Tuesday, August 2, 2011

Interesting SM4 Paper

Enrico Lunghi and Amarjiit Soni, "Demise of CKM & its aftermath" (June 27, 2011):

Using firmrmly established experimental inputs . . . along with corresponding lattice matrix elements which have been well studied and are in full QCD such as BK, SU3 breaking ratio, BBs and in particular without using Vub or the pseudoscalar decay constants fBd or fBs from the lattice, we show that the CKM-paradigm now appears to be in serious conflict with the data. Specifically the SM predicted value of sin 2 beta seems too high compared to direct experimental measured value by over 3 sigma. Furthermore, our study shows that new physics predominantly effects B-mixings . . . and not primarily in kaon-mixing . . . . Model independent operator analysis suggests the scale of underlying new physics, accompanied by a BSM CP-odd phase, responsible for breaking of the SM is less than a few TeV, possibly as low as a few hundred GeV. . . . While SM with 4th generation (SM4) is a very simple way to account for the observed anomalies, SM4 is also well motivated due to its potential role in dynamical electroweak symmetry breaking via condensation of heavy quarks and in baryogenesis.

The main motivation for SM4 is excessive CP violation in bottom to strange quark situations which additional CP violating phases in SM4 can fit. The CP violating sin2 beta parameter estimated to be about 0.85 in the Standard Model is closer to 0.66 and may even be a bit lower. The hierarchy problem disappears in SM4 (eliminating one of the biggest justifications for SUSY) as does the question of the suppression of flavor changing neutral current processes, which it explains.

Also attractively, given the apparent lack of a light Higgs signal from LHC, the "[n]atural mass scale for a Higgs particle in SM4, where the heavy quarks are geared towards EW symmetry breaking, is around [twice the fourth generation bottom quark mass]. Such a heavy Higgs would of course have very clean decays to H => ZZ. Electroweak precision tests do not rule out the existence of a 4th generation though they restrict the mass splitting between the 4th generation doublet (t'; b') of quarks to be less than around 75 GeV. This requires some 10% degeneracy in their masses. . . Furthermore LEP experiments require that the 4th generation neutral lepton has to be rather heavy [greater than about half the Z particle mass]; this begs the question as to why there should be such a huge disparity with the three almost massless neutrinos of the conventional SM3. . . . experimental searches for quarks (t', b') of the 4th generation have already been underway at Fermilab leading to a lower bound of around 350 GeV. . . . It is expected that after several years of efforts, LHC should be able to find these quarks or put a bound close to a TeV."

In the SM4 model the Higgs boson mass would significantly exceed 700 GeV, which is both large enough not to be ruled out by experiment and small enough to be within the realm of what experiment could discovery in the medium term future.

The heavy fourth generation neutrino is attractive, of course, because it would provide a dark matter candidate without the necessity of inventing a new class of fermion that behaves very much like a neutrino.

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