Noetherian not implies zero divisor in minimal prime
Statement
It is possible to have a Noetherian ring with a zero divisor that is not contained in any minimal prime ideal.
Related facts
- Noetherian implies every element in minimal prime is zero divisor
- Reduced Noetherian implies zero divisor in minimal prime
- Reduced not implies zero divisor in minimal prime
Proof
Let be a field. Consider the ring . We have:
- is an affine ring over a field, hence is Noetherian.
- The element is a zero divisor, since .
- The only minimal prime in is the ideal generated by : Since is nilpotent, any prime ideal must contain , and hence must contain the ideal generated by . On the other hand, the ideal generated by is prime, because the quotient is isomorphic to , which is an integral domain. Thus, is the unique minimal prime.
- is not in the ideal generated by : This is clear from the above remarks: the quotient can naturally be identified with a polynomial ring in , hence is nonzero in the quotient, and not in .
Thus, we have a Noetherian ring with a zero divisor outside all minimal prime ideals.