Tuesday, November 21, 2017

Dark matter explanation for the cosmic ray positron excess favoured

The old PAMELA experiment and perhaps newer ones by Fermi-LAT and AMS-02 have discovered lots of positrons in the cosmic rays, whose flux is generally higher than expected. The energies of positrons show steady rise in the range [10,100] GeV and presumably the rise will continue. Such positrons may originate from dark matter and could amount to an "almost direct detection" of the particles that make up dark matter. There are also other interpretations.

1. Dark matter explanations for the positron excess

Consider first new physics explanations postulating dark matter.

  1. Dark spin 1 particles could decay to electron positron pair. The energy spectrum of energies is however discrete for dominating decay modes. For instance, vector mesons of new hadron physics could produce these events. Many neutral vector mesons say (Psi/J) were discovered in electron-positron annihilation.

  2. Pion-like spin 0 pseudoscalars decaying to electron-positron pairs and gamma rays predicts continuous spectrum. In the case of ordinary pion most decays are to gamma pairs. The decay to electron-positron pair and gamma ray has quite reasonable branching ratio .01. The reason is that the diagram describing this process is diagram for the decay to gamma pair with second gamma decaying to e+e- so that the rate is roughly the rate for the decay to gamma pair multiplied by &alpha_em≈ 1/137. This relation is expected to hold true for the decays of all pion-like states. For the decay to electron positron pair branching ratio about 6.5× 10-8. For pion-like states X the decay X→ e+e- + γ for pion-like state could give a continuous spectrum. The mass of X should be of order 100 GeV for this option.

2. Standard physics explanation for the positron excess

One of the standard physics explanations is that the positrons emerge from pulsars. The beams from pulsars contain electrons accelerated to very high energies in the gigantic magnetic field of pulsar. This beam collides with the matter surrounding the pulsar and both gamma rays and positrons are generated in these interactions.

The standard physics proposal has been put to a test. One can predict the intensity of gamma rays coming from pulsars using standard model physics and deduce from it the density of electrons needed to generate it. Both positrons and gamma rays would be created when electrons from the pulsar are accelerated to very high energies in enormous magnetic field of the pulsar and collide with surrounding matter. This is like particle accelerator. The energies of the produced gamma rays and also positrons extend to TeV range, which corresponds to the energy range for LHC. It turns out that the flux of electrons implied by the gamma ray intensity is too low to explain the flux of positrons detected by PAMELA and some other experiments: see the popular article and the research article "Extended gamma-ray sources around pulsars constrain the origin of the positron flux at Earth" in Science.

3. TGD based model for positron excess

Also TGD suggests an explanation for the positron excess (I learned about PAMELA experiment at my birth day and it was excellent birthday present!). TGD allows a hierarchy of scaled up copies of hadron physics labelled by ordinary Mersenne primes Mn= 2n-1 or by Gaussian Mersennes MG,n= (1+i)n-1 . Ordinary hadron physics would correspond to M107.

  1. M89 hadron physics would have mass scale which is 512 times higher than that for ordinary hadron physics: the size scale of these hadrons is by factor 1/512 shorter than that for ordinary hadrons (see this). There are indications for the copies also in other scales: M79 for instance. X boson provides indication for MG,113 pions in nuclear scale. Even copies of hadron physics in biologically important length scales labelled by Gaussian Mersennes MG,k, k= 151,157,163,167 could exist and play key role in living matter (see this). By the way, the appearance of four Gaussian Mersennes in this length scale range is number theoretical mircale.

  2. M89 hadrons can also appear as dark states with Planck constant heff=n×h. For n=512 they would have the size of ordinary hadrons. This could explain the strange anomalies observed at RHIC and later at LHC and hinting about the presence of string like structures in what was expected to be color deconfinement phase transition predicting thermal spectrum should have been observed instead of strong correlations suggesting for quantum criticality characterized by long range correlations and fluctuations for which heff/h=n would be an explanation.

  3. A large number of bumps, whose masses correspond to the masses of ordinary hadron physics scaled up by factor 512, have been reported at LHC. Unfortunately these bumps cannot be explained by SUSY and other main stream models so that they have been forgotten.

TGD based model could be combined with the pulsar model for the positron excess. The collisions between protons from the pulsar accelerated in its magnetic field and the matter surrounding the pulsar would be analogous to those taking place between proton beams at LHC. If the collision energy is high enough (as it seems since gamma rays up to TeV range have been observed) they could produce dark M89 mesons, in particular pions, which then decay to gamma rays and lepton pairs, in particular electron-positron pairs. Similar collisions could occur also in the atmosphere of Earth between ultrahigh energy cosmic rays and nuclei of atmosphere and be responsible for the exotic cosmic ray events like Centauro challenging standard model physics (see this).

4. Other evidence for dark pion like states

There is also other evidence for pion-like states dark in TGD sense.

  1. There is an old observation that gamma ray pairs with energy essential that of electrons rest must come from the center of Milky Way presumably resulting in decays of a particle with mass slightly larger than two times the mass of electron. These particles would also decay to electron positron pairs and the resulting electrons and positrons would be accelerated in the magnetic field of say pulsar to high energies. The rate for the decay to electron positron pairs is quite too slow as compared to the decay rate to gamma pairs. Therefore this mechanism cannot explain positron surplus.

  2. The TGD model for the pion-like states decaying to gamma pairs is as leptopion (see this), which would be a pion-like bound state of color excitations of electrons predicted to be possible in TGD Universe. "Electropion" like states were discovered experimentally in CERN already at seventies and later evidence also for the muopions and taupions has emerged but since they did not fit with standard model, their existence was forgotten. This has been the fate of many other anomalies in particle physics. In nuclear physics there are century old forgotten anomalies re-discovered several times only to be "forgotten" again. The laws of Nature are not discovered nowadays as in good old days: they are decided by the hegemony, which happens to be in power. SUSY, superstring models, and M-theory already disappearing in the sands of time are basic examples of this new political science.

  3. The reason for not accepting the existence of leptopion like states was that in standard model intermediate bosons should decay to them and their decay widths would be larger than their experimental values. However, if leptopions are dark matter in TGD sense having non-standard value of Planck constant heff/h=n, the problem can be circumvented.
See the chapter Recent status of leptopion hypothesis.

For a summary of earlier postings see Latest progress in TGD.

Articles and other material related to TGD.

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