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On the strong law of large numbers for $\varphi$-subgaussian random variables

Probability 2021-09-22 v5

Abstract

For p1p\ge 1 let φp(x)=x2/2\varphi_p(x)=x^2/2 if x1|x|\le 1 and φp(x)=1/pxp1/p+1/2\varphi_p(x)=1/p|x|^p-1/p+1/2 if x>1|x|>1. For a random variable ξ\xi let τφp(ξ)\tau_{\varphi_p}(\xi) denote inf{a0:  λR  lnEexp(λξ)φp(aλ)}\inf\{a\ge 0:\;\forall_{\lambda\in\mathbb{R}}\; \ln\mathbb{E}\exp(\lambda\xi)\le\varphi_p(a\lambda)\}; τφp\tau_{\varphi_p} is a norm in a space Subφp={ξ:  τφp(ξ)<}Sub_{\varphi_p}=\{\xi:\;\tau_{\varphi_p}(\xi)<\infty\} of φp\varphi_p-subgaussian random variables. We prove that if for a sequence (ξn)Subφp(\xi_n)\subset Sub_{\varphi_p} (p>1p>1) there exist positive constants cc and α\alpha such that for every natural number nn the following inequality τφp(i=1nξi)cn1α\tau_{\varphi_p}(\sum_{i=1}^n\xi_i)\le cn^{1-\alpha} holds then n1i=1nξin^{-1}\sum_{i=1}^n\xi_i converges almost surely to zero as nn\to\infty. This result is a generalization of the SLLN for independent subgaussian random variables (Taylor and Hu \cite{TayHu}) to the case of dependent φp\varphi_p-subgaussian random variables.

Keywords

Cite

@article{arxiv.1607.03035,
  title  = {On the strong law of large numbers for $\varphi$-subgaussian random variables},
  author = {Krzysztof Zajkowski},
  journal= {arXiv preprint arXiv:1607.03035},
  year   = {2021}
}

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7 pages