### Neutrino08 Day 5c

One of the best talks of the conference (I might be biased) was S. King's outline of neutrino mass models. The introduction explained why we really need to go beyond the Standard Model (where neutrinos should be massless) to understand neutrino mass. King then presented his personal roadmap, a large flowchart (ultimately ending in Some Big Theory) to guide one through a series of true and false questions. He opted to begin with the LSND result, now assumed false. What about large extra dimensions and the string scale? The Majorana option seems nicer, because one can get naturally small neutrino masses via a lepton number violating operator involving some heavier particle. Following the chart, if the hierarchy is normal, then the natural mixing appears to be tribimaximal. This would make $\theta_{13} = 0$. Why should this be precise?

Consider instead an expansion around the TBM matrix (see here). This suggests a new family symmetry such as the $A_{4}$ group of the tetrahedron! This could arise from something like 6D orbifolding. See also here. Due to its agreement so far with experimental results, the TBM matrix is considered a key question. In summary, he stresses that the status quo is not an option.

Consider instead an expansion around the TBM matrix (see here). This suggests a new family symmetry such as the $A_{4}$ group of the tetrahedron! This could arise from something like 6D orbifolding. See also here. Due to its agreement so far with experimental results, the TBM matrix is considered a key question. In summary, he stresses that the status quo is not an option.

## 3 Comments:

The basic question is this: As we get deeper, elementary particles should become more, well, elementary. That means they should be easier to understand and our models should be simpler. The tribimaximal is a stab at simpler.

Instead, what happens with string theory and most phenomenology is that the models get more complicated.

Koide's formula is strange because it applies at zero momentum. If you believe that the only clean way of modeling elementary particles should be perturbation theory, then this is strange because perturbation theory works best when you have the least interaction and that means higher energy. That's why they're always talking about the interactions being unified at extremely high energies.

Hi Carl. I confess that I skimmed over the parts of the talk which focused on stringy physics.

"Simplicity is the Ultimate Sophistication"

-- Leonardo da Vinci

[ seen @Caltech CS Dept, Asyncrhonous Computing Group ]

"complicated models" is a red-flag.

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