mercredi 27 août 2014

Et si Bert, Ernie* et Big Bird** étaient les fils du big broson***?

Joyeux anniversaire au modèle standard spectral presque commutatif dont le blogueur fête aujourd'hui symboliquement le second anniversaire de la renaissance!

IceCube a peut-être déjà détecté indirectement des neutrinos droits d'énergie voisine d'1 PeV
Supposant que le big broson n'est autre que le boson de Higgs associé à la brisure de la symétrie de jauge U(1)B-L évoquée hier, le blogueur saute allègrement de la théorie à une de ses possibles phénoménologies, analysée sous des hypothèses que l'on espère suffisamment proches de celles discutées dans le précédent billet pour que le lien avec celui d'aujourd'hui garde une certaine pertinence:
The Standard Model of particle physics fails to explain the important pieces in the standard cosmology, such as inflation, baryogenesis, and dark matter of the Universe. We consider the possibility that the sector to generate small neutrino masses is responsible for all of them; the inflation is driven by the Higgs field to break B −L gauge symmetry which provides the Majorana masses to the right- handed neutrinos, and the reheating process by the decay of the B−L Higgs boson supplies the second lightest right-handed neutrinos whose CP violating decays produce B−L asymmetry, à la, leptogenesis. The lightest right-handed neutrinos are also produced by the reheating process, and remain today as the dark matter of the Universe. In the minimal model of the inflaton potential, one can set the parameter of the potential by the data from CMB observations including the BICEP2 and the Planck experiments. In such a scenario, the mass of the dark matter particle is predicted to be of the order of PeV. We find that the decay of the PeV right-handed neutrinos can explain the high-energy neutrino flux observed at the IceCube experiments if the lifetime is of the order of 1028 s. 
(Submitted on 30 Apr 2014 (v1), last revised 8 Jul 2014 (this version, v2))

Bert et Ernie, les Deux Neutrinos les Plus Energétiques du Monde
** A growing astrophysical neutrino signal in IceCube now features a 2-PeV neutrino
*** Est-ce que le boson de Higgs a un grand frère (le big broson)?



(Source IceCube 21 Mai 2014)

Remarque en guise d'avertissement 
L'hypothèse évoquée dans le titre de ce billet est pour le moins hardie sinon hasardeuse. Pour une revue de détail d'autres hypothèses sur l'origine des neutrinos "pévatroniques" et en savoir plus sur la nouvelle fenêtre expérimentale qu'ouvre IceCube sur le monde des astroparticules le mieux est peut-être de se plonger dans la lecture de : Cosmic Neutrino Pevatrons: A Brand New Pathway to Astronomy, Astrophysics, and Particle Physics

mardi 26 août 2014

Un, deux voire trois diamants de plus dans la poche du Mendiant* / One, two or three more diamonds in the pocket of the Beggar

Le grand frère du boson de Higgs est-il le scalaire complexe de charge +2 sous le groupe de jauge local U(1)B-L? / Is the big br(other of the Higgs b)oson a complex scalar with +2 charge under the local gauge group U(1)B-L?
Le blogueur rentre de vacances pour découvrir que l'hypothétique boson scalaire réel qui permettait (il y a presque deux ans jour pour jour) de corriger la prédiction de masse du boson de Higgs électrofaible dans le modèle standard spectral presque commutatif, est peut-être bien complexe, du moins si on le conçoit comme le boson de Higgs "baryoleptonique" (B-L) responsable de la brisure de symétrie associée à U(1)B-L:
In our previous paper [16], we found a reformulation of non-commutative geometry (NCG) that simplified and unified the mathematical axioms while, at the same time, resolving a problem with the NCG construction of the standard model Lagrangian, by precisely eliminating 7 terms which had previously been problematic. In this paper, we show that this same reformulation leads to a new perspective on the gauge symmetries associated to a given NCG, uncovering some that were previously missed. In particular, when we apply our formalism to the NCG traditionally used to describe the standard model of particle physics, we find a new U(1)B-L gauge symmetry (and, correspondingly, a new B−L gauge boson [Cµ ]). This, in turn, implies the existence of a new complex Higgs field σ that is a singlet under SU(3)C×SU(2)L×U(1) but transforms with charge +2 under U(1)B-L, allowing it to form a majorana-like yukawa coupling σνRνR with two right-handed neutrinos (so that, if it obtains a large VEV, it induces see-saw masses for the neutrinos). It is striking that, on the one hand, this precise extension of the standard model has been previously considered in the literature [22, 23] on the basis of its cosmological advantages; and, on the other hand, that the new field σ can resolve a previous discrepancy between the observed Higgs mass and the NCG prediction [18, 1921]. Note that in the previous works [181921] which introduced the σ field for this purpose, it was a real field, and a gauge singlet. By contrast, from the perspective presented here, the fact that σ is complex, and transforms under U(1)B-L, is the key to its existence: had it been real, it would not have been induced by the covariance argument of the previous section
Shane Farnsworth, Latham Boyle (Submitted on 22 Aug 2014)

