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Journal articles on the topic 'QCD axion'

Author: Grafiati

Published: 14 March 2023

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1

Bonnefoy, Quentin, and Emilian Dudas. "Axions and anomalous U(1)’s." International Journal of Modern Physics A 33, no. 34 (December 10, 2018): 1845001. http://dx.doi.org/10.1142/s0217751x1845001x.

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Inspired by recent studies of high-scale decay constant or flavorful QCD axions, we review and clarify their existence in effective string models with anomalous U(1) gauge groups. We find that such models, when coupled to charged scalars getting vacuum expectation values, always have one light axion, whose mass can only come from nonperturbative effects. If the main nonperturbative effect is from QCD, then it becomes a Peccei–Quinn axion candidate for solving the strong CP problem. We then study simple models with universal Green–Schwarz mechanism and only one charged scalar field: in the minimal gaugino condensation case the axion mass is tied to the supersymmetry breaking scale and cannot be light enough, but slightly refined models maintain a massless axion all the way down to the QCD scale. Both kinds of models can be extended to yield intermediate scale axion decay constants. Finally, we gauge flavorful axion models under an anomalous U(1) and discuss the axion couplings which arise.

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2

Mazde, Kratika, and Luca Visinelli. "The interplay between the dark matter axion and primordial black holes." Journal of Cosmology and Astroparticle Physics 2023, no. 01 (January 1, 2023): 021. http://dx.doi.org/10.1088/1475-7516/2023/01/021.

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Abstract If primordial black holes (PBHs) had come to dominate the energy density of the early Universe when oscillations in the axion field began, we show that the relic abundance and expected mass range of the QCD axion would be greatly modified. Since the QCD axion is a potential candidate for dark matter (DM), we refer to it as the DM axion. We predominantly explore PBHs in the mass range (106 - 5× 108)g. We investigate the relation between the relic abundance of DM axions and the parameter space of PBHs. We numerically solve the set of Boltzmann equations, that governs the cosmological evolution during both radiation and PBH-dominated epochs, providing the bulk energy content of the early Universe. We further solve the equation of motion of the DM axion field to obtain its present abundance. Alongside non-relativistic production mechanisms, light QCD axions are generated from evaporating PBHs through the Hawking mechanism and could make up a fraction of the dark radiation (DR). If the QCD axion is ever discovered, it will give us insight into the early Universe and probe into the physics of the PBH-dominated era. We estimate the bounds on the model from DR axions produced via PBH evaporation and thermal decoupling, and we account for isocurvature bounds for the period of inflation where the Peccei-Quinn symmetry is broken. We assess the results obtained against the available CMB data and we comment on the forecasts from gravitational wave searches. We briefly state the consequences of PBH accretion and the uncertainties this may further add to cosmology and astroparticle physics modeling.

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3

Lombardo, Maria Paola, and Anton Trunin. "Topology and axions in QCD." International Journal of Modern Physics A 35, no. 20 (July 15, 2020): 2030010. http://dx.doi.org/10.1142/s0217751x20300100.

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QCD axions are at the crossroads of QCD topology and Dark Matter searches. We present here the current status of topological studies on the lattice, and their implication on axion physics. We outline the specific challenges posed by lattice topology, the different proposals for handling them, the observable effects of topology on the QCD spectrum and its interrelation with chiral and axial symmetries. We review the transition to the quark–gluon plasma, the fate of topology at the transition, and the approach to the high temperature limit. We discuss the extrapolations needed to reach the regime of cosmological relevance, and the resulting constraints on the QCD axion.

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4

Rosenberg, Leslie J. "Dark-matter QCD-axion searches." Proceedings of the National Academy of Sciences 112, no. 40 (January 12, 2015): 12278–81. http://dx.doi.org/10.1073/pnas.1308788112.

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In the late 20th century, cosmology became a precision science. Now, at the beginning of the next century, the parameters describing how our universe evolved from the Big Bang are generally known to a few percent. One key parameter is the total mass density of the universe. Normal matter constitutes only a small fraction of the total mass density. Observations suggest this additional mass, the dark matter, is cold (that is, moving nonrelativistically in the early universe) and interacts feebly if at all with normal matter and radiation. There’s no known such elementary particle, so the strong presumption is the dark matter consists of particle relics of a new kind left over from the Big Bang. One of the most important questions in science is the nature of this dark matter. One attractive particle dark-matter candidate is the axion. The axion is a hypothetical elementary particle arising in a simple and elegant extension to the standard model of particle physics that nulls otherwise observable CP-violating effects (where CP is the product of charge reversal C and parity inversion P) in quantum chromo dynamics (QCD). A light axion of mass 10−(6–3) eV (the invisible axion) would couple extraordinarily weakly to normal matter and radiation and would therefore be extremely difficult to detect in the laboratory. However, such an axion is a compelling dark-matter candidate and is therefore a target of a number of searches. Compared with other particle dark-matter candidates, the plausible range of axion dark-matter couplings and masses is narrowly constrained. This focused search range allows for definitive searches, where a nonobservation would seriously impugn the dark-matter QCD-axion hypothesis. Axion searches use a wide range of technologies, and the experiment sensitivities are now reaching likely dark-matter axion couplings and masses. This article is a selective overview of the current generation of sensitive axion searches. Not all techniques and experiments are discussed, but I hope to give a sense of the current experimental landscape of the search for dark-matter axions.

