Theorem 3.2. If K is a field and f∈K[x] has degree n>1, then there exists a splitting field F of f with [F:K]<n!

In the case of the polynomial t²+1∈ R [t], the situation is quite clear; its splitting field is C since t²+1=(t+i)(t-i) where i=√.

Example 4.3. By definition, Q (i) is the splitting field of x²+1 over Q , and C is the splitting field for the same polynomial, over R .
Example 4.4. The splitting field F of x⁸-1 over Q is generated by ζ:=2; indeed, the roots of x⁸-1 are all the 8-th roots of 1, and all of them are powers of ζ:[…]In fact, ζ is a root of the polynomial x⁴+1, which is irreducible over Q ; therefore F= Q (ζ) is 'already' the splitting field of x⁴+1.

The terminology "splitting field of a K-algebra" is motivated by the same terminology regarding a polynomial. A splitting field of a K-algebra A is a field extension K↦L such that A⊗_KL is split; in the special case A=K[x]/f(x) this is the same as a splitting field of the polynomial f(x).

2001, T. Y. Lam, A First Course in Noncommutative Rings, Springer, 2nd Edition, page 117,
Ex. 7.6. For a finite-dimensional k-algebra R, let T(R)= operatorname radR+[R,R], where [R,R] denotes the subgroup of R generated by ab-ba for all a,b∈R. Assume that k has characteristic p>0. Show that
T(R)⊆a∈R:aforsomem>1,
with equality if k is a splitting field for R.

Group algebras are defined over the prime field Q or 𝔽_𝕡 (depending on the characteristic), and by what we have just proved Q G and 𝔽_𝕡G have splitting fields that are finite degree extensions of the prime field.[…]
Some other basic facts about splitting fields are left to the exercises at the end of this chapter. Thus, if A is a finite-dimensional algebra over a field F that is a splitting field for A and E⊃F is a field extension, it is the case that every simple E⊗_FA-module can be written in F (Exercises 4 and 8).

Every finite dimensional central simple algebra has a splitting field: moreover, if said CSA is a division algebra, then a maximal subfield of it is a splitting field.

1955, Shimshon A. Amitsur, Generic Splitting Fields of Central Simple Algebras, Annals of Mathematics, Volume 62, Number 1, Reprinted in 2001, Avinoam Mann, Amitai Regev, Louis Rowen, David J. Saltman, Lance W. Small (editors), Selected Papers of S. A. Amitsur with Commentary, Part 2, American Mathematical Society, page 199,
The main tool in studying the structure of division algebras, or more generally, of central simple algebras (c.s.as) over a field ℭ are the extensions of ℭ that split the algebras. A field 𝔉⊇ℭ is said to split a c.s.a. 𝔄 if 𝔄⊗𝔉 is a total matrix ring over 𝔉. The present study is devoted to the study of the set of all splitting fields of a given c.s.a. 𝔄.

1999, P. Shumyatsky, V. Zobina (translators), David Louvish (editor of translation), Ya. G. Berkovich, E. M. Zhmud’, Characters of Finite Groups, Volume 2, American Mathematical Society, page 165,
DEFINITION 2. A field K is called a splitting field of a character χ of a group G if χ∈ operatorname Char_K(G), i.e., χ is afforded by a K-representation of G.
Let T be a representation of G affording the character χ. It follows from Definition 2 that K is a splitting field of χ if and only if T is equivalent to Δ, where Δ is a K-representation of G. In other words, K is a splitting field of a character χ if and only if a representation T affording χ is realized over K. Every character of G has a splitting field (for example, C is a splitting field of any character of G). If K is a splitting field of both characters χ₁,χ₂, then K is a splitting field of χ₁+χ₂, Therefore, in studying splitting fields, we may consider irreducible characters only.
DEFINITION 3. A field K is called a splitting field of a group G if it is a splitting field for every χ∈ operatorname Irr(G).

Splitting field

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