Differential simplicity and complete integral closure

Tight Closure and Differential Simplicity

The behavior of the Hasse–Schmidt algebra under étale extension is used to show that the Hasse–Schmidt algebra of a smooth algebra of finite type over a field equals the ring of differential operators. These techniques show that the formation of Hasse–Schmidt derivations does not commute with localization, providing a counterexample to a question of Brown and Kuan; their conjecture is reformula...

On Complete Integral Closure and Archimedean Valuation Domains

Suppose D is an integral domain with quotient eld K and that L is an extension eld of K. We show in Theorem 4 that if the complete integral closure of D is an intersection of Archimedean valuation domains on K, then the complete integral closure of D in L is an intersection of Archimedean valuation domains on L; this answers a question raised by All rings considered in this paper are assumed to...

Specialization and integral closure

I ′/(x) = I ′/(x) , where x = ∑n i=1 ziai is a generic element for I defined over the polynomial ring R ′ = R[z1, . . . , zn] and I ′ denotes the extension of I to R. This result can be paraphrased by saying that an element is integral over I if it is integral modulo a generic element of the ideal. Other, essentially unrelated, results about lifting integral dependence have been proved by Teiss...

Computing Integral Closure Workshop

Simplicity and closure constraints in spin foam models of gravity

We revise imposition of various constraints in spin foam models of 4-dimensional general relativity. We argue that the usual simplicity constraint must be supplemented by a constraint on holonomies and together they must be inserted explicitly into the discretized path integral. At the same time, the closure constraint must be relaxed so that the new constraint expresses covariance of intertwin...