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5

Barman, Basabendu, Nicolás Bernal, Nicklas Ramberg, and Luca Visinelli. "QCD Axion Kinetic Misalignment without Prejudice." Universe 8, no. 12 (November 29, 2022): 634. http://dx.doi.org/10.3390/universe8120634.

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The axion field, the angular direction of the complex scalar field associated with the spontaneous symmetry breaking of the Peccei–Quinn (PQ) symmetry, could have originated with initial non-zero velocity. The presence of a non-zero angular velocity resulting from additional terms in the potential that explicitly break the PQ symmetry has important phenomenological consequences such as a modification of the axion mass with respect to the conventional PQ framework or an explanation for the observed matter-antimatter asymmetry. We elaborate further on the consequences of the “kinetic misalignment” mechanism, assuming that axions form the entirety of the dark matter abundance. The kinetic misalignment mechanism possesses a weak limit in which the axion field starts to oscillate at the same temperature as in the conventional PQ framework, and a strong limit corresponding to large initial velocities which effectively delay the onset of oscillations. Following a UV-agnostic approach, we show how this scenario impacts the formation of axion miniclusters, and we sketch the details of these substructures along with potential detecting signatures.

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6

Moore, Guy. "Axion dark matter and the Lattice." EPJ Web of Conferences 175 (2018): 01009. http://dx.doi.org/10.1051/epjconf/201817501009.

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First I will review the QCD theta problem and the Peccei-Quinn solution, with its new particle, the axion. I will review the possibility of the axion as dark matter. If PQ symmetry was restored at some point in the hot early Universe, it should be possible to make a definite prediction for the axion mass if it constitutes the Dark Matter. I will describe progress on one issue needed to make this prediction – the dynamics of axionic string-wall networks and how they produce axions. Then I will discuss the sensitivity of the calculation to the high temperature QCD topological susceptibility. My emphasis is on what temperature range is important, and what level of precision is needed.

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7

Zhang, Hong. "Axion Stars." Symmetry 12, no. 1 (December 20, 2019): 25. http://dx.doi.org/10.3390/sym12010025.

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The dark matter particle can be a QCD axion or axion-like particle. A locally over-densed distribution of axions can condense into a bound Bose–Einstein condensate called an axion star, which can be bound by self-gravity or bound by self-interactions. It is possible that a significant fraction of the dark matter axion is in the form of axion stars. This would make some efforts searching for the axion as the dark matter particle more challenging, but at the same time it would also open up new possibilities. Some of the properties of axion stars, including their emission rates and their interactions with other astrophysical objects, are not yet completely understood.

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8

D'Eramo, Francesco, Eleonora Di Valentino, William Giarè, Fazlollah Hajkarim, Alessandro Melchiorri, Olga Mena, Fabrizio Renzi, and Seokhoon Yun. "Cosmological bound on the QCD axion mass, redux." Journal of Cosmology and Astroparticle Physics 2022, no. 09 (September 1, 2022): 022. http://dx.doi.org/10.1088/1475-7516/2022/09/022.

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Abstract We revisit the joint constraints in the mixed hot dark matter scenario in which both thermally produced QCD axions and relic neutrinos are present. Upon recomputing the cosmological axion abundance via recent advances in the literature, we improve the state-of-the-art analyses and provide updated bounds on axion and neutrino masses. By avoiding approximate methods, such as the instantaneous decoupling approximation, and limitations due to the limited validity of the perturbative approach in QCD that forced to artificially divide the constraints from the axion-pion and the axion-gluon production channels, we find robust and self-consistent limits. We investigate the two most popular axion frameworks: KSVZ and DFSZ. From Big Bang Nucleosynthesis (BBN) light element abundances data we find for the KSVZ axion ΔN eff < 0.31 and an axion mass bound ma < 0.53 eV (i.e., a bound on the axion decay constant fa > 1.07 × 107 GeV) both at 95% CL. These BBN bounds are improved to Δ N eff < 0.14 and ma < 0.16 eV (fa > 3.56 × 107 GeV) if a prior on the baryon energy density from Cosmic Microwave Background (CMB) data is assumed. When instead considering cosmological observations from the CMB temperature, polarization and lensing from the Planck satellite combined with large scale structure data we find Δ N eff < 0.23, ma < 0.28 eV (fa > 2.02 × 107 GeV) and ∑ mν < 0.16 eV at 95% CL. This corresponds approximately to a factor of 5 improvement in the axion mass bound with respect to the existing limits. Very similar results are obtained for the DFSZ axion. We also forecast upcoming observations from future CMB and galaxy surveys, showing that they could reach percent level errors for ma ∼ 1 eV.

