International Journal of Mathematics

We establish a general integral formula over sphere, and then apply it to give a geometrical proof of the celebrated topological theorem of Lashof and Smale, which asserts that the tangential degree of the tangent sphere bundle coincides with the normal Euler number for an immersion Mⁿ → E²ⁿ of an oriented closed manifold into Euclidean space of twice dimension.

Let ϕ(z) = (ϕ₁(z),…,ϕ_n(z)) be a holomorphic self-map of B and ψ(z) a holomorphic function on B, where B is the unit ball of ℂⁿ. Let 0 < p, s < +∞, -n - 1 < q < +∞, q+s > -1 and α ≥ 0, this paper characterizes boundedness and compactness of weighted composition operator W_ψ,ϕ induced by ϕ and ψ between the space F(p, q, s) and α-Bloch space .

Hypertoric varieties are hyperkähler analogues of toric varieties, and are constructed as abelian hyperkähler quotients T*ℂⁿ//// T of a quaternionic affine space. Just as symplectic toric orbifolds are determined by labelled polytopes, orbifold hypertoric varieties are intimately related to the combinatorics of hyperplane arrangements. By developing hyperkähler analogues of symplectic techniques developed by Goldin, Holm, and Knutson, we give an explicit combinatorial description of the Chen–Ruan orbifold cohomology of an orbifold hypertoric variety in terms of the combinatorial data of a rational cooriented weighted hyperplane arrangement . We detail several explicit examples, including some computations of orbifold Betti numbers (and Euler characteristics).

We study Ruelle's type zeta and L-functions for a torsion free abelian group Γ of rank ν ≥ 2 defined via an Euler product. It is shown that the imaginary axis is a natural boundary of this zeta function when ν = 2, 4 and 8, and in particular, such a zeta function has no determinant expression. Thus, conversely, expressions like Euler's product for the determinant of the Laplacians of the torus ℝ^ν/Γ defined via zeta regularizations are investigated. Also, the limit behavior of an arithmetic function arising from the Ruelle type zeta function is observed.

We generalize the notions of transversally harmonic maps between foliated Riemannian manifolds into transversally biharmonic maps. We show that a transversally biharmonic map into a foliated manifold of non-positive transverse curvature is transversally harmonic. Then we construct examples of transversally biharmonic non-harmonic maps into foliated manifolds of positive transverse curvature. We also prove that if f is a stable transversally biharmonic map into a foliated manifold of positive constant transverse sectional curvature and f satisfies the transverse conservation law, then f is a transversally harmonic map.

We consider pairs (V, H) of subgroups of a connected unipotent complex Lie group G for which the induced V × H-action on G by multiplication from the left and from the right is free. We prove that this action is proper if the Lie algebra 𝔤 of G is 3-step nilpotent. If 𝔤 is 2-step nilpotent, then there is a global slice of the action that is isomorphic to ℂⁿ. Furthermore, a global slice isomorphic to ℂⁿ exists if dim V = 1 = dim H or dim V = 1 and 𝔤 is 3-step nilpotent. We give an explicit example of a 3-step nilpotent Lie group and a pair of 2-dimensional subgroups such that the induced action is proper but the corresponding geometric quotient is not affine.