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We present a proof of Chows theorem using two results of Errett Bishop retated to volumes and limits of analytic varieties. We think this approach suggested a long time ago in the beautiful book by Gabriel Stolzenberg, is very attractive and easier for students and newcomers to understand, also the theory presented here is linked to areas of mathematics that are not usually associated with Chows theorem. Furthermore, Bishops results imply both Chows and Remmert-Steins theorems directly, meaning that this approach is more economic and just as profound as Remmert-Steins proof. At the end of the paper there is a comparison table that explains how Bishops theorems generalize to several complex variables classical results of one complex variable.
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We prove the following two results 1. For a proper holomorphic function $ f : X to D$ of a complex manifold $X$ on a disc such that ${df = 0 } subset f^{-1}(0)$, we construct, in a functorial way, for each integer $p$, a geometric (a,b)-module $E^p$ associated to the (filtered) Gauss-Manin connexion of $f$. This first theorem is an existence/finiteness result which shows that geometric (a,b)-modules may be used in global situations. 2. For any regular (a,b)-module $E$ we give an integer $N(E)$, explicitely given from simple invariants of $E$, such that the isomorphism class of $Ebig/b^{N(E)}.E$ determines the isomorphism class of $E$. This second result allows to cut asymptotic expansions (in powers of $b$) of elements of $E$ without loosing any information.
A generalized Euler sequence over a complete normal variety X is the unique extension of the trivial bundle V otimes O_X by the sheaf of differentials Omega_X, given by the inclusion of a linear space V in Ext^1(O_X,Omega_X). For Lambda, a lattice of Cartier divisors, let R_Lambda denote the corresponding sheaf associated to V spanned by the first Chern classes of divisors in Lambda. We prove that any projective, smooth variety on which the bundle R_Lambda splits into a direct sum of line bundles is toric. We describe the bundle R_Lambda in terms of the sheaf of differentials on the characteristic space of the Cox ring, provided it is finitely generated. Moreover, we relate the finiteness of the module of sections of R_Lambda and of the Cox ring of Lambda.
Historically, Ehrenfests theorem (1927) is the first one which shows that classical physics can emerge from quantum physics as a kind of approximation. We recall the theorem in its original form. Next, we highlight its generalizations to the relativistic Dirac particle, and to a particle with spin and izospin. We argue that apparent classicality of the macroscopic world can probably be explained within the framework of standard quantum mechanics.
In 1947, M. S. Macphail constructed a series in $ell_{1}$ that converges unconditionally but does not converge absolutely. According to the literature, this result helped Dvoretzky and Rogers to finally answer a long standing problem of Banach Space Theory, by showing that in all infinite-dimensional Banach spaces, there exists an unconditionally summable sequence that fails to be absolutely summable. More precisely, the Dvoretzky--Rogers Theorem asserts that in every infinite-dimensional Banach space $E$ there exists an unconditionally convergent series ${textstylesum}x^{(j)}$ such that ${textstylesum}Vert x^{(j)}Vert^{^{2-varepsilon}}=infty$ for all $varepsilon>0.$ Their proof is non-constructive and Macphails result for $E=ell_{1}$ provides a constructive proof just for $varepsilongeq1.$ In this note we revisit Machphails paper and present two alternative constructions that work for all $varepsilon>0.$
According to the Goldstone theorem a scalar theory with a spontaneously broken global symmetry contains strictly massless states. In this letter we identify a loophole in the current-algebra proof of the theorem. Therefore, the question whether in models with Mexican hat potential the tangential excitations are strictly massless or are just almost massless as compared to the radial ones remains open. We also argue that mass of the tangential excitations approaches zero even if the symmetry is not spontaneously broken but a combination of the field components invariant under the symmetry transformations acquires a large vacuum expectation value.
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