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9

Kitajima, Naoya, Kazuhiro Kogai, and Yuko Urakawa. "New scenario of QCD axion clump formation. Part I. Linear analysis." Journal of Cosmology and Astroparticle Physics 2022, no. 03 (March 1, 2022): 039. http://dx.doi.org/10.1088/1475-7516/2022/03/039.

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Abstract The QCD axion acquires the potential through the non-perturbative effect of the QCD matters around the QCD phase transition. During this period, the direct interaction between the axion and the QCD matters sets in. Focusing on the impact of this direct interaction, we propose two scenarios where the fluctuation of the axion can rapidly grow, potentially leading to the formation of axion miniclusters even if the Peccei-Quinn (PQ) symmetry was already broken during inflation. The first scenario assumes that the primordial curvature perturbation at the horizon scale during the QCD epoch was significantly enhanced and the second one assumes that the initial misalignment was tuned around the hilltop of the potential.

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10

D’Eramo, Francesco. "Thermal Axions: What’s next?" EPJ Web of Conferences 274 (2022): 01007. http://dx.doi.org/10.1051/epjconf/202227401007.

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Scattering and decay processes of thermal bath particles in the early universe can dump relativistic axions in the primordial plasma. If produced with a significant abundance, their presence can leave observable signatures in cosmological observables probing both the early and the late universe. We focus on the QCD axion and present recent and significant improvements for the calculation of the axion production rate across the different energy scales during the expansion of the universe. We apply these rates to predict the abundance of produced axions and to derive the latest cosmological bounds on the axion mass and couplings.

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11

Lee, Chang, Xiaoyue LiJ, Derek Strom, and Olaf Reimann. "MADMAX: a QCD dark matter axion direct-detection experiment." Journal of Physics: Conference Series 2156, no. 1 (December 1, 2021): 012041. http://dx.doi.org/10.1088/1742-6596/2156/1/012041.

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Abstract Peccei and Quinn proposed axions to solve the strong CP problem. Axions later turned out to be an excellent candidate for cold dark matter. They may have a mass of around 100 μeV if generated after cosmic inflation. The MADMAX collaboration aims to detect post-inflationary QCD axion using a new detector concept, the dielectric haloscope. It detects axion-induced traveling waves from boundaries of different media, boosted by layers of dielectrics. We report the current progress and future measurement plan for a proof-of-principle setup. We also report the current development of the prototype detector and the full MADMAX experiment.

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12

GABADADZE, GREGORY, and M. SHIFMAN. "QCD VACUUM AND AXIONS: WHAT'S HAPPENING?" International Journal of Modern Physics A 17, no. 26 (October 20, 2002): 3689–727. http://dx.doi.org/10.1142/s0217751x02011357.

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A deeper understanding of the vacuum structure in QCD invites one to rethink certain aspects of axion physics. The recent advances are mostly due to developments in super-symmetric gauge theories and the brane theory, in which QCD can be embedded. They include, but are not limited to, the studies of metastable vacua in multicolor gluo-dynamics, and the domain walls. We briefly review basics of axion physics and then present a modern perspective on a rich interplay between the QCD vacuum structure and axion physics.

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13

Gaillard, Mary K., and Ben Kain. "Is the universal string axion the QCD axion?" Nuclear Physics B 734, no. 1-2 (January 2006): 116–37. http://dx.doi.org/10.1016/j.nuclphysb.2005.11.009.

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14

Higaki, Tetsutaro, Kwang Sik Jeong, Naoya Kitajima, and Fuminobu Takahashi. "The QCD axion from aligned axions and diphoton excess." Physics Letters B 755 (April 2016): 13–16. http://dx.doi.org/10.1016/j.physletb.2016.01.055.

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15

Ruggieri, M., D. E. A. Castillo, A. G. Grunfeld, and Bonan Zhang. "The axion potential in quark matter." EPJ Web of Conferences 270 (2022): 00024. http://dx.doi.org/10.1051/epjconf/202227000024.

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We study the QCD axion potential in hot and dense quark matter, within an NJL-like model that includes the coupling of the axion to quarks. Firstly we compute the effect of the chiral QCD crossover on the axion mass and self-coupling. Then, we compute the axion potential and study the domain walls. We find that the energy barrier between two adjacent vacuum states decreases in the chirally restored phase: this results in a lower surface tension of the walls. Finally we comment on the possibility of abundant production of walls in hot and dense quark matter.

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16

Salvio, Alberto. "A fundamental QCD axion model." Physics Letters B 808 (September 2020): 135686. http://dx.doi.org/10.1016/j.physletb.2020.135686.

