Moduli stabilisation and the statistics of axion physics in the landscape

Broeckel, Igor; Cicoli, Michele; Maharana, Anshuman; Singh, Kajal; Sinha, Kuver

doi:10.1007/jhep08(2021)059

Cited by 22 publications

(27 citation statements)

References 60 publications

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“…The data of a model includes specification of a Calabi-Yau compactification at a given point in its moduli space, but our results turn out to be rather insensitive to the choice of point (see §IV.2), and thus independent of the interplay with moduli stabilization discussed e.g. in[10][11][12][13].…”

mentioning

confidence: 82%

“…The magnitude of ( 18) is controlled by the properties of QCD at high energies. Depending on the matter content of QCD, and assuming O(1) CP breaking in the UV, small gauge instantons may give a contribution to the axion potential that dominates over the IR potential (13), and thus spoils the PQ solution to the strong CP problem. This problem can be arbitrarily severe if one makes no further assumptions about the QCD spectrum at high energies.…”

Section: Iii2 Ultraviolet Contributionsmentioning

confidence: 99%

“…14 We estimate the coupling g aγγ by taking the axion that couples to F µν F µν to be a general linear combination of all mass and kinetic eigenstate axions in the theory, with O(1) coefficients. Then we define 13 We do not incorporate mixings of axion species, though it would be interesting to do so. For a study of an effect of axion mixing on dark matter abundance, see [55].…”

Section: V1 Cosmological and Astrophysical Boundsmentioning

confidence: 99%

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PQ Axiverse

Demirtaş¹,

Gendler²,

Long³

et al. 2021

Preprint

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We show that the strong CP problem is solved in a large class of compactifications of string theory. The Peccei-Quinn mechanism solves the strong CP problem if the CP-breaking effects of the ultraviolet completion of gravity and of QCD are small compared to the CP-preserving axion potential generated by low-energy QCD instantons. We characterize both classes of effects. To understand quantum gravitational effects, we consider an ensemble of flux compactifications of type IIB string theory on orientifolds of Calabi-Yau hypersurfaces in the geometric regime, taking a simple model of QCD on D7-branes. We show that the D-brane instanton contribution to the neutron electric dipole moment falls exponentially in N 4 , with N the number of axions. In particular, this contribution is negligible in all models in our ensemble with N > 17. We interpret this result as a consequence of large N effects in the geometry that create hierarchies in instanton actions and also suppress the ultraviolet cutoff. We also compute the CP breaking due to high-energy instantons in QCD. In the absence of vectorlike pairs, we find contributions to the neutron electric dipole moment that are not excluded, but that could be accessible to future experiments if the scale of supersymmetry breaking is sufficiently low. The existence of vectorlike pairs can lead to a larger dipole moment. Finally, we show that a significant fraction of models are allowed by standard cosmological and astrophysical constraints.

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confidence: 82%

Section: Iii2 Ultraviolet Contributionsmentioning

confidence: 99%

Section: V1 Cosmological and Astrophysical Boundsmentioning

confidence: 99%

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PQ Axiverse

Demirtaş¹,

Gendler²,

Long³

et al. 2021

Preprint

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“…of the manifold is exponentially large in string units (see [98] for a recent study) or by employing highly warped extra dimensions. We do not consider these cases further.…”

Section: Jhep09(2021)207mentioning

confidence: 99%

The stochastic axiverse

Reig

2021

J. High Energ. Phys.

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In addition to spectacular signatures such as black hole superradiance and the rotation of CMB polarization, the plenitude of axions appearing in the string axiverse may have potentially dangerous implications. An example is the cosmological overproduction of relic axions and moduli by the misalignment mechanism, more pronounced in regions where the signals mentioned above may be observable, that is for large axion decay constant. In this work, we study the minimal requirements to soften this problem and show that the fundamental requirement is a long period of low-scale inflation. However, in this case, if the inflationary Hubble scale is lower than around O(100) eV, no relic DM axion is produced in the early Universe. Cosmological production of some axions may be activated, via the misalignment mechanism, if their potential minimum changes between inflation and today. As a particular example, we study in detail how the maximal-misalignment mechanism dilutes the effect of dangerous axions and allows the production of axion DM in a controlled way. In this case, the potential of the axion that realises the mechanism shifts by a factor ∆θ = π between the inflationary epoch and today, and the axion starts to oscillate from the top of its potential. We also show that axions with masses ma ∼ O(1 − 100) H0 realising the maximal-misalignment mechanism generically behave as dark energy with a decay constant that can take values well below the Planck scale, avoiding problems associated to super-Planckian scales. Finally, we briefly study the basic phenomenological implications of the mechanism and comment on the compatibility of this type of maximally-misaligned quintessence with the swampland criteria.

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“…Note added. While finishing this project, a related work appeared [88]. Although that work focuses on realizing the QCD axion, there is some overlap in the analysis.…”

Section: Jhep10(2021)248mentioning

confidence: 99%

Aligned natural inflation in the Large Volume Scenario

Angus

Choi

Shin

2021

J. High Energ. Phys.

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We embed natural inflation in an explict string theory model and derive observables in cosmology. We achieve this by compactifying the type IIB string on a Calabi-Yau orientifold, stabilizing moduli via the Large Volume Scenario, and configuring axions using D7-brane stacks. In order to obtain a large effective decay constant, we employ the Kim-Nilles-Peloso alignment mechanism, with the required multiple axions arising naturally from generically anisotropic bulk geometries. The bulk volumes, and hence the axion decay constants, are stabilized by generalized one-loop corrections and subject to various conditions: the Kähler cone condition on the string geometry; the convex hull condition of the weak gravity conjecture; and the constraint from the power spectrum of scalar perturbations. We find that all constraints can be satisfied in a geometry with relatively small volume and thus heavy bulk axion mass. We also covariantize the convex hull condition for the axion-dilaton-instanton system and verify the normalization of the extremal bound.

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Moduli stabilisation and the statistics of axion physics in the landscape

Cited by 22 publications

References 60 publications

PQ Axiverse

PQ Axiverse

The stochastic axiverse

Aligned natural inflation in the Large Volume Scenario

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