The scaling density of axion strings

Abstract

In the QCD axion dark matter scenario with post-inflationary Peccei-Quinn symmetry breaking, the number density of axions, and hence the dark matter density, depends on the length of string per unit volume at cosmic time $t$, by convention written $\zeta /t^2$. The expectation has been that the dimensionless parameter $\zeta$ tends to a constant ${\zeta }_0$, a feature of a string network known as scaling. It has recently been claimed that in larger numerical simulations $\zeta$ shows a logarithmic increase with time, while theoretical modelling suggests an inverse logarithmic correction. Either case would result in a large enhancement of the string density at the QCD transition, and a substantial revision to the axion mass required for the axion to constitute all of the dark matter. With a set of new simulations of global strings we compare the standard scaling (constant-$\zeta$) model to the logarithmic growth and inverse-logarithmic correction models. In the standard scaling model, by fitting to linear growth in the mean string separation $\xi =t/\sqrt{\zeta }$, we find ${\zeta }_0=1.19\pm 0.20$. We conclude that the apparent corrections to $\zeta$ are artefacts of the initial conditions, rather than a property of the scaling network. The residuals from the constant-$\zeta$ (linear $\xi$) fit also show no evidence for logarithmic growth, restoring confidence that numerical simulations can be simply extrapolated from the Peccei-Quinn symmetry-breaking scale to the QCD scale. Re-analysis of previous work on the axion number density suggests that recent estimates of the axion dark matter mass in the post-inflationary symmetry-breaking scenario we study should be increased by about 50%.

8 pages including supplemental material; 5 figures. v2 matches published version

References in corpus (19)

• Cosmic strings
• Axion dark matter from topological defects
• Quantitative String Evolution
• Axion Cosmology Revisited
• Extending the Velocity-dependent One-scale String Evolution Model
• Axions from Strings: the Attractive Solution
• Production of dark matter axions from collapse of string-wall systems
• Early seeds of axion miniclusters
• The dark-matter axion mass
• Update of axion CDM energy density
• Evolution of Axionic Strings and Spectrum of Axions Radiated from Them
• Improved estimation of radiated axions from cosmological axionic strings
• Axion dark matter: strings and their cores
• CMB power spectra from cosmic strings: predictions for the Planck satellite and beyond
• Long-term dynamics of cosmological axion strings
• How to simulate global cosmic strings with large string tension
• Cosmic Microwave Background constraints for global strings and global monopoles
• Quantitative evolution of global strings from the Lagrangian viewpoint
• Scaling properties of cosmological axion strings

Cited by in corpus (56)

• Cosmology with the Laser Interferometer Space Antenna
• Beyond the Standard Models with Cosmic Strings
• The art of simulating the early Universe -- Part I
• Observing Invisible Axions with Gravitational Waves
• The Science of the Einstein Telescope
• Gravitational Waves from Global Cosmic Strings and Cosmic Archaeology
• Approach to scaling in axion string networks
• New Perspectives on Axion Misalignment Mechanism
• Lepto-Axiogenesis
• Primordial Black Hole Archaeology with Gravitational Waves from Cosmic Strings
• Irreducible background of gravitational waves from a cosmic defect network: update and comparison of numerical techniques
• Spectrum of global string networks and the axion dark matter mass
• Hubble-induced phase transitions on the lattice with applications to Ricci reheating
• Simulations of axion-like particles in the post-inflationary scenario
• The DFSZ axion in the CMB
• CMB birefringence from ultra-light axion string networks
• Global cosmic string networks as a function of tension
• Friction on ALP domain walls and gravitational waves
• Radiation from Global Topological Strings using Adaptive Mesh Refinement: Methodology and Massless Modes
• Axion Miniclusters Made Easy
• Searching for axion-like particles through CMB birefringence from string-wall networks
• Recurrent Axinovae and their Cosmological Constraints
• High Quality QCD Axion at Gravitational Wave Observatories
• Comments on Axions, Domain Walls, and Cosmic Strings
• ALP Dark Matter Mini-Clusters from Kinetic Fragmentation
• QCD Axion Dark Matter from a Late Time Phase Transition
• Gravitational Wave Emission from a Cosmic String Loop, I: Global Case
• Polarimetric signatures of the photon ring of a black hole that is pierced by a cosmic axion string
• Axion strings are superconducting
• The non-linear dynamics of axion inflation: a detailed lattice study
• ALP dark matter with non-periodic potentials: parametric resonance, halo formation and gravitational signatures
• Cosmic string gravitational waves from global $U(1{)}_{B-L}$ symmetry breaking as a probe of the type I seesaw scale
• Radiation from Global Topological Strings using Adaptive Mesh Refinement: Massive Modes
• Superradiant Leptogenesis
• Effective Field Theory for Dark Matter Absorption on Single Phonons
• Absorption of Axion Dark Matter in a Magnetized Medium
• Abelian-Higgs Cosmic String Evolution with CUDA
• Symmetrically Tuned Large-Volume Conic Shell-Cavities for Axion Searches
• A-B transition in superfluid ${}^3$He and cosmological phase transitions
• Revisiting isocurvature bounds in models unifying the axion with the inflaton
• Present and future of CosmoLattice
• Probing axion dark matter with 21cm fluctuations from minihalos
• Future targets for light gauge bosons from cosmic strings
• Statistical Uncertainties of the $N_{\text{DW}}=1$ QCD Axion Mass Window from Topological Defects
• Parametric Resonances in Axionic Cosmic Strings
• QCD Axion Strings or Seeds?
• Ultimate light-shining-through-a-wall experiments to establish QCD axions as the dominant form of dark matter
• Reduced Axion Abundance from an Extended Symmetry
• Probing cosmic strings via gravitational-wave lensing
• Spectrum of radiation from global strings and the relic axion density
• Wormhole-Induced ALP Dark Matter
• From $U(1)\times U(1)$ Symmetry Breaking to Majoron Cosmology: Insights from NANOGrav 15-year Data
• Constraining Affleck-Dine Leptogenesis after Thermal Inflation
• Comment on "More Axions from Strings''
• Emission of Nambu-Goldstone bosons from the semilocal string network
• Internal Excitations of Global Vortices