Could matter in the universe come from some process other than the decay of inflaton field?

Do we have any theoretical reasons that support the idea that matter was created from the decay of inflaton field?

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    $\begingroup$ Are you asking if there are other mechanisms within inflationary scenario that could produce matter, or if there are alternatives to inflation? $\endgroup$ – A.V.S. Jul 18 '18 at 9:01
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    $\begingroup$ Possible duplicate of Where does matter come from? $\endgroup$ – StephenG Jul 18 '18 at 9:04
  • $\begingroup$ @A.V.S. I’m asking about the possibility of alternatives. $\endgroup$ – parker Jul 18 '18 at 9:36
  • $\begingroup$ In the suggested duplicate it’s about energy conservation in GR which is not what I’m asking about. $\endgroup$ – parker Jul 18 '18 at 9:41
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    $\begingroup$ I actually know of only one other mechanism, that associated with particle production in quintessential inflation, an idea from the late nineties that tries to unify primordial inflation and the current accelerated expansion of the universe by positing a single field responsible for both. Since the inflaton in this model is still driving the accelerated expansion, it couldn't have decayed after the primordial epoch. Instead, cosmological particle production due to the expansion, of the type studied by Parker, Ford, and others in the 70's, is invoked to create matter. $\endgroup$ – bapowell Jul 19 '18 at 14:03

The expansion of the universe can induce particle creation even without inflation. Sec. 3.4 of Birrell and Davies 1982 discusses the special case $a^2=A+B\tanh\rho\eta$, with $A,\,B,\,\rho$ positive constants and $\eta$ conformal time running from $-\infty$ to $\infty$. (I think the analysis dates to the 1960s, but B&D is a popular textbook summary.) This example causes the scale factor to gradually increase from $\sqrt{A-B}$ to $\sqrt{A+B}$, and is chosen because it makes for a tractable calculation. The basic idea is that the Klein-Gordon equation's solution in such a universe time-evolves, so an initially positive-frequency solution gains a negative-frequency part over time. In fact, the particle density produced is proportional to this part's squared amplitude.

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  • $\begingroup$ So in this model, energy wasn’t created but it already existed at the beginning of the universe, right? And the expansion of the universe just induced particle creation from that energy? $\endgroup$ – parker Jul 20 '18 at 12:03
  • $\begingroup$ @parker To quote from Sec. 3.5, "The changing 'gravitational field' feeds energy into the perturbed scalar field modes." I should have mentioned it's a model of the production of massive scalars. $\endgroup$ – J.G. Jul 20 '18 at 12:11

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