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Neutrino Minimal Standard Model 
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#1
Jan1913, 09:17 PM

P: 755

Marcus suggested that the nuMSM deserves its own thread and I agree.
The nuMSM is the context in which the ShaposhnikovWetterich prediction of the Higgs mass was made. (PF thread.) A search on "nuMSM" at InspireHEP turns up 29 papers, a lot of them about cosmology. Shaposhnikov in his recent talk makes a number of striking claims and suggestions: 


#2
Jan1913, 10:09 PM

Astronomy
Sci Advisor
PF Gold
P: 23,228

How right you are! I didn't realize the extent to which it has become so. I just now simply googled "nuMSM" (without even going to arxiv.) and got a lot of hits. The first page of hits:
Baryon Asymmetry of the Universe in the NuMSM arxiv.org › hepphby L Canetti  2010  Cited by 18  Related articles Jun 1, 2010 – Abstract: We perform a detailed analysis of baryon asymmetry generation in the NuMSM (an extension of the Standard Model by three singlet ... nuMSM and its experimental tests arxiv.org › hepphby F Bezrukov  2007  Cited by 1  Related articles Oct 12, 2007 – Abstract: $\nu$MSM is a minimal renormalizable extension of the Standard Model by right handed neutrinos. This model explains the neutrino ... The masses of active neutrinos in the nuMSM from Xray astronomy arxiv.org › hepphby A Boyarsky  2006  Cited by 55  Related articles Jan 12, 2006 – Abstract: In an extention of the Standard Model by three relatively light right handed neutrinos (the nuMSM model) the role of the dark matter ... Dark matter, singlet extensions of the nuMSM, and symmetries arxiv.org › hepphby K Allison  2012 Oct 25, 2012 – Abstract: We consider an extension of the nuMSM in which sterile neutrino masses originate from the VEV of a Higgs singlet phi and dark ... The nuMSM, dark matter and neutrino masses  INSPIREHEP inspirehep.net/record/677890by T Asaka  2005  Cited by 258  Related articles Mar 7, 2005 – We investigate an extension of the Minimal Standard Model by righthanded neutrinos (the $\nu$MSM) to incorporate neutrino masses ... A possible symmetry of the nuMSM infoscience.epfl.ch › Infoscienceby M Shaposhnikov  2007  Cited by 75  Related articles Sep 7, 2010 – A possible symmetry of the nuMSM. Shaposhnikov, Mikhail. Published in: Nucl. Phys., vol. B763, p. 4959; Publication date: 2007. To explain ... [PDF] nuMSM: predictions for neutrino mass and neutrinoless double beta ... http://www.mpihd.mpg.de/gerda/dubna..._nuMSM.pdfFile Format: PDF/Adobe Acrobat  Quick View νMSM: predictions for neutrino mass and. 0νββdecay hepph/0505247. F. Bezrukov1. M. Shaposhnikov2. 1Institute for Nuclear Research, Moscow, Russia ... Sterile neutrino dark matter as a consequence of nuMSMinduced ... iopscience.iop.org/14757516/.../14757516_2008_06_031.pdfby M Laine  2008  Cited by 56  Related articles Sterile neutrino dark matter as a consequence of νMSMinduced lepton asymmetry. This article has been downloaded from IOPscience. Please scroll down to ... Baryon Asymmetry of the Universe in the NuMSM  ResearchGate http://www.researchgate.net/.../4592...of_the_Un...We perform a detailed analysis of baryon asymmetry generation in the NuMSM ( an extension of the Standard Model by three singlet Majorana fermions with ... [PDF] nuMSM: predictions for neutrinoless double beta decay moriond.in2p3.fr/EW/2006/Transparencies/F.Bezrukov.pdfFile Format: PDF/Adobe Acrobat  Quick View by F Bezrukov  2005  Cited by 21  Related articles νMSM: predictions 0νββdecay and neutrino masses. Phys. Rev. D 72 (2005) 071303. F. Bezrukov1,2. M. Shaposhnikov1. 1EPFL, Lausanne, Switzerland ... 


#3
Jan2013, 08:42 PM

Astronomy
Sci Advisor
PF Gold
P: 23,228

I think Dario Benedetti's paper that appeared today is an important landmark in Asym Safe GR. This strengthens the interest in nuMSM of Shaposhnikove et al.
It makes Asym Safe GR seem very likely to be right. http://arxiv.org/abs/1301.4422 On the number of relevant operators in asymptotically safe gravity Dario Benedetti (Submitted on 18 Jan 2013) In this short note we answer a long standing question about the asymptotic safety scenario for quantum gravity. The term asymptotic safety refers to the conjecture that (i) the quantum field theory of gravity admits a nontrivial ultraviolet fixed point, and that (ii) this has only a finite number of relevant perturbations, i.e. a finite number of UVstable directions (or in other words, a finite number of free parameters to be fixed experimentally). Within the f(R) approximation of the functional renormalization group equation of gravity, we show that assuming the first half of the conjecture to be true, the remaining half follows from general arguments, that is, we show that assuming the existence of a nontrivial fixed point, the fact that the number of relevant directions is finite is a general consequence of the structure of the equations. 5 pages ====================== To recap, for the better part of 10 years the main concern has been to show that you only have to fix a finite number of parameters (determined by experiment) in order to get in the critical submanifold of theory spacewhere the flow takes you to the fixed point. Benedetti has finally proved this (assuming no mistake in the proof.) So only a finite number of constants have to be determined by experiment and then the renormalization group flow does the rest. People have been trying numerical experiments with truncations that tended to make one SUSPECT that the critical sub manifold (of "good" theories i.e. that flow to the fixed point) was finite dimensional. But until now it was not proven. =============== If Benedetti's proof checks out, as I suppose it will, then we can expect a big increase in the number of Asym Safe GR papers, and in particular and upsurge of research in the Neutrino Minimal Standard Model of Shaposhnikov. 


