Maybe all that exists is the standard model...or even less

Throughout the previous decade Gia Dvali was arguing that there are $10^{32}$ copies of the standard model out there. Now, he made a U-turn and says that there is only 1. Or even less. Let me explain.

The reason why we are pretty sure that we are going to observe new phenomena in the LHC goes under the nickname unitarity of WW scattering. What hides behind this is, technically speakin, that the tree-level scattering amplitude of longitudinally polarized W bosons computed in the standard model without the Higgs particle grows as a square of the scattering energy, and at some point around 1 TeV it becomes inconsistent with unitarity, that is with conservation of probability. In the full standard model this problem is cured: the contribution from the Higgs exchange cancels the dangerously growing terms and the full amplitude is well behaving for arbitrary high energies. A slightly different mechanism is realized in technicolor theories, where the consistent UV behavior of the amplitude is ensured by the exchange of spin-1 resonances.
In spite of 40 years of intensive research we are only aware of these 2 ways of unitarizing the WW amplitude. Thus the LHC should see either the Higgs or new spin-1 resonances. Time will tell which of the 2 possibilities is realized in nature.

A paper last week by Dvali and co. suggests that there may be a 3rd possibility. The authors conjecture that the standard model without a Higgs and without any other embellishments could be a fully consistent theory, even though it appears to be in conflict with unitarity. They argue that the uncontrolled growth of the WW scattering amplitude is just an artifact of the perturbative approximation, while at the non-perturbative level the theory could be completely sane. The idea is that, as the scattering energy increases above TeV, the theory defends itself by producing "large" classical configurations during the scattering process. The higher the energy, we get the larger and more classical objects which then decay preferentially to many-body (rather than 2-body) final states. This way the 2-to-2 WW scattering remains unitary at energies above TeV. The authors, somewhat dully, call this mechanism classicalization. To put it differently, as we increase the scattering energy at some point we stop probing the physics at short distance scales; these small distances are screened from external observers, similar in spirit to black holes screening the short distance physics in transplanckian scattering when gravity is in the game.

If this is the case, what would it mean in practice, that is in experiment? Much as in technicolor, at TeV energies the LHC should observe resonances in WW scattering who ensure the unitarity of the perturbative amplitude in the low-energy effective theory. However, as the scattering energy is increased the resonances become more and more classical and spectacularly decay into many-particle final states. There is no new fundamental degrees of freedom at high energies, no new fundamental forces to discover, just the standard model and its non-perturbative classical dynamics.

Now, can this be true? The paper is rather cryptic, and provides few technical details. In this sense it feels like another emergent gravity. What it demonstrates is that in a class of theories that includes the standard model there exist classical solutions whose large distance behavior only depends on how much energy is sourcing it, and whose size grows in a universal way with the energy. The rest seems to be just words, and there is a long way to proving that classicalization can indeed lead to a fully consistent quantum theory. Nevertheless, given the scarcity of ideas concerning electroweak symmetry breaking, there is definitely some philosophical potential in the paper. We'll see whether it leads to something more concrete...

Update: See also Lubos' stance.