Bahri–Xu linear algebraic conjecture

Let x1,,xpx_1,\dots,x_p with p2p\geq 2 be distinct vectors in Rm\mathbb R^m. Define the symmetric matrix A=(aij)1i,jpA=(a_{ij})_{1\leq i,j\leq p} by

aij={0,i=j,1xixj,ij.a_{ij}=\begin{cases}0,&i=j,\\\\ \dfrac{1}{|x_i-x_j|},&i\ne j. \end{cases}

For k=1,,pk=1,\dots,p, let Axk=(aijxk)1i,jp\dfrac{\partial A}{\partial x_k}=\left(\dfrac{\partial a_{ij}}{\partial x_k}\right)_{1\leq i,j\leq p}, regarded as a vector-valued p×pp\times p matrix, and let U=(u1,,up)TRpU=(u_1,\dots,u_p)^{\mathrm T}\in\mathbb R^p. Bahri–Xu's linear algebraic conjecture. There is a positive constant c=c(p,m)c=c(p,m) depending only on pp and mm such that

AU2+sup1ipUT(Axi)Uc(p,m)i,j\jiuj2xixj2.|AU|^2+\sup_{1\leq i\leq p}\left|U^{\mathrm T}\left(\frac{\partial A}{\partial x_i}\right)U\right|\geq c(p,m)\sum_{\substack{i,j\\\j\ne i}}\frac{u_j^2}{|x_i-x_j|^2}.

This is the purely linear-algebraic assumption introduced by Bahri and Xu in connection with asymptotic expansions for the Yamabe functional and the Morse lemma at infinity. The supplied source does not establish the assertion or provide evidence of its resolution, so its status remains open.

Sources & referencesView supporting material

Primary source

Hong Chen, Jianquan Ge, Kai Jia and Zhiqin Lu, “On a Conjecture of Bahri-Xu”, arXiv:2101.10023 (2021).

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