Thursday, December 15, 2011

Higgs Announcement Reactions In The Physics Blogosphere

Lubos explains why he thinks the finding is real and notes alleged consistency with a four generation of fermions Standard Model (SM4) as well as SUSY in his view.

He is convinced (not entirely unreasonably) that the Standard Model with a 125 GeV-126 GeV Higgs boson implies vaccum instability below the Planck scale which is 1.22*10^19 GeV (perhaps as low as 10^9 to 10^13 GeV, but perhaps actually as high as 10^20 GeV), and hence the existence of new physics at some scale above the electroweak energy scale and possibly beyond the range of the ability of the LHC to detect it. FWIW, I think it is very plausible that the vacuum instability threshold is precisely the Planck scale, eliminating the need for all new physics, but there is plenty of room for disagreement both due to uncertainty concerning the values for masses that are close to the threshold of critical threshold in the relevant Standard Model equations and the difficulty involved in using perturbative approximations of the Standard Model equations in energy ranges so far from the energy scale that those approximations were designed to provide accurate calculations in. For example, the coupling constants of the Standard Model are "running constants" that depend upon the energy level of interaction involved and a slight tweak in how those constants run could become very material as such extremely high energy levels in a manner similar to the way that the Lorentz factors in special relativity become much more important in a non-linear way as one approaches the upper bound of the velocity "c" (the speed of light). Assuming that a running formula and running constant values calibrated on energies of less than 10^3 GeV will still be valid at energies more than a million times as great is not a safe assumption. In his view, "One may say that the apparently observed Higgs mass favors squarks in the multi-dozen TeV scale. . . . "garden variety" supersymmetric models with light squarks and "gauge mediation" of the supersymmetry breaking have become almost hopelessly contrived and fine-tuned, and have been nearly euthanized. The apparently observed SUSY-compatible but not-too-low value of the Higgs mass favors scenarios with heavy scalars (especially heavy stop squark); or extensions of MSSM with additional particle species. See another new paper by Carena et al. trying to obtain new possibilities with various hierarchies between slepton and squark masses." In particular, the Minimally Supersymmetric Standard Model (MSSM) is pretty much dead. One paper he cites also concludes that the "gravity mediated constrained MSSM would still be viable, provided the scalar top quarks are heavy and their trilinear coupling large. Significant areas of the parameter space of models with heavy supersymmetric particles, such as split or high-scale supersymmetry, could also be excluded as, in turn, they generally predict a too heavy Higgs particle."

Matt Strassler is more skeptical about the data supporting a Higgs boson discovery at all.

Kea at Arcadian Pseudofactor, after months of diatribes against the existence of a Higgs boson is pretty much convinced and is now looking for big picture contexts that could have the Standard Model with that kind of Higgs boson in it that parallel her previous theoretical lines of inquiry.

For my druthers, I think that a whole variety of constraints are going to make beyond the Standard Model physics for the next decade or two much more timid than they have been in the last few decades. Among the features of models that are going to be increasingly disfavored are:

1. Single digit TeV or lighter new particles.
2. Boson number or lepton number violations at less than extremely high energies.
3. Proton decay (the minimal period just gets longer and longer).
4. Magnetic monopoles.
5. CPT violations.
6. Additional generations of bosons.
7. Additional large scale dimensions.
8. Technicolor.
9. Simpler SUSY models.
10. New gauge symmetries that operate outside the neutrino sector.

I personally seriously doubt that we will find right handed neutrinos or Majorana mass in neutrinos (something that would be shown, for example, by neutrinoless double beta decay, which I doubt will be discovered), although neutrino physics are one of the least experimentally constrained area of fundamental physics today. I doubt that we will find a fourth generation of Standard Model particles, sterile neutrinos outside the three generations observed and outside a fourth generation, scalar or vector gravitons, or other fundamental particles that could be WIMPs like a lightest supersymmetric particle. I doubt that we will find when the dusts settles, anomalous CP violations that hold up after having seen so many disappointments.

I personally think that dark matter effects will turn out to be some combination of (1) a neutrino condensate (or something similar that is a composite effect of non-quarks), (2) undercounted ordinary matter that is "dim", (3) underestimated general relativistic effects in large complex systems, (4) glueballs, and (5) quantum gravity modifications of the equations of general relativity that are only relevant in very weak gravitational fields. In other words, I think that the only particle potentially missing from the list of fundamental particles with any meaningful probability is a plain vanilla, spin-2, zero mass graviton although we could discover that space-time is discrete or that the number of space-time dimensions is ill defined at tiny scales and is only an emergent property of the universe.

Another hot area will be firming up the calculations under the existing Standard Model equations in more extreme and complicated scenarios (e.g. meson molecules, or extremely rare and ephemeral top quark hadrons).

I also think that there is considerable room for exploration of non-locality in fundamental physics.

Some interesting new papers about BSM physics phenomonology include:

An argument that sterile neutrinos may be less experimentally constrained than they seem.

A conclusion based on the apparent Higgs boson mass that "current data, in particular from the XENON experiment, essentially exclude fermionic dark matter as well as light, i.e. with masses below 50 GeV, scalar and vector dark matter particles."

A paper looking at two Higgs-doublet extensions of the Standard Model in light of the new information on the Higgs boson mass, which finds that some versions of possible while others are not.

A look at experimental bounds on lepton number violating models, since: "In the Standard Model (SM), the lepton L and baryon B numbers are conserved due to the accidental U(1)L × U(1)B symmetry. But the L and B nonconservation is a generic feature of various extensions of the SM. That is why lepton-number violating processes are sensitive tools for testing theories beyond the SM." Indirect bounds on branching ratios for lepton number violations from experiments as incorporated into popular lepton number violating theories are extremely stringent.

Superluminal neutrinos could be applied to explain CP violations.

The LHC may be able to see supersymmetric particles of less than 1 to 1.6 TeV when it has acquired a particular volume of data.

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