Charge (physics)

Charge (physics)

In physics, a charge may refer to one of many different quantities, such as the electric charge in electromagnetism or the color charge in quantum chromodynamics. Charges are associated with conserved quantum numbers.

Formal definition

More abstractly, a charge is any generator of a continuous symmetry of the physical system under study. When a physical system has a symmetry of some sort, Noether's theorem implies the existence of a conserved current. The thing that "flows" in the current is the "charge", the charge is the generator of the (local) symmetry group. This charge is sometimes called the Noether charge.

Thus, for example, the electric charge is the generator of the U(1) symmetry of electromagnetism. The conserved current is the electric current.

In the case of local, dynamical symmetries, associated with every charge is a gauge field; when quantized, the gauge field becomes a gauge boson. The charges of the theory "radiate" the gauge field. Thus, for example, the gauge field of electromagnetism is the electromagnetic field; and the gauge boson is the photon.

Sometimes, the word "charge" is used as a synonym for "generator" in referring to the generator of the symmetry. More precisely, when the symmetry group is a Lie group, then the charges are understood to correspond to the root system of the Lie group; the discreteness of the root system accounting for the quantization of the charge.


Various charge quantum numbers have been introduced by theories of particle physics. These include the charges of the Standard Model:

Charges of approximate symmetries:

  • The strong isospin charges. The symmetry groups is SU(2) flavor symmetry; the gauge bosons are the pions. The pions are not fundamental particles, and the symmetry is only approximate. It is a special case of flavor symmetry.
  • Particle flavor charges, such as strangeness or charm. These generate the global SU(6) flavor symmetry of the fundamental particles; this symmetry is badly broken by the masses of the heavy quarks.

Hypothetical charges of extensions to the Standard Model:

  • The magnetic charge, another charge in the theory of electromagnetism. Magnetic charges are not seen experimentally in laboratory experiments, but would be present for theories including magnetic monopoles.

In the formalism of particle theories charge-like quantum numbers can sometimes be inverted by means of a charge conjugation operator called C. Chiral fermions often cannot. Charge conjugation simply means that a given symmetry group occurs in two inequivalent (but still isomorphic) group representations. It is usually the case that the two charge-conjugate representations are fundamental representations of the Lie group. Their product then forms the adjoint representation of the group.

Thus, a common example is that the product of two charge-conjugate fundamental representations of SL(2,C) (the spinors) forms the adjoint rep of the Lorentz group SO(3,1); abstractly, one writes

2\otimes\overline{2}=3\oplus 1.\

Wikimedia Foundation. 2010.

Игры ⚽ Поможем сделать НИР

Look at other dictionaries:

  • Charge — or charged may refer to: Charge (basketball), illegal contact by pushing or moving into another player s torso Charge (fanfare), a six note trumpet or bugle piece denoting the call to rush forward Charge (heraldry), any object depicted on a… …   Wikipedia

  • Charge (physique) — Pour les articles homonymes, voir charge. En physique, une charge peut faire référence à différentes quantités, telle que la charge électrique en électromagnétisme ou la charge de couleur en chromodynamique quantique. Les charges sont associées… …   Wikipédia en Français

  • Physics — (Greek: physis φύσις), in everyday terms, is the science of matter [R. P. Feynman, R. B. Leighton, M. Sands (1963), The Feynman Lectures on Physics , ISBN 0 201 02116 1 Hard cover. p.1 1 Feynman begins with the atomic hypothesis.] and its motion …   Wikipedia

  • Charge ordering — (CO) is a (first or second order) phase transition occurring mostly in strongly correlated materials such as transition metal oxides or organic conductors. Due to the strong interaction, the charge is localized on different sites leading to a… …   Wikipedia

  • charge conjugation — Physics. the mathematical operation of replacing every elementary particle by its antiparticle. Symbol: C * * * ▪ physics       in particle physics, an operation that replaces particles with antiparticles (antiparticle) (and vice versa) in… …   Universalium

  • Charge invariance — refers to the fixed electrostatic potential of a particle, regardless of speed. For example, an electron has a specific rest charge. Accelerate that electron, and the charge remains the same (as opposed to the relativistic mass and energy… …   Wikipedia

  • charge conservation — ▪ physics       in physics, constancy of the total electric charge in the universe or in any specific chemical or nuclear reaction. The total charge in any closed system never changes, at least within the limits of the most precise observation.… …   Universalium

  • Physics Processing Unit — Un physics processing unit (PPU), est un microprocesseur, qui est dédié aux calculs physiques, plus particulièrement dans les jeux vidéo. Un PPU peut matériellement prendre en charge les calculs suivants : dynamique des corps rigides… …   Wikipédia en Français

  • Charge number — or just valance[1] of an ion is the coefficient that, when multiplied by the elementary charge, gives the ion s charge. [2] For example, the charge on a chloride ion, Cl − , is , where e is the elementary charge. This means the charge number for… …   Wikipedia

  • Charge-exchange ionization — (also known as charge transfer ionization) is a gas phase reaction between an ion and an atom or molecule in which the charge of the ion is transferred to the neutral species.[1] For example . See also Associative ionization Chemi ionization… …   Wikipedia

Share the article and excerpts

Direct link
Do a right-click on the link above
and select “Copy Link”