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17

Rosenberg, Leslie J. "Dark-matter QCD-axion searches." Journal of Physics: Conference Series 203 (January 1, 2010): 012008. http://dx.doi.org/10.1088/1742-6596/203/1/012008.

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18

Choi, Kang-Sin, Ian-Woo Kim, and Jihn E. Kim. "String compactification, QCD axion and axion–photon–photon coupling." Journal of High Energy Physics 2007, no. 03 (March 28, 2007): 116. http://dx.doi.org/10.1088/1126-6708/2007/03/116.

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19

Bai, Yang, Xiaolong Du, and Yuta Hamada. "Diluted axion star collisions with neutron stars." Journal of Cosmology and Astroparticle Physics 2022, no. 01 (January 1, 2022): 041. http://dx.doi.org/10.1088/1475-7516/2022/01/041.

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Abstract Diluted axion star, a self-gravitating object with the quantum pressure balancing gravity, has been predicted in many models with a QCD axion or axion-like particle. It can be formed in the early universe and composes a sizable fraction of dark matter. One could detect the transient radio signals when it passes by a magnetar with the axion particle converted into photon in the magnetic field. Using both numerical and semi-analytic approaches, we simulate the axion star's dynamic evolution and estimate the fraction of axion particles that can have a resonance conversion during such a collision event. We have found that both self-gravity and quantum pressure are not important after the diluted axion star enters the Roche radius. A free-fall approximate can capture individual particle trajectories very well. With some optimistic cosmological and astrophysical assumptions, the QCD axion parameter space can be probed from detecting such a collision event by radio telescopes.

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20

POLLOCK, M. D. "ON THE EXISTENCE OF THE SUPERSTRING AXION MINI-STAR." Modern Physics Letters A 17, no. 03 (January 30, 2002): 171–74. http://dx.doi.org/10.1142/s0217732302006345.

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It is shown that the lasing mechanism of axion solitonic stars found by Tkachev is suppressed above a critical value of the QCD decay constant fa ≈ 1015 GeV . This means, in particular, that the heterotic superstring axion mini-star — for which theory [Formula: see text], where λ ≡ fB/fA is the ratio of the decay constants of the second and model-independent axions, respectively, and [Formula: see text] is the strong-interaction coupling — is allowed to form, the laser amplification being exp A, where [Formula: see text]. Relaxation may occur either by the "gravitational cooling" proposed by Seidel and Suen, and by Khlebnikov, and/or by the four-axion self-interaction studied by Tkachev.

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21

Kim, Jihn E., and Se-Jin Kim. "“Invisible” QCD axion rolling through the QCD phase transition." Physics Letters B 783 (August 2018): 357–63. http://dx.doi.org/10.1016/j.physletb.2018.07.020.

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22

Aja, Beatriz, Sergio Arguedas Cuendis, Ivan Arregui, Eduardo Artal, R. Belén Barreiro, Francisco J. Casas, Marina C. de Ory, et al. "The Canfranc Axion Detection Experiment (CADEx): search for axions at 90 GHz with Kinetic Inductance Detectors." Journal of Cosmology and Astroparticle Physics 2022, no. 11 (November 1, 2022): 044. http://dx.doi.org/10.1088/1475-7516/2022/11/044.

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Abstract We propose a novel experiment, the Canfranc Axion Detection Experiment (CADEx), to probe dark matter axions with masses in the range 330–460 μeV, within the W-band (80–110 GHz), an unexplored parameter space in the well-motivated dark matter window of Quantum ChromoDynamics (QCD) axions. The experimental design consists of a microwave resonant cavity haloscope in a high static magnetic field coupled to a highly sensitive detecting system based on Kinetic Inductance Detectors via optimized quasi-optics (horns and mirrors). The experiment is in preparation and will be installed in the dilution refrigerator of the Canfranc Underground Laboratory. Sensitivity forecasts for axion detection with CADEx, together with the potential of the experiment to search for dark photons, are presented.

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23

Takahashi, Fuminobu, and Wen Yin. "Challenges for heavy QCD axion inflation." Journal of Cosmology and Astroparticle Physics 2021, no. 10 (October 1, 2021): 057. http://dx.doi.org/10.1088/1475-7516/2021/10/057.

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24

Conlon, Joseph P. "The QCD axion and moduli stabilisation." Journal of High Energy Physics 2006, no. 05 (June 1, 2006): 078. http://dx.doi.org/10.1088/1126-6708/2006/05/078.

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25

Di Luzio, Luca, Maurizio Giannotti, Enrico Nardi, and Luca Visinelli. "The landscape of QCD axion models." Physics Reports 870 (July 2020): 1–117. http://dx.doi.org/10.1016/j.physrep.2020.06.002.

