ON THE SYMMETRIC NORMALISER GRAPH OF A GROUP

Abstract In this paper, we introduce the symmetric normaliser graph of a group G . The vertex set of this graph consists of the elements of the group. Vertices x and y are adjacent if x lies in the normaliser of <mml:math xmlns:xlink="http://www.w3.org/1999/xlink" xmlns:mnf="http://cambridge.org/core/manifest" xmlns:cup="http://contentservices.cambridge.org" xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:m="http://cambridge.org/core/metadata" xmlns:core="http://cambridge.org/core" xmlns:c="http://cambridge.org/core/content" display="inline"> <mml:mo stretchy="false" fence="false">⟨</mml:mo> <mml:mi>y</mml:mi> <mml:mo stretchy="false" fence="false">⟩</mml:mo> </mml:math> $\langle y \rangle $ left angle bracket y right angle bracket and y lies in the normaliser of <mml:math xmlns:xlink="http://www.w3.org/1999/xlink" xmlns:mnf="http://cambridge.org/core/manifest" xmlns:cup="http://contentservices.cambridge.org" xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:m="http://cambridge.org/core/metadata" xmlns:core="http://cambridge.org/core" xmlns:c="http://cambridge.org/core/content" display="inline"> <mml:mo stretchy="false" fence="false">⟨</mml:mo> <mml:mi>x</mml:mi> <mml:mo stretchy="false" fence="false">⟩</mml:mo> </mml:math> $\langle x \rangle $ left angle bracket x right angle bracket . We investigate the position this graph occupies in the hierarchy of graphs defined on groups. We show that the existing hierarchy is further refined by this graph and that the edges of this graph lie between the edges of the commuting graph and the nilpotent graph. For finite groups, we prove a necessary and sufficient condition for the symmetric normaliser graph to be equal to the commuting graph, and similarly, for equality with the nilpotent graph. The edge set of the symmetric normaliser graph is also a subset of the edge set of the Engel graph of a group and has connections to the nongenerating graph of a group.