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In physics, '''vector meson dominance''' (VMD) was a model developed by [[J. J. Sakurai]]<ref>Theory of strong interactions, [[J. J. Sakurai]], Ann. Phys., 11 (1960)</ref> in the 1960s before the introduction of [[quantum chromodynamics]] to describe interactions between energetic [[photon]]s and [[hadron]]ic matter.
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In particular the hadronic components of the physical photon consist of the lightest vector mesons <math>\rho, \omega</math> and <math>\phi</math>. Therefore, interactions between photons and hadronic matter occur by the exchange of a hadron between the dressed photon and the hadronic target.
 
==Background==
Measurements of the interaction between energetic photons and hadrons show that the interaction is much more intense than expected by the interaction of merely photons with the hadron's electric charge. Furthermore, the interaction of energetic photons with protons is similar to the interaction of photons with neutrons<ref>Bauer, T. H., Spital, R. D., Yennie, D. R. and Pipkin, F. M, The hadronic properties of the photon in high-energy interactions, Rev. Mod. Phys. 50, 261–436 (1978), pages 292-293</ref> in spite of the fact that the electric charge structures of protons and neutrons are substantially different.
 
According to VMD, the photon is a superposition of the pure electromagnetic photon (which interacts only with electric charges) and vector meson.  
 
Just after 1970, when more accurate data on the above processes became available, some discrepancies with the VMD predictions appeared and new extensions of the model were published.<ref>Generalized vector dominance and inelastic electron nucleon scattering—the small <math>\omega</math>′ region, Sakurai J. J. and Schildknecht D., Phys. Lett., 40B (1972) 121</ref> These theories are known as Generalized Vector Meson Dominance theories (GVMD).
 
==VMD and Hidden Local Symmetry==
Whilst the ultraviolet description of the standard model is based on  QCD, work over many decades has involved writing a low energy effective description of QCD, and further, positing a possible ``dual`` description.  One such popular description is that of the hidden local symmetry.<ref>Nonlinear Realization and Hidden Local Symmetries, Bando, Masako and Kugo, Taichiro and Yamawaki, Koichi, DOI: 10.1016/0370-1573(88)90019-1</ref>  The dual description is based on the idea of emergence of gauge symmetries in the infrared of strongly coupled theories. Gauge symmetries are not really physical symmetries (only the global elements of the local gauge group are physical).  This emergent property of gauge symmetries was demonstrated in Seiberg duality  <ref>Electric - magnetic duality in supersymmetric nonAbelian gauge theories , Seiberg, N., hep-th/9411149</ref> and later in the development of the AdS/CFT correspondence.<ref>The Large N limit of superconformal field theories and
                        supergravity, Maldacena, Juan Martin, hep-th/9711200</ref>  In its generalised form, Vector Meson Dominance appears in AdS/CFT, AdS/QCD , AdS/condensed matter  and some Seiberg dual constructions.  It is therefore a common place idea within the theoretical physics community.
 
==Attacks on VMD==
Measurements of the photon-hadron interactions in higher energy levels show that VMD cannot predict the interaction in such levels. In his Nobel lecture<ref>[[Jerome Isaac Friedman|J.I. Friedman]], Nobel Lecture, Deep Inelastic Scattering, Comparisons with the Quark Model, Rev. Mod. Phys. vol 63 3 1991</ref> [[Jerome Isaac Friedman|J.I. Friedman]] summarizes the situation of VMD as follows:
"...this eliminated the model [VMD] as a possible description of deep inelastic scattering... calculations of the generalized vector-dominance failed in general to describe the data over the full kinematic range..."
 
The theoretical basis of VMD raised doubts as well. According to VMD a photon is a superposition of pure electromagnetic photon which always moves in the speed of light and hadronic matter which always moves in lower speed. Therefore the VMD idea seems to contradict [[Special Relativity]].<ref>[[Eliyahu Comay|E. Comay]] Remarks on Photon-Hadron Interactions, Apeiron vol. 10,  87 (2003)</ref>
 
Today, VMD is not considered as part of the [[Standard Model]].<ref>H.B. O’Connell, B.C. Pearce, A.W. Thomas and A.G. Williams, Rho-omega mixing, vector meson dominance and the pion form-factor, Prog. Nucl. Part. Phys. 39 (1997) 201-252</ref>
 
[[Image:VMD1.png|thumb| Hadronic contribution to the photon propagator in the VMD model]]
 
==Notes==
<references/>
 
[[Category:Particle physics]]
[[Category:Nuclear physics]]

Latest revision as of 17:46, 20 November 2014

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