Friday, 26 October 2007

ag.algebraic geometry - Mirror of local Calabi-Yau

The physicists (see e.g. this paper of Aganagic and Vafa) will write the mirror as a threefold XX which is an affine conic bundle over the holomorphic symplectic surface mathbbCtimestimesmathbbCtimesmathbbCtimestimesmathbbCtimes with discriminant a Seiberg-Witten curve SigmasubsetmathbbCtimestimesmathbbCtimesSigmasubsetmathbbCtimestimesmathbbCtimes. In terms of the affine coordinates (u,v)(u,v) on mathbbCtimestimesmathbbCtimesmathbbCtimestimesmathbbCtimes, the curve SigmaSigma is given by the equation
Sigma:u+v+auv1+1=0,Sigma:u+v+auv1+1=0,
and so XX is the hypersurface in mathbbCtimestimesmathbbCtimestimesmathbbC2mathbbCtimestimesmathbbCtimestimesmathbbC2 given by the equation
X:xy=u+v+auv1+1.X:xy=u+v+auv1+1.



From geometric point of view it may be more natural to think of the mirror not as an affine conic fibration over a surface but as an affine fibration by two dimensional quadrics over a curve. The idea will be to start with the Landau-Ginzburg mirror of mathbbP1mathbbP1, which is mathbbCtimesmathbbCtimes equipped with the superpotential w=s+as1w=s+as1 and to consider a bundle of affine two dimensional quadrics on mathbbCtimesmathbbCtimes which degenerates along a smooth fiber of the superpotential, e.g. the fiber w1(0)w1(0). In this setting the mirror will be a hypersurface in mathbbCtimestimesmathbbC3mathbbCtimestimesmathbbC3 given by the equation
xyz2=s+as1.xyz2=s+as1.
Up to change of variables this is equivalent to the previous picture but it also makes sense in non-toric situations. Presumably one can obtain this way the mirror of a Calabi-Yau which is the total space of a rank two (semistable) vector bundle of canonical determinant on a curve of higher genus.

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