Arithmetic and geometry of the curve y³+1=x⁴
We give an estimation for the arithmetic genus of an integral space curve which is not contained in a surface of degree . Our main technique is the Bogomolov-Gieseker type inequality for proved by Macrì.
We find a generator of the function field on the modular curve X₁(4) by means of classical theta functions θ₂ and θ₃, and estimate the normalized generator which becomes the Thompson series of type 4C. With these modular functions we investigate some number theoretic properties.
Let Sigma C PN be a smooth connected arithmetically Cohen-Macaulay surface. Then there are at most finitely many complete linear systems on Sigma, not of the type |kH - K| (H hyperplane section and K canonical divisor on Sigma), containing arithmetically Gorenstein curves.