Axion Research Articles

OUP accepted manuscript

Abstract We discuss a natural scenario to solve the strong CP problem in the framework of the higher dimensional gauge theory. An axion-like field Ay has been built-in as the extra-space component of the higher dimensional gauge field. The coupling of Ay with gluons is attributed to the radiatively induced “Chern-Simons” (CS) term. We adopt a toy model with some unknown gauge symmetry U(1)X. The CS term is obtained in two ways: first by a concrete 1-loop calculation and next by use of the Fujikawa’s method to deal with the chiral anomaly in 4D space-time. The obtained results are identical, which implies that the radiative correction to the CS term is “1-loop exact” and is also free from UV-divergence even though the theory itself is non-renormalizable. As a novel feature of this scenario, such obtained CS term is no longer linear in the field Ay as in the usually discussed CS term in 5D space-time but a periodic function of Ay, since Ay has a physical meaning as the Wilson-loop phase. We argue how such novel feature of this scenario causes the modification of the ordinary solutions of the strong CP problem based on the axion fields.

Establishment and proliferation under climate change: temperate tunicates in south-western Iceland

Context Botryllus schlosseri and Diplosoma listerianum are spreading along the south-western coast of Iceland. Both species are non-indigenous and originated from the temperate zone. In some geographic regions, these species have been associated with negative ecological and economic impacts. The proliferation of these colonial tunicates in newly colonised areas will benefit from the projected warming of sea-surface temperatures. Aims Owing to the influence of temperature in physiological processes of marine invertebrates, the determination of the temporal dynamic of breeding activity is crucial for operational field control actions aiming to keep population abundances below a density-dependent adverse effect. Methods Colonies of B. schlosseri and D. listerianum were collected during a 12-month period, in Sandgerði, south-western Iceland. The number of oocytes and larvae were counted. Key results This study showed that both species are present year-round in south-western Iceland. The release of larvae is more intense during the warmer months. Conclusions To control their population density levels, field actions should be applied during the winter months before the onset of sexual reproduction and recruitment. Implications In the light of the findings, it is now possible to suggest the best time for countermeasures for both species and optimise resources for marine management.

Gravitational wave trispectrum in the axion-SU(2) model

We study the trispectrum of the gravitational waves (GWs) generated through the dynamics of an axionic spectator field and SU(2) gauge fields during inflation. In non-Abelian gauge theory, the gauge fields have four-point self-interactions, which induce the tree-level GW trispectrum. We formulate this type of the GW trispectrum including the non-dynamical contributions and evaluate it in the equilateral limit as a unique signal of this model. We find that the ratio of the GW trispectrum to the cube of the scalar power spectrum can be as large as \U0001d4aa(106) in the viable parameter space, which could be captured in the CMB observations.

A method for controlling the magnetic field near a superconducting boundary in the ARIADNE axion experiment

The QCD axion is a particle postulated to exist since the 1970s to explain the strong-CP problem in particle physics. It could also account for all of the observed dark matter in the Universe. The axion resonant interaction detection experiment (ARIADNE) intends to detect the QCD axion by sensing the fictitious ‘magnetic field’ created by its coupling to spin. Short-range axion-mediated interactions can occur between a sample of laser-polarized 3He nuclear spins and an unpolarized source-mass sprocket. The experiment must be sensitive to magnetic fields below the 10−19 T level to achieve its design sensitivity, necessitating tight control of the experiment’s magnetic environment. We describe a method for controlling three aspects of that environment which would otherwise limit the experimental sensitivity. Firstly, a system of superconducting magnetic shielding is described to screen ordinary magnetic noise from the sample volume at the 108 level, which should be sufficient to reduce the contribution of Johnson noise in the sprocket-shaped source mass, expected to be at the 10−12 T level, to below the threshold for signal detection. Secondly, a method for reducing magnetic field gradients within the sample up to 102 times is described, using a simple and cost-effective design geometry. Thirdly, a novel coil design is introduced which allows the generation of fields similar to those produced by Helmholtz coils in regions directly abutting superconducting boundaries. This method allows the nuclear Larmor frequency of the sample to be tuned to match the axion field modulation frequency set by the sprocket rotation. Finally, we experimentally investigate the magnetic shielding factor of sputtered thin-film superconducting niobium on quartz substrates for various geometries and film thicknesses relevant for the ARIADNE axion experiment using SQUID magnetometry. The methods may be generally useful for magnetic field control near superconducting boundaries in other experiments where similar considerations apply.

