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We perform an extensive analysis of the statistics of axion masses and interactions in compactifications of type IIB string theory, and we show that black hole superradiance excludes some regions of Calabi-Yau moduli space. Regardless of the cosmological model, a theory with an axion whose mass falls in a superradiant band can be probed by the measured properties of astrophysical black holes, unless the axion self-interaction is large enough to disrupt formation of a condensate. We study a large ensemble of compactifications on Calabi-Yau hypersurfaces, with $1 leq h^{1,1} leq 491$ closed string axions, and determine whether the superradiance conditions on the masses and self-interactions are fulfilled. The axion mass spectrum is largely determined by the Kahler parameters, for mild assumptions about the contributing instantons, and takes a nearly-universal form when $h^{1,1} gg 1$. When the Kahler moduli are taken at the tip of the stretched Kahler cone, the fraction of geometries excluded initially grows with $h^{1,1}$, to a maximum of $approx 0.5$ at $h^{1,1} approx 160$, and then falls for larger $h^{1,1}$. Further inside the Kahler cone, the superradiance constraints are far weaker, but for $h^{1,1} gg 100$ the decay constants are so small that these geometries may be in tension with astrophysical bounds, depending on the realization of the Standard Model.
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We construct a model of quintessence in string theory based on the idea of axion monodromy as discussed by McAllister, Silverstein and Westphal arXiv:0808.0706. In the model, the quintessence field is an axion whose shift symmetry is broken by the presence of 5-branes which are placed in highly warped throats. This gives rise to a potential for the axion field which is slowly varying, even after incorporating the effects of moduli stabilization and supersymmetry breaking. We find that the resulting time dependence in the equation of state of Dark Energy is potentially detectable, depending on the initial conditions. The model has many very light extra particles which live in the highly warped throats, but these are hard to detect. A signal in the rotation of the CMB polarization can also possibly arise.
We obtain constraints from black hole superradiance in an ensemble of compactifications of type IIB string theory. The constraints require knowing only the axion masses and self-interactions, and are insensitive to the cosmological model. We study more than $2 cdot 10^5$ Calabi-Yau manifolds with Hodge numbers $1leq h^{1,1}leq 491$ and compute the axion spectrum at two reference points in moduli space for each geometry. Our computation of the classical theory is explicit, while for the instanton-generated axion potential we use a conservative model. The measured properties of astrophysical black holes exclude parts of our dataset. At the point in moduli space corresponding to the tip of the stretched K{a}hler cone, we exclude $approx 50%$ of manifolds in our sample at 95% C.L., while further inside the K{a}hler cone, at an extremal point for realising the Standard Model, we exclude a maximum of $approx 7%$ of manifolds at $h^{1,1}=11$, falling to nearly zero by $h^{1,1}=100$.
We propose a mechanism for the natural inflation with and without modulation in the framework of type IIB string theory on toroidal orientifold or orbifold. We explicitly construct the stabilization potential of complex structure, dilaton and Kahler moduli, where one of the imaginary component of complex structure moduli becomes light which is identified as the inflaton. The inflaton potential is generated by the gaugino-condensation term which receives the one-loop threshold corrections determined by the field value of complex structure moduli and the axion decay constant of inflaton is enhanced by the inverse of one-loop factor. We also find the threshold corrections can also induce the modulations to the original scalar potential for the natural inflation. Depending on these modulations, we can predict several sizes of tensor-to-scalar ratio as well as the other cosmological observables reported by WMAP, Planck and/or BICEP2 collaborations.
We propose the natural inflation from the heterotic string theory on Swiss-Cheese Calabi-Yau manifold with multiple $U(1)$ magnetic fluxes. Such multiple $U(1)$ magnetic fluxes stabilize the same number of the linear combination of the universal axion and Kahler axions and one of the Kahler axions is identified as the inflaton. This axion decay constant can be determined by the size of one-loop corrections to the gauge kinetic function of the hidden gauge groups, which leads effectively to the trans-Planckian axion decay constant consistent with the WMAP, Planck and/or BICEP2 data. During the inflation, the real parts of the moduli are also stabilized by employing the nature of the Swiss-Cheese Calabi-Yau manifold.
We study a racetrack model in the presence of the leading alpha-correction in flux compactification in Type IIB string theory, for the purpose of getting conceivable de-Sitter vacua in the large compactified volume approximation. Unlike the Kahler Uplift model studied previously, the alpha-correction is more controllable for the meta-stable de-Sitter vacua in the racetrack case since the constraint on the compactified volume size is very much relaxed. We find that the vacuum energy density Lambda for de-Sitter vacua approaches zero exponentially as the volume grows. We also analyze properties of the probability distribution of Lambda in this class of models. As in other cases studied earlier, the probability distribution again peaks sharply at Lambda=0. We also study the Racetrack Kahler Uplift model in the Swiss-Cheese type model.
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