Cauchy distribution conjecture for weighted ratios of correlated normals

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Let X=(X1,X2,…,Xk)TX=(X_1,X_2,\ldots,X_k)^T and Y=(Y1,Y2,…,Yk)TY=(Y_1,Y_2,\ldots,Y_k)^T be independent random vectors with the same distribution Nk(0,Σ)\mathcal{N}_k(0,\Sigma), where Σ\Sigma has positive diagonal entries. Let p1,p2,…,pkp_1,p_2,\ldots,p_k be nonnegative numbers satisfying

p1+p2+⋯+pk=1.p_1+p_2+\cdots+p_k=1.

Cauchy ratio conjecture. The random variable

p1Y1X1+p2Y2X2+⋯+pkYkXk\frac{p_1Y_1}{X_1}+\frac{p_2Y_2}{X_2}+\cdots+\frac{p_kY_k}{X_k}

has the standard Cauchy distribution. This is presented as an equivalent formulation of the monomial conjecture. The paper notes that an induction argument involving ratios of normal variables with nonzero means was considered but not successfully carried out.

References

Primary source

Mathias Drton and Han Xiao, “Wald tests of singular hypotheses”, arXiv:1304.6746 (2016).

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