The slope sgs_g is computed by the quotient of the lambda and nonseparating-boundary coefficients

Let Mg\overline{\mathcal{M}}_g be the moduli space of stable curves of genus gg, and let sgs_g be its slope. For an effective divisor DD on Mg\overline{\mathcal{M}}_g, write

Daλi=0g/2biδi,D\equiv a\lambda-\sum_{i=0}^{\lfloor g/2\rfloor}b_i\delta_i,

where λ\lambda is the Hodge class and the δi\delta_i are the boundary divisor classes. Its slope is denoted by s(D)s(D). Slope quotient conjecture. The statement of the theorem holds in arbitrary genus: for every genus gg, there exists ϵg>0\epsilon_g>0 such that every effective divisor DD on Mg\overline{\mathcal{M}}_g satisfying

sgs(D)sg+ϵgs_g\leq s(D)\leq s_g+\epsilon_g

has

s(D)=ab0,b0bi for all i1.s(D)=\frac{a}{b_0},\qquad b_0\leq b_i\text{ for all }i\geq 1.

The theorem in the paper establishes this assertion for g23g\leq 23; the displayed statement is the authors' conjectural extension to arbitrary genus.

Sources & referencesView supporting material

Primary source

Gavril Farkas and Mihnea Popa, “Effective divisors on M_g and a counterexample to the Slope Conjecture”, arXiv:math/0209171 (2002).

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