The stochastic axiverse

Abstract In addition to spectacular signatures such as black hole superradiance and the rotation of CMB polarization, the plenitude of axions appearing in the string axiverse may have potentially dangerous implications. An example is the cosmological overproduction of relic axions and moduli by the misalignment mechanism, more pronounced in regions where the signals mentioned above may be observable, that is for large axion decay constant. In this work, we study the minimal requirements to soften this problem and show that the fundamental requirement is a long period of low-scale inflation. However, in this case, if the inflationary Hubble scale is lower than around O(100) eV, no relic DM axion is produced in the early Universe. Cosmological production of some axions may be activated, via the misalignment mechanism, if their potential minimum changes between inflation and today. As a particular example, we study in detail how the maximal-misalignment mechanism dilutes the effect of dangerous axions and allows the production of axion DM in a controlled way. In this case, the potential of the axion that realises the mechanism shifts by a factor ∆θ = π between the inflationary epoch and today, and the axion starts to oscillate from the top of its potential. We also show that axions with masses ma ∼ O(1 − 100) H0 realising the maximal-misalignment mechanism generically behave as dark energy with a decay constant that can take values well below the Planck scale, avoiding problems associated to super-Planckian scales. Finally, we briefly study the basic phenomenological implications of the mechanism and comment on the compatibility of this type of maximally-misaligned quintessence with the swampland criteria.

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Cosmologically allowed regions for the axion decay constant F

Physics Letters B ◽

10.1016/j.physletb.2018.05.014 ◽

2018 ◽

Vol 782 ◽

pp. 181-184 ◽

Cited By ~ 7

Author(s):

Masahiro Kawasaki ◽

Eisuke Sonomoto ◽

Tsutomu T. Yanagida

Keyword(s):

Decay Constant ◽

Axion Decay Constant ◽

Axion Decay

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Numerical analysis of Coleman–de Luccia tunneling

International Journal of Modern Physics A ◽

10.1142/s0217751x16501311 ◽

2016 ◽

Vol 31 (24) ◽

pp. 1650131 ◽

Cited By ~ 2

Author(s):

Yuhei Goto ◽

Kazumi Okuyama

Keyword(s):

Decay Constant ◽

Periodic Potential ◽

Thin Wall ◽

False Vacuum ◽

Vacuum Decay ◽

Text Type ◽

Axion Decay Constant ◽

Axion Decay ◽

Range Of Values ◽

Type Potential

In this paper, we study the false vacuum decay of a single scalar field [Formula: see text] coupled to gravity described by the Coleman–de Luccia (CdL) instanton. We show that it is possible to numerically calculate the bounce factor, which is related to the CdL tunneling rate, without using the thin-wall approximation. In this paper, we consider [Formula: see text]- and [Formula: see text]-type potentials as examples, which have cosmological and phenomenological applications. Especially, in the [Formula: see text]-type potential, we show that the range of values in which axion decay constant can take is restricted by the form of the periodic potential if the CdL tunneling occurs.

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ON THE SUPERSTRING AXION MINI-STAR

Modern Physics Letters A ◽

10.1142/s021773239800108x ◽

1998 ◽

Vol 13 (13) ◽

pp. 1007-1017 ◽

Cited By ~ 8

Author(s):

M. D. POLLOCK

Keyword(s):

Gravitational Collapse ◽

Mass Formula ◽

Decay Constant ◽

Gravitational Constant ◽

Large Magellanic Cloud ◽

Magellanic Cloud ◽

Planck Mass ◽

Upper Limit ◽

Axion Decay Constant ◽

Axion Decay

The theory of the pressure-free-boson mini-star of mass M, whose radius r=2GM/v2 is equated via the indeterminacy principle to ℏ/mv, where [Formula: see text] is the Newton gravitational constant, M P being the Planck mass and m the mass of the boson, travelling at velocity v, is applied to the superstring axion. For a bounded object, the upper limit to the axion potential [Formula: see text] constrains the axions to move at non-relativistic velocities [Formula: see text] where [Formula: see text] GeV is the axion decay constant, predicting the existence of an axion mini-star of mass [Formula: see text]. Such objects can in principle form by gravitational collapse below the temperature T≈100 eV, and are tentatively identified with the microlensing objects recently detected in our Galaxy and in the direction of the Large Magellanic Cloud.

