Irena Hinterleitner,
                                
                                Volodymyr A. Kiosak  
                                   (2008)   
                
                
                    
                        
                            
            In this paper we study vector fields in Riemannian spaces, which satisfy , ,  We investigate the properties of these fields and the conditions of their coexistence with concircular vector fields. It is shown that in Riemannian spaces, noncollinear concircular and -vector fields cannot exist simultaneously. It was found that Riemannian spaces with -vector fields of constant length have constant scalar curvature. The conditions for the existence of -vector fields in symmetric spaces...