There are two observed candidates for ford particles what would form the speculative galactic dark matter halo. They would have as decay products monochromatic gamma rays at energy of around .5 MeV and 3.5 keV X rays having no standard identification. The recent findings exclude the possibility that these particles reside in the conjectured galactic dark matter halo. They could however reside in galactic centers so that their existence is not challenged.
A. .5 MeV gamma ray signal
There is an old gamma ray signal from Milky Way at gamma ray energy of slightly more than electron mass. It has been proposed that it results as dark particle and antiparticle almost at res with respect to each other annihilate.
Now it seems that the interpretation as in the proposed sense seems to be excluded.
One can of course, why not a particle which has mass nearly twice the electron mass could not decay to two gamma rays. For some reason this option haven not been experienced as interesting.
- Support from the existence of pseudoscalar with this mass emerged already at seventies but because it did not fit witht he standard model picture it was forgotten. Later evidence for a particle with masses twice the mass of muon and tau lepton with similar interpretation emerged. For the same reason also these pieces of evidence were forgotten.
- TGD led long time ago to what I call leptopion hypothesis (see this). In TGD color is not spin-like but angular momentum-like quantum number. Color correspond to the analog of angular momentum for the analog of rigid body rotation in CP_2 degrees fredom. In particular, TGD allows colored excitations of leptons: for instance, electron could appear in color octet state. Color excited electron and positron might form a pion-like color confined pion with mass very nearly 2 times electron mass. Same for muon and tau.
- These states could be dark in the sense that they have non-standard value of effective Planck constant heff=n×h0. This would explain why they are not produced in the decays of Z0 boson and therefore do not affect its decay rate. Otherwise Z0 and W decays widths exclude leptopions.
- This darkness has however nothing to do with the darkness of galactic matter, which reside as energy and possibly dark matter at long very cosmic strings to which linear structures formed by galaxies can be assigned. These cosmic strings can locally thicken to flux tubes and liberate energy as particles forming galaxies. They generate radial gravitational force predicting the flat velocity spectrum of distant stars.
B. 3.5 keV X ray signal
Also 3.5 keV X rays appearing as an unidentified mono-chromatic line in X ray spectrum have been proposed to result from the annilation of dark particles having mass about 7 keV. The experimental findings exclude the possibility that these X rays are produced in the proposed galactic halo.
- In TGD framework also 3.5 keV X rays could result in a decay of pion-like state with mass of 7 keV. TGD indeed predicts new nuclear physics in keV scale.
As a matter fact, TGD leads to a new vision about nuclear physics on basis of model of "cold fusion" (see this) . Magnetic flux carrying monopole flux serve as basic building bricks also now: TGD Universe is indeed fractal.
- Nuclear string models relies on the assumption that nuclei are sequences of nucleons connected by pionlike bonds - loopy flux tubes much longer than the M^4 distance between nucleons. These loopy flux tubes have length of order electron Compton length are essential for the TGD based model of nuclear reactions and also of "cold fusion". These flux tubes would be like pions with mass about 7 keV decaying to two X rays with energy 3.5 keV. They might be produced even in nuclear physics laboratory. Also now darkness in TGD sense (heff =n×h0>h) is essential and one can talk about dark nuclei.