Graviphoton
Encyclopedia
In theoretical physics
, a graviphoton (aka gravivector) is a hypothetical particle which emerges as an excitation of the metric tensor
(i.e. gravitational field) in spacetime dimensions higher than four, as described in Kaluza-Klein theory.
However, its crucial physical properties are analogous to a (massive) photon
: it induces a "vector force", sometimes dubbed a "fifth force
". The electromagnetic potential
emerges from an extra component of the metric tensor 
, where the figure 5 labels an additional, fifth dimension.
In gravity theories with extended supersymmetry (extended supergravities
), a graviphoton is normally a superpartner
of the graviton
that behaves like a photon, and is prone to couple with gravitational strength, as was appreciated in the late 1970s. Unlike the graviton, however, it may provide a repulsive (as well as an attractive) force, and thus, in some technical sense, a type of anti-gravity
. Under special circumstances, then, in several natural models, often descending from five-dimensional theories mentioned, it may actually cancel the gravitational attraction in the static limit. Joël Scherk
investigated semirealistic aspects of this phenomenon, thereby opening up an ongoing search for physical manifestations of the mechanism.
Theoretical physics
Theoretical physics is a branch of physics which employs mathematical models and abstractions of physics to rationalize, explain and predict natural phenomena...
, a graviphoton (aka gravivector) is a hypothetical particle which emerges as an excitation of the metric tensor
Metric tensor
In the mathematical field of differential geometry, a metric tensor is a type of function defined on a manifold which takes as input a pair of tangent vectors v and w and produces a real number g in a way that generalizes many of the familiar properties of the dot product of vectors in Euclidean...
(i.e. gravitational field) in spacetime dimensions higher than four, as described in Kaluza-Klein theory.
However, its crucial physical properties are analogous to a (massive) photon
Photon
In physics, a photon is an elementary particle, the quantum of the electromagnetic interaction and the basic unit of light and all other forms of electromagnetic radiation. It is also the force carrier for the electromagnetic force...
: it induces a "vector force", sometimes dubbed a "fifth force
Fifth force
Occasionally, physicists have postulated the existence of a fifth force in addition to the four known fundamental forces. The force is generally believed to have roughly the strength of gravity Occasionally, physicists have postulated the existence of a fifth force in addition to the four known...
". The electromagnetic potential
emerges from an extra component of the metric tensor , where the figure 5 labels an additional, fifth dimension.In gravity theories with extended supersymmetry (extended supergravities
Supergravity
In theoretical physics, supergravity is a field theory that combines the principles of supersymmetry and general relativity. Together, these imply that, in supergravity, the supersymmetry is a local symmetry...
), a graviphoton is normally a superpartner
Superpartner
In particle physics, a superpartner is a hypothetical elementary particle. Supersymmetry is one of the synergistic theories in current high-energy physics which predicts the existence of these "shadow" particles....
of the graviton
Graviton
In physics, the graviton is a hypothetical elementary particle that mediates the force of gravitation in the framework of quantum field theory. If it exists, the graviton must be massless and must have a spin of 2...
that behaves like a photon, and is prone to couple with gravitational strength, as was appreciated in the late 1970s. Unlike the graviton, however, it may provide a repulsive (as well as an attractive) force, and thus, in some technical sense, a type of anti-gravity
Anti-gravity
Anti-gravity is the idea of creating a place or object that is free from the force of gravity. It does not refer to the lack of weight under gravity experienced in free fall or orbit, or to balancing the force of gravity with some other force, such as electromagnetism or aerodynamic lift...
. Under special circumstances, then, in several natural models, often descending from five-dimensional theories mentioned, it may actually cancel the gravitational attraction in the static limit. Joël Scherk
Joël Scherk
Joël Scherk was a French theoretical physicist who studied string theory and supergravity. Together with John H. Schwarz, he figured out that string theory was a theory of quantum gravity in 1974...
investigated semirealistic aspects of this phenomenon, thereby opening up an ongoing search for physical manifestations of the mechanism.