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26

Horvatić, Davor, Dalibor Kekez, and Dubravko Klabučar. "Temperature Dependence of the Axion Mass in a Scenario Where the Restoration of Chiral Symmetry Drives the Restoration of the UA(1) Symmetry." Universe 5, no. 10 (October 8, 2019): 208. http://dx.doi.org/10.3390/universe5100208.

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The temperature (T) dependence of the axion mass is predicted for T ′ s up to ∼ 2 . 3 × the chiral restoration temperature of QCD. The axion is related to the U A ( 1 ) anomaly. The squared axion mass m a ( T ) 2 is, modulo the presently undetermined scale of spontaneous breaking of Peccei–Quinn symmetry f a (squared), equal to QCD topological susceptibility χ ( T ) for all T. We obtain χ ( T ) by using quark condensates calculated in two effective Dyson–Schwinger models of nonperturbative QCD. They exhibit the correct chiral behavior, including the dynamical breaking of chiral symmetry and its restoration at high T. This is reflected in the U A ( 1 ) symmetry breaking and restoration through χ ( T ) . In our previous studies, such χ ( T ) yields the T-dependence of the U A ( 1 ) -anomaly-influenced masses of η ′ and η mesons consistent with experiment. This in turn supports our prediction for the T-dependence of the axion mass. Another support is a rather good agreement with the pertinent lattice results. This agreement is not spoiled by our varying u and d quark mass parameters out of the isospin limit.

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Choi, Gongjun, and Enrico D. Schiappacasse. "PBH assisted search for QCD axion dark matter." Journal of Cosmology and Astroparticle Physics 2022, no. 09 (September 1, 2022): 072. http://dx.doi.org/10.1088/1475-7516/2022/09/072.

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Abstract The entropy production prior to BBN era is one of ways to prevent QCD axion with the decay constant Fa ∈ [1012 GeV, 1016 GeV] from overclosing the universe when the misalignment angle is θ i = 𝒪(1). As such, it is necessarily accompanied by an early matter-dominated era (EMD) provided the entropy production is achieved via the decay of a heavy particle. In this work, we consider the possibility of formation of primordial black holes during the EMD era with the assumption of the enhanced primordial scalar perturbation on small scales (k > 104 Mpc-1). In such a scenario, it is expected that PBHs with axion halo accretion develop to ultracompact minihalos (UCMHs). We study how UCMHs so obtained could be of great use in the experimental search for QCD axion dark matter with Fa ∈ [1012 GeV, 1016 GeV].

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28

Azcoiti, Vicente. "Topology in the SU(Nf) chiral symmetry restored phase of unquenched QCD and axion cosmology." EPJ Web of Conferences 175 (2018): 04007. http://dx.doi.org/10.1051/epjconf/201817504007.

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The axion is one of the more interesting candidates to make the dark matter of the universe, and the axion potential plays a fundamental role in the determination of the dynamics of the axion field. Moreover, the way in which the U(1)A anomaly manifests itself in the chiral symmetry restored phase of QCD at high temperature could be tested when probing the QCD phase transition in relativistic heavy ion collisions. With these motivations, we investigate the physical consequences of the survival of the effects of the U(1)A anomaly in the chiral symmetric phase of QCD, and show that the free energy density is a singular function of the quark mass m, in the chiral limit, and that the σ and π susceptibilities diverge in this limit at any T ≥ Tc. We also show that the difference between the π and δ susceptibilities diverges in the chiral limit at any T ≥ Tc, a result that can be contrasted with the existing lattice calculations; and discuss on the generalization of these results to the Nf ≥ 3 model.

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29

Jeong, Kwang Sik, Kohei Matsukawa, Shota Nakagawa, and Fuminobu Takahashi. "Cosmological effects of Peccei-Quinn symmetry breaking on QCD axion dark matter." Journal of Cosmology and Astroparticle Physics 2022, no. 03 (March 1, 2022): 026. http://dx.doi.org/10.1088/1475-7516/2022/03/026.

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Abstract We study cosmological effects of explicit Peccei-Quinn breaking on the QCD axion dark matter. We find that the axion abundance decreases or increases significantly depending on the initial position, even for a tiny Peccei-Quinn breaking that satisfies the experimental bound of the neutron electric dipole measurements. If the axion first starts to oscillate around a wrong vacuum and if it gets trapped there until the false vacuum disappears due to non-perturbative QCD effects, its abundance increases significantly and is independent of the decay constant fa , as first pointed out in ref. [1]. Thus, the axion produced by the trapping mechanism can explain dark matter even when the decay constant is close to the lower limit due to stellar cooling arguments. On the other hand, if the axion starts to oscillate about a potential minimum close to the low-energy vacuum, its abundance is significantly reduced because of the adiabatic suppression mechanism. This relaxes the upper limit of the axion window to large values of fa . We also discuss how the axionic isocurvature perturbation is affected by the Peccei-Quinn breaking term, and show that it can be suppressed in both regimes. In particular, the isocurvature bound on the inflation scale is relaxed by many orders of magnitudes for fa ≳ 1011 GeV compared to the conventional scenario.