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Challenges for an axion explanation of the muon g − 2 measurement

Journal of High Energy Physics ◽

10.1007/jhep09(2021)101 ◽

2021 ◽

Vol 2021 (9) ◽

Author(s):

Manuel A. Buen-Abad ◽

JiJi Fan ◽

Matthew Reece ◽

Chen Sun

Keyword(s):

Decay Constant ◽

Standard Model Prediction ◽

New Physics ◽

Effective Theory ◽

General Sense ◽

Weak Scale ◽

Initial Application ◽

The Standard Model ◽

Axion Decay Constant ◽

Axion Decay

Abstract The discrepancy between the muon g − 2 measurement and the Standard Model prediction points to new physics around or below the weak scale. It is tantalizing to consider the loop effects of a heavy axion (in the general sense, also known as an axion-like particle) coupling to leptons and photons as an explanation for this discrepancy. We provide an updated analysis of the necessary couplings, including two-loop contributions, and find that the new physics operators point to an axion decay constant on the order of 10s of GeV. This poses major problems for such an explanation, as the axion couplings to leptons and photons must be generated at low scales. We outline some possibilities for how such couplings can arise, and find that these scenarios predict new charged matter at or below the weak scale and new scalars can mix with the Higgs boson, raising numerous phenomenological challenges. These scenarios also all predict additional contributions to the muon g−2 itself, calling the initial application of the axion effective theory into question. We conclude that there is little reason to favor an axion explanation of the muon g – 2 measurement relative to other models postulating new weak-scale matter.

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Axions from heterotic stringThis paper was presented at the Theory CANADA 4 conference, held at Centre de recherches mathématiques, Montréal, Québec, Canada on 4–7 June 2008.

Canadian Journal of Physics ◽

10.1139/p08-126 ◽

2009 ◽

Vol 87 (3) ◽

pp. 267-270

Author(s):

Keshav Dasgupta ◽

Hassan Firouzjahi ◽

Rhiannon Gwyn

Keyword(s):

String Theory ◽

Decay Constant ◽

Mass Scale ◽

Heterotic String ◽

Explicit Model ◽

Heterotic String Theory ◽

Natural Mechanism ◽

Axion Decay Constant ◽

Axion Decay

We study the axion in a warped heterotic background. It is shown that the axion decay constant, fa, is sensitive to the warped mass scale of the throat. As an explicit model, we construct a novel AdS-like geometry in heterotic string theory. We demonstrate that in this background fa is given by the mass scale of the longest throat in the compactification. The question of obtaining fa within the required bound 109–1012 GeV is reduced to the construction of a throat inside the heterotic string theory compactification with warped mass scale in the above range. This provides a natural mechanism for realising the axion in heterotic string theory.

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Natural inflation with natural trans-planckian axion decay constant from anomalous U(1) X

Journal of High Energy Physics ◽

10.1007/jhep07(2014)052 ◽

2014 ◽

Vol 2014 (7) ◽

Cited By ~ 13

Author(s):

Tianjun Li ◽

Zhijin Li ◽

Dimitri V. Nanopoulos

Keyword(s):

Decay Constant ◽

Axion Decay Constant ◽

Axion Decay

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Precision axion physics with running axion couplings

Journal of High Energy Physics ◽

10.1007/jhep08(2021)058 ◽

2021 ◽

Vol 2021 (8) ◽

Author(s):

Kiwoon Choi ◽

Sang Hui Im ◽

Hee Jung Kim ◽

Hyeonseok Seong

Keyword(s):