Heterodyne broadband detection of axion dark matter

We propose a new broadband search strategy for ultralight axion dark matter that interacts with electromagnetism. An oscillating axion field induces transitions between two quasi-degenerate resonant modes of a superconducting cavity. In two broadband runs optimized for high and low masses, this setup can probe unexplored parameter space for axion-like particles covering fifteen orders of magnitude in mass, including astrophysically long-ranged fuzzy dark matter.

Gauge-invariant formulation of axion-electrodynamics

In this paper, we propose a simple generalization of axion-electrodynamics (AED) for the general case in which Dirac fermion fields and scalar/pseudoscalar axion-like fields are present in the local [Formula: see text]([Formula: see text])[Formula: see text] gauge-invariant Lagrangian of the system. Our primary goal (which is not explored here) is to understand and predict novel phenomena that have no counterpart in standard (pseudoscalar) AED. With this end in view, we discuss on very general grounds, possible processes in which a Dirac field is coupled to axionic fields via the electromagnetic (EM) field.

Torsion in String-Inspired Cosmologies and the Universe Dark Sector

Several aspects of torsion in string-inspired cosmologies are reviewed. In particular, its connection with fundamental, string-model independent, axion fields associated with the massless gravitational multiplet of the string are discussed. It is argued in favour of the role of primordial gravitational anomalies coupled to such axions in inducing inflation of a type encountered in the “Running-Vacuum-Model (RVM)” cosmological framework, without fundamental inflaton fields. The gravitational-anomaly terms owe their existence to the Green–Schwarz mechanism for the (extra-dimensional) anomaly cancellation, and may be non-trivial in such theories in the presence of (primordial) gravitational waves at early stages of the four-dimensional string universe (after compactification). The paper also discusses how the torsion-induced stringy axions can acquire a mass in the post inflationary era, due to non-perturbative effects, thus having the potential to play the role of (a component of) dark matter in such models. Finally, the current-era phenomenology of this model is briefly described with emphasis placed on the possibility of alleviating tensions observed in the current-era cosmological data. A brief phenomenological comparison with other cosmological models in contorted geometries is also made.

Surface plasmon resonance in the presence of topological insulators

The plasmonic resonance of the free electrons at a metal-topological insulator interface is studied with the application of axion electrodynamics. The additional red-shift due to the axion field previously observed in the literature is accounted for by a mechanical model similar to that used in the hybridization model for coupled plasmonic resonances in metallic nanoshells. Such model sheds light on the origin of the red-shift being caused by the decrease in interaction potential energy for the free electron fluid due to the axion-induced charges at the interface of the metal and the topological insulator.

Impedance matching to axion dark matter: considerations of the photon-electron interaction

We introduce the concept of impedance matching to axion dark matter by posing the question of why axion detection is difficult, even though there is enough power in each square meter of incident dark-matter flux to energize a LED light bulb. By quantifying backreaction on the axion field, we show that a small axion-photon coupling does not by itself prevent an order-unity fraction of the dark matter from being absorbed through optimal impedance match. We further show, in contrast, that the electromagnetic charges and the self-impedance of their coupling to photons provide the principal constraint on power absorption integrated across a search band. Using the equations of axion electrodynamics, we demonstrate stringent limitations on absorbed power in linear, time-invariant, passive receivers. Our results yield fundamental constraints, arising from the photon-electron interaction, on improving integrated power absorption beyond the cavity haloscope technique. The analysis also has significant practical implications, showing apparent tension with the sensitivity projections for a number of planned axion searches. We additionally provide a basis for more accurate signal power calculations and calibration models, especially for receivers using multi-wavelength open configurations such as dish antennas and dielectric haloscopes.

