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.

Holographic RG flows dual to QFTs on maximally symmetric curved manifolds (dS d , AdS d , and S d ) are considered in the framework of Einstein-dilaton gravity in d + 1 dimensions. A general dilaton potential is used and the flows are driven by a scalar relevant operator. The general properties of such flows are analyzed and the UV and IR asymptotics computed. New RG flows can appear at finite curvature which do not have a zero curvature counterpart. The so-called 'bouncing' flows, where the β-function has a branch cut at which it changes sign, are found to persist at finite curvature. Novel quantum first-order phase transitions are found, triggered by a variation in the d-dimensional curvature in theories allowing multiple ground states.

We present a new model of large field inflation along a winding trajectory in the field space of two axionic fields, where the "axions" originate from the complex structure moduli sector of a Calabi-Yau 3-fold at large complex structure. The winding trajectory arises from fixing one combination of axions by bulk fluxes and allows for a transplanckian effective field range. The inflaton potential arises from small "instantonic" corrections to the geometry and realises natural inflation. By working in a regime of large complex structure for two complex structure moduli the inflaton potential can be made subdominant without severe tuning. We also discuss the impact of the recent 'no-go theorems' for transplanckian axion periodicities on our work. Interestingly, our setup seems to realise a loophole pointed out in arXiv:1503.00795 and arXiv:1503.04783: our construction is a candidate for a string theory model of large field inflation which is consistent with the mild form of the weak gravity conjecture for axions. arXiv:1503.07912v4 [hep-th]

We identify a characteristic pattern in the scalar-induced stochastic gravitational wave background from particle production during inflation. If particle production is sufficiently efficient, the scalar power spectrum exhibits O(1) oscillations periodic in k, characteristic of a sharp feature, with an exponentially enhanced envelope. We systematically study the properties of the induced spectrum of gravitational waves sourced after inflation and find that this inherits the periodic structure in k, resulting in a peak in the gravitational wave energy density spectrum with O(10%) modulations. The frequency of the oscillation in the scalar power spectrum is determined by the scale of the feature during inflation and in turn sets the frequency of modulations in the gravitational wave signal. We present an explicit realisation of this phenomenon in the framework of multifield inflation, in the form of a strong sharp turn in the inflationary trajectory. The resulting stochastic background is potentially detectable in future gravitational wave observatories, and considerations of backreaction and perturbativity can be used to constrain the parameter space from the theoretical side. Our work motivates more extensive research linking primordial features to observable properties of the stochastic background of gravitational waves, and dedicated development in data analysis for their detection.

No abstract

We show that the soft X-ray excess in the Coma cluster can be explained by a cosmic background of relativistic axions converting into photons in the cluster magnetic field. We provide a detailed self-contained review of the cluster soft X-ray excess, the proposed astrophysical explanations and the problems they face, and explain how a 0.1 − 1 keV axion background naturally arises at reheating in many string theory models of the early universe. We study the morphology of the soft excess by numerically propagating axions through stochastic, multi-scale magnetic field models that are consistent with observations of Faraday rotation measures from Coma. By comparing to ROSAT observations of the 0.2 − 0.4 keV soft excess, we find that the overall excess luminosity is easily reproduced for g aγγ ∼ 2 × 10 −13 GeV −1 . The resulting morphology is highly sensitive to the magnetic field power spectrum. For Gaussian magnetic field models, the observed soft excess morphology prefers magnetic field spectra with most power in coherence lengths on O(3 kpc) scales over those with most power on O(12 kpc) scales. Within this scenario, we bound the mean energy of the axion background to 50 eV E a 250 eV, the axion mass to m a 10 −12 eV, and derive a lower bound on the axion-photon coupling g aγγ 0.5/∆N eff 1.4 × 10 −13 GeV −1 .In the enlightening case of sufficiently high axion energies or small ambient electron densities, the conversion probability for a fixed domain is given bywhere B ⊥ denotes the magnetic field component transverse to the axion velocity and L denotes the corresponding coherence length [11]. This conversion allows the potential detection of a CAB through axion-photon conversion.Galaxy clusters support magnetic fields that are modest in magnitude (B ≈ µG) but are extended over megaparsec distances and have kiloparsec coherence scales, allowing observationally significant axion-photon conversion probabilities. In [1], a crude single-domain model with a fixed magnitude and coherence length for the magnetic field was used to estimate the axion-photon coupling M that would be required to reproduce the soft excess in Coma from a CAB, finding M ≈ 10 13 GeV.In this paper we continue the study of axion-photon conversion in the Coma cluster using a far more detailed model of the Coma magnetic field. This model was constructed in [12] to fit rotation measure (RM) observations of seven polarised light sources, using the Coma cluster as a Faraday screen. The model describes the central Mpc 3 of Coma (see also [13] for a magnetic field model describing the region 1.5 Mpc to the southwest of the cluster centre). We review the observational evidence for cluster magnetic fields in section 4 and describe the model for the Coma magnetic field in detail in section 4.2. Using this stochastic model, we construct a numerical simulation of the magnetic field in the central region of the cluster, propagate axions through it and quantitatively study the resulting predictions for the soft excess morphology. This paper is organised as follo...

We continue the development of axion monodromy inflation, focusing in particular on the backreaction of complex structure moduli. In our setting, the shift symmetry comes from a partial large complex structure limit of the underlying type IIB orientifold or F-theory fourfold. The coefficient of the inflaton term in the superpotential has to be tuned small to avoid conflict with Kähler moduli stabilisation. To allow such a tuning, this coefficient necessarily depends on further complex structure moduli. At large values of the inflaton field, these moduli are then in danger of backreacting too strongly. To avoid this, further tunings are necessary. In weakly coupled type IIB theory at the orientifold point, implementing these tunings appears to be difficult if not impossible. However, fourfolds or models with mobile D7-branes provide enough structural freedom. We calculate the resulting inflaton potential and study the feasibility of the overall tuning given the limited freedom of the flux landscape. Our preliminary investigations suggest that, even imposing all tuning conditions, the remaining choice of flux vacua can still be large enough for such models to provide a promising path to large-field inflation in string theory.

No abstract