Warped Passages - Lisa Randall [174]
We can try to make models that explain different masses. But almost invariably, any model would also contain unwanted interactions that would change flavor identities. What we need is something that can safely distinguish flavors without producing these problematic interactions.
Nima Arkani-Hamed and the German-born physicist Martin Schmaltz assumed that different Standard Model particles were housed on separate branes and that they could explain some masses. Nima and Savas Dimopoulos found another, even simpler possibility. They assumed that there was a brane on which particles of the Standard Model were confined, and that the interactions among particles on this brane treated all flavors identically. But with only flavor-symmetric interactions, which treat all the flavors the same, all particles would have exactly the same mass. Clearly, we can explain the different masses only if something treats the particles differently.
Nima and Savas assumed that other particles responsible for flavor-symmetry breaking were sequestered on other branes. As with sequestered supersymmetry breaking, flavor-symmetry breaking could then be communicated to Standard Model particles only via interactions with particles in the bulk. If there were many bulk particles interacting with the Standard Model, each of which communicated flavor-symmetry breaking from a different brane at a different distance, their model could explain the different masses of the Standard Model flavors. Symmetry breaking communicated from distant branes would induce smaller masses than symmetry breaking communicated from nearby branes. Nima and Savas named their idea shining to emphasize this fact. Just as light looks dimmer when its source is further away, the effect of symmetry breaking is smaller when it originates on a more distant brane. In their scenario, different flavors of quarks and leptons would be different because they each interact with a different brane at a different distance.
Extra dimensions and sequestering are novel and exciting ways to address problems in particle physics. And it doesn’t necessarily stop there. Recently we have shown that sequestering could even play an important role in cosmology, the science of the evolution of our universe. It’s clear that we have yet to discover all the merits of a universe (or multiverse) that contains sequestered particles, and new ideas are still to come.
What’s New
Particles can be sequestered on different branes.
Even tiny extra dimensions can have consequences for the properties of observable particles.
Sequestered particles are not necessarily subject to the anarchic principle. Not all interactions necessarily occur, since distant particles cannot directly interact.
In a model in which particles that play a role in supersymmetry breaking are sequestered from Standard Model particles, supersymmetry can be broken without introducing interactions that would change particles into other flavors.
Sequestered supersymmetry breaking is testable. If gauginos are produced at high-energy colliders, we can compare gaugino masses and see whether they agree with predictions.
Sequestered flavor-symmetry breaking might help to explain disparate particle masses.
18
Leaky Passages: Fingerprints of Extra Dimensions
I was peeking
But it hasn’t happened yet
I haven’t been given
My best souvenir
I miss you
But I haven’t met you yet.
Bjork
Athena had to admit that she missed Ike. Even though she had often found him annoying, she was pretty lonely without him. She was looking forward to spending time with K. Square, an exchange student who was planning to visit. But she was appalled by the closed-mindedness of her neighbors, who were all apprehensive about K. Square’s impending arrival. It didn’t matter that he spoke the same language and behaved the same way as everyone else. In the current climate, K. Square’s foreign origin alone was enough to make them wary.
When Athena asked her neighbors why they were so anxious, they replied, “What