Update of D3/D7-Brane Inflation on K3 x T^2/Z_2

TL;DR

This paper updates the D3/D7-brane inflation model on K3 x T^2/Z_2 by incorporating g_s corrections, analyzing the inflaton potential, and exploring its compatibility with cosmological data, including cosmic strings and eternal inflation scenarios.

Contribution

It provides a detailed analysis of quantum corrections and their effects on the inflationary potential and field range, enhancing the model's phenomenological viability.

Findings

The inflaton field range depends on the complex structure, allowing large values.

The model can fit CMB data with or without cosmic string contributions.

Quantum corrections enable a regime of eternal inflation.

Abstract

We update the D3/D7-brane inflation model on K3 x T^2/Z_2 with branes and fluxes. For this purpose, we study the low energy theory including g_s corrections to the gaugino condensate superpotential that stabilizes the K3 volume modulus. The gauge kinetic function is verified to become holomorphic when the original N=2 supersymmetry is spontaneously broken to N=1 by bulk fluxes. From the underlying classical N=2 supergravity, the theory inherits a shift symmetry which provides the inflaton with a naturally flat potential. We analyze the fate of this shift symmetry after the inclusion of quantum corrections. The field range of the inflaton is found to depend significantly on the complex structure of the torus but is independent of its volume. This allows for a large kinematical field range for the inflaton. Furthermore, we show that the D3/D7 model may lead to a realization of the recent CMB fit by Hindmarsh et al. with an 11% contribution from cosmic strings and a spectral index close to n_s=1. On the other hand, by a slight change of the parameters of the model one can strongly suppress the cosmic string contribution and reduce the spectral index n_s to fit the WMAP5 data in the absence of cosmic strings. We also demonstrate that the inclusion of quantum corrections allows for a regime of eternal D3/D7 inflation.