Wakamatsu Tilting Modules , U - Dominant Dimension and k - Gorenstein Modules ∗ †

Let Λ and Γ be left and right noetherian rings and ΛU a Wakamatsu tilting module with Γ = End(ΛT ). We introduce a new definition of U -dominant dimensions and show that the U -dominant dimensions of ΛU and UΓ are identical. We characterize k-Gorenstein modules in terms of homological dimensions and the property of double homological functors preserving monomorphisms. We also study a generalization of k-Gorenstein modules, and characterize it in terms of some similar properties of kGorenstein modules.