Searching for

Magnetic Monopoles

Barry BarishCaltech

Magnets in Natureancient history

in this stone you should thoroughly comprehend there are two points of which one is called the North, the remaining one the South.--- Petrus Peregrinus (1269 AD)

Magnetic Monopoleshistory

Coulomb, in 1788, established inverse square force law for bothelectric charges and magnetic poles

Single Electric Charge

Magnet Monopoleshistory

u Ampere for multiple charges -

electric dipole

bar magnet

Magnetic Monopoleshistory

u Ampere, in 1820, asserted that all magnetism is due to electric currents [and, responding to criticism of Faraday, invents microscopic currents]

loop of wire

Magnetic Monopoleshistory

u Ampere postulated magnets as solenoids, following Oersteds discovery that electric currents deflect compass needle

Solenoid - field like bar magnet

Magnetic Monopoleshistory

u By this point, the connection between electricity and magnetism is becoming evident, but what is magnetic analog of single electric charge??

u are there single magnetic poles?

Magnetic Monopolesmodern history

u Maxwell, in 1873, makes the connection between electricity and magnetism

u introducing magnetic monopole makes equations symmetric

=&

E 4 pi pi

= +&

&

Bc

Et c

j1 4pi

= &

&

Ec

Bt

1

=&B 0 ( )+ 4pipim

4pic

jm

Magnetic monopoleterms

Maxwells equationsconsequences

u making music electronically

u recording music

Maxwell Equations electromagnetic waves

u electromagnetic waves

u spectrum of em waves

Magnetic Monopolesquantization of charge

u Electric charge always comes in discrete values a multiple of the charge of the electron

u Dirac, in 1931, made connection of isolated poles and quantization of electric charge

u The first strong scientificmotivation for magnetic monopoles. It inspired a large variety of

imaginative experiments.

egc

N2! =

Q n q n coulombse= = 16 10 19.

Dirac Monopolesaccelerator searches

u direct detection: (immediately after production in high-energy collisions)

thin plastic sheets surround interaction regions.

u indirect searches: (where monopoles are searched for a long time after their production)

dump beam into ferromagnetic materials. Later put in 200 Kgauss pulsed magnetic field to pull monopoles out

Fermilabproton-antiproton

collider

Dirac Monopolesmore experiments

u Cosmic Rays Price reported event

from 18 m2 plastic detector in 1975. Later excluded by Alvarez. Then they published an upper limit.

u Moon Rocks One of the first scientific

experiments with moon rocks was to search for a concentration of magnetic monopoles by Alvarez.

Magnetic MonopolesGrand Unified Theories

u t Hooft and Polyakov (1974) discovered that monopoles are fundamental solutions to non-Ablelian gauge theories may be primordial monopoles

present in the Universe

GUT monopoles are superheavy, and therefore, not producable from particle accelerators

Search for GUT monopoles as rare non relativistic particles in the cosmic rays

m O m O 10 GeVM X16

=

FHG

IKJ GUT c h

Grand Unificationenergy scale

u SU(3), SU(2), U(1) couplings converge at energy scale ~ 1015 GeV

not quite (e.g. needs supersymmetry or ??)u Unification scale appears to be well

below Planck mass, where quantum gravity effects ~ O(1)

GUT MonopoleStructure

u grand unification core virtual X-bosons (10-29 cm)

u electroweak unification virtual W, Z, , g (10-16 cm)

u confinement region g, (10-13 cm)

u condensate fermion-antifermion pairs (r ~ mf-1)

GUT Monopolesflux vs

u escape velocity earth : = 3.7 10-5 solar system : = 10-4 galaxy : = 10-3 cluster of galaxies : = 3 10-3

ln Nm

105 104 103 102 101

localgalactic

extragalactic

Monopole Abundanceearly universe

u GUTS + standard cosmology leads to glut of monopoles for a monopole mass ~ 1016 GeV

taking Hubble constant ~ (1010 yr)-1

u The Monopole Problem !!!!!!

M gm cm 5 10 18 3/

and

pi

c

c

HG

gm / cm

t yrs

=

E

38

8 10

3 10 30 000

229 3

110 ,

Monopole Abundanceinflationary scenario

u idea defer the phase transition to much

later, after extreme supercooling solves monopole problem also, resolves horizon and flatness

problems In the simplest version, the number

of monopoles is very small however, not SU(5) and the calculated

flux depends critically on several parameters (mass of GUT monopole, temperature to which the universereheats, etc)

u conclusion no guidance from cosmology about

monopole flux -- could be a glut or a famine

Monopole Fluxastrophysical bounds

u mass density of the universe uniformly distribution (nM < 2 10-21 cm-3) clumped distribution (nM < 10-16 cm-3)

u galactic magnetic field B ~ 3 10-6 gauss Parker limit - too many monopoles would

short out this field

Magnetic Monopolesconclusions

u Theory/Motivation Charge Quantization has been

primary motivation for magnetic monopole (Dirac)

Grand Unification - superheavymonopoles are intrinsic to theory

Could be contributor to dark matter of the Universe

u Experiment NO evidence for Dirac Monoples

from accelerator searches, etc NO evidence for Grand Unified

Monopoles at level of Astrophysics bounds (~ 10-15 cm-2 sr-1 s-1 )

Present searches (eg. MACRO) will probe factor of 10-20 below bound