Sunday, April 27, 2014

Similarities and Differences between the CKM & PMNS Matrices

In the Minimal Standard Model (MSM), neutrinos do not have mass. They do not have mass because the creators of the MSM assumed that there are no sterile neutrinos (i.e. right-handed neutrinos and left-handed anti-neutrinos.) By including sterile neutrinos, it's fairly easy to build a theory that predicts massive neutrinos and neutrino mixing. (This is not new...see neutrino minimal standard model, vMSM.) However, the vMSM has yet to be confirmed experimentally, and there are still some remaining questions that need to be answered in the vMSM, such as: what is the mass of the sterile neutrinos? Can the masses of the neutrinos be predicted in advance of experimental measurements?

Given that neutrinos mix into each other, scientists have indirectly shown that neutrinos have mass. (Other indirect evidence for neutrino mass is that neutrinos from the 1987 supernova explosion arrived later than photons from the explosion...and the less energetic neutrinos on average arrived later than the more energetic neutrinos...in line with the special theory of relativity.) So, it's now been obvious that the MSM is not a valid theory of the universe (and this is not news.) But the MSM seems to do quite well at predicting the rates of interaction between quarks and leptons. So, we are looking into how to tweak the MSM to account for neutrino mixing, but without messing up the parts of the MSM that work extraordinarily well.

In this post, I want to discuss the similarities and the differences between the CKM and PMNS matrices because this are the two matrixes (that we know of so far) in which there is CP-symmetry violating physics (and hence T-symmetry violating physics. ) There is an eerily close resemblance between the CKM matrix and the PMNS matrix, but the eigenvalues of the matrices are not exactly the same. It is the PMNS that shows the strongest CP-violation, but it is also the matrix that has the most uncertainty in the values. Hence, it is crucially important that we decease the uncertainty in the values of the PMNS matrix by creating more precise measurements of neutrinos. Only by decreasing the uncertainyty will it be clear what is the strength of the CP-violating term in the matrix, and perhaps whether we need to include sterile neutrinos into the PMNS matrix.



Thursday, April 24, 2014

News update on Sterile Neutrinos

I'm currently working on a post on how the CP-violating term in the PMNS matrix is indirect evidence both for massive neutrinos and for a sterile neutrino.
In the mean time, I wanted to let readers of this blog know that you can read the following paper that was just recently published by Physical Review Letters, in which the author shows that a 7 keV sterile neutrino is an extremely plausible candidate for dark matter. The paper can also be found on the Arxiv website, where it was posted back on March 4th.
Their main results are summarized in Figure 1 of the paper. They suggest that recent observation of a 3.57 keV X-ray line can be explained by a 7.1 keV sterile neutrino with a mixing parameter of approximately 3*10^-11  (sin squared of two times the mixing angle to be precise.) This leads to predictions of the temperature at which the sterile neutrinos were produced.

I think that this is certainly interesting research, and the model works much better than ColdDarkMatter models. However, there are still a lot of assumptions in the model, and I would hesitant to make any firm statements about whether a sterile neutrinos have been discovered. There is clearly no discovery because the research is no where near "5sigma" certainty (like what has been required to claim discovery of new particles.)

The reason that I mentioned this article is that hopefully NSF, NASA and European equivalent agencies devote more time and effort to searching for WarmDarkMatter and Sterile Neutrinos.
(Sterile neutrinos can explain why ordinary neutrinos have mass and are intriguing candidates for dark matter. I'm still a little shocked that so much time/money/effort has gone into looking for GeV ColdDarkMatter. Unfortunately, this is likely all just a side-effect of the physics community irrational devotion to supersymmetry and superstring theory. It's good to see that the hype of supersymmetry, superstring theory, and ColdDarkMatter is finally being realized by the public at large.)

Wednesday, April 16, 2014

Cold Dark Matter is an Oxymoron

(Note that this is a continuation of previous post in which I point out that Heavy Dark Matter is an Oxymoron.)

Anybody else tired of the science media jumping on every piece of evidence for Cold Dark Matter, and turning it into possible evidence for string theory, supersymmetry, and the multiverse. I wish that the scientific journalists at Scientific American and New Scientist thought critically about the physics news that they are reporting. How can a particle be heavier than a proton, but have no electric charge or strong nuclear 'charge'?
Cold Dark Matter is an oxymoron because the rest mass of a particle is related to its capability to interact with other particles and/or fields (especially the Higgs field.) Heavier particles have more interactions with other particles, whereas lighter particles have less interactions. Mass is proportional to the number and strength of the particles interactions with other particles. Saying the words "Cold dark matter" is like saying the words "Skinny fat people." It just doesn't make sense because a particle can't be both heavy in mass but light in interactions.  (Note that this is also why I think that supersymmetry and any supersymmetric string theories are silly...if your theory invents new particles that are really heavy, but hardly interact with anything...such as gravitinos or neutralinos...then please throw your theory away and start from scratch. You are missing the whole point...the mass of a particle is proportional to its capability to interact and/or decay. Note that the same goes for a theories that predict 'sterile' neutrinos of GeV or TeV mass.)

But let's step back for a second, and ask the question: what are the implications of GeV dark matter?

In order to have GeV dark matter, you need to explain the following:
(1) Why there's no evidence for the GeV dark matter particles in any of the particle collider experiments? Why haven't we seen any of these particles when we collide together matter/anti-matter pairs with TeV of energy?
(2) Why doesn't the GeV dark matter just clump together at the center of galaxies?  The reason that we invented the concept of dark matter was to explain the higher than expected velocity of stars on the outer-edge of galaxies (and of higher than expected velocity of entire galaxies rotating about each other.)
GeV cold dark matter would just clump together because there's nothing (except Fermi-Dirace statistics and perhaps the weak force) to keep the particles from clumping together into an extremely tight ball. The fact that the recent "evidence" for GeV dark matter is coming from GeV gamma ray emission only in the center of the galaxy is a tell-tale sign that it's not coming from dark matter, but rather that it's coming from objects with extreme temperatures.
(3) According to astrophysical observation, there's no spike in the density of dark matter in the center of galaxies. Dark matter is actually quite diffuse in galaxies, and even extends out past where there's no more stars. (see image below from the new movie Dark Universe.) So, why would there be spike in the GeV emission at the center of galaxies?  (It's not due to dark matter collisions, or else it would be diffuse throughout the galaxy.)