Moduli spaces of nonspecial pointed curves of arithmetic genus 1

Abstract: In this paper we study the moduli stack ${\mathcal U}{1,n}^{ns}$ of curves of arithmetic genus 1 with n marked points, forming a nonspecial divisor. In arXiv:1511.03797 this stack was realized as the quotient of an explicit scheme $\widetilde{\mathcal U}{1,n}^{ns}$, affine of finite type over ${\Bbb P}^{n-1}$, by the action of ${\Bbb G}m^n$. Our main result is an explicit description of the corresponding GIT semistable loci in $\widetilde{\mathcal U}{1,n}^{ns}$. This allows us to identify some of the GIT quotients with some of the modular compactifications of ${\mathcal M}_{1,n}$ defined by Smyth in arXiv:0902.3690 and arXiv:0808.0177.