toric fibrations
Mathematics - Number Theory, ellipsoidal capacity functions, continued fractions, Symplectic manifolds (general theory), symplectic embeddings, Mathematics - Symplectic Geometry, 53D05, 11Y99, FOS: Mathematics, Symplectic Geometry (math.SG), Number Theory (math.NT), symplectic staircases, Symplectic structures in 4 dimensions, almost toric fibrations
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