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DTSTART;TZID=America/New_York:20211102T093000
DTEND;TZID=America/New_York:20211102T103000
DTSTAMP:20240213T062436Z
CREATED:20240213T062436Z
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UID:10002107-1635845400-1635849000@cmsa.fas.harvard.edu
SUMMARY:Counting invariant curves on a Calabi-Yau threefold with an involution
DESCRIPTION:Abstract: Gopakumar-Vafa invariants are integers n_beta(g) which give a virtual count of genus g curves in the class beta on a Calabi-Yau threefold. In this talk\, I will give a general overview of two of the sheaf-theoretic approaches to defining these invariants: via stable pairs a la Pandharipande-Thomas (PT) and via perverse sheaves a la Maulik-Toda (MT). I will then outline a parallel theory of Gopakumar-Vafa invariants for a Calabi-Yau threefold X with an involution. They are integers n_beta(g\,h) which give a virtual count of curves of genus g in the class beta which are invariant under the involution and whose quotient by the involution has genus h. I will give two definitions of n_beta(g\,h) which are conjectured to be equivalent\, one in terms of a version of PT theory\, and one in terms of a version of MT theory. These invariants can be computed and the conjecture proved in the case where X=SxC where S is an Abelian or K3 surface with a symplectic involution. In these cases\, the invariants are given by formulas expressed with Jacobi modular forms. In the case where S is an Abelian surface\, the specialization of n_beta(g\,h) to h=0 recovers the count of hyperelliptic curves on Abelian surfaces first computed by B-Oberdieck-Pandharipande-Yin. This is joint work with Stephen Pietromonaco.
URL:https://cmsa.fas.harvard.edu/event/counting-invariant-curves-on-a-calabi-yau-threefold-with-an-involution/
CATEGORIES:Joint Harvard-CUHK-YMSC Differential Geometry
ATTACH;FMTTYPE=image/png:https://cmsa.fas.harvard.edu/media/Jim-Bryan_poster_3Nov2021.png
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DTSTART;TZID=America/New_York:20211110T160000
DTEND;TZID=America/New_York:20211110T170000
DTSTAMP:20240213T063355Z
CREATED:20240213T063355Z
LAST-MODIFIED:20240213T063355Z
UID:10002116-1636560000-1636563600@cmsa.fas.harvard.edu
SUMMARY:Higher rank DT theory from rank 1
DESCRIPTION:Abstract: Fix a Calabi-Yau 3-fold X. Its DT invariants count stable bundles and sheaves on X. The generalised DT invariants of Joyce-Song count semistable bundles and sheaves on X. I will describe work with Soheyla Feyzbakhsh showing these generalised DT invariants in any rank r can be written in terms of rank 1 invariants. By the MNOP conjecture the latter are determined by the GW invariants of X. Along the way we also show they are determined by rank 0 invariants counting sheaves supported on surfaces in X. These invariants are predicted by S-duality to be governed by (vector-valued\, mock) modular forms.
URL:https://cmsa.fas.harvard.edu/event/higher-rank-dt-theory-from-rank-1/
CATEGORIES:Joint Harvard-CUHK-YMSC Differential Geometry
ATTACH;FMTTYPE=image/png:https://cmsa.fas.harvard.edu/media/20211110_Richard-Thomas_poster-1.png
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BEGIN:VEVENT
DTSTART;TZID=America/New_York:20211124T160000
DTEND;TZID=America/New_York:20211124T170000
DTSTAMP:20240226T111010Z
CREATED:20240213T065022Z
LAST-MODIFIED:20240226T111010Z
UID:10002133-1637769600-1637773200@cmsa.fas.harvard.edu
SUMMARY:Quantum cohomology as a deformation of symplectic cohomology
DESCRIPTION:Abstract: Let X be a compact symplectic manifold\, and D a normal crossings symplectic divisor in X. We give a criterion under which the quantum cohomology of X is the cohomology of a natural deformation of the symplectic cochain complex of X \ D. The criterion can be thought of in terms of the Kodaira dimension of X (which should be non-positive)\, and the log Kodaira dimension of X \ D (which should be non-negative). We will discuss applications to mirror symmetry. This is joint work with Strom Borman and Umut Varolgunes.
URL:https://cmsa.fas.harvard.edu/event/11-24-21-joint-harvard-cuhk-ymsc-differential-geometry-seminar/
CATEGORIES:Joint Harvard-CUHK-YMSC Differential Geometry
ATTACH;FMTTYPE=image/png:https://cmsa.fas.harvard.edu/media/20211124_Nick-Sheridan_RESCHEDULED_poster.png
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