How to simulate global cosmic strings with large string tension

Klaer, Vincent B.; Moore, Guy D.

doi:10.1088/1475-7516/2017/10/043

Cited by 71 publications

(124 citation statements)

References 68 publications

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“…Additionally, the constant physical core radius corresponds to a decreasing comoving one. Modern simulations therefore work with a variety of methods to maintain numerically resolved strings by making the mass of the radial mode explicitly time-dependent [195,196] or auxiliary fields to achieve higher effective string tensions [197]. Although it is understood that insufficient spatial resolution can lead to the unphysical decay of domain walls [24], current results indicate that the final axion yield depends only weakly on the numerical string tension [197].…”

Section: Early Non-gravitational Structure Formationmentioning

confidence: 99%

Small-scale structure of fuzzy and axion-like dark matter

Niemeyer

2020

Progress in Particle and Nuclear Physics

164

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Axion-like particle (ALP) dark matter shows distinctive behavior on scales where wavelike effects dominate over self-gravity. Ultralight axions are candidates for fuzzy dark matter (FDM) whose de Broglie wavelength in virialized halos reaches scales of kiloparsecs. Important features of FDM scenarios are the formation of solitonic halo cores, suppressed small-scale perturbations, and enhanced gravitational relaxation. More massive ALPs, including the QCD axion, behave like CDM on galactic scales but may be clumped into axion miniclusters if they were produced after inflation. Just as FDM halos, axion miniclusters may host the formation of coherent bound objects (axion stars) by Bose-Einstein condensation. This article presents a selection of topics in this field that are currently under active investigation.

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Section: Early Non-gravitational Structure Formationmentioning

confidence: 99%

Small-scale structure of fuzzy and axion-like dark matter

Niemeyer

2020

Progress in Particle and Nuclear Physics

164

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“…An argument for expecting a scaling violation is based on the logarithmic growth in the effective string tension of a global string with their mean separation. If there is no corresponding change in the energy loss rate per unit length, the string length density parameter should grow [28][29][30]. Indeed, frustrated strings [31], which have the same long-range axion field as global strings but higher tension, have greater length density [28][29][30].…”

Section: Introductionmentioning

confidence: 99%

Scaling Density of Axion Strings

et al. 2020

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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 ζ/t 2 . The expectation has been that the dimensionless parameter ζ tends to a constant ζ0, a feature of a string network known as scaling. It has recently been claimed that in larger numerical simulations ζ 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-ζ) 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 ξ = t/ √ ζ, we find ζ0 = 1.19 ± 0.20. The linear fit to ξ in standard scaling model also allows a time offset, t0, which takes into account the initial string evolution. We show that the convergence of ζ to its scaling value depends on t0, that the coefficients of the logarithm and inverse-logarithm are consistent with zero when t0/t f → 0, where t f is the final time of the fit, and that the constant terms in the models are consistent with the standard scaling measurement. We conclude that the apparent growth in ζ is an artefact of the time offset in the initial conditions, rather than a property of the scaling network. The residuals from the constant-ζ (linear ξ) 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%. Introduction:The Peccei-Quinn (PQ) mechanism, which solves the strong CP problem of QCD by extending the Standard Model with an extra U(1) global symmetry [1], brings with it a long-lived pseudoscalar particle, the axion [2]. A universe where light axions [3,4] constitute the dark matter [5] is one of the most promising scenarios in the current cosmological paradigm.If the PQ symmetry is spontaneously broken after primordial inflation, axion strings are formed [6], a variety of global cosmic string [7,8]. They survive until the QCD confinement transition at around 150 MeV, when they become connected by domain walls made of the CP-odd gluon condensate [9,10], and are annihilated. Most of the energy is left behind in the form of axion radiation, produced through the lifetime of the string network and during the annihilation phase. The axion radiation can also be viewed as light massive particles, whose number density depends on the length of string per unit ...

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“…In Fig. 2, we also show the expected reach of the haloscope searches [35,[159][160][161] by ADMX [162][163][164][165] and KLASH [166], which are also going to explore values of the axion mass that are lighter than what has been recently inferred by numerical computations of the dynamics of the PQ field [16][17][18][19]36] in a different cosmological scenario. On a theoretical viewpoint, the results obtained do not depend on the coupling of the QCD axion with the photons [167][168][169][170], which is nonetheless present when considering the experimental setup [171][172][173][174][175][176].…”

Section: Connection To Observablesmentioning

confidence: 85%

“…[8]. The level of precision reached in the assessment of the mass of the QCD axion and its dependence on the temperature of the QCD plasma from basic principles is quickly progressing, advancing in both extracting the QCD susceptibility from lattice computations [9][10][11][12] as well as in simulations of the string-wall network [13][14][15][16][17][18][19].…”

Section: Introductionmentioning

confidence: 99%

“…Light QCD axions that spectate inflation have recently received attention both from the theory perspective [23-27, 29, 30, 34] and from the perspective of detection in proposed and ongoing experiments [35]. In such a scenario, topological defects are washed out by inflation, and considerable additional effort to assess inhomogeneities like axion strings [16,36,37] or axion miniclusters [38][39][40][41][42] is not required. However, the challenge in this scenario relies on building a consistent theory of inflation that leads to a low enough scale of inflation, so that the axion can constitute all dark matter and simultaneously avoid the current bounds from the non-detection of dark matter isocurvature fluctuations.…”

Section: Introductionmentioning

confidence: 99%

See 1 more Smart Citation

Axion dark matter from Higgs inflation with an intermediate H_*

Tenkanen

Visinelli

2019

J. Cosmol. Astropart. Phys.

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In order to accommodate the QCD axion as the dark matter (DM) in a model in which the Peccei-Quinn (PQ) symmetry is broken before the end of inflation, a relatively low scale of inflation has to be invoked in order to avoid bounds from DM isocurvature fluctuations, H * O(10 9 ) GeV. We construct a simple model in which the Standard Model Higgs field is non-minimally coupled to Palatini gravity and acts as the inflaton, leading to a scale of inflation H * ∼ 10 8 GeV. When the energy scale at which the PQ symmetry breaks is much larger than the scale of inflation, we find that in this scenario the required axion mass for which the axion constitutes all DM is m 0 0.05 µeV for a quartic Higgs self-coupling λ φ = 0.1, which correspond to the PQ breaking scale v σ 10 14 GeV and tensor-to-scalar ratio r ∼ 10 −12 . Future experiments sensitive to the relevant QCD axion mass scale can therefore shed light on the physics of the Universe before the end of inflation.

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How to simulate global cosmic strings with large string tension

Cited by 71 publications

References 68 publications

Small-scale structure of fuzzy and axion-like dark matter

Small-scale structure of fuzzy and axion-like dark matter

Scaling Density of Axion Strings

Axion dark matter from Higgs inflation with an intermediate H_*

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How to simulate global cosmic strings with large string tension

Cited by 71 publications

References 68 publications

Small-scale structure of fuzzy and axion-like dark matter

Small-scale structure of fuzzy and axion-like dark matter

Scaling Density of Axion Strings

Axion dark matter from Higgs inflation with an intermediate H*

Contact Info

Product

Resources

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Axion dark matter from Higgs inflation with an intermediate H_*