“…To our best knowledge, the study in the existing literature has only focused on χ-processes and fields indexed by intervals or hyper cubes, but not low-dimensional manifolds. See, for example, Albin et al [2], Bai [4], Hashorva and Ji [19], Ji et al [20], Konstantinides et al [22], Lindgren [23], Ling and Tan [24], Liu and Ji [25,26], Piterbarg [30,31], Tan and Hashorva [38,39], Tan and Wu [40]. Also it is worth mentioning that it is often assumed that X 1 , • • • , X r are independent copies of a Gaussian process or field X in the literature, while the cross-dependence among X 1 , • • • , X r is allowed under certain constraints in this work.…”