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30

Kovacs, Tamas G. "Temperature-dependence of the QCD topological susceptibility." EPJ Web of Conferences 175 (2018): 01013. http://dx.doi.org/10.1051/epjconf/201817501013.

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We recently obtained an estimate of the axion mass based on the hypothesis that axions make up most of the dark matter in the universe. A key ingredient for this calculation was the temperature-dependence of the topological susceptibility of full QCD. Here we summarize the calculation of the susceptibility in a range of temperatures from well below the finite temperature cross-over to around 2 GeV. The two main difficulties of the calculation are the unexpectedly slow convergence of the susceptibility to its continuum limit and the poor sampling of nonzero topological sectors at high temperature. We discuss how these problems can be solved by two new techniques, the first one with reweighting using the quark zero modes and the second one with the integration method.

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31

Nakagawa, Shota, Fuminobu Takahashi, and Masaki Yamada. "Trapping effect for QCD axion dark matter." Journal of Cosmology and Astroparticle Physics 2021, no. 05 (May 1, 2021): 062. http://dx.doi.org/10.1088/1475-7516/2021/05/062.

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32

Kitajima, Naoya, and Fuminobu Takahashi. "Primordial black holes from QCD axion bubbles." Journal of Cosmology and Astroparticle Physics 2020, no. 11 (November 27, 2020): 060. http://dx.doi.org/10.1088/1475-7516/2020/11/060.

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33

Evans, Nick, Stephen D. H. Hsu, Andreas Nyffeler, and Myckola Schwetz. "QCD at large θ-angle axion cosmology." Nuclear Physics B 494, no. 1-2 (June 1997): 200–210. http://dx.doi.org/10.1016/s0550-3213(97)00174-0.

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34

Rybka, Gray. "Laboratory searches for QCD axion dark matter." Journal of Physics G: Nuclear and Particle Physics 44, no. 12 (November 15, 2017): 124002. http://dx.doi.org/10.1088/1361-6471/aa8f20.

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35

Lee, Billy K. K., Ming-chung Chu, and Lap-Ming Lin. "Could the GW190814 Secondary Component Be a Bosonic Dark Matter Admixed Compact Star?" Astrophysical Journal 922, no. 2 (December 1, 2021): 242. http://dx.doi.org/10.3847/1538-4357/ac2735.

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Abstract We investigate whether the recently observed 2.6 M ⊙ compact object in the gravitational wave event GW190814 can be a bosonic dark matter (DM) admixed compact star. By considering the three constraints of mass, radius, and the stability of such an object, we find that if the DM is made of QCD axions, their particle mass m is constrained to a range that has already been ruled out by the independent constraint imposed by the stellar-mass black hole superradiance process. The 2.6 M ⊙ object can still be a neutron star admixed with at least 2.0 M ⊙ of DM made of axion-like particles (or even a pure axion-like particle star) if 2 × 10−11 eV ≤ m ≤ 2.4 × 10−11 eV (2.9 × 10−11 eV ≤ m ≤ 3.2 × 10−11 eV) with a decay constant of f ≥ 8 × 1017 GeV.

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36

POLLOCK, M. D. "IS NEUTRALINO DARK MATTER POSSIBLE IN THE SUPERSTRING THEORY?" International Journal of Modern Physics D 13, no. 05 (May 2004): 819–30. http://dx.doi.org/10.1142/s0218271804004797.

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In the heterotic superstring theory, the decay constant of the QCD axion lies within the range 3×1016≲fa GeV ≲1018, the lower limit referring to the model-independent axion, while the upper limit is due to dimension-five, non-renormalizable effects first calculated by Cvetič. Consequently, the neutralino χ0, assumed to be a nearly pure B-ino, decays into the axino ã on the time scale obtained by Covi et al., [Formula: see text], which is ≲10-3 times the age of the Universe t0≈4×1017 s , but can only be made less than the time t≈1 s of the onset of Big-Bang nucleosynthesis by revising mχ0 to an unnaturally high level, mχ0≳500 TeV . Therefore, it is necessary to set the coefficient Ca YY =0, which is possible for the Kim–Shifman–Vainshtein–Zakharov invisible-axion model if the electric charge q c of the heavy-quark colour representation C vanishes. The neutralino does not then decay and can constitute some fraction of the dark matter of the Universe, depending upon the value of mχ0 (for a gaugino-dominated state, [Formula: see text] where [Formula: see text] is the SU(2) singlet slepton). The consequences of an ultra-light axion with fa≈1018 GeV are also discussed.

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37

Bonati, Claudio, Massimo D’Elia, Marco Mariti, Guido Martinelli, Michele Mesiti, Francesco Negro, Francesco Sanfilippo, and Giovanni Villadoro. "Recent progress on QCD inputs for axion phenomenology." EPJ Web of Conferences 137 (2017): 08004. http://dx.doi.org/10.1051/epjconf/201713708004.

