When atomic nuclei fuse, energy is released. Is there anything about the CMB energy distribution that suggests that dark matter could have formed from other particles that released energy?
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2 Answers
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Please feel free to specify your question further in case I'm not hitting your nail with my answer-hammer.
How (and when) dark matter formed is an open question and depend on the particular dark matter model that is invoked. For a broad class of models called "thermal relic particles", dark matter was in equilibrium with the primordial thermal bath. Thus, dark matter particles and "normal matter" constantly annihilated, into each other, and back and forth. In that sense there are many models where "dark matter formed from other particles that released energy".
The CMB is emitted some 300,000 years after the Big Bang. At that point, dark matter already exists in abundance; in fact, we expect that it formed less than a minute after the Big Bang. Thus, all that is left as a possible imprint in the CMB is the overall temperature of the thermal bath (the temperature of the universe) and one shouldn't expect any signature in the CMB from dark matter production or annihilation.
Taking this even further through the evolution of the universe, what is known from structure formation is that dark matter is non-relativistic ("cold"). That places limits on the amount of energy that can be pumped from our baryonic world into the dark sector.
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1$\begingroup$ "in case I'm not hitting your nail with my answer-hammer." -- what a terrific metaphor! $\endgroup$– AndrewMar 2 at 1:47
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$\begingroup$ @DaveTheWave I don't see the connection between your comment and your question or this answer. Neither your question nor my answer mention "dark energy" at all. $\endgroup$– rflMar 2 at 20:03
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$\begingroup$ I agree and have deleted the comment. $\endgroup$– user359635Mar 3 at 7:59
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This recent paper discusses the amount of energy that can be injected into the primordial plasma without excessively altering the cosmic microwave background (CMB) or the abundance of light elements emerging from primordial nucleosynthesis. The most stringent constraint comes from the deuterium abundance, which enforces that an entropy-injecting process occurring after nucleosynthesis ($\sim$ minutes) can contribute to the energy density at only the few-percent level without violating observational limits.
The CMB is also constraining, through limits on spectral distortions and on $N_\mathrm{eff}$ (the relative energy density of neutrinos), but its constraints are typically weaker.
We generally assume dark matter was created before nucleosynthesis. Energy injections that occur prior to about 1 second (the time of neutrino decoupling) have no impact on anything we observe.
However, it is possible for dark matter to form much later, even as late as tens of years ($z\sim 10^6$); see this paper. It must then form by a process, like decay, that does not add energy to the plasma.
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$\begingroup$ What if dark matter increased its mass while baryonic matter lost some mass keeping the total mass the same Would that show up as a feature in the cmb? I ask this because we assume that interactions with the Higgs field and constants such as G for gravity have always been the same. $\endgroup$– user359635Mar 3 at 12:02
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$\begingroup$ @DaveTheWave That's pretty much the scenario discussed in my second link. They consider an electrically charged exotic particle that decays into dark matter. Since the exotic particle is charged, it couples to the primordial plasma, behaving just like baryonic matter. This scenario can alter the CMB, primarily because the presence of more electromagnetically coupled matter in the early universe changes the behavior of sound waves. However, if the dark matter formed before a few tens of years ($z\sim 10^6$), we would not detect this influence with current measurements. $\endgroup$– StenMar 3 at 12:35
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$\begingroup$ I doubt that dark matter formed from an electrically charged exotic particle decaying because the decay products would have a net charge of one sign and the universe would be flooded with charge now.Perhaps these charges are repelling one another and are dark energy expanding the universe! Also would there have been an anti exotic charged particle yielding anti dark matter? $\endgroup$– user359635Mar 3 at 17:36
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$\begingroup$ @DaveTheWave That can be avoided by having exotic charged particles of both signs, as described in more detail in this paper $\endgroup$– StenMar 3 at 18:17