Monday, 9 August 2010

ag.algebraic geometry - What is the Euler characteristic of a Hilbert scheme of points of a singular algebraic curve?

Let X be a smooth surface of genus g and SnX its n-symmetrical product (that is, the quotient of Xtimes...timesX by the symmetric group Sn). There is a well known, cool formula computing the Euler characteristic of all these n-symmetrical products:



sumdgeq0chileft(X[d]right)qd=(1q)chi(X)



It is known that SnXcongX[n], the Hilbert scheme of 0-subschemes of length n over X. Hence, the previous formula also computes the Euler characteristic of these spaces.



What about for singular surfaces? More precisely, if X is a singular complex algebraic curve, do you know how to compute the Euler characteristic of its n-symmetrical powers SnX? More importantly: what is the Euler characteristic of X[n], the Hilbert scheme of 0-schemes of length n over X?



I guess it is too much to hope for a formula as neat as the one given for the smooth case. Examples, formulas for a few cases or general behaviour (e.g. if for large n, chileft(X[n]right)=0) are all very welcome!

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