Constraints on brane inflation after Planck 2015: Impacts of the latest local measurement of the Hubble constant

TL;DR

This study assesses how the latest local Hubble constant measurement influences the viability of various brane inflation models using combined observational data, revealing that some models remain compatible while others are slightly alleviated from fine-tuning issues.

Contribution

It provides a comprehensive analysis of brane inflation models under new Hubble constant constraints, highlighting their compatibility with current observational data.

Findings

Prototype brane inflation model remains consistent within 2σ.

H_{0} measurement broadens the parameter space for the KKLMMT model.

IR DBI model's fit is unaffected by the H_{0} measurement.

Abstract

We investigate the observational constraints on three typical brane inflation models by considering the latest local measurement of the Hubble constant in the global fit. We also employ other observational data, including the Planck 2015 CMB data, the BICEP2/Keck Array B-mode data, and the baryon acoustic oscillations data, in our analysis. Previous studies have shown that the addition of the latest local $H_{0}$ measurement favors a larger spectral index, and can exert a significant influence on the model selection of inflation. In this work, we investigate its impacts on the status of brane inflation models. We find that, when the direct $H_{0}$ measurement is considered, the prototype model of brane inflation is still in good agreement with the current observational data within the $2\sigma$ level range. For the KKLMMT model, the consideration of the $H_{0}$ measurement allows the range of the parameter $\beta$ to be amplified to ${\cal O}(10^{-2})$, which slightly alleviates the fine-tuning problem. For the IR DBI model, the addition of the $H_{0}$ measurement does not provide a better fit. These results show that the consideration of the new $H_{0}$ prior can exert a considerable influence on the brane inflation models. At last, we show that, when $\beta \lesssim 1.1$, the equilateral non-Gaussianity in the IR DBI inflation model is compatible with the current CMB data at the 1$\sigma$ level.