We study gravitational wave production in an expanding Universe during the first stages following inflation, and investigate the consequences of the Gauss–Bonnet term on the inflationary parameters for a power-law inflation model with a GB coupling term. Moreover, we perform the analyses on the preheating parameters involving the number of e-folds $$N_{pre}$$
N
pre
, and the temperature of thermalization $$T_{th},$$
T
th
,
and show that it’s sensitive to the parameters n, and $$\gamma $$
γ
, the parameter $$\gamma $$
γ
is proposed to connect the density energy at the end of inflation to the preheating energy density. We set a correlation of gravitational wave energy density spectrum with the spectral index $$n_{s}$$
n
s
detected by the cosmic microwave background experiments. The density spectrum $$\varOmega _{gw}$$
Ω
gw
shows good consistency with observation for $$\gamma =$$
γ
=
$$10^{3}$$
10
3
and $$10^{6}$$
10
6
. Our findings suggest that the generation of gravitational waves (GWs) during preheating can satisfy the constraints from Planck’s data.
We propose a scenario where preheating occurs for a specific duration that is parametrized by an [Formula: see text]-folds number [Formula: see text], our results suggest a direct correlation between the preheating duration and the density of gravitational waves (GWs) produced during this phase. Moreover, we investigate the consequences of the inflationary parameters on the [Formula: see text]-attractor [Formula: see text] model in the small [Formula: see text] limits. In this framework, we perform investigations on the preheating parameters involving the number of [Formula: see text]-folds [Formula: see text], and the temperature of reheating [Formula: see text], then we show that the parameter [Formula: see text] associated with the [Formula: see text] model of [Formula: see text]-attractor inflation has a negligible effect on the preheating duration, and we demonstrate that gravitational wave generation during preheating satisfies the restrictions from Planck’s recent data.
We study a new reheating approach in the framework of standard and braneworld inflation. Using the technique developed in Ref. 1, we consider a small field arctangent potential and show that this approach can be similarly applied within Randall–Sundrum type 2 scenario and provide additional constraints to reheating temperature [Formula: see text] and duration of reheating [Formula: see text]. We found that in brane case the effective equation-of-state parameter [Formula: see text] must be close to 1, to satisfy Planck-2018 joint constraints on [Formula: see text].
We study the two-phase scenario following inflation, where the initial step is preheating, accompanied by a step of perturbative reheating at which inflaton field decays transferring all of its energy to create relativistic particles, the interaction of these particles will evolve towards a state of thermal equilibrium with a temperature T re called the reheating temperature. It is observed that the scenario of reheating normally predicts the maximum reheating temperature that corresponds to an almost instantaneous transition from inflation to the radiation domination era. This will naturally lead to a nonperturbative preheating. In this framework, we propose constraints on the reheating duration parameters expressed in terms of the cosmic microwave background (CMB) inflationary scalar spectral index. In this work we study the compatibility of polynomial and Higgs models of inflation with the observational data obtained from Planck 2018.
We investigate a new possible solution to the Hubble constant tension. we propose a simple resolution to the problem assuming that a first-order phase transition related to H0 transition occurred in the early Universe. The early evolution of the Universe is a result of hybrid inflation that has lasted for a specific period until symmetry breaking takes place. Fitting our model to measurements from P lanck and SH0ES data provides a key explanation of discrepancies of H0 measurements. The quantum fluctuations calculated in this model have significant results on the reheating parameters Nre and Tre. Therefore, new constraints must be taken into consideration to fit these parameters to recent results.I.
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