256 Inflation I: homogeneous limit
the total preheating and reheating time in terms of the inflaton oscillations number
NT, we obtain the following estimate for the reheating temperature:
TR∼
m^1 /^2
NT^1 /^2 N^1 /^4, (5.106)
whereNis the effective number degrees of freedom of the light fields atT∼TR.
Assuming thatNT∼ 106 , and takingN∼ 102 andm 1013 GeV, we obtainTR∼
1012 GeV. This does not mean, however, that we can ignore physics beyond this
scale. As we have already pointed out, nonequilibrium preheating processes can
play a nontrivial role.
Reheating is an important ingredient of inflationary cosmology. We have seen
that there is no general obstacle to arranging successful reheating. A particle theory
should be tested on its ability to realize reheating in combination with baryogenesis.
In this way, cosmology enables us to preselect realistic particle physics theories
beyond the Standard Model.
5.6 “Menu” of scenarios
All we need for successful inflation is a scalar condensate satisfying the slow-roll
conditions. Building concrete scenarios then becomes a “technical” problem. In-
volving two or more scalar condensates, and assuming them to be equally relevant
during inflation, extends the number of possibilities, but simultaneously diminishes
the predictive power of inflation. This especially concerns cosmological perturba-
tions, which are among the most important robust predictions of inflation. Because
inflation can be falsified experimentally (or more accurately, observationally) only
if it makes such predictions, we consider only simple scenarios with a single in-
flaton component. Fortunately all of them lead to very similar predictions which
differ only slightly in the details. This makes a unique scenario, the one actually
realized in nature, less important. The situation here is very different from particle
physics, where the concrete models are as important as the ideas behind them. This
does not mean we do not need the correct scenario; if one day it becomes avail-
able, we will be able to verify more delicate predictions of inflation. However, even
in the absence of the true scenario, we can nonetheless verify observationally the
most important predictions of the stage of cosmic acceleration. The purpose of this
section is to give the reader a very brief guide to the “menu of scenarios” discussed
in the literature.
Inflaton candidatesThe first question which naturally arises is “what is the most
realistic candidate for the inflaton field?”. There are many because the only require-
ment is that this candidate imitates a scalar condensate in the slow-roll regime. This