QCD θ-vacuum energy and axion properties

Lù, Zhongwen; Du, Meng-Lin; Guo, Feng-Kun; Meißner, Ulf‐G.; Vonk, Thomas

doi:10.1007/jhep05(2020)001

Cited by 21 publications

(20 citation statements)

References 83 publications

(134 reference statements)

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“…The θ dependence is then encoded in correlation functions of pseudo-Goldstone bosons in the chiral expansion. This way, contributions from all topological charge configurations are taken into account and the free energy also deviates substantially from the simple cos θ behavior [68][69][70][71]. In this case, it is in principle possible to extract the contributions from different topological charges by means of a Fourier transformation of the free energy with respect to θ [68].…”

Section: Discussionmentioning

confidence: 99%

Higher topological charge and the QCD vacuum

Rennecke

2020

Phys. Rev. Research

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It is shown that gauge field configurations with higher topological charge modify the structure of the QCD vacuum, which is reflected in its dependence on the CP-violating topological phase θ. To explore this, topological susceptibilities and the production of axion dark matter are studied here. The formers characterize the topological charge distribution and are therefore sensitive probes of the topological structure of QCD. The latter depends on the effective potential of axions, which is determined by the θ dependence of QCD. The production of cold dark matter through the vacuum realignment mechanism of axions can, therefore, be affected by higher topological charge effects. This is discussed qualitatively in the deconfined phase at high temperatures, where a description based on a dilute gas of instantons with arbitrary topological charge is valid. As a result, topological susceptibilities exhibit a characteristic temperature dependence due to anharmonic modifications of the θ dependence. Furthermore, multi-instanton effects give rise to a topological mechanism to increase the amount of axion dark matter.

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Section: Discussionmentioning

confidence: 99%

Higher topological charge and the QCD vacuum

Rennecke

2020

Phys. Rev. Research

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“…9 In order for the axion vacuum expectation value to be relaxed to zero, the PQ global symmetry has to be preserved from explicit breaking to a great degree of accuracy, such that m a,0 ≈ 0 to a precision compatible with the upper bound on θ arising from the non-observation of the neutron electric dipole moment. [452][453][454]) or lattice QCD [455], resulting in the prediction 10…”

Section: Phenomenology Of Axions/alps As Dm Candidates or Dm Mediatorsmentioning

confidence: 99%

Feebly-interacting particles: FIPs 2020 workshop report

et al. 2021

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With the establishment and maturation of the experimental programs searching for new physics with sizeable couplings at the LHC, there is an increasing interest in the broader particle and astrophysics community for exploring the physics of light and feebly-interacting particles as a paradigm complementary to a New Physics sector at the TeV scale and beyond. FIPs 2020 has been the first workshop fully dedicated to the physics of feebly-interacting particles and was held virtually from 31 August to 4 September 2020. The workshop has gathered together experts from collider, beam dump, fixed target experiments, as well as from astrophysics, axions/ALPs searches, current/future neutrino experiments, and dark matter direct detection communities to discuss progress in experimental searches and underlying theory models for FIPs physics, and to enhance the cross-fertilisation across different fields. FIPs 2020 has been complemented by the topical workshop “Physics Beyond Colliders meets theory”, held at CERN from 7 June to 9 June 2020. This document presents the summary of the talks presented at the workshops and the outcome of the subsequent discussions held immediately after. It aims to provide a clear picture of this blooming field and proposes a few recommendations for the next round of experimental results.

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“…In vacuum. These coupling have been precisely calculated including RGE effects [25] and more recently at next-to-next-to-leading order in ChPT [68,69]. We review here how the couplings to protons and neutrons are derived in ChPT, following closely the discussion in [25].…”

Section: Axion Couplingsmentioning

confidence: 99%

The QCD axion at finite density

Balkin

Serra

Springmann

et al. 2020

J. High Energ. Phys.

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We show how the properties of the QCD axion change in systems at finite baryonic density, such as neutron stars. At nuclear saturation densities, where corrections can be reliably computed, we find a mild reduction of the axion mass and up to an order of magnitude enhancement in the model-independent axion coupling to neutrons. At moderately higher densities, if realized, meson (kaon) condensation can trigger axion condensation. We also study the axion potential at asymptotically large densities, where the color-superconducting phase of QCD potentially leads to axion condensation, and the mass of the axion is generically several orders of magnitude smaller than in vacuum due to the suppressed instantons. Several phenomenological consequences of the axion being sourced by neutron stars are discussed, such as its contribution to their total mass, the presence of an axionic brane, or axion-photon conversion in the magnetosphere.

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QCD θ-vacuum energy and axion properties

Cited by 21 publications

References 83 publications

Higher topological charge and the QCD vacuum

Higher topological charge and the QCD vacuum

Feebly-interacting particles: FIPs 2020 workshop report

The QCD axion at finite density

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