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Glimmers from the Axiverse
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abstract
We study axion-photon couplings in compactifications of type IIB string theory. We find that these couplings are systematically suppressed compared to the inverse axion periodicity, as a result of two effects. First, couplings to the QED theta angle are suppressed for axion mass eigenstates that are light compared to the mass scale set by stringy instantons on the cycle supporting QED. Second, in compactifications with many axions the intersection matrix is sparse, making kinetic mixing weak. We study the resulting phenomenology in an ensemble of $200{,}000$ toy models constructed from the Kreuzer-Skarke database up to the maximum Hodge number $h^{1,1}=491$. We examine freeze-in production and decay of thermal axions, birefringence of the cosmic microwave background, X-ray spectrum oscillations, and constraints on the QCD axion from supernovae. We conclude that compactifications in this corner of the landscape involve many invisible axions, as well as a handful that may be detectable via photon couplings.
Forward citations
Cited by 25 Pith papers
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The Dark Dimension meets the Axiverse
Dark dimension dark matter can evade decay constraints if N≳50 axion KK towers share the tower energy, diluting Standard Model energy injection by roughly 1/N.
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Heterotic String Theory Suggests a QCD Axion Near 0.5 neV
Heterotic string theory implies the QCD axion mass is bounded below by 0.5 neV and typically falls in [0.5, 0.8] neV across most compactifications.
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Constraining axion quadratic couplings with the Hulse-Taylor binary system
Orbital timing of the Hulse-Taylor binary pulsar gives the strongest published limits on quadratic axion-muon couplings for axion masses below about 10^-12 eV, and complementary limits on axion-neutron and axion-elect...
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String Axiverse Enhancement of Superradiant Dark Matter Production
O(100–10^5) light string axions enhance PBH spin-up during Hawking evaporation, boosting superradiant dark-matter cloud efficiency and expanding the micro-boson-star parameter space while contributing negligibly to ΔN_eff.
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Testing F-theory GUTs with the Axiverse
In F-theory GUTs, non-universal ALPs induced by hypercharge flux satisfy g_aγ/m_a well below the QCD axion prediction when gauge couplings unify near the string scale.
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Searches for GeV-Scale ALPs at RHIC
Proposes searching for GeV-scale ALPs in ultra-peripheral collisions at RHIC via γγ → a → γγ, estimating sensitivity to m_a ~2-5 GeV and g_aγγ ≳4e-4 GeV^{-1} with existing PHENIX data.
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The structure of multi-axion solutions to the strong CP problem
Multi-axion solutions to the strong CP problem produce varied mass-coupling patterns set by PQ symmetry breaking structure and QCD-EM anomaly alignment, summarized by a general sum rule for N-axion systems.
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The structure of multi-axion solutions to the strong CP problem
Multi-axion theories solving the strong CP problem produce varied mass-coupling relations via a general sum rule that depends on the details of PQ symmetry breaking and anomaly alignments.
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Axiverse Lampposts
In a hierarchical multi-axion theory with random couplings, axion field ranges shrink with 1/sqrt(N), generic axion–SM couplings are suppressed, but the QCD axion's coupling is unsuppressed.
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The String Theory Photoverse
Massless string-theory hidden photons acquire dimension-six dipole couplings to SM fermions with suppression scale Λ = αM_s, converting dipole measurements into constraints on the string scale.
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Towards a Heterotic Axiverse
Generic heterotic axions are heavier than in type IIB; the Strong CP problem is typically unsolved, and a light fuzzy dark matter axion requires a no-gaugino-condensation anisotropic fibred Calabi-Yau.
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Axion lines from nuclear de-excitations in galactic stellar populations
No 14.4 keV axion line from 57Fe de-excitations is seen by NuSTAR toward M87, M82, M31, or the Galactic Center, yielding |g_ann x g_aγγ| < 1.1e-22 GeV^-1 for m_a < 1e-10 eV.
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Universality in the Axiverse
Normalized divisor volumes in toric Calabi-Yau threefolds appear universal, and a GOE level-spacing model with a fitted mean reproduces axion statistics across the Kreuzer-Skarke axiverse.
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No Evidence for Superradiant Axions in LIGO-Virgo-KAGRA GWTC-5 Binary Black Hole Spins
Hierarchical Bayesian analysis of GWTC-5 binary black hole spins finds no evidence for superradiant axions and excludes masses 1.7e-14 to 3.3e-12 eV at 95% CL.
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Quantum Gravity Cutoff from Axions: A Type IIB Landscape Study
The bound Λ_QG ≲ 2π √S f holds for C2 and C4 axions in Type IIB Calabi-Yau compactifications even near Kähler moduli space boundaries where co-scaling fails.
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Counting axions with IAXO
Projections for IAXO in two-axion parameter space plus spectral analysis of flavor oscillations show where the experiment can discriminate multi-axion signals from single-axion ones, extending to N-axion cases.
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String Axiverse Enhancement of Superradiant Dark Matter Production
O(100-10^5) string axions enhance PBH superradiance efficiency via increased spin, expanding viable mass-spin regions for micro-boson star dark matter while too many axions cause overly rapid evaporation.
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Tachyonic Encore: A universal shift of inflationary observables
A light axion spectator induces post-inflation tachyonic phases that produce a nearly scale-invariant boost to the curvature power spectrum and alter key inflationary observables in a largely potential-independent manner.
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The Atacama Cosmology Telescope: Probing new signatures of ultralight axions with gravitational lensing
New upper limits on ultralight axion dark matter fraction (<1.5% at 10^{-26} eV, <9% at 10^{-25} eV at 95% CL) from combined CMB lensing data, plus marginal 2.1σ preference at 10^{-24.5} eV driven by few points.
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Magnetic Turbulence Boosts Supernova Signals of Axion-Photon Conversion
Turbulent magnetic fields enhance axion-photon conversion signals from supernovae, improving limits on axion-proton and axion-photon couplings by up to two orders of magnitude.
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Constraining F-theory Model Building with QCD Axions
F-theory models with the Standard Model spectrum are constrained by QCD axion physics, yielding typical detectable axion masses around 10^{-9} eV and decay constants around 10^{15} GeV in allowed regions.
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Constraining F-theory Model Building with QCD Axions
QCD axions constrain F-theory base threefolds to have rigid or flux-rigidified divisors, yielding typical axion masses around 10^{-9} eV and decay constants near 10^{15} GeV in allowed regions.
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Direct detection of solar chameleons with electron recoil data from XENONnT
XENONnT electron-recoil data bound solar chameleons to log10 β_eff < −6.9, independent of the potential index n for inverse power-law chameleons at the dark-energy scale.
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Nucleosynthesis and CMB bounds on photophilic ALPs: a fresh look
Updated model-independent BBN and CMB bounds on photophilic ALPs that incorporate rare decays to light hadrons, show extended constraints for multiple reheating temperatures, and flag parameter space that may alleviat...
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Axions at the meV Crossroads: Theory, Cosmology, Astrophysics, and Experiments
The meV axion window is presented as a coherent, cross-validated search program in which string theory, stellar cooling, dark matter, and new detector concepts converge on the same mass range.
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