Videos

Introductory Workshop - Graph Theory: Extremal, Probabilistic and Structural: Uniform Turán density of hypergraphs

Presenter
February 10, 2025
Keywords:
  • extremal graph theory
  • random graphs
  • probabilistic methods
  • structural graph theory
  • Ramsey theory
MSC:
  • 05C35 - Extremal problems in graph theory [See also 90C35]
  • 05C55 - Generalized Ramsey theory [See also 05D10]
  • 05C75 - Structural characterization of families of graphs
  • 05C80 - Random graphs (graph-theoretic aspects) [See also 60B20]
  • 05D40 - Probabilistic methods in extremal combinatorics
  • including polynomial methods (combinatorial Nullstellensatz
  • etc.)
Abstract
In the early 1980s, Erdős and Sós initiated the study of Turán problems with an additional uniformity condition: the uniform Turán density of a hypergraph H is the infimum over all d such for which any sufficiently large hypergraph with the property that all its linear-size subhypergraphs have density at least d contains H. In particular, Erdős and Sós raised the questions on determining the uniform Turán densities of the complete 4-vertex 3-uniform hypergraph and the complete 4-vertex 3-uniform hypergraph with an edge missing. The former remains open after almost 40 years since its statement while the latter was resolved about a decade ago only. We will survey recent progress in this area particularly focusing on corollaries of the major result of Lamaison who showed that the palette lower bound constructions are always optimal.