Structure conjecture for sRC quotients of smooth klt pairs

Let (X,D)(X,D) be a klt pair with XX smooth and (KX+D)-(K_X+D) nef. An orbifold morphism is a morphism of orbifold pairs. The pair (X,D)(X,D) is sRC if its slope rationally connected quotient has the vanishing property described in the preceding definition. An orbifold fiber (Xr,Dr)(X_r,D_r) is a fiber of such a morphism equipped with its induced orbifold structure.

Structure conjecture for sRC quotients. There exists an orbifold morphism

ρ:(X,D)(R,DR)\rho:(X,D)\rightarrow(R,D_R)

with the following properties:

  1. (R,DR)(R,D_R) is a klt pair, RR is smooth, and
c1(KR+DR)=0.c_1(K_R+D_R)=0.
  1. General orbifold fibers (Xr,Dr)(X_r,D_r) are sRC.
  2. The fibration is locally trivial with respect to pairs: for any small open set URU\subset R,
(ρ1(U),D)(U,DRU)×(Xr,DXr)(\rho^{-1}(U),D)\cong(U,D_R|_U)\times(X_r,D_{X_r})

over UYU\subset Y, where XrX_r is a general fiber of ρ\rho.

This conjecture seeks a structure theorem for sRC quotients analogous to the known structure theorem for the sRC quotient of an lc pair. It predicts that, under nefness of the anti-canonical divisor, the quotient has a smooth klt base with numerically trivial log canonical class, sRC general fibers, and local product structure; its resolution status is not specified in the source.

Sources & referencesView supporting material

Primary source

Frédéric Campana, Junyan Cao and Shin-ichi Matsumura, “Projective klt pairs with nef anti-canonical divisor”, arXiv:1910.06471 (2019).

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