charge operators

In physics, a charge is any of many different quantities, such as the electric charge in electromagnetism or the color charge in quantum chromodynamics. Charges correspond to the time-invariant generators of a symmetry group, and specifically, to the generators that commute with the Hamiltonian. Charges are often denoted by



Q


{\displaystyle Q}

, and so the invariance of the charge corresponds to the vanishing commutator



[
Q
,
H
]
=
0


{\displaystyle [Q,H]=0}

, where



H


{\displaystyle H}

is the Hamiltonian. Thus, charges are associated with conserved quantum numbers; these are the eigenvalues of the generator



Q


{\displaystyle Q}

. A "charge" can also refer to a point-shaped object with an electric charge and a position, such as in the method of image charges.

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