dimanche 25 mai 2014

Simple comme le nouveau (mais déjà ancien) modèle standard minimal

Rubrique : Sans commentaire //ou presque

Un modèle simple avant d'être beau...
//Début mai on évoquait l'apparente simplicité des lois de la Nature qui sont aujourd'hui presque toutes condensées dans le Modèle Standard Minimal ( MSM en anglais) de la physique des particules et la théorie de la relativité générale (voir ce billet pour un aperçu de l'expression mathématique de cette relative simplicité). On dit bien presque parce que depuis l'achèvement du MSM au début des années 70 de nouveaux faits expérimentaux ont été mis en évidence à la fin des années 90 ou au début des années 2000 qui ne sont pas prédit par ce dernier...
There exist many possible directions to go beyond the Minimal Standard Model (MSM): supersymmetry,extra dimensions, extra gauge symmetries (e.g., grand unification), etc. They are motivated to solve aesthetic and theoretical problems of the MSM, but not necessarily to address empirical problems. It is embarrassing that all currently proposed frameworks have some phenomenological problems, e.g., excessive flavor-changing effects, CP violation, too-rapid proton decay, disagreement with electroweak precision data, and unwanted cosmological relics. In this letter, we advocate a different and conservative approach to physics beyond the MSM. We include the minimal number of new degrees of freedom to accommodate convincing (e.g., > 5σ) evidence for physics beyond the MSM. We do not pay attention to aesthetic problems, such as fine-tuning, the hierarchy problem, etc. We stick to the principle of minimality seriously to write down the Lagrangian that explains everything we know. We call such a model the New Minimal Standard Model (NMSM). In fact, the MSM itself had been constructed in this spirit, and it is a useful exercise to follow through with the same logic at the advent of the major discoveries we have witnessed. Of course, we require it to be a consistent Lorentz-invariant renormalizable four-dimensional quantum field theory, the way the MSM was constructed.


Hooman Davoudiasl, Ryuichiro Kitano, Tianjun Li, Hitoshi Murayama,The New Minimal Standard Model 12/05/2004


...aux prévisions cosmologiques vieilles de 10 ans déjà...
... The spectrum index of the ϕ^2 chaotic inflation modelis predicted to be 0.96. This may be confirmed in improved  cosmic- microwave background anisotropy data, with more years of WMAP and Planck. The tensor-to-scalar ratio is 0.16.

... et toujours robustes aujourd'hui jusqu'à preuve du contraire
The Planck nominal mission temperature anisotropy measurements, combined with the WMAP large-angle polarization, constrain the scalar spectral index to ns=0.9603±0.0073.
Subtracting the various dust models and re-deriving the r constraint still results in high significance of detection. For the model which is perhaps the most likely to be close to re- ality (DDM2 cross) the maximum likelihood value shifts to r = 0.16+0.0616 −0.05 with r = 0 disfavored at 5.9σ.

Quid d(')u(ne) prochain(e extension du) nouveau modèle standard minimal?
 //Rédaction encore en cours

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