Coefficient-wise Wright log-convexity and log-concavity in the first parameter of the normalized incomplete beta function

For a,b,α,β>0a,b,\alpha,\beta>0 and x\tsim(0,1)x\tsim(0,1), write the relevant generalized Turán expression as a power series whose coefficients are denoted by ψk\psi_k. Coefficient-wise first-parameter conjecture. The coefficients ψk\psi_k are negative for all a,α,β>0a,\alpha,\beta>0 and x\tsim(0,1)x\tsim(0,1) when 0<b<10<b<1, and positive when b>1b>1. Consequently, axa(1x)bIx(a,b)a\to x^{-a}(1-x)^{-b}I_x(a,b) is strictly coefficient-wise Wright log-convex on (0,)(0,\infty) for α,β>0\alpha,\beta>0, x\tsim(0,1)x\tsim(0,1) and 0<b<10<b<1, and strictly coefficient-wise Wright log-concave on (0,)(0,\infty) for α,β>0\alpha,\beta>0, x\tsim(0,1)x\tsim(0,1) and b>1b>1. This is presented as a substantial strengthening of the earlier parameter-log-concavity theorem; the supplied text gives no resolution.

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Primary source

Dmitrii Karp, “Normalized incomplete beta function: log-concavity in parameters and other properties”, arXiv:1509.05120 (2015).

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