Fifth
Force |

**In General** > s.a. Hyperphoton.

* __Idea__: In principle, any hypothetical force in addition to the four interactions of the standard model of particle physics; In practice, there are a few types of fifth force that have been considered more than others, such as a hypercharge-dependent one studied in the late 1980s in connection with a reanalysis of the Eötvös experiment by Fischbach et al, and various dilaton-field-dependent forces motivated by low-energy limits of Kaluza-Klein theories and string theory, or by scalar-tensor theories of gravity more generally; The latter need not violate the weak equivalence principle.

* __Hypercharge-dependent__: A type of force that could be coupled to
a combination *B* cos*θ* + *S* sin*θ* of baryon number and strangeness
(hypercharge seems antiquated) which, for bulk matter, gives rise to a dependence on the material, e.g., because near the center of the periodic table nuclear binding
is tightest, and *B*/mass highest; If one interprets the fifth force as a component of gravity, then the fifth force violates the weak equivalence principle; The potential is parametrized by a Yukawa-type form given by, if *Y*_{1} and *Y*_{2} are
the hypercharges of the two particles involved,

*U*(*r*) = *f*^{ 2} *Y*_{1} *Y*_{2} exp{–*r*/*λ*}/
*r* .

**Phenomenology and Tests** > s.a. Eötvös
Experiment; tests
of general relativity and of newtonian gravitation.

* __History__: Some indications
of the possible existence of a fifth force had been coming from geophysical methods of testing newtonian gravitation,
but the question received a lot of attention with the reanalysis of the Eötvös data by
Fischbach et al (1986), following anomalous results in neutral *K*-meson experiments
at Fermilab, which could be explained by a long-range force coupled to *Y*;
It stimulated many new gravitational gradiometer, free fall, Cavendish or
Eötvös-type experiments.

* __Bounds__: 2005, At the
AU-scale, planet motion studies constrain the strength of this force to a
10^{–12}–10^{–13} level.

@ __Tests and bounds__:
Iorio PSS(07)gq/05
[AU-scale, from
planet motion]; Farrar & Rosen PRL(07)
+ pw(07)may
[galaxy cluster-scale, from Bullet Cluster]; Ferreira et al a1612 [no fifth force in a scale-invariant universe].

> __Related topics__: see dark
matter; Galileon Field; Unparticles.

**References**

@ __Books__: Franklin
93; Franklin & Fischbach 16.

@ __General__: Fischbach et al PRL(86),
PRL(86), AP(88);
De Rújula PLB(86);
Eckhardt PRL(86);
Nussinov
PRL(86);
Thieberger PRL(87);
Nieto et al PRD(88);
Burgess & Cloutier PRD(88)
[from binary precession]; Fischbach & Talmadge
Nat(92)mar;
Romaides et al PRD(97)
[tower experiment].

@ __News__: Stubbs Nat(89)mar;
Waldrop Sci(89)nov; NS(90)jul21,
p18.

@ __From 5th dimension__: Wesson et al PLB(99);
Dahia et al MPLA(03).

@ __Related topics__: Krauss PT(08)oct
[re spoof].

> __Online resources__: see Wikipedia page.

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send feedback and suggestions to bombelli at olemiss.edu – modified 5
jan
2017