Warped Passages - Lisa Randall [126]
What to Remember
Although we know that the Higgs mechanism is responsible for particle masses, the simplest known example that implements the Higgs mechanism works only with a huge fudge. In the simplest theory you’d expect the masses of weak gauge bosons and quarks to be about ten million billion times greater than they are. The hierarchy problem is the question of why this is not the case.
The hierarchy problem arises from the discrepancy between the low weak scale mass and the enormous Planck scale mass (see Figure 63). This latter mass is important for gravity—the large value of the Planck scale mass tells us that gravity is very weak. So another way of phrasing the hierarchy problem is to ask why gravity is so feeble, so much weaker than the other nongravitational forces.
Any theory that solves the hierarchy problem will be experimentally testable because it will necessarily have experimental implications at colliders operating at energies above the weak scale energy. The Large Hadron Collider will explore such energies very soon.
Figure 63. The hierarchy problem is the question of why the Planck scale energy is so much bigger than the weak scale energy.
13
Supersymmetry: A Leap Beyond the Standard Model
You were meant for me.
And I was meant for you.
Gene Kelly (“Singing in the Rain”)
When Icarus first arrived in Heaven, he was directed to an orientation seminar where the authorities explained the local rules. To his surprise, he learned that right-wing religious groups were essentially correct, and family values were indeed a cornerstone of his new environment. The authorities had long ago established a traditional family structure premised on the separation of generations and the stability of marriages; a top would always marry a bottom, a charmer would always align with a strange bird, and an uptown girl would always marry a downtown cool cat. Everyone, including Ike, was satisfied with the arrangement.
But Ike later learned that the social structure in Heaven had not always been so secure. Originally, dangerous energetic infiltrators had threatened the hierarchical foundation of society. In Heaven, however, most problems can be solved. God had sent everyone a personal guardian angel, and the angels and their charges had heroically worked together to avert the threat to the hierarchy and preserve the ordered society that Ike could now enjoy.
Even so, Heaven was not entirely safe. The angels turned out to be free agents, with no contract binding them to a single generation. The fickle angels, who had so bravely rescued the hierarchy, now threatened to destroy Heaven’s family values. Ike was appalled. Despite Heaven’s well-advertised attractions, he was finding it a surprisingly stressful place.
“Super” words abound in physics terminology. We have superconducting, supercooling, supersaturated, superfluid, the Super conducting Supercollider (the SSC)—which would have been the highest-energy collider today had Congress not canceled it in 1993—and the list goes on. So you can imagine the excitement when physicists discovered that spacetime symmetry itself has a bigger, “super” version.
The discovery of supersymmetry was truly surprising. At the time when supersymmetric theories were first developed, physicists thought they knew all the symmetries of space and time. Spacetime symmetries are the more familiar symmetries that we saw in Chapter 9, which declare that you can’t tell where you are or which way you’re facing or what time it is solely from physical laws. The trajectory of a basketball, for example, doesn’t depend on which side of the court you’re on or if you play the game in California or New York.
In 1905, with the arrival of relativity theory, the list of spacetime symmetry transformations expanded to include those that change velocity (speed and direction of motion). But, physicists thought, that topped the list. No one believed that there could be other undiscovered symmetries involving