Fiber cones of ideals with almost minimal multiplicity

Abstract

Fiber cones of $0$-dimensional ideals with almost minimal multiplicity in Cohen-Macaulay local rings are studied. Ratliff-Rush closure of filtration of ideals with respect to another ideal is introduced. This is used to find a bound on the reduction number with respect to an ideal. Rossi's bound on reduction number in terms of Hilbert coefficients is obtained as a consequence. Sufficient conditions are provided for the fiber cone of $0$-dimensional ideals to have almost maximal depth. Hilbert series of such fiber cones are also computed.