#4
Jan2013, 09:22 PM

PF Gold
P: 1,961

Neutrino Minimal Standard Model



#5
Jan2713, 08:21 AM

P: 755

If you look into the details of neutrino mass in the nuMSM (original paper), you'll find that there's a lot of unnaturalness (parameters that are orders of magnitude away from 1) and finetuning (quantities which have to be tuned to, e.g., 1 part in 1 million).
For neutrinos, we have to consider Dirac mass and Majorana mass. Dirac mass is the sort of mass possessed by all the other SM fermions, arising from the coupling of left and righthanded helicities via the Higgs. Majorana mass terms have a fermion of a given helicity coupled to itself. For a lefthanded neutrino, such a mass term is nonrenormalizable and can only be an effective interaction arising from something deeper; but a righthanded neutrino (in a SM extension) can be coupled to itself in this way without further problems, because it is a singlet of the SM gauge group. We know that lefthanded neutrinos have a mass several orders of magnitude smaller than that of the electron. In principle, this could result from a standard Dirac mass coupling to a RH neutrino via the Higgs, but the "yukawa", the coefficient of the coupling, is unnaturally small compared to those of all the other fermions. So people prefer the seesaw mechanism, in which a righthanded neutrino has a GUTscale Majorana mass, and then a naturallysized neutrino yukawa induces a very light effective mass for the observed SM neutrino. In the nuMSM, the lefthanded neutrinos have their measured, very light masses; there are three righthanded neutrinos, which have keVGeV masses in order to explain cosmology; and the lefthanded masses are Dirac masses, while the righthanded masses are Majorana masses. So the nuMSM has the problem of positing unnaturally small neutrino yukawas, in order to explain the observed masses as Dirac masses. The Majorana masses also have a peculiar spectrum (two GeV masses, which must be the same to one part in one million). Shaposhnikov was onto this problem early, and by now there are many papers trying to explain this pattern of masses  see references 7 to 10 in 1112.5819. I haven't checked whether these proposals are consistent with Shaposhnikov's new requirement of no new physics between the Fermi scale and the Planck scale, which was required in order to obtain the Higgs mass. (There's also the requirement of a large theta13 angle in the neutrino mixing matrix, a recent discovery which may have an impact on some of the older models.) I do wonder if it might be possible to have a "Planckscale seesaw". I got the idea from Ron Maimon's remark that the basic seesaw just requires an "HHLL" interaction, in which the lefthanded neutrino scatters off two Higgses, that resolves into new physics at the GUT scale  but "the GUT scale is so close to the quantum gravity scale". The resolution should involve at least one intermediate state  L hits a Higgs vertex, becomes something else, hits another Higgs vertex and turns back to L  and the intermediate state could be something quantumgravitational (i.e. with a Planckscale mass... a fancy example would be a virtual fermionic black hole). It seems like this is an option to consider, for people trying to employ the ShaposhnikovWetterich mechanism; but it may mess with the cosmological tuning of the nuMSM (i.e. the arguments from dark matter, baryon asymmetry... which lead to the specific spectrum of RH neutrino masses). 


#6
Apr1813, 09:47 AM

P: 755

Could the GeVmass sterile neutrinos of the nuMSM cause the CDMSII events?? In the nuMSM, the dark matter consists of a keVmass righthanded neutrino, but there are two GeVmass RH neutrinos too. There would be two things to check: whether they can cause a nuclear recoil at all, and whether the rate of such events is consistent with the (minuscule) cosmologically expected abundance...



#7
Apr1813, 10:51 AM

P: 2,179




#8
Apr1813, 05:32 PM

P: 755

http://arxiv.org/abs/1001.5273 discusses recoil interactions for the keVmass sterile neutrinos. The interaction is possible because of "sterileactive mixing" (i.e. the sterile neutrino turns into a neutrino that feels the weak force), and "the momentum transferred from the sterile neutrino to a target particle is of the order of sterile neutrino mass".



#9
Apr1813, 05:52 PM

P: 2,179

Thanks for posting this  I was not aware. So it sounds like future detection of these particles might be possible. However, it sounds like both the energy transfer (25eV compared to ~10keV for CDMSII events) and the rate are far too low to explain the CDMSII events.



#10
Apr1813, 08:54 PM

P: 755

nuMSM contains keV and GeV mass neutrinos. 25 eV collisional energy transfer is for keV mass... But I think the real problem here is the lifetime of the GeV neutrinos. They decay; the presentday dark matter is supposed to be all keV because of this.
edit: Possibly a nuMSM GeV neutrino could be stable if it was charged under a discrete symmetry, such as occurs in a number of refinements of nuMSM meant to explain the neutrino mass spectrum. But then you would have to reexamine the cosmological and astrophysical consequences. edit #2: Andrew OhWilleke has suggested that an unstable GeV neutrino might be produced by cosmic rays. 


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