Mixed Killing Vector Fields on Cigar Ricci-Bourguignon Solitons

Abstract

In this article, we study mixed Killing vector fields, defined by the condition $L_V L_V g = f\,L_V g$, on Cigar Ricci--Bourguignon solitons. While conformal vector fields are always mixed Killing, the converse fails in flat and open cylinders with base manifold geometries, where the mixed Killing class is infinite-dimensional. We establish a rigidity phenomenon for Cigar Ricci--Bourguignon solitons: any complete steady almost gradient Ricci--Bourguignon soliton on a surface with positive curvature is, up to homothety, Hamilton's Cigar soliton. We then characterise complete mixed Killing fields and show that locally any mixed Killing field is the sum of a rotational Killing field and a mixed Killing radial field. Finally, we establish that the dimension of the vector space of complete mixed Killing fields of Cigar Ricci--Bourguignon solitons is $5$. Moreover, we explicitly determine a basis. Our results show that Cigar Ricci--Bourguignon solitons exhibit behaviour completely different from that of Euclidean space. Finally, we provide a complete description of the geodesic structure of Cigar Ricci--Bourguignon solitons.