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We know that according the standard model of cosmology $\Lambda {\rm CDM}$, there is a primordial plasma after the inflation. And then we study the non-equilibrium evolution of this plasma such as neutrino decoupling, nucleosynthesis, photo decoupling etc. But do anyone know where do the particles in the primordial plasma come from? Are they produced during the inflation? Take any particular kind of particle (baryon, lepton) as an example, where do the primordial particles come from?

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  • $\begingroup$ Which particles, in particular? If you want to know about all of them, this is rather too broad. $\endgroup$ – Kyle Oman May 9 '16 at 6:56
  • $\begingroup$ @KyleOman We know that there are neutrinos leptons and baryons in the plasma. Where do they come from? $\endgroup$ – Wein Eld May 9 '16 at 7:01
  • $\begingroup$ @KyleOman, if you please, you can take any particular kind of particle as an example, to explain where do the primordial particles come from. $\endgroup$ – Wein Eld May 9 '16 at 7:03
  • $\begingroup$ This is all highly speculative, but the original particles in the primordial plasma could have either been formed from raw energy from the big bang within a very very short period after the big bang or they already existed in the small space prior to the explosion. The first atoms only formed during the recombination period when the amount of energy was low enough to allow particles to fall into lower energy states (albeit still incredibly hot). So it seems logical that the first particles formed from the "cooling" of energy, though we'll never be able to test that idea. $\endgroup$ – Neil May 9 '16 at 7:10
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    $\begingroup$ There were no more particles in that quark-gluon plasma than there are particles today. The particle concept is a misunderstanding based on what can be seen in particle detectors where high energy states of quantum fields are weakly interacting with matter. In the primordial universe the energy density and temperature was much higher and these fields coupled more strongly to each other. Some of them thermalized at a certain temperatures and then effectively decoupled, leaving background "radiation" of a certain energy, which then got "redshifted" by the cosmological expansion. $\endgroup$ – CuriousOne May 9 '16 at 8:11
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The process by which particles are created after inflation is known as "reheating". One needs a coupling between the inflaton and another particle's field for this to happen. Generally it occurs at the end of inflation when the inflaton is oscillating in the well of its potential and the expansion rate falls below the interaction rate between the inflaton and the particle. See for example: https://en.wikipedia.org/wiki/Inflation_(cosmology)#Reheating and references for more details.

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