Kohayakawa-Nagle-R{ö}dl-Schacht conjecture for subdivisions

Abstract: In this paper, we study the well-known Kohayakawa-Nagle-R{\"o}dl-Schacht (KNRS) conjecture, with a specific focus on graph subdivisions. The KNRS conjecture asserts that for any graph $H$, locally dense graphs contain asymptotically at least the number of copies of $H$ found in a random graph with the same edge density. We prove the following results about $k$-subdivisions of graphs (obtained by replacing edges with paths of length $k+1$): (1). If $H$ satisfies the KNRS conjecture, then its $(2k-1)$-subdivision satisfies Sidorenko's conjecture, extending a prior result of Conlon, Kim, Lee and Lee; (2). If $H$ satisfies the KNRS conjecture, then its $2k$-subdivision satisfies a constant-fraction version of the KNRS conjecture; (3). If $H$ is regular and satisfies the KNRS conjecture, then its $2k$-subdivision also satisfies the KNRS conjecture. These findings imply that all balanced subdivisions of cliques satisfy the KNRS conjecture, improving upon a recent result of Brada\v{c}, Sudakov and Wigerson. Our work provides new insights into this pivotal conjecture in extremal graph theory.