CCR and CAR algebras

Encyclopedia : C : CC : CCR : CCR and CAR algebras

In quantum field theory, if V is a real vector space equipped with a nonsingular real antisymmetric bilinear form (,) (i.e. a symplectic vector space), the unital *-algebra generated by elements of V subject to the relations

[fg-gf=i(f,g)]

f*=f

for any f, g in V is called the canonical commutation relations (CCR) algebra. The uniqueness of the representations of this algebra when V is finite dimensional is discussed in the Stone-von Neumann theorem.

There is also a corresponding unital C*-algebra, often referred to as the Weyl form of the algebra, generated by e^if subject to

[e^e^=e^]

[e^e^=e^e^e^]

(e^if)*=e^-if

for real numbers c₁, c₂.

If V is equipped with a nonsingular real symmetric bilinear form (,) instead, the unital *-algebra generated by the elements of V subject to the relations

[fg+gf=(f,g)]

f*=f

for any f, g in V is called the canonical anticommutation relations (CAR) algebra.

If V is a real Z₂-graded vector space equipped with a nonsingular antisymmetric bilinear superform (,) (i.e. (g,f)=-(-1)^|f||g|(g,f) ) such that (f,g) is real if either f or g is an even element and imaginary if both of them are odd, the unital *-algebra generated by the elements of V subject to the relations

[fg-(-1)^

>gf=i(f,g)]

f*=f, g*=g

for any two pure elements f, g in V is the obvious super generalization which unifies CCRs with CARs.

CCR and CAR algebras

See also