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(It is recommended that readers read the following introduction
before reading this page:
click here).
The neutron is an uncharged particle but its mean-square charge
radius takes a small negative value. In this page it is
shown that the Regular Charge-Monopole Theory (RCMT)
provides a qualitative explanation for
this property of the neutron.
(Click here
for reading an overview of RCMT
and its applications to strong interactions.)
This result of RCMT can be regarded from another viewpoint.
Thus, if the neutron's
mean-square charge radius takes a different value then this
property can be regarded as a grave argument against the
validity of RCMT as the underlying theory of strong interaction.
The quantum mechanical state of the neutron is analogous to
that of the proton, which is its isospin counterpart.
Hence, the discussion presented below uses principles
explained on the proton's page.
(Click here
for reading a qualitative discussion of the proton's state.)
The neutron's state is the isospin analog of the proton's state and
it is characterized by the udd valence quarks. Thus,
properties of the dd pair are analogous to those of
the proton's uu pair. It is shown below that
two different effects push electrically negative components of
the neutron to outer regions. Obviously, these effects increase
the negative value of the neutron's mean-square charge radius.
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Arguments which are analogous to those used for the proton
indicate that the neutron's state favors spatially
antisymmetric terms of the dd quarks.
These states can be created by a
spatial excitation of one or two d quarks of
the neutron. For this reason, the neutron's d quarks
are more likely to be found at outer regions. Thus,
due to the negative charge of the d quark,
the r2 weight of the neutron's negative
charge increases.
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The neutron contains configurations having additional
qq
quarks. Now, using isospin symmetry of the
proton's data, one finds that in the case of a
neutron, a
uu
pair is more likely to be found than a
dd
pair. An examination of the data also proves that
the antiquarks' volume of the nucleon is larger than
that of quarks.
(Click here
for reading a discussion of this topic.) The electric
charge of the
u quark is
-2e/3 whereas that of the
d quark is
e/3. The overall arguments presented here boil
down to the conclusion that the existence of antiquarks
in the neutron increases the contribution to the negative
value of the neutron's mean-square charge radius.
These points provide a qualitative explanation of the negative
value of the neutron's mean-square charge radius and show that
it is consistent with RCMT. Moreover, if
a positive value would have been found for the neutron's mean
charge radius then it
could be regarded as a grave argument against the relevance of
RCMT to strong interactions.
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