*  Mendiant =  Modèle Standard vu sous l'angle spectral presque commutatif 
Beggar = Standard Model in the spectral and almost commutative framework


Une nouvelle raison d'être pour les neutrinos de chiralité droite? / A new raison d'être for right-handed neutrinos? 
Or donc le modèle spectral non commutatif et sa possible extension sous  un angle non associatif révèlent aux yeux des physiciens la présence de deux joyaux cachés dans  les arcannes du Modèle Standard à savoir deux bosons de jauge "baryoleptoniques" (l'un au sens ordinaire) Cµ et (l'autre au sens non commutatif) σ. A ces deux nouvelles particules il faut naturellemment en ajouter une troisième, le neutrino de chiralité droite dont l'existence, si elle était déjà subodorée de longue date, gagne néanmoins un supplément de sens en la mariant aux deux bosons précités, c'est du moins le message de l'extrait suivant:
The ordinary standard model makes sense, with or without the right-handed neutrino. In particular, since the right-handed neutrino is a singlet under the standard model gauge group, it does not contribute to anomaly cancellation: in the standard model, the anomalies cancel whether or not the right-handed neutrino exists. The right-handed neutrino has recently been tacked on to the standard model in order to account for the observed neutrino oscillations – but not for any independent theoretical reason. It is important to emphasize that the situation is very different in a Minimal Dimensionless Standard Model (MDSM) [that would consist of a standard model plus 3 right-handed neutrinos with the additional constraint of classical conformal invariance to eliminate all dimensionful couplings, augmented by a new U(1)B-L gauge symmetry carried by a new gauge boson Cµ and a complex scalar field, singlet under SU(3)C×SU(2)L×U(1)Y  that couples to the new symmetry with charge +2]... 
In this case, the right-handed neutrino is charged under U(1)B-L, and thus plays an essential role in the anomaly cancellation [requirement for renormalizability]...  Relative to the standard model, this [MDSM] contains two new fields: the complex scalar field [σ] and the (B−L) gauge field Cµ. In this subsection, we would like to stress the elegantly economical way in which [σ] simultaneously accomplishes several important phenomenological tasks in this model. On the one hand, its properties – i.e. its SU(3)C×SU(2)L×U(1)Y×U(1)B-L charges ... – were determined by requirement that it should be able to provide a Majorana-like Yukawa coupling to right-handed neutrinos, in order to give a see-saw mechanism for neutrino mass. 
On the other hand, these same properties are precisely what is needed in order for [σ] to perform another crucial task: spontaneously break (B−L) symmetry, and give mass to the Cµ boson via the Higgs mechanism, without leaving any additional unwanted Goldstone bosons. 
At the same time, we have seen that [σ] expands the scalar sector in a way that leads to successful electroweak symmetry breaking via the Coleman-Weinberg mechanism, an inflaton candidate, a dark matter candidate, and a possible explanation for the cosmological matter/anti-matter asymmetry. 
Finally, this model contains 4 different quantities that all must be rather large, for very different phenomenological/cosmological reasons: (i) the mass of the Z′µ boson, (ii) the masses of the heavy neutrinos; (iii) the mass of the [σ] boson, and (iv) the inflaton VEV. And yet, in [MDSM], all 4 large dimensionful quantities have a common origin in the large VEV of the field [σ].
(Submitted on 1 Nov 2011 (v1), last revised 12 Mar 2013 (this version, v2)).

Remark : in the original article the complex scalar field σ is written ϕ and the MDSM discussed here is MDSM3