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Bounds on Betti Numbers

Published online by Cambridge University Press:  20 November 2018

Mark Ramras*
Affiliation:
Northeastern University, Boston, Massachusetts
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The Betti numbers βn(k) of the residue class field k = R/m of a commutative local ring (R, m) have been studied for about 20 years, primarily as the coefficients of the Poincaré series of E . Several authors have obtained results about the growth of the sequence {βn(k)}.For example, Gulliksen [3] showed that when R is non-regular, the sequence is non-decreasing. More recently, Avramov [1] studied asymptotic properties of {βn(k)} and found that under certain conditions the growth is exponential, i.e., there is a natural number p such that for all n, βpn(k) ≧ 2n.

In this paper, we examine the sequence {βn(M)} for arbitrary finitely generated non-free modules M over any commutative local artin ring R. We establish the following bounds:

1

2

3

where l(X) is the length of X.

Type
Research Article
Copyright
Copyright © Canadian Mathematical Society 1982

References

1. Avramov, L., Sur la croissance des nombres de Betti d'un anneau local, C. R. Acad. Se. Paris t. 289 (1979), 369372.Google Scholar
2. Cartan, H. and Eilenberg, S., Homologuai algebra (Princeton Univ. Press, Princeton, N.J., 1956.Google Scholar
3. Gulliksen, T., A proof of the existence of minimal R- Igebra resolutions, Acta Math. 120 (1968), 5358.Google Scholar
4. Ramras, M., Betti numbers and reflexive modules, in Ring theory (Academic Press, 1972.Google Scholar
5. Ramras, M., Sequences of Betti numbers, J. Alg. 66 (1980), 193204.Google Scholar
6. Ramras, M. and Gover, E., Increasing sequences of Betti numbers, Pacific J. Math. 87 (1980), 6568.Google Scholar