Mutated Hilltop Inflation in the Era of Present and Future CMB Experiments

Abstract

In this article we confront both large-field and small-field sectors of mutated hilltop inflation model with the recent observational results. We begin with confrontation of predictions from mutated hilltop inflation with the joint analysis of Planck-2018 and BICEP/Keck-2018 data. Subsequently, we extend our analysis by incorporating the ACT-DR6 data in combination with Planck-2018, BICEP/Keck-2018, and DESI-Y1 observations. In both cases, the predictions of mutated hilltop inflation show good consistency with the observational constraints. We have also forecasted the constraints on mutated hilltop inflation model from upcoming CMB experiments, LiteBIRD and Simons Observatory along with their combinations. Here also we find that the prediction from mutated hilltop inflation are in tune with those upcoming CMB experiments. The small-field sector of mutated hilltop inflation, in principle, can probe up to $r\sim \mathcal{O}(10^{-4})$, resulting in a tensor amplitude consistent with current bounds and potentially detectable by next-generation CMB missions. However, accommodating the high observational value of the scalar spectral index may demand relatively higher e-foldings in mutated hilltop inflation. A key appealing feature of the mutated hilltop inflation model turns out to be its ability to remain consistent with a potential non-detection of primordial gravitational waves by LiteBIRD and/or Simons Observatory.

Figures (20)

• Figure 1: Variation of the scalar spectral index (Left Panel) and tensor-to-scalar ratio (Right Panel) with the model parameter $\alpha$ in MHI.
• Figure 2: Variation of the permeable minimum (Left Panel) and maximum (Right Panel) values of the model parameter $\alpha$ with number of e-foldings for large-field sector MHI. For the plot we have considered the latest constraint on primordial gravity waves $r<0.032$tristram2022improved to get $\alpha_{_{\rm Min}}$ and solution of $\Delta{\phi=m_{_P}}$ for $\alpha_{_{\rm Max}}$.
• Figure 3: Left Panel: The plot of scalar spectral index with the model parameter, $\alpha$, for three different values of e-foldings. The scalar spectral index exhibits negligible variation with the model parameter. Right Panel: Plot of tensor-to-scalar ratio with the model parameter for $N=55,\ 60, \ 65$.
• Figure 4: The $68\%$ and $95\%$ confidence regions in the $r-n_{_S}$ plane obtained from MHI. The contours are generated by varying the model parameter $\alpha$ within its allowed for large-field MHI and the number of e-folds between $55$ and $65$. The black point indicates the mean prediction of the large-field MHI.
• Figure 5: Variation of the tensor-to-scalar ratio, $r$, with the scalar spectral index, $n_{_S}$, for three different values of e-foldings, $N = 55,\ 60,\ 65$. Black, blue, and green dashed lines correspond to predictions from the MHI (Large Field Sector) model for varying values of the model parameter and for $N = 55,\ 60,\ 65$, respectively. Marginalized $68\%$ and $95\%$ confidence regions in the plane of $r-n_{_S}$ from the Planck-2018 data planck2015infade2018constraintsade2021improved joint with BK18 tristram2022improved. The constraint on $r$ is driven by BICEP2/Keck (BK18) data ade2018constraints, while the constraint on $n_{_S}$ is obtained from Planck-2018 data