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The data prove that the interaction of an energetic photon with a
proton is (nearly) the same as its interaction with a neutron
(see [1] or [2], section 10.10). It is now recognized
that the photon's electromagnetic
interaction cannot explain the data.
The Vector Meson Dominance (VMD) idea was proposed at about 1960
in order to explain this effect.
It argues that the physical photon is a combination of a
pure electromagnetic photon and a vector meson. More general
ideas are called generalized vector-dominance models.
The expression "hadronic structure of the photon" is
another version of this idea.
A search by Google proves that the string
of words "hadronic structure of the photon"
is found on the web more than 5000 times. Here the acronym VMD
refers to the idea that a real photon takes the following form
where Φ denotes a real photon, Φ0 is the pure
electromagnetic component of the photon and Φh
is the hadronic structure of the photon.
a0 and ah
are appropriately normalized coefficients whose relative value
depends on the photon's energy. Here the hadronic contribution for
low-energy photons is insignificant and high energy photons comprise an
experimentally detectable hadronic component
(see [1], p. 271 or [2], pp. 318, 319).
Referring to VMD, one should remember Wigner's work:
"On Unitary Representations of the Inhomogeneous Lorentz Group" [3].
(Hereafter this article is called Wigner's work.)
The significance of Wigner's work
is described by the following words: "It is difficult to overestimate
the importance of
this paper, which will certainly stand as one of the great
intellectual achievements of our century" (see [4], p. 149).
A discussion of Wigner's work can be found in
[5], pp. 57-74 and in [6], pp. 44-53.
A physically important outcome of Wigner's work says that
a quantum particle belongs to one of the following categories: particles
whose rest mass is greater than zero and massless particles.
Massive particles are characterized by the value of their mass
and of their spin. Massless particles are characterized by their
helicity. Evidently, this Wigner's work is a mathematical
analysis of the inhomogeneous Lorentz group. Hence, its results
are inherent properties of special relativity.
It turns out that the VMD idea (1) argues that a physically real photon
is a sum of two states - an electromagnetic massless photon and
a massive hadron. This idea is clearly inconsistent with the above mentioned
results of Wigner's work. Conclusion: VMD is
physically unacceptable because it violates special relativity.
An examination of Wigner's work shows that it uses general mathematical
arguments. The correctness of its results means that one may find
specific physical examples that illustrate the inconsistency
between VMD and special relativity. For reading some discussions of
this matter
click here
.
The photon is a very important elementary particle and the proton and
the neutron are the most well-known hadronic states.
There is no doubt that physical
properties of hard photon-nucleon interaction
deserve a serious discussion
in particle physics textbooks. The present status
of hard photon-nucleon interaction is as follows:
The subject index part of quite a few particle physics textbooks
indicates that the phenomenon of
hard photon-nucleon interaction is not discussed
in these textbooks. The same is true for the VMD idea.
It means that the present physical
community adopts an Ostrich policy and
simply ignores this Standard Model serious failure.
It can be concluded that the Standard Model provides no explanation
for the hard photon-nucleon scattering data.
References:
[1] T. H. Bauer, R. D. Spital, D. R. Yennie
and F. M. Pipkin, Rev. Mod. Phys. 50, 261 (1978).
[2] E. M. Henley and A. Garcia, Subatomic Physics (3rd edition)
(World Scientific Publishing, Singapore, 2007).
[3] E. Wigner, Ann. Math., 40, 149 (1939).
[4] S. Sternberg, Group Theory and Physics
(Cambridge University Press, Cambridge, 1994).
[5] S. Weinberg, The Quantum Theory of Fields, Vol. I, (Cambridge
University Press, Cambridge, 1995).
[6] S. S. Schweber, An Introduction to Relativistic
Quantum Field Theory (Harper \& Row, New York, 1962).
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