Lattice simulations show axion misalignment production splits into two regimes during first-order phase transitions, unified by a semi-analytical relic density formula that also alters isocurvature and small-scale power spectrum.
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The type IIB string axiverse and its low-energy phenomenology
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abstract
We study closed string axions in type IIB orientifold compactifications. We show that for natural values of the background fluxes the moduli stabilisation mechanism of the LARGE Volume Scenario (LVS) gives rise to an axiverse characterised by the presence of a QCD axion plus many light axion-like particles whose masses are logarithmically hierarchical. We study the phenomenological features of the LVS axiverse, deriving the masses of the axions and their couplings to matter and gauge fields. We also determine when closed string axions can solve the strong CP problem, and analyse the first explicit examples of semi-realistic models with stable moduli and a QCD axion candidate which is not eaten by an anomalous Abelian gauge boson. We discuss the impact of the choice of inflationary scenario on the LVS axiverse, and summarise the astrophysical, cosmological and experimental constraints upon it. Moreover, we show how models can be constructed with additional light axion-like particles that could explain some intriguing astrophysical anomalies, and could be searched for in the next generation of axion helioscopes and light-shining-through-a-wall experiments.
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ALPS II reports no detection of axion-like particles and establishes improved 95% CL upper limits on di-photon couplings of 1.5e-9 GeV^-1 for masses below 0.1 meV, plus limits for scalar, vector, and tensor bosons.
Axions produced in supernovae generate a diffuse gamma-ray signal through conversion in magnetic fields, yielding competitive constraints on the axion-photon coupling from COMPTEL, EGRET, and Fermi-LAT data plus forecasts for future MeV telescopes.
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.
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.
Lattice simulations of Abelian-Higgs cosmic strings with axion-gauge coupling show multimodal axion production that can account for GeV-scale dark matter while predicting observable dark radiation.
Pre-inflationary QCD axions form dense stars with densities up to 10^4 eV^4 that contain up to 50% of dark matter after moduli domination.
Electroweak-symmetric domain walls produce the observed baryon asymmetry when CP-odd sources and the hierarchy of wall, source, and diffusion lengths suppress face-to-face cancellation.
Two-field axion-like early dark energy reduces Hubble tension to 1.5 sigma residual and improves high-ell CMB fits over single-field models.
An analytic bound on axion parameters in thawing quintessence is derived independently of initial conditions and used with cosmological observations plus quantum gravity constraints to exclude large regions of axion dark energy parameter space.
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.
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.
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.
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.
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.
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.
Numerical and analytic modeling of boson star-black hole systems in the nonrelativistic limit, with Fisher analysis indicating LISA sensitivity to ultralight dark matter mass and self-coupling via gravitational wave dephasing.
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 alleviate tensions in N_eff and deuterium abundance.
Model-independent forecasts for the stochastic gravitational-wave background from ultralight dark matter decaying into gravitons and the sensitivity of current and future detectors to this signal.
Double level crossings are common in multi-axion mass mixing of Z_N axions and ALPs, occurring multiple times for large N in the light axion case but prevented by excessively large or small N in light and heavy scenarios respectively.
This work sets new upper limits on decay lifetimes and couplings for axion-like particles, dark photons, scalars, and B-L or L_i-L_j vector bosons using 511 keV line, X-ray continuum, and cosmic-ray flux observations.
The thesis presents a new 3-to-2 freezeout mechanism, bound-state effects on searches, a new axion interferometric search, reionization assessments, 21-cm constraints, and the DarkHistory code for ionization and thermal histories.
A proposed Chinese charm factory could detect heavy neutral leptons from axionlike-particle decays with a displaced-vertex search, reaching electron-neutrino mixing one to two orders of magnitude below current bounds.
Stochastic axion mixing is a broad mechanism for axion interactions in multi-axion systems that occurs naturally under distinct mass conditions and does not depend on decay constant hierarchies.
citing papers explorer
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Axion Misalignment Across First-Order Phase Transitions
Lattice simulations show axion misalignment production splits into two regimes during first-order phase transitions, unified by a semi-analytical relic density formula that also alters isocurvature and small-scale power spectrum.
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Any Light Particle Searches with ALPS II: first science results
ALPS II reports no detection of axion-like particles and establishes improved 95% CL upper limits on di-photon couplings of 1.5e-9 GeV^-1 for masses below 0.1 meV, plus limits for scalar, vector, and tensor bosons.
