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Principle Seminar of the Department of Probability Theory, Moscow State University
September 12, 2018 16:45–17:45, Moscow, MSU, auditorium 12-24
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Limit theorems in the theory of random hypergraphs
A. S. Semenov Lomonosov Moscow State University, Faculty of Mechanics and Mathematics
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Abstract:
The report is devoted to one of the central directions of the probabilistic combinatorics — theory
of random hypergraphs. The classical binomial model of a random hypergraph H(n,k,p), where
each k-subset (edge) of the set of n vertices is included in a random hypergraph independently of
the others with probability p, is the main object of the analysis. The report briefly highlights the
history of the research and the new results obtained by the author. The report consists of two
parts. 

In the first part of the report, we will discuss the limit behavior of the independence number of
the random hypergraph H(n,k,p) and its parametric generalizations, j-independence number. The
most incomplete case in this area is the case of a sparse random hypergraph, when the
expectation of the number of edges is linear with respect to the number of vertices. Here the
author established the laws of large numbers for the j-independence numbers in the form of the
existence theorem. For a strongly sparse case, it is even possible to indicate the explicit form of
the limit constant. 

The second big topic considers colorings of random hypergraphs. Here the limit distribution of
the j-chromatic number of a random hypergraph in a sparse case has been studied. The first new
result gives very accurate estimates of the threshold probability for the property of j-chromatic
number equals two. The second new result in this direction establishes the limit distribution of
the j-chromatic number of the random hypergraph H(n,k,p) in the case j=k-2. In particular, it is
shown that the set of limit values is either one-point or consists of two adjacent values which can
be found explicitly.
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