Warped Passages - Lisa Randall [136]
What to Remember
Supersymmetry essentially doubles the particle spectrum. For every boson in the theory, supersymmetry introduces a partnered fermion, and for every fermion, it introduces a partnered boson.
Quantum mechanical effects make it difficult (without supersymmetry) to keep the Higgs particle light enough for the Standard Model to work. Until the advent of extra-dimensional theories, supersymmetry was the only known way to address this problem.
Supersymmetry won’t necessarily tell us why the Higgs particle is light, but it does address the hierarchy problem by making a light Higgs particle a plausible assumption.
The large virtual contributions that Standard Model particles and their superpartners make to the Higgs particle’s mass add up to zero. Therefore a light Higgs particle is not problematic in a supersymmetric theory.
Even though supersymmetry might solve the hierarchy problem, it cannot be exact. If it were, superpartners would have the same masses as Standard Model particles, and we would have already found experimental evidence of supersymmetry.
Superpartners, should they exist, must be more massive than their Standard Model partners. Because high-energy colliders can produce particles only up to a certain mass, these colliders might not yet have had enough energy to produce them. This would explain why we have not yet seen them.
Once supersymmetry is broken, flavor-changing interactions can occur. These are processes that change quarks or leptons into quarks or leptons of another generation (that is, ones that are heavier or lighter) with the same charges. These are very strange processes—they change the identity of known particles, and they occur only rarely in nature. But most theories of broken supersymmetry predict that they should occur very often—more often than we see in experiments.
14
Allegro (Ma Non Troppo) Passage for Strings
I’ve got the world on a string.
Frank Sinatra
Fast forward a millennium.
Icarus Rushmore XLII was trying out his new Alicxvr Device, Model 6.3, that he had recently purchased from the Spacernet. (Icarus III’s interest in speed and gadgets had apparently been passed down through many generations.) The Alicxvr was designed to let the user view things of any size, from the very small to the very large. Ike was pretty sure that all of his friends who had purchased the Alicxvr Device would first try the large settings, of many megaparsecs, so they could see into outer space beyond the known universe. But Ike thought, “I know just as little about what is happening at extremely tiny distances,” and decided to investigate a minuscule size instead.
However, Ike was an impatient sort. He couldn’t be bothered to read the extensive instruction manual accompanying his device and instead decided to plunge right in. Blithely ignoring the red indicator overlapping the smallest sizes, he adjusted his dial to the 10-33 cm setting and pressed the button labeled “Go.”
To his horror, he found himself space-sick in a wildly oscillating, precipitous landscape filled with strings. Space was no longer the smooth, anonymous background he was accustomed to. Instead it was jiggling rapidly in places, heading into pointy sections in others, or wandering off into loops that pinched off or later rejoined the surface. Ike fumbled desperately for the “Stop” button and only just managed to press it in time to return to normal with his senses intact.
After recovering his stability, Ike decided he probably should have read the manual after all. He turned to the “Warning” section and read: “Your new Alicxvr Device Model 6.3 works only for sizes larger than 10-33 cm. We have not yet incorporated the latest string theory developments, whose predictions physicists and mathematicians