Monday, December 24, 2012

Review of review of 2012

Andrew Oh-Willeke has posted "A Review of Fundamental Physics in 2012 ".

Clearly the discovery of "boson X(126)" is the big event, the major payoff so far from the LHC. We agree on that.

The failure of anything else to show up so far - not just supersymmetry - is also significant, for its impact on the hierarchy problem. The mainstream discussion continues to be framed as a choice between "naturalness" - unknown particles like super-partners or top-partners make the Higgs mass more natural than it seems - and "finetuning" - e.g. there are anthropic reasons for having a Higgs mass in this range. The third way due to Shaposhnikov and Wetterich - the Higgs mass comes from special boundary condition to the RG flow at high energies - is long overdue for attention.

Technicolor in a narrow sense may be "dead", but the idea of a composite Higgs is still very alive.

"Dark Energy Is Still A Solved Problem" says Andrew - it's just a cosmological constant. Maybe that's what it is, maybe it isn't, but even if it is, we still wouldn't know why it has that magnitude or what it is that cancels out the enormous vacuum energy implied by standard QFT. Since he likes "physics numerology", he should look at some of the numerology that has been proposed regarding the size of the dark energy, e.g. by Riofrio, Chernin, and Padmanabhan.

Andrew is one of the handful of people aware of the generalizations of Koide's formula being pursued by Brannen, Rivero, and others in recent years, so this part of his review you definitely won't find elsewhere. I would quibble with one detail: he mentions Sumino and Goffinet as providing ideas about how to explain the exactness of the Koide relation for the pole masses of the charged leptons, when such relations should instead connect the running masses at high energies. But really it's only Sumino who has proposed a mechanism to cancel the deviations that should be produced by RG flow. Goffinet notices the problem, and his work is of interest for other reasons (e.g. the attempt to relate mixing matrices to the formula), but he doesn't have an answer, unlike Sumino.

As for quantum gravity, I remain pro-string and anti-loop, where "string" means, not just geometric phases of superstring theory, but also a variety of string-like possibilities. I consider the key "stringlike" properties to be (1) the existence of holographic dual descriptions of ordinary space-time physics (2) the possession of very special relations among amplitudes for quantum processes, like those discovered in the twistor revival.

There's a lot more in his review, especially on dark matter. Thanks to Andrew for posting it!

1 comment:

  1. As far as the hierarchy problem goes, my personal belief is that the cancellations are due to hidden structure and symmetry in the formulas for particle masses that give rise to the Higgs mass in deeper theory. Lots of "big numbers" virtually cancelling out is only a surprise if the big numbers aren't made up of lots of subterms that obviously cancel each other out. The kind of deeper theory that Koide is pointing at very likely does just this.

    Put another way, SUSY deals with the hierarchy problem by offering a formulation that transparently leads to cancellations of bosonic and fermionic contributions to the Higgs boson mass. My suspicion is that the SM fermions and bosons already cancel each other out in the same way and that it is not as transparent only because the formulas that produce the SM fermion and boson masses from one or two experimentally measured constants are not known.

    The note on the death of Technicolor is a bit pedantic. I wouldn't and I don't think that most people in ordinary discussion would equate "Technicolor" which is a fairly specific scheme and variations on it, with all composite Higgs models of any kind.

    I am not too impressed with the efforts by Riofrio and Chernin, although Padmanabhan's paper is interesting. Padmanabhan's paper can be understood as an effort to basically reverse engineer the cosmological constant back to a Plank length Big Bang scale.

    Your point on the nuances of allocation of credit to Sumino and Goffinet respectively is well taken.

    Re quantum gravity, the biggest distinction I see between string-like and loop-like formulations is that string-like formulations are typically formulated as graviton exchanges ON branes in a specified number of dimensions, while loop-like formulations have emergent dimensionality and gravity emerges as a property OF space-time rather than a particle exchange ON a four-dimensional (or higher dimensional) brane. Loop-like formulations also show considerable promise at showing all particles to be excitations OF space-time.

    A lot of the bridge between all over the place string theory and relatively well defined SUSY arises from the need to dilute a unified force into a much weaker one when it manifests as gravity and this approach is not convincing.