721 research outputs found
Precalibre pairs of measure algebras
AbstractWe consider Radon measures μ and pairs (κ,λ) of cardinals such that among every κ many positive measure sets there are λ many whose intersection is nonempty. Such families are connected with the cardinal invariants of the ideal of μ-null sets and have found applications in various subjects of topological measure theory. We survey many of such connections and applications and give some new ones. In particular we show that it is consistent to have a Corson compact space carrying a Radon measure of type c>ℵ1 and we partially answer a question of Haydon about measure precalibres
Universally Kuratowski-Ulam spaces and open-open games
We examine the class of spaces in which the second player has a winning
strategy in the open--open game. We show that this spaces are not universally
Kuratowski-Ulam. We also show that the games G and G7 introduced by P. Daniels,
K. Kunen, H. Zhou [Fund. Math. 145 (1994), no. 3, 205--220] are not equivalent
Sequential closure in the space of measures
We show that there is a compact topological space carrying a measure which is
not a weak* limit of finitely supported measures but is in the sequential
closure of the set of such measures. We construct compact spaces with measures
of arbitrarily high levels of complexity in this sequential hierarchy. It
follows that there is a compact space in which the sequential closure cannot be
obtained in countably many steps. However, we show that this is not the case
for our spaces where the sequential closure is always obtained in countably
many steps.Comment: (18 pages, a gap in an argument from the previous version fixed
Measure Recognition Problem
This is an article in mathematics, specifically in set theory. On the example
of the Measure Recognition Problem (MRP) the article highlights the phenomenon
of the utility of a multidisciplinary mathematical approach to a single
mathematical problem, in particular the value of a set-theoretic analysis. MRP
asks if for a given Boolean algebra \algB and a property of measures
one can recognize by purely combinatorial means if \algB supports a strictly
positive measure with property . The most famous instance of this problem
is MRP(countable additivity), and in the first part of the article we survey
the known results on this and some other problems. We show how these results
naturally lead to asking about two other specific instances of the problem MRP,
namely MRP(nonatomic) and MRP(separable). Then we show how our recent work D\v
zamonja and Plebanek (2006) gives an easy solution to the former of these
problems, and gives some partial information about the latter. The long term
goal of this line of research is to obtain a structure theory of Boolean
algebras that support a finitely additive strictly positive measure, along the
lines of Maharam theorem which gives such a structure theorem for measure
algebras
Measurable centres in convolution semigroups
In a convolution semigroup over a locally compact group, measurability of the
translation by a fixed element implies continuity. In other words, the
measurable centre coincides with the topological centre.Comment: 8 page
Competition between standard and exotic double beta decays
We discuss the contributions of higher order terms in weak Hamiltonian to the
standard two-neutrino double beta decay. The formalism for the unique first
forbidden transitions has been developed, and it is shown that they can alter
the two-electron energy spectrum. Yet, their effect is too small to screen the
detection of exotic neutrinoless double beta decays, which are candidates for
testing the physics beyond the standard model.Comment: 9 pages, latex, 1ps figures, minor changes, to appear in Phys. Lett.
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