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 consider a Chaplygin gas model with an exponential potential in framework of braneworld inflation. We apply the slow-roll approximation in the high-energy limit to derive various inflationary spectrum perturbation parameters. We show that the inflation observables depend only on the e-folding number N and the final value of the slow-roll parameter e(end). Whereas for small running of the scalar spectral index dns/dlnk, the inflation observables are in good agreement with recent WMAP7 data.Comment: 5 pages, 3 figure

Using, the harmonic analysis of the 3- and 2-spheres, we study the compactification of the IKKT model on the F 0 Hirzebruch complex surface. Like for tori and orbifolds, we show that here there also exists a possibility of compactifications of matrix models of M-theory on non-commutative F 0 geometry. Other features, such as the extension of Connes et al 's projective module solutions to non-commutative F 0 are studied.

In this paper, we present a spatially homogeneous and anisotropic Bianchi type-I cosmological model with a viscous bulk fluid in [Formula: see text] gravity where [Formula: see text] and [Formula: see text] are the Ricci scalar and trace of the energy-momentum tensor, respectively. The field equations are solved explicitly using the hybrid law of the scale factor, which is related to the average Hubble parameter and gives a time-varying deceleration parameter (DP). We found the deceleration parameter describing two phases in the universe, the early deceleration phase [Formula: see text] and the current acceleration phase [Formula: see text]. We have calculated some physical and geometric properties and their graphs, whether in terms of time or redshift. Note that for our model, the bulk viscous pressure [Formula: see text] is negative and the energy density [Formula: see text] is positive. The energy conditions and the [Formula: see text] analysis for our spatially homogeneous and anisotropic Bianchi type-I model are also discussed.