English

On continuous Polish group actions and equivalence relations

Logic 2015-03-17 v4

Abstract

Let X={P[0,1]N:(νN)(P({ν})>0)ν=0P({ν})=1}X = \left\{P \in [0,1]^{\bf N} : \left(\forall \nu \in {\bf N} \right) \left(P \left(\{\nu \} \right) > 0 \right) \wedge \sum\limits_{\nu = 0}^{\infty} P \left(\{\nu \} \right) = 1 \right\} be the Polish space of probability measures on N{\bf N}, each of which assigns positive probability to every elementary event, while for any PXP \in X, let ΓP={ξL1(N,P):(νN)(ξ(ν)>0)ν=0ξ(ν)P({ν})=1}{\Gamma}_{P} = \left\{\xi \in L^{1}({\bf N}, P) : \left(\forall \nu \in {\bf N} \right) \left(\xi (\nu) > 0 \right) \wedge \sum\limits_{\nu = 0}^{\infty} \xi (\nu) P \left(\{\nu \} \right) = 1 \right\} and let ΦP:ΓPξΦP(ξ)X{\Phi}_{P} : {\Gamma}_{P} \ni \xi \mapsto {\Phi}_{P}(\xi) \in X be defined by the relation (ΦP(ξ))({ν})=ξ(ν)P({ν})\left({\Phi}_{P}(\xi) \right) \left(\{\nu \} \right) = \xi (\nu) P \left(\{\nu \} \right) , whenever νN\nu \in {\bf N}. If we consider the equivalence relation E={(P,Q)X2:(ξΓP)(Q=ΦP(ξ))}E = \left\{(P,Q) \in X^{2} : \left(\exists \xi \in {\Gamma}_{P} \right) \left(Q = {\Phi}_{P}(\xi) \right) \right\} , the Polish space P={x1(R):(nN)(x(n)>0)}{\bf P} = \left\{{\bf x} \in {\ell}^{1} \left({\bf R} \right) : \left(\forall n \in {\bf N} \right) \left({\bf x}(n) > 0 \right) \right\} and the commutative Polish group G={g(0,)N:limng(n)=1}{\bf G} = \left\{{\bf g} \in (0, \infty)^{\bf N} : \lim\limits_{n \rightarrow \infty}{\bf g}(n) = 1 \right\} , while we set (gx)(n)=g(n)x(n)\left({\bf g} \cdot {\bf x} \right) (n) = {\bf g}(n){\bf x}(n), whenever gG{\bf g} \in {\bf G}, xP{\bf x} \in {\bf P} and nNn \in {\bf N}, then EE is definable and it admits a strong approximation by the turbulent Polish group action of G{\bf G} on P{\bf P}.

Keywords

Cite

@article{arxiv.1408.2097,
  title  = {On continuous Polish group actions and equivalence relations},
  author = {Nikolaos E. Sofronidis},
  journal= {arXiv preprint arXiv:1408.2097},
  year   = {2015}
}
R2 v1 2026-06-22T05:23:58.328Z