Resurrecting low-mass axion dark matter via a dynamical QCD scale

In the framework where the strong coupling is dynamical, the QCD sector may confine at a much higher temperature than it would in the Standard Model, and the temperature-dependent mass of the QCD axion evolves in a non-trivial way. We find that, depending on the evolution of ΛQCD, the axion field may undergo multiple distinct phases of damping and oscillation leading generically to a suppression of its relic abundance. Such a suppression could therefore open up a wide range of parameter space, resurrecting in particular axion dark-matter models with a large Peccei-Quinn scale fa ≫ 1012 GeV, i.e., with a lighter mass than the standard QCD axion.

Axion fragmentation on the lattice

We analyze the phenomenon of axion fragmentation when an axion field rolls over many oscillations of a periodic potential. This is particularly relevant for the case of relaxion, in which fragmentation provides the necessary energy dissipation to stop the field evolution. We compare the results of a linear analysis with the ones obtained from a classical lattice simulation, finding an agreement in the stopping time of the zero mode between the two within an mathcal{O}(1) difference. We finally speculate on the generation of bubbles with different VEVs of the axion field, and discuss their cosmological consequences.

Dynamical piezomagnetic effect in time-reversal-invariant Weyl semimetals with axionic charge density waves

Charge density waves (CDWs) in Weyl semimetals (WSMs) have been shown to induce an exotic axionic insulating phase in which the sliding mode (phason) of the CDW acts as a dynamical axion field, giving rise to a large positive magnetoconductance [Wang et al., Phys. Rev. B 87, 161107(R) (2013); Roy et al., Phys. Rev. B 92, 125141 (2015); J. Gooth et al., Nature (London) 575, 315 (2019)]. In this work, we predict that dynamical strain can induce a bulk orbital magnetization in time-reversal (TR)-invariant WSMs that are gapped by a CDW. We term this effect the ``dynamical piezomagnetic effect'' (DPME). Unlike in J. Gooth et al. [Nature (London) 575, 315 (2019)], the DPME introduced in this work occurs in a bulk-constant (i.e., static and spatially homogeneous in the bulk) CDW, and does not rely on fluctuations, such as a phason. By studying the low-energy effective theory and a minimal tight-binding (TB) model, we find that the DPME originates from an effective valley axion field that couples the electromagnetic gauge field with a strain-induced pseudogauge field. In particular, whereas the piezoelectric effects studied in previous works are characterized by 2D Berry curvature, the DPME represents the first example of a fundamentally 3D strain effect originating from the Chern-Simons 3-form. We further find that the DPME has a discontinuous change at a critical value of the phase of the CDW order parameter. We demonstrate that, when there is a jump in the DPME, the surface of the system undergoes a topological quantum phase transition (TQPT), while the bulk remains gapped. Hence, the DPME provides a bulk signature of the boundary TQPT in a TR-invariant Weyl CDW.

R-parity violation axiogenesis

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.

Inflationary physics and trans-Planckian conjecture in the stringy running vacuum model: from the phantom vacuum to the true vacuum