Top Quark ◽

Decay Constant ◽

Higgs Field ◽

Energy Scale ◽

Low Energy ◽

Loop Contribution ◽

The Standard Model ◽

Axion Decay Constant ◽

Axion Decay ◽

Sizable Difference

Abstract We study the renormalization group running of axion couplings while taking into account that the Standard Model can be extended to its supersymmetric extension at a certain energy scale below the axion decay constant. We then apply our results to three different classes of axion models, i.e. KSVZ-like, DFSZ-like, and string-theoretic axions, and examine if string-theoretic axions can be distinguished from others by having a different pattern of low energy couplings to the photon, nucleons and electron. We find that the low energy couplings of string-theoretic axions have a similar pattern as those of KSVZ-like axions but yet reveal a sizable difference which might be testable in future axion search experiments. We also note that the coupling of KSVZ-like QCD axions to the electron is dominated by a three-loop contribution involving the exotic heavy quark, gluons, top quark and Higgs field.

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R-parity violation axiogenesis

Journal of High Energy Physics ◽

10.1007/jhep11(2021)210 ◽

2021 ◽

Vol 2021 (11) ◽

Author(s):

Raymond T. Co ◽

Keisuke Harigaya ◽

Zachary Johnson ◽

Aaron Pierce

Keyword(s):

Parity Violation ◽

Decay Constant ◽

Big Bang ◽

Proton Decay ◽

Big Bang Nucleosynthesis ◽

Chiral Asymmetry ◽

Axion Field ◽

Axion Decay Constant ◽

Axion Decay ◽

The Universe

Abstract We show that the rotation of the QCD axion field, aided by B−L violation from supersymmetric R-parity violating couplings, can yield the observed baryon abundance. Strong sphaleron processes transfer the angular momentum of the axion field into a quark chiral asymmetry, which R-parity violating couplings convert to the baryon asymmetry of the Universe. We focus on the case of dimensionless R-parity violating couplings with textures motivated by grand unified theories and comment on more general scenarios. The axion decay constant and mass spectrum of supersymmetric particles are constrained by Big Bang nucleosynthesis, proton decay from the R-parity violation, and successful thermalization of the Peccei-Quinn symmetry breaking field. Axion dark matter may be produced by the axion rotation via the kinetic misalignment mechanism for axion decay constants below 1010 GeV, or by the conventional misalignment mechanism for 1011-12 GeV. The viable parameter region can be probed by proton decay and axion searches. This scenario may also have connections with collider experiments, including searches for long-lived particles, and observations of gravitational waves.

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Digging into Axion Physics with (Baby)IAXO

Universe ◽

10.3390/universe8010037 ◽

2022 ◽

Vol 8 (1) ◽

pp. 37

Author(s):

Theopisti Dafni ◽

Javier Galán

Keyword(s):

Decay Constant ◽

Fourth Generation ◽

Special Issue ◽

X Ray ◽

Axion Mass ◽

Wide Range ◽

Discovery Potential ◽

Axion Decay Constant ◽

Axion Decay ◽

Main Candidate

Dark matter searches have been ongoing for three decades; the lack of a positive discovery of the main candidate, the WIMP, after dedicated efforts, has put axions and axion-like particles in the spotlight. The three main techniques employed to search for them complement each other well in covering a wide range in the parameter space defined by the axion decay constant and the axion mass. The International AXion Observatory (IAXO) is an international collaboration planning to build the fourth generation axion helioscope, with an unparalleled expected sensitivity and discovery potential. The distinguishing characteristic of IAXO is that it will feature a magnet that is designed to maximise the relevant parameters in sensitivity and which will be equipped with X-ray focusing devices and detectors that have been developed for axion physics. In this paper, we review aspects that motivate IAXO and its prototype, BabyIAXO, in the axion, and ALPs landscape. As part of this Special Issue, some emphasis is given on Spanish participation in the project, of which CAPA (Centro de Astropartículas y Física de Altas Energías of the Universidad de Zaragoza) is a strong promoter.

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