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38

Kim, Jihn E., and Hans Peter Nilles. "Axionic dark energy and a composite QCD axion." Journal of Cosmology and Astroparticle Physics 2009, no. 05 (May 18, 2009): 010. http://dx.doi.org/10.1088/1475-7516/2009/05/010.

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39

Jeong, Kwang Sik, and Fuminobu Takahashi. "Suppressing isocurvature perturbations of QCD axion dark matter." Physics Letters B 727, no. 4-5 (December 2013): 448–51. http://dx.doi.org/10.1016/j.physletb.2013.10.061.

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40

McLerran, Larry, Emil Mottola, and Mikhail E. Shaposhnikov. "Sphalerons and axion dynamics in high-temperature QCD." Physical Review D 43, no. 6 (March 15, 1991): 2027–35. http://dx.doi.org/10.1103/physrevd.43.2027.

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41

Chen, Zhe, Archil Kobakhidze, Ciaran A. J. O’Hare, Zachary S. C. Picker, and Giovanni Pierobon. "Phenomenology of the companion-axion model: photon couplings." European Physical Journal C 82, no. 10 (October 23, 2022). http://dx.doi.org/10.1140/epjc/s10052-022-10909-6.

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AbstractWe study the phenomenology of the ‘companion-axion model’ consisting of two coupled QCD axions. The second axion is required to rescue the Peccei–Quinn solution to the strong-CP problem from the effects of colored gravitational instantons. We investigate here the combined phenomenology of axion–axion and axion–photon interactions, recasting present and future single-axion bounds onto the companion-axion parameter space. Most remarkably, we predict that future axion searches with haloscopes and helioscopes may well discover two QCD axions, perhaps even within the same experiment.

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42

Agrawal, Prateek, Michael Nee, and Mario Reig. "Axion couplings in grand unified theories." Journal of High Energy Physics 2022, no. 10 (October 20, 2022). http://dx.doi.org/10.1007/jhep10(2022)141.

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Abstract We show that the couplings of axions to gauge bosons are highly restricted in Grand Unified Theories where the standard model is embedded in a simple 4D gauge group. The topological nature of these couplings allows them to be matched from the UV to the IR, and the ratio of the anomaly with photons and gluons for any axion is fixed by unification. This implies that there is a single axion, the QCD axion, with an anomalous coupling to photons. Other light axion-like particles can couple to photons by mixing through the QCD axion portal and lie to the right of the QCD line in the mass-coupling plane. Axions which break the unification relation between gluon and photon couplings are necessarily charged under the GUT gauge group and become heavy from perturbative mass contributions. A discovery of an axion to the left of the QCD line can rule out simple Grand Unified models. Axion searches are therefore tabletop and astrophysical probes of Grand Unification.

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Co, Raymond T., Soubhik Kumar, and Zhen Liu. "Searches for heavy QCD axions via dimuon final states." Journal of High Energy Physics 2023, no. 2 (February 10, 2023). http://dx.doi.org/10.1007/jhep02(2023)111.

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Abstract Heavy QCD axions are well-motivated extensions of the QCD axion that address the quality problem while still solving the strong CP problem. Owing to the gluon coupling, critical for solving the strong CP problem, these axions can be produced in significant numbers in beam dump and collider environments for axion decay constants as large as PeV, relevant for addressing the axion quality problem. In addition, if these axions have leptonic couplings, they can give rise to long-lived decay into lepton pairs, in particular, dominantly into muons above the dimuon threshold and below the GeV scale in a broad class of axion models. Considering existing constraints, primarily from rare meson decays, we demonstrate that current and future neutrino facilities and long-lived particle searches have the potential to probe significant parts of the heavy QCD axion parameter space via dimuon final states.

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Co, Raymond T., Tony Gherghetta, and Keisuke Harigaya. "Axiogenesis with a heavy QCD axion." Journal of High Energy Physics 2022, no. 10 (October 19, 2022). http://dx.doi.org/10.1007/jhep10(2022)121.

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Abstract We demonstrate that the observed cosmological excess of matter over anti-matter may originate from a heavy QCD axion that solves the strong CP problem but has a mass much larger than that given by the Standard Model QCD strong dynamics. We investigate a rotation of the heavy QCD axion in field space, which is transferred into a baryon asymmetry through weak and strong sphaleron processes. This provides a strong cosmological motivation for heavy QCD axions, which are of high experimental interest. The viable parameter space has an axion mass ma between 1 MeV and 10 GeV and a decay constant fa< 105 GeV, which can be probed by accelerator-based direct axion searches and observations of the cosmic microwave background.

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Gorghetto, Marco, Edward Hardy, and Giovanni Villadoro. "More axions from strings." SciPost Physics 10, no. 2 (February 26, 2021). http://dx.doi.org/10.21468/scipostphys.10.2.050.

