A three-body force is a
force
In physics, a force is an influence that can cause an Physical object, object to change its velocity unless counterbalanced by other forces. In mechanics, force makes ideas like 'pushing' or 'pulling' mathematically precise. Because the Magnitu ...
that does not exist in a system of two objects but appears in a three-body system. In general, if the behaviour of a system of more than two objects cannot be described by the two-body interactions between all possible pairs, as a first approximation, the deviation is mainly due to a three-body force.
The fundamental
strong interaction
In nuclear physics and particle physics, the strong interaction, also called the strong force or strong nuclear force, is one of the four known fundamental interaction, fundamental interactions. It confines Quark, quarks into proton, protons, n ...
does exhibit such behaviour, the most important example being the stability experimentally observed for the
helium-3 isotope, which can be described as a 3-body quantum cluster entity of two protons and one neutron
NPin stable superposition. Direct evidence of a 3-body force in helium-3 is known
The existence of stable
NPcluster calls into question models of the atomic nucleus that restrict nucleon interactions within shells to 2-body phenomenon. The three-nucleon-interaction is fundamentally possible because
gluon
A gluon ( ) is a type of Massless particle, massless elementary particle that mediates the strong interaction between quarks, acting as the exchange particle for the interaction. Gluons are massless vector bosons, thereby having a Spin (physi ...
s, the mediators of the strong interaction, can couple to themselves. In
particle physics
Particle physics or high-energy physics is the study of Elementary particle, fundamental particles and fundamental interaction, forces that constitute matter and radiation. The field also studies combinations of elementary particles up to the s ...
, the interactions between the three quarks that compose
hadron
In particle physics, a hadron is a composite subatomic particle made of two or more quarks held together by the strong nuclear force. Pronounced , the name is derived . They are analogous to molecules, which are held together by the electri ...
s can be described in a
diquark model which might be equivalent to the hypothesis of a three-body force. There is growing evidence in the field of
nuclear physics
Nuclear physics is the field of physics that studies atomic nuclei and their constituents and interactions, in addition to the study of other forms of nuclear matter.
Nuclear physics should not be confused with atomic physics, which studies th ...
that three-body forces exist among the
nucleons inside
atomic nuclei for many different isotopes (three-nucleon force).
See also
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Faddeev equation
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Few-body systems
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N-body problem
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Hydrogen molecular ion
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Borromean nucleus
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Efimov state
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Chiral perturbation theory
References
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{{DEFAULTSORT:Three-Body Force
Force
Nuclear physics