Homology of connected sum

From Topospaces
Revision as of 01:24, 28 July 2011 by Vipul (talk | contribs)
(diff) ← Older revision | Latest revision (diff) | Newer revision → (diff)

This article describes the effect of the connected sum operation on the following invariant: homology groups

Statement

Suppose M1 and M2 are the connected manifolds of dimension n whose connected sum is being taken. Assume both We have:

Case for p Additional condition on M1,M2 What is known about Hp(M1) and Hp(M2)? Formula for Hp(M1#M2) in terms of homology groups of M1 and M2
0 none both isomorphic to Z Z (because both are connected, so is their connected sum).
Greater than 0, less than n1 none both are finitely generated abelian groups Hp(M1)Hp(M2)
n1 Both manifolds are compact, at least one of them is orientable both are finitely generated abelian groups, at least one is free abelian Hn1(M1)Hn1(M2)
n1 other cases ? ?
n Both are compact and orientable both are Z Z
n other cases ? ?
Greater than n none both are zero groups 0

Euler characteristic

The Euler characteristics are related by the following formula when both M1 and M2 are compact connected manifolds:

χ(M1#M2)=χ(M1)+χ(M2)χ(Sn)