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We study the contribution to the QCD axion dark matter abundance that is produced by string defects during the so-called scaling regime. Clear evidence of scaling violations is found, the most conservative extrapolation of which strongly suggests a large number of axions from strings. In this regime, nonlinearities at around the QCD scale are shown to play an important role in determining the final abundance. The overall result is a lower bound on the QCD axion mass in the post-inflationary scenario that is substantially stronger than the naive one from misalignment.

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Broeckel, Igor, Michele Cicoli, Anshuman Maharana, Kajal Singh, and Kuver Sinha. "Moduli stabilisation and the statistics of axion physics in the landscape." Journal of High Energy Physics 2021, no. 8 (August 2021). http://dx.doi.org/10.1007/jhep08(2021)059.

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Abstract String theory realisations of the QCD axion are often said to belong to the anthropic window where the decay constant is around the GUT scale and the initial misalignment angle has to be tuned close to zero. In this paper we revisit this statement by studying the statistics of axion physics in the string landscape. We take moduli stabilisation properly into account since the stabilisation of the saxions is crucial to determine the physical properties of the corresponding axionic partners. We focus on the model-independent case of closed string axions in type IIB flux compactifications and find that their decay constants and mass spectrum feature a logarithmic, instead of a power-law, distribution. In the regime where the effective field theory is under control, most of these closed string axions are ultra-light axion-like particles, while axions associated to blow-up modes can naturally play the role of the QCD axion. Hence, the number of type IIB flux vacua with a closed string QCD axion with an intermediate scale decay constant and a natural value of the misalignment angle is only logarithmically suppressed. In a recent paper we found that this correlates also with a logarithmic distribution of the supersymmetry breaking scale, providing the intriguing indication that most, if not all, of the phenomenologically interesting quantities in the string landscape might feature a logarithmic distribution.

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Choi, Kiwoon, Sang Hui Im, Hee Jung Kim, and Hyeonseok Seong. "Precision axion physics with running axion couplings." Journal of High Energy Physics 2021, no. 8 (August 2021). http://dx.doi.org/10.1007/jhep08(2021)058.

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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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Huang, Junwu, Amalia Madden, Davide Racco, and Mario Reig. "Maximal axion misalignment from a minimal model." Journal of High Energy Physics 2020, no. 10 (October 2020). http://dx.doi.org/10.1007/jhep10(2020)143.

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Abstract The QCD axion is one of the best motivated dark matter candidates. The misalignment mechanism is well known to produce an abundance of the QCD axion consistent with dark matter for an axion decay constant of order 1012 GeV. For a smaller decay constant, the QCD axion, with Peccei-Quinn symmetry broken during inflation, makes up only a fraction of dark matter unless the axion field starts oscillating very close to the top of its potential, in a scenario called “large-misalignment”. In this scenario, QCD axion dark matter with a small axion decay constant is partially comprised of very dense structures. We present a simple dynamical model realising the large-misalignment mechanism. During inflation, the axion classically rolls down its potential approaching its minimum. After inflation, the Universe reheats to a high temperature and a modulus (real scalar field) changes the sign of its minimum dynamically, which changes the sign of the mass of a vector-like fermion charged under QCD. As a result, the minimum of the axion potential during inflation becomes the maximum of the potential after the Universe has cooled through the QCD phase transition and the axion starts oscillating. In this model, we can produce QCD axion dark matter with a decay constant as low as 6 × 109 GeV and an axion mass up to 1 meV. We also summarise the phenomenological implications of this mechanism for dark matter experiments and colliders.

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Buchbinder, Evgeny I., Andrei Constantin, and Andre Lukas. "Heterotic QCD axion." Physical Review D 91, no. 4 (February 25, 2015). http://dx.doi.org/10.1103/physrevd.91.046010.

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50

Di Luzio, Luca, Javier Galan, Maurizio Giannotti, Igor G. Irastorza, Joerg Jaeckel, Axel Lindner, Jaime Ruz, et al. "Probing the axion–nucleon coupling with the next generation of axion helioscopes." European Physical Journal C 82, no. 2 (February 2022). http://dx.doi.org/10.1140/epjc/s10052-022-10061-1.

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AbstractA finite axion–nucleon coupling, nearly unavoidable for QCD axions, leads to the production of axions via the thermal excitation and subsequent de-excitation of $$^{57}$$ 57 Fe isotopes in the sun. We revise the solar bound on this flux adopting the up to date emission rate, and investigate the sensitivity of the proposed International Axion Observatory IAXO and its intermediate stage BabyIAXO to detect these axions. We compare different realistic experimental options and discuss the model dependence of the signal. Already BabyIAXO has sensitivity far beyond previous solar axion searches via the nucleon coupling and IAXO can improve on this by more than an order of magnitude.

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