Field theory and polynomials Definition
Pseudo algebraically closed field
Builds on FieldAlgebraic closureAlgebraically closed fieldFinite field
Definition
Let be a field with algebraic closure . An affine variety defined over is the set of common zeros in of a set of polynomials in . It is absolutely irreducible if it is irreducible as a variety over . This means that it is not the union of two proper closed subsets defined over . A point of is -rational if all its coordinates lie in . The field is pseudo algebraically closed (PAC) if every nonempty absolutely irreducible affine variety defined over has a -rational point.
Remarks
It is equivalent to ask the condition only for curves, that is, for varieties of dimension .
Example: every algebraically closed field is PAC, since then and every point of a nonempty variety is -rational. Every infinite algebraic extension of a finite field is PAC.
Non-example: and are not PAC. The curve defined by is absolutely irreducible, since is irreducible over , and is nonempty, since it contains . But it has no point with real coordinates, because for real .
Non-example: a finite field is not PAC. For instance, the curve is absolutely irreducible, because the degree of the right side is prime to the characteristic of . It has no -rational point, because for , while for .
Reading path
To understand this page from the ground up, read these 5 pages in order. The foundations come first.
Show the path as a graph
- no evidence level
- Algebraic closure concept
- Algebraically closed field concept
- Field concept
- Finite field concept
- Pseudo algebraically closed field definition
Further reading
About this page
| Tag | P32FQE1H0D |
|---|---|
| URI | m2://P32FQE1H0D |
| Kind | definition |
| Writing | W0 stub |
| MSC | 12E30, 12L12, 14G05 |
| Defines | Pseudo algebraically closed field |
| Uses | Field, Algebraic closure, Algebraically closed field, Finite field |
| Changed | 2 November 2026 |
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