D7-brane chaotic inflation

Abstract

We analyze string-theoretic large-field inflation in the regime of spontaneously-broken supergravity with conventional moduli stabilization by fluxes and non-perturbative effects. The main ingredient is a shift-symmetric Kähler potential, supplemented by flux-induced shift symmetry breaking in the superpotential. The central technical observation is that all these features are present for D7brane position moduli in Type IIB orientifolds, allowing for a realization of the axion monodromy proposal in a controlled string theory compactification. On the one hand, in the large complex structure regime the D7-brane position moduli inherit a shift symmetry from their mirror-dual Type IIA Wilson lines. On the other hand, the Type IIB flux superpotential generically breaks this shift symmetry and allows, by appealing to the large flux discretuum, to tune the relevant coefficients to be small. The shift-symmetric direction in D7-brane moduli space can then play the role of the inflaton: While the D7-brane circles a certain trajectory on the Calabi-Yau many times, the corresponding F -term energy density grows only very slowly, thanks to the above-mentioned tuning of the flux. Thus, the large-field inflationary trajectory can be realized in a regime where Kähler, complex structure and other brane moduli are stabilized in a conventional manner, as we demonstrate using the example of the Large Volume Scenario.

Can gravitational instantons really constrain axion inflation?

“…Note that in order to avoid destabilisation of the Kähler moduli the compactification volume is at most of order O(10 3 ), see e.g. [59,60,65]. Nevertheless, the suppression by e −S remains dominant in all regimes we considered.…”

The challenge of realizing F-term axion monodromy inflation in string theory

“…These four-dimensional axions can descend from higher p-form fields in ten dimensions, but also geometric moduli of shiftsymmetric backgrounds can show such a behavior. Recently discussed examples include the real parts of complex-structure moduli U = u + iv on a torus [7] or the deformation moduli ξ of a D7-brane wrapping a transverse four-cycle of the internal manifold [8,9]. On a generic Calabi-Yau manifold, such symmetries can also appear at special points in the moduli space, for instance in the large complex-structure limit.…”

“…In [34] a scenario based on the universal axion C 0 was discussed, where it was argued that this axion provides a natural mechanism for reheating to occur mainly into Standard Model degrees of freedom. In [8,35] the inflaton was given by a deformation modulus of a D7-brane which was argued to enjoy a shift symmetry (at special points in the moduli space). In [9] the axion was identified with an open-string modulus, namely the superpartner in the Higgs sector of the MSSM.…”

“…The complex three-form flux defined in equation (3.1) can therefore be written in the following way 8) and in this notation the contribution to the C 4 -tadpole shown in (3.4) becomes…”

Tunneling in axion monodromy

“…and so the potential can be seen as multiple quadratic branches labeled by the integer m. It has been shown in [15] that (2.1) arises as the low energy effective theory of a wide class of string theory constructions (see also [25,26]). In string theory, the membrane is interpreted as a naturally occurring object, such as a D-brane, charged under some gauge field which compactifies to C 3 .…”