Neutrino Minimal Standard Model

[mitchell porter]

Marcus suggested that the nuMSM deserves its own thread and I agree.

The nuMSM is the context in which the Shaposhnikov-Wetterich 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 http://higgs.ph.ed.ac.uk/sites/default/files/higgs_symp.pdf makes a number of striking claims and suggestions:

slide 5:

"There is no new energy scale between the Fermi and Planck scales
"Electroweak scale is determined by Planck physics
"New physics responsible for dark matter, baryon asymmetry of the universe and neutrino masses is hidden below the Fermi scale"

slide 14:

126 GeV "is a critical point for Higgs inflation"

slide 16:

"SM + Gravity is a final theory"

slide 41:

Or maybe "SM + Gravity + new physics below the EW scale"

So the nuMSM has become a paradigm in itself, at the intersection of many issues.

 

[marcus]

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 › hep-phby 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 › hep-phby 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 X-ray astronomy
arxiv.org › hep-phby 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 › hep-phby 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 - INSPIRE-HEP
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 right-handed 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. 49-59; Publication date: 2007. To explain ...
[PDF]
nuMSM: predictions for neutrino mass and neutrinoless double beta ...
www.mpi-hd.mpg.de/gerda/dubna05/bezrukov_nuMSM.pdfFile Format: PDF/Adobe Acrobat - Quick View
νMSM: predictions for neutrino mass and. 0νββ-decay hep-ph/0505247. F. Bezrukov1. M. Shaposhnikov2. 1Institute for Nuclear Research, Moscow, Russia ...
Sterile neutrino dark matter as a consequence of nuMSM-induced ...
iopscience.iop.org/1475-7516/.../1475-7516_2008_06_031.pdfby M Laine - 2008 - Cited by 56 - Related articles
Sterile neutrino dark matter as a consequence of νMSM-induced lepton asymmetry. This article has been downloaded from IOPscience. Please scroll down to ...
Baryon Asymmetry of the Universe in the NuMSM | ResearchGate
www.researchgate.net/.../45920988_Baryon_Asymmetry_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 0νββ-decay and neutrino masses. Phys. Rev. D 72 (2005) 071303. F. Bezrukov1,2. M. Shaposhnikov1. 1EPFL, Lausanne, Switzerland ...

 

[marcus]

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 non-trivial ultraviolet fixed point, and that (ii) this has only a finite number of relevant perturbations, i.e. a finite number of UV-stable 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 non-trivial 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 space---where 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.

 

[MTd2]

I think this strengthens even more:

http://resonaances.blogspot.com/2013/01/how-many-neutrinos-in-sky.html

 

[mitchell porter]

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 right-handed helicities via the Higgs. Majorana mass terms have a fermion of a given helicity coupled to itself. For a left-handed neutrino, such a mass term is nonrenormalizable and can only be an effective interaction arising from something deeper; but a right-handed 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 left-handed 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 right-handed neutrino has a GUT-scale Majorana mass, and then a naturally-sized neutrino yukawa induces a very light effective mass for the observed SM neutrino.

In the nuMSM, the left-handed neutrinos have their measured, very light masses; there are three right-handed neutrinos, which have keV-GeV masses in order to explain cosmology; and the left-handed masses are Dirac masses, while the right-handed 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 "Planck-scale seesaw". I got the idea from Ron Maimon's remark that the basic seesaw just requires an "HHLL" interaction, in which the left-handed 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 quantum-gravitational (i.e. with a Planck-scale 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 Shaposhnikov-Wetterich 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).

 

[mitchell porter]

Could the GeV-mass sterile neutrinos of the nuMSM cause the CDMS-II events?? In the nuMSM, the dark matter consists of a keV-mass right-handed neutrino, but there are two GeV-mass 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...

 

[phyzguy]

Could the GeV-mass sterile neutrinos of the nuMSM cause the CDMS-II events?? In the nuMSM, the dark matter consists of a keV-mass right-handed neutrino, but there are two GeV-mass 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...

I thought that in the nuMSM model the RH neutrinos are "sterile" and hence do not interact, even weakly. So they could not cause the CDMS-II events. Someone correct me if I am wrong.

 

[mitchell porter]

http://arxiv.org/abs/1001.5273 discusses recoil interactions for the keV-mass sterile neutrinos. The interaction is possible because of "sterile-active 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".

 

[phyzguy]

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 CDMS-II events) and the rate are far too low to explain the CDMS-II events.

 

[mitchell porter]

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 present-day 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 Oh-Willeke has suggested that an unstable GeV neutrino might be produced by cosmic rays.