New partial orders on Rickart *-rings

In this paper, we define and study partial orders on a Rickart *-ring obtained by imposing an additional condition on the star and the one-sided star partial orders.

For each such order, we show that the down-set of any element is order-isomorphic to a suitable subset of self-adjoint idempotent elements.

As an application, we characterize the elements which are below a given element with respect to each of the new orders.

We further prove that the down-set of any element is a lattice whenever the ring is regular.

We analyze the existence of supremum and infimum of pairs of elements in a regular Rickart *-ring and provide characterizations of these operations whenever they exist.

Finally, we extend the latter results for a nonempty subset of elements for regular Baer *-rings.