In previous works we have embedded the Running Vacuum Model (RVM) of Cosmology in the framework of string theory. Specifically, we considered a string-inspired Cosmology with primordial gravitational waves (GW) and gravitational anomalies, which were argued to lead, via appropriate condensation during the very-early-universe era, to dynamical inflation, of RVM type, without the need for extra inflaton fields. A crucial role for the associated slow-roll nature of the inflationary era was played by the fundamental axion field that exists in the gravitational multiplet of strings, viz. the Kalb-Ramond (KR) axion. In this paper, we study further this model and demonstrate several novel facts, completing our previous studies. We clarify the different roles played by the background KR axions, which constitute a form of stiff matter that dominates a pre-RVM-inflationary epoch of the Universe. We show that the KR axion when combined with the gravitational Chern-Simons contribution obey together a peculiar equation of state $p=-\rho$, with negative energy density $\rho < 0$, which we call `phantom vacuum'. Eventually, this state transmutes into the standard vacuum state thanks to the contribution from the gravitational Chern-Simons condensate, which makes the total $\rho_{\rm total} =-p_{\rm total} >0$. At this point the RVM vacuum picture emerges naturally, with an overall equation of state of true vacuum type. We find that our scenario is consistent with the trans-Planckian censorship hypothesis, given that the rate of change of the KR axion takes only sub-Planckian values. We also discuss some explicit scenarios on the creation of GWs within the context of supergravity models that could be embedded in our string theory framework. {Finally, we argue how the RVM in our context can help to alleviate the current tensions of the $\Lambda$CDM.}

Nonlinear Axion Electrodynamics: Axionically Induced Electric Flares in the Early Magnetized Universe

We consider the nonlinearly extended Einstein–Maxwell-axion theory, which is based on the account for two symmetries: first, the discrete symmetry associated with the properties of the axion field, and second, the Jackson’s symmetry, prescribing to the electrodynamics to be invariant with respect to the rotation in the plane coordinated by the electric and magnetic fields. We derive the master equations of the nonlinearly extended theory and apply them to the Bianchi-I model with magnetic field. The main result, describing the behavior of the nonlinearly coupled axion, electromagnetic, and gravitational fields is the anomalous growth of the axionically induced electric field in the early magnetized Universe. The character of behavior of this anomalous electric field can be indicated by the term flare. We expect, that these electric flares can produce the electron–positron pair creation, significant acceleration of the born charged particles, and the emission of the electromagnetic waves by these accelerated particles.

Holographic complexity for black branes with momentum relaxation

We employ the "complexity equals action" conjecture to investigate the action growth rate for the charged and neutral AdS black branes of a holographic toy model consisting of Einstein-Maxwell theory in $d + 1$-dimensional bulk spacetime with $d - 1$ massless scalar fields which is called Einstein-Maxwell-Axion (EMA) theory. From the holographic point of view, the scalar fields source a spatially dependent field theory with momentum relaxation on the boundary, which is dual to the homogeneous and isotropic black branes. We find that the growth rate of the holographic complexity within the Wheeler-DeWitt (WDW) patch saturates the corresponding Lloyd's bound at the late time limit. Especially for the neutral AdS black branes, it will be shown that the complexity growth rate at late time vanishes for a particular value of relaxation parameter $\beta_{max}$ where the temperature of the black hole is minimal. Then, we investigate the transport properties of the holographic dual theory in the minimum temperature. A non-linear contribution of the axion field kinetic term in the context of k-essence model in the four-dimensional spacetime is considered as well. We also study the time evolution of the holographic complexity for the dyonic AdS black branes in this model.

Documenting experiential knowledge to enhance breast and cervical cancers screening uptake in France

