MAGNETIC MONOPOLESAndrey ShmakovPhysics 129 Fall 2010UC Berkeley

OVERVIEW

Dirac Monopoles Appeal to symmetry Quantum Mechanical explanation

GUT Monopoles Symmetry Breaking Gauge Theories

Monopole Searches Methods Experiments

Current Experimental Limits Nothing! Graphs!

DIRAC MONOPOLE

The Dirac Relation:

Angular Momentum of a test particle around a magnetic charge:

DIRAC MONOPOLE

GUT MONOPOLE

Symmetry is lost during phase transitions

Water: isotropic, fullRotational symmetry

Ice: Crystal LatticeWith preferred axis

GUTMONOPOLE

GUT MONOPOLE

Phase transitions cause topological defects

Causality forces distant regions to precipitate into different states

ASIDE: GAUGE INVARIANCE We intuitively understand position, time,

rotational, and potential invariance These transformations are universal

What if our transformation was a smooth function of space-time?

ASIDE: GAUGE INVARIANCE

UGH! Let’s Try that again

✔

http://www.vttoth.com/gauge.htm

http://www.vttoth.com/gauge.htm

EXPERIMENTALISTS!MEET MR MONO POLE!

Charge:

Coupling constant:

Mass Assume monopole classical radius ~ electron

radius

GUT Mass depends on symmetry breaking

EXPERIMENTAL SEARCHES: EXPLOITABLE PROPERTIES

o Monopoles acquire energy in the galactic MF

oMonopoles can get trapped in ferromagnetic materials, stopped in celestial bodies

o Interactions:•High Energy: Behave like electrons:

synchrotron radiation, heavy energy loss, measurablewith scintillation counters.

•Slow Monopoles: ionizing radiation, detectable

•Very Slow Monopoles: elastic collisions,infrared radiation

•Interaction with superconducting magnets: regardless of

velocity

EXPERIMENTAL SEARCHES:SQUIDS

A magnetic monopole passing through a superconducting loop will induce a very distinct signal

Equally sensitive at all velocities and monopole masses

Used to test materials for embedded monopoles

EXPERIMENTAL SEARCHES: TANTALIZING CANDIDATES

On Valentines Day, 1982, a superconductinginduction coil detector recorded thisevent

Phys Rev. Lett. 48 1378 (1982)

EXPERIMENTAL SEARCHES:COSMOLOGY Experiments are conducted to measure a flux

of magnetic monopoles that hit the earth as cosmic rays

There are theoretical limits on the flux of heavy MM from the galactic MF

Monopole, Astrophysics and Cosmic Ray Observatory (MACRO) searched for superheavy MM in the beta < 1 range.

EXPERIMENTAL SEARCHES: COSMOLOGICAL LIMITS

EXPERIMENTAL SEARCHES:DIRECT TESTS Accelerators used to probe for possible light

Dirac monopoles

Tevatron collision exclude energies below 850GeV

EXPERIMENTAL SEARCHES: DIRECT TESTS

CONCLUSION Monopoles are hypothetical, but predicted by

the most major theoretical models No confirmed repeatable monopole events

have been recorded Strong lower limits on energy place Dirac

monopoles out of reach of colliders Strong upper limits on cosmic ray flux

Maybe finding reason they don’t exist is more interesting than finding them?