Cosmology, Inflation, & Compact Extra Dimensions
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Transcript Cosmology, Inflation, & Compact Extra Dimensions
A Theoretical Investigation of
Magnetic Monopoles
Chad A. Middleton
Mesa State College
October 22, 2009
A Brief History of the Magnetic Monopole….
“On the Magnet”, Pierre de Maricourt, Letter to Siger de Foucaucourt (1269)
Petrus Peregrinus defines magnetic poles and observes that they are never seen in isolation.
“Law of Magnetic Force”, C.A. Coulomb (1788)
Establishes for magnetic poles that force varies inversely as the square and is proportional to the
product of the pole strength.
“The Action of Currents on Magnets”, H.C Oersted (1820)
Provides the first sign that electricity and magnetism are connected.
“Electrodynamic Model of Magnetism”, A. M. Ampere (1820)
Asserts that all magnetism is due to moving electric charges, explaining why magnets do not have
isolated poles.
Principle of magnetic ambiguity
A Brief History of the Magnetic Monopole….
“On the Possible Existence of Magnetic Conductivity and Free Magnetism”, P.
Curie, Seances Soc. Phys. (Paris, 1894) pp. 76-77
1st post-Amperian proposal of isolated poles
“Quantized Singularities in the Electromagnetic Field”, P.A.M. Dirac, Proc. R. Soc.
London Ser. A 133, 60-72 (1931)
“The Theory of Magnetic Monopoles”, P.A.M. Dirac, Phys. Rev. 74, 817-830 (1948)
Concludes that product of magnitude of an isolated electric charge and magnetic pole must be an
integral multiple of a smallest unit.
“First Results from a Superconductive Device for Moving Magnetic
Monopoles”, B. Cabrera, Phys. Lett. 48, 1378-1380 (1982)
Reports a signal in an induction detector, which in principle is unique to a monopole.
Maxwell’s Equations in Integral form
(in vacuum)
E dA dV
1
e
Gauss’ Law for E-field
0 V
A
B dA 0
Gauss’ Law for B-field
A
C
B
Ed
dA
A t
E
B d 0 Je 0 t dA
C
A
Faraday’s Law
Ampere’s Law with
Maxwell’s Correction
Using the Divergence Theorem
and Stokes’ Theorem…
F dA
FdV
A
F dA
Fd
C
• The Divergence
Theorem
V
• Stokes’ Theorem
A
… for a general vector field
F F (x,t)
Maxwell’s Equations in differential form
(in vacuum)
E
1
0
e
Gauss’ Law for E-field
B 0
Gauss’ Law for B-field
B
E
t
Faraday’s Law
E
B 0 J e 00
t
these plus
F qe E v B
Ampere’s Law with
Maxwell’s Correction
the Lorentz force completely describe
Classical Electromagnetic Theory
Taking the divergence of the 4th Maxwell Eqn yields..
e
Je
t
Equation of Continuity
=
Conservation of Electric Charge
Taking the curl of the 3rd & 4th eqns
(in free space when e = Je = 0) yield..
2
1
E
2
E 2 2
c t
2
1 B
2
B 2 2
c t
The wave equations for the
E-, B-fields with
predicted wave speed
c
1
00
3.0 108 m /s
Light = EM wave!
Back to Maxwell’s Equations…
E
1
0
e
B 0
E
Gauss’ Law for E-field
Gauss’ Law for B-field
B
t
E
B 0 J e 00
t
Faraday’s Law
Ampere’s Law with
Maxwell’s Correction
Maxwell’s equations are almost symmetrical
F qe E v B
allow for the existence of a
magnetic charge density, m & a magnetic current, Jm
Maxwell’s Equations become…
1
e
Gauss’ Law for E-field
B 0m
Gauss’ Law for B-field
B
E 0 J m
t
Faraday’s Law
E
0
E
B 0 J e 00
t
the Lorentz force becomes
Ampere’s Law with
Maxwell’s Correction
E
F qe E v B qm B v 2
c
Taking the divergence of the 3rd & 4th eqns yield..
e
Je
t
m
Jm
t
Equation of Continuity
Electric & Magnetic Charge are each
conserved separately
Does the existence of
magnetic charges have
observable EM
consequences?
Not if all particles have
the same ratio of qm/qe !
Maxwell’s Equations are Invariant under the
Duality Transformations
E E 'cos cB'sin
cB E 'sin cB'cos
cq ,cJ cq ',cJ 'cos q ',J 'sin
q ,J cq ',cJ 'sin q ',J 'cos
e
m
e
m
e
e
m
m
e
e
m
m
Matter of convention to speak of a particle possessing
qe & not qm
(so long as qe / qm = constant for all particles)
So long as qe / qm = constant for all particles…
Set:
qm 0 cq e 'sin qm 'cos
This sets the Mixing Angle:
qm '
tan
cqe '
and yields:
Jm 0
Notice:
• for this choice of α, our original Maxwell’s
Equations are recovered!
• existence of monopoles = existence of particles with different α
Dirac Quantization Condition
Dirac showed that the existence of even a single
Magnetic Monopole (a.k.a a particle with a different
mixing angle) requires qe , qm be quantized.
0qeqm
n
2
where
n
“Quantized Singularities in the Electromagnetic Field”, P.A.M. Dirac, Proc. R. Soc.
London Ser. A 133, 60-72 (1931)
“The Theory of Magnetic Monopoles”, P.A.M. Dirac, Phys. Rev. 74, 817-830 (1948)