Abstract Issue Improving uptake of Cancer Screening programs (CS) remains a public health priority in France, as stated in the latest national cancer control strategy. The French Society for Public Health designed in 2020 a project to document Interventions Promoting CS Participation (IPCSP) for vulnerable groups, for both breast and cervical cancers. This project provides experiential and practical evidence built up from IPCSP and offers relevant insights for the new strategy. Methods The project aims at capitalizing, i.e. collecting, documenting and circulating, experiential knowledge from practitioners who implement IPCSP locally (health professionals, social workers, grassroots organizations, etc.). The project consists in 3 main steps: 1/identify promising IPCSP through a nationwide call for applications; 2/ document the key mechanisms impacting how IPCSP unfold (context, partnerships, barriers and levers, ethics), 3/ publish a summary for each IPCSP, available online. The goal is to build up original knowledge from field actions, documenting how IPCSP tackle several factors that can hinder uptake, in various contexts. Results 20 IPCSP were selected. IPCSP targets included: women of low-income neighborhoods, allophone women, inhabitants of healthcare deserts, handicapped persons, etc. Most IPCSP (16 out of 20) featured reaching out strategies, such as: peer education, on-site screenings, etc. All promoted informed choice. A cross-case analysis of IPCSP highlighted key, recurring implementation levers. One is co-constructing IPCSP throughout within local, multi-professional, long-standing partnerships, in which partners bring complementary skills: medical expertise, proximity with target populations, project management skills, community engagement skills, etc. Lessons 20 detailed summaries will offer concrete data on how to put insights to enhance CS uptake into action. Other stakeholders and policymakers alike can benefit from experiential knowledge built up from IPCSP. Key messages Documenting interventions promoting uptake of breast and cervical cancer screening programs and detailing how they work is crucial to building knowledge and to helping enhance participation for all. Partnerships can provide effective, population-specific and context-specific levers to promote uptake of cancer screening programs in France. Co-constructing the intervention throughout is key.

First Constraints on Nuclear Coupling of Axionlike Particles from the Binary Neutron Star Gravitational Wave Event GW170817.

Light axion fields, if they exist, can be sourced by neutron stars due to their coupling to nuclear matter, and play a role in binary neutron star mergers. We report on a search for such axions by analyzing the gravitational waves from the binary neutron star inspiral GW170817. We find no evidence of axions in the sampled parameter space. The null result allows us to impose constraints on axions with masses below 10^{-11} eV by excluding the ones with decay constants ranging from 1.6×10^{16} to 10^{18} GeV at a 3σ confidence level. Our analysis provides the first constraints on axions from neutron star inspirals, and rules out a large region in parameter space that has not been probed by the existing experiments.

B modes from postinflationary gravitational waves sourced by axionic instabilities at cosmic reionization

We show that axion-like particles that only couple to invisible dark photons can generate visible B-mode signals around the reionization epoch. The axion field starts rolling shortly before reionization, resulting in a tachyonic instability for the dark photons. This generates an exponential growth of the dark photon quanta sourcing both scalar metric modes and gravitational waves that leave an imprint on the reionized baryons. The tensor modes modify the cosmic microwave background (CMB) polarization at reionization, generating visible B-mode signatures for the next generation of CMB experiments for parameter ranges that satisfy the current experimental constraints.

Non-Hermitian Yukawa interactions of fermions with axions: potential microscopic origin and dynamical mass generation

In this mini review, we discuss some recent developments regarding properties of (quantum) field-theory models containing anti-Hermitian Yukawa interactions between pseudoscalar fields (axions) and Dirac (or Majorana) fermions. Specifically, we first motivate physically such interactions, in the context of string-inspired low-energy effective field theories, involving right-handed neutrinos and axion fields. Then we proceed to discuss their formal consistency within the so-called Parity-Time-reversal(PT)-symmetry framework. Subsequently, we review dynamical mass generation, induced by the Yukawa interactions, for both fermions and axions. The Yukawa couplings are assumed weak, given that they are conjectured to have been generated by non-perturbative effects in the underlying microscopic string theory. The models under discussion contain, in addition to the Yukawa terms, also anti-Hermitian anomalous derivative couplings of the pseudoscalar fields to axial fermion currents, as well as interactions of the fermions with non-Hermitian axial backgrounds. We discuss the role of such additional couplings on the Yukawa-induced dynamically-generated masses. For the case where the fermions are right-handed neutrinos, we compare such masses with the radiative ones induced by both, the anti-Hermitian anomalous terms and the anti-Hermitian Yukawa interactions in phenomenologically relevant models.