Consider critical site percolation on $mathbb{Z}^d$ with $d geq 2$. We prove a lower bound of order $n^{- d^2}$ for point-to-point connection probabilities, where $n$ is the distance between the points. Most of the work in our proof concerns a `construction which finally reduces the problem to a topological one. This is then solved by applying a topological fact, which follows from Brouwers fixed point theorem. Our bound improves the lower bound with exponent $2 d (d-1)$, used by Cerf in 2015 to obtain an upper bound for the so-called two-arm probabilities. Apart from being of interest in itself, our result gives a small improvement of the bound on the two-arm exponent found by Cerf.
We prove an almost constant lower bound of the isoperimetric coefficient in the KLS conjecture. The lower bound has the dimension dependency $d^{-o_d(1)}$. When the dimension is large enough, our lower bound is tighter than the previous best bound which has the dimension dependency $d^{-1/4}$. Improving the current best lower bound of the isoperimetric coefficient in the KLS conjecture has many implications, including improvements of the current best bounds in Bourgains slicing conjecture and in the thin-shell conjecture, better concentration inequalities for Lipschitz functions of log-concave measures and better mixing time bounds for MCMC sampling algorithms on log-concave measures.
Let $alpha=1/2$, $theta>-1/2$, and $ u_0$ be a probability measure on a type space $S$. In this paper, we investigate the stochastic dynamic model for the two-parameter Dirichlet process $Pi_{alpha,theta, u_0}$. If $S=mathbb{N}$, we show that the bilinear form begin{eqnarray*} left{ begin{array}{l} {cal E}(F,G)=frac{1}{2}int_{{cal P}_1(mathbb{N})}langle abla F(mu), abla G(mu)rangle_{mu} Pi_{alpha,theta, u_0}(dmu), F,Gin {cal F}, {cal F}={F(mu)=f(mu(1),dots,mu(d)):fin C^{infty}(mathbb{R}^d), dge 1} end{array} right. end{eqnarray*} is closable on $L^2({cal P}_1(mathbb{N});Pi_{alpha,theta, u_0})$ and its closure $({cal E}, D({cal E}))$ is a quasi-regular Dirichlet form. Hence $({cal E}, D({cal E}))$ is associated with a diffusion process in ${cal P}_1(mathbb{N})$ which is time-reversible with the stationary distribution $Pi_{alpha,theta, u_0}$. If $S$ is a general locally compact, separable metric space, we discuss properties of the model begin{eqnarray*} left{ begin{array}{l} {cal E}(F,G)=frac{1}{2}int_{{cal P}_1(S)}langle abla F(mu), abla G(mu)rangle_{mu} Pi_{alpha,theta, u_0}(dmu), F,Gin {cal F}, {cal F}={F(mu)=f(langle phi_1,murangle,dots,langle phi_d,murangle): phi_iin B_b(S),1le ile d,fin C^{infty}(mathbb{R}^d),dge 1}. end{array} right. end{eqnarray*} In particular, we prove the Mosco convergence of its projection forms.
The multicolor Ramsey number problem asks, for each pair of natural numbers $ell$ and $t$, for the largest $ell$-coloring of a complete graph with no monochromatic clique of size $t$. Recent works of Conlon-Ferber and Wigderson have improved the longstanding lower bound for this problem. We make a further improvement by replacing an explicit graph appearing in their constructions by a random graph. Graphs useful for this construction are exactly those relevant for a problem of ErdH{o}s on graphs with no large cliques and few large independent sets. We also make some basic observations about this problem.