In slow-roll inflation models, the early inflation of the universe is driven by the flat non-zero part of the inflaton potential, and it ends as the ball rolls down the cliff and the potential energy released leads then to the formation of matter.

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However, as I have heard such slow-roll models are no longer deemed realistic today in inflationary cosmology, instead other models where the end of the inflation is explained by quantum tunneling of the universe from a state with higher vacuum energy density to another state with lower vacuum energy density are considered for example.

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Why (from a physical point of view) are slow-roll inflation models no longer considered to be realistic, what are their disadvantages? What can models that explain (the end of) the early inflation by a tunneling transition between to vacua explain or describe, that slow roll models can not do?

  • $\begingroup$ Do you have references that can be included in this question? $\endgroup$ – user8 Oct 15 '13 at 11:22
  • $\begingroup$ @UV-D I certainly could find some references ..., I first learned about these things in Lenny Susskind's online cosmology course. $\endgroup$ – Dilaton Oct 15 '13 at 14:24
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    $\begingroup$ @TildalWave I have cleaned up the comments about the on-topicness of this post. The discussion about where cosmology and theoretical astrophysics, as well as astrophysics in general, fall in our scope has moved to Meta. $\endgroup$ – called2voyage Oct 15 '13 at 18:40
  • $\begingroup$ @Dilaton that'd be a good and helpful addition to this excellent question. $\endgroup$ – user8 Oct 15 '13 at 19:33

I...think you've got it backwards? Slow-roll inflation is alive and well, unlike models which involve tunneling between two vacua. The model of inflation first proposed by Alan Guth back in 1980 was a tunneling model. But it had a serious problem: it didn't reheat. Tunneling from a false vacuum to a true one (or a lower-energy false one) wouldn't release any radiation. And we need that radiation, because we are that radiation, cooled down and condensed after nearly 14 billion years of expansion. The solution was slow-roll inflation: as you mentioned in your question, rolling down the potential well releases a great deal of energy, which in turn leads to the wide variety of matter and radiation in the universe today. Slow-roll inflation also does a nice job of predicting the tiny density fluctuations in the early universe that seeded the formation of all the structures in the universe. Wikipedia has more on all of this.

A small disclaimer: there's a lot of inflationary models out there in the literature (there's a hilarious partial list in footnote 3 of this excellent paper by Yadav and Wandelt), and for all I know, one or more of them involve vacuum decay. But the dominant paradigm for inflation today is definitely slow-roll.

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  • $\begingroup$ Thanks for this nice answer, these explanations are indeed the other way round from what I have heared or read ... What I do not yet see right now is why the "latent energy" released by some kind of a vacuum transition (the difference between the two values for the cosmological constant constants) can not be turned into radiation (= photons?) apart from other stuff ... Will have to look deeper at the reheating problem a bit. $\endgroup$ – Dilaton Nov 21 '13 at 17:10

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