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Lights, Camera, Axion: Tracing Axions from Supernovae in the Diffuse $\gamma$-ray Sky
Axions produced in supernovae generate a diffuse gamma-ray signal through conversion in magnetic fields, yielding competitive constraints on the axion-photon coupling from COMPTEL, EGRET, and Fermi-LAT data plus forecasts for future MeV telescopes.
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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.
-
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.
-
Multimodal axion emissions from Abelian-Higgs cosmic strings
Lattice simulations of Abelian-Higgs cosmic strings with axion-gauge coupling show multimodal axion production that can account for GeV-scale dark matter while predicting observable dark radiation.
-
Pre-inflationary QCD axion stars after moduli domination
Pre-inflationary QCD axions form dense stars with densities up to 10^4 eV^4 that contain up to 50% of dark matter after moduli domination.
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DMRadio-Core: A new approach for GUT-scale axion searches
Electroweak-symmetric domain walls produce the observed baryon asymmetry when CP-odd sources and the hierarchy of wall, source, and diffusion lengths suppress face-to-face cancellation.
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Double the axions, half the tension: multi-field early dark energy eases the Hubble tension
Two-field axion-like early dark energy reduces Hubble tension to 1.5 sigma residual and improves high-ell CMB fits over single-field models.
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Bounding axion dark energy
An analytic bound on axion parameters in thawing quintessence is derived independently of initial conditions and used with cosmological observations plus quantum gravity constraints to exclude large regions of axion dark energy parameter space.
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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.
-
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.
-
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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Boson Stars Hosting Black Holes
Numerical and analytic modeling of boson star-black hole systems in the nonrelativistic limit, with Fisher analysis indicating LISA sensitivity to ultralight dark matter mass and self-coupling via gravitational wave dephasing.
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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 alleviate tensions in N_eff and deuterium abundance.
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Sensitivity forecasts for gravitational-wave detectors to dark matter decaying into gravitons
Model-independent forecasts for the stochastic gravitational-wave background from ultralight dark matter decaying into gravitons and the sensitivity of current and future detectors to this signal.
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Completing Axion Double Level Crossings
Double level crossings are common in multi-axion mass mixing of Z_N axions and ALPs, occurring multiple times for large N in the light axion case but prevented by excessively large or small N in light and heavy scenarios respectively.
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INTEGRAL, eROSITA and Voyager Constraints on Light Bosonic Dark Matter: ALPs, Dark Photons, Scalars, $B-L$ and $L_{i}-L_{j}$ Vectors
This work sets new upper limits on decay lifetimes and couplings for axion-like particles, dark photons, scalars, and B-L or L_i-L_j vector bosons using 511 keV line, X-ray continuum, and cosmic-ray flux observations.
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Dark Matter Energy Deposition and Production from the Table-Top to the Cosmos
The thesis presents a new 3-to-2 freezeout mechanism, bound-state effects on searches, a new axion interferometric search, reionization assessments, 21-cm constraints, and the DarkHistory code for ionization and thermal histories.
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Long-lived sterile neutrinos from axionlike particles at the Super Tau-Charm Facility
A proposed Chinese charm factory could detect heavy neutral leptons from axionlike-particle decays with a displaced-vertex search, reaching electron-neutrino mixing one to two orders of magnitude below current bounds.
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Stochastic Axion Mixing: A General Mechanism Beyond Decay Constant Constraints
Stochastic axion mixing is a broad mechanism for axion interactions in multi-axion systems that occurs naturally under distinct mass conditions and does not depend on decay constant hierarchies.
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Probing the dark axion portal via $J/\psi$ decays at BESIII and STCF
Monte Carlo studies show BESIII data already reaches previously unexplored regions of the dark axion portal via J/ψ → a γ' decays, with STCF projected to improve sensitivity by about an order of magnitude.
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What to do with a Ricci-flat Calabi--Yau metric?
Numerical Ricci-flat Calabi–Yau metrics turn string compactifications from topological existence statements into computable geometries, unlocking normalized couplings, spectra, and metric-level tests of mirror symmetry.
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Breaking Free from the Swampland of Impossible Universes through the DESI Portal
A review of string-inspired dynamical dark energy models claiming compatibility with DESI's hints of evolving dark energy under swampland constraints.
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Axions as Dark Matter, Dark Energy, and Dark Radiation
A mini-review of axion phenomenology showing how light bosons can account for dark matter, drive cosmic acceleration, or contribute to relativistic backgrounds in the early and late Universe.
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Lectures on Naturalness, String Landscape and Multiverse
Lecture notes providing a technical introduction to naturalness problems and the string theory landscape for graduate students.