Sorry. I know it, but every time I use the habitual notation, writing a post.

New Physical laws must be discovered. At least those ones, which explain why dark matter is stable.

Why do you think that it is not stable? If Dark Matter is unstable, why is there so much of it (25%) in the universe? Possibly it is and it has converted into Dark Energy in a manner analogous to E=MC^2?

But I wrote that it is stable. It can't be described by existing physical laws.
It is obvious that dark matter is stable; its particles don’t decompose (like electron, which is the lightest particle with electric charge and that is why it doesn’t separate into neutrino and photon, for example). Thus, there is undiscovered Law of Stability, which doesn’t allow these particle to decompose. Besides, particles of dark matter hardly interact with common matter.
By the way, there is a hypothesis that particles of dark matter are about 100-1000 heavier than proton and their interaction with common particles are similar to that with neutrino. This hypothesis claims that particles of dark matter born and annihilated intensively in the very early Universe at the temperature of 10E15 K (1000000000000000 K); and part of them lived out our days.

Your right. My fingers got ahead of my brain. So I'll show my flexibility by restating the question in reverse. Why do you think that Dark Matter is stable? Oh, you already answered that.

I'm not sure whether you are funning me or are seriously out of my league. My knowledge of current physics is sadly deficient. Hell, my formal study of the subject was limited to Newton, Maxwell, etc.-- mechanics/heat/sound, thermodynamics, electricity, optics and such. I graduated 15 years after Hiroshima and any advanced physics was largely Government Classified. My professional career was down-to-earth engineering (well, some occasional space-flight, but no further than the moon's surface).

Assuming that you are serious, "--an undiscovered Law of Stability???" "It is obvious that dark matter is stable; its particles don’t decompose." How can we know that?

I wonder if there is a book, "Modern Physics for Dummies".

If it wasn't stable, it would has already decomposed.



I'm not Physicist as well.



Don't forget that I'm Russian and all aricles I read about dark matter were in Russian. Maybe "Law of Conservation" is a more correct translation.



Really, unknown, undetectable matter... how can we know...
I tell about the hypothesis. Theoretical matter, theoretical properties and... calculations prove it, but... hypotetical dark matter itself is a result of wrong calculations (at least they weren't correct).
In short, we know nothing. It was a hypothesis, which explained why reality doesn't match with calculations. Scientists built a lot of colliders all over the world. They detect nothing except this one we discuss. Nobody doubts that flashes were really detected, but interpretations of these data can be very different.

Maybe it has a loooong half-life. We still have some naturally occuring radioactive materials on Earth, don't we? Hmm. Maybe that is because they were (and still are being) formed in stars that eventually blow up and spread their matter, some of which ends up here.

Using that logic, I would hypothesize that there is no dark matter analog to stars and nuclear reactions. If you mean our Law of Conservation of Mass + Energy, a similar law for the conservation of Dark Matter + Dark Energy would make sense; implying a constant for the Dark Matter to Dark Energy conversion (the Speed of Dark Light?) Quite true, but that one experiment does seem to be a hint that at least some of the hypotheses contain some degree of validity. Rather like Newton just after he first got the concept of mutual attraction of matter: we know a lot more about gravity today, but his work was seminal. I would expect that our knowledge of Dark Matter will snowball* now that we have a small start.

* American jargon for how a ball of snow increases in size as it rolls down a hill. It is probably in your dictionary as noun, but not as a verb.

How does the 'string' theory work into this?

Maybe. Maybe the products of their decomposition have a long period of half-life as well as the products of the decomposition of these products. Is there anything stable in this world?



Maybe similar, maybe not. Who knows? Especially about dark light...
Btw,this hypothesis assumes that Dark Matter is under antigravitation.



As for Newton... he used a concept of God to explain the stability of orbits. Now undiscovered force (matter and energy) was named Dark Matter and Dark Energy.

Yes. String theory -> supersymmetry -> dark matter consists of supersymmetrical partners of bosons, quarks and leptons.