Ricci almost soliton and almost Yamabe soliton on Kenmotsu manifold

We prove that a Ricci almost soliton on a Kenmotsu manifold of dimension [Formula: see text] reduces to an expanding Ricci soliton satifying certain condition on the potential vector field or on the soliton function. Next, we show that any Ricci almost soliton on a Kenmotsu manifold is trivial (Einstein) if the soliton vector leaves the contact form [Formula: see text] invariant. Finally, we classify (locally) a Kenmotsu manifold admitting an almost Yamabe soliton. Some examples have been constructed of almost Yamabe solitons on different class of warped product spaces.

Compact Einstein multiply warped product space with nonpositive scalar curvature

In this paper, we characterize the Einstein multiply warped product space with nonpositive scalar curvature. As a result, it is shown that, if [Formula: see text] is Einstein multiple-warped product spaces with compact base and nonpositive scalar curvature, then [Formula: see text] is simply a Riemannian manifold. Next, we apply our result on Generalized Robertson–Walker space-time and Generalized Friedmann–Robertson–Walker space-time.

On Einstein warped products with a quarter-symmetric connection

This paper characterizes the warping functions for a multiply generalized Robertson–Walker space-time to get an Einstein space [Formula: see text] with a quarter-symmetric connection for different dimensions of [Formula: see text] (i.e. (1). dim [Formula: see text] (2). dim [Formula: see text]) when all the fibers are Ricci flat. Then we have also computed the warping functions for a Ricci flat Einstein multiply warped product spaces M with a quarter-symmetric connection for different dimensions of [Formula: see text] (i.e. (1). dim [Formula: see text] (2). dim [Formula: see text] (3). dim [Formula: see text]) and all the fibers are Ricci flat. In the last section, we have given two examples of multiply generalized Robertson–Walker space-time with respect to quarter-symmetric connection.