<p>Axions, originally proposed to resolve the <math xmlns="http://www.w3.org/1998/Math/MathML" display="inline"><mrow><mi>C</mi><mi>P</mi></mrow></math> problem in the strong interaction, remain a leading dark matter candidate. While cavity haloscopes offer the most sensitive technique for detecting axions, searches have largely been limited to masses below <math xmlns="http://www.w3.org/1998/Math/MathML" display="inline"><mrow><mn>10</mn><mtext> </mtext><mtext> </mtext><mi>μeV</mi></mrow></math>. We report a sensitive search for axion dark matter with masses around <math xmlns="http://www.w3.org/1998/Math/MathML" display="inline"><mrow><mn>21</mn><mtext> </mtext><mtext> </mtext><mi>μeV</mi></mrow></math>, utilizing the <math xmlns="http://www.w3.org/1998/Math/MathML" display="inline"><mrow><msub><mrow><mi>TM</mi></mrow><mrow><mn>020</mn></mrow></msub></mrow></math> mode of a cylindrical cavity equipped with an innovative tuning mechanism. Our search achieved a sensitivity of <math xmlns="http://www.w3.org/1998/Math/MathML" display="inline"><mn>1.7</mn><mo>×</mo></math> the Kim-Shifman-Vainshtein-Zakharov benchmark over a 100-MHz range, representing a significant advance in this mass range. These results demonstrate that higher-order modes provide a viable strategy for extending haloscope searches into previously unexplored higher-mass regions.</p>

South Korea

Sungjae Bae

Sweden

Junu Jeong

Germany

Younggeun Kim

SungWoo Youn

Jinsu Kim

Japan

Arjan F. van Loo

Yasunobu Nakamura

Seonjeong Oh

Taehyeon Seong

Sergey Uchaikin

Jihn E. Kim

Yannis K. Semertzidis

Axion Dark Matter Search with Sensitivity near the Kim-Shifman-Vainshtein-Zakharov Benchmark Using the <math xmlns="http://www.w3.org/1998/Math/MathML" display="inline"><mrow><msub><mrow><mi>TM</mi></mrow><mrow><mn>020</mn></mrow></msub></mrow></math> Mode

We study multi-component dark matter scenarios and the Galactic 511 keV $\textit{γ}$-ray emission line signal in the framework of a local, dark U(1) extension of the Standard Model. A light vector dark matter particle associated with the dark U(1) may decay and annihilate to electron-positron pairs. The produced positrons may in turn form positroniums that subsequently annihilate to two photons, accounting for the observed line signal of the Galactic 511 keV $\textit{γ}$-ray emission. Three scenarios are investigated. First, we consider the minimal U(1) extension where a dark gauge boson and a dark Higgs boson are newly introduced to the particle content. As a second scenario, we consider WIMP-type dark matter with the introduction of an extra dark fermion which, in addition to the dark gauge boson, may contribute to the dark matter relic abundance. It is thus a multi-component dark matter scenario with a UV-complete dark U(1) symmetry. In particular, the vector dark matter may account for a small fraction of the total dark matter relic abundance. Finally, we consider the scenario where the dark matter particles are of the FIMP-type. In this case, both the light vector and fermion dark matter particles may be produced via the freeze-in and super-WIMP mechanisms. Considering theoretical and observational constraints, we explore the allowed parameter space where the Galactic 511 keV $\textit{γ}$-ray line signal and the dark matter relic can both be explained. We also discuss possible observational signatures.

Sarif Khan

China

Jongkuk Kim

Pyungwon Ko

Multi-component dark matter and Galactic 511 keV $\textit{γ}$-ray emission

We investigate dark matter phenomenology and Higgs inflation in a dark U(1) D -extended model. The model features two dark matter candidates, a dark fermion and a dark vector boson. When the fermion dark matter ψ is heavier than the vector dark matter W  D , there is an ample parameter space where ψ is dominant over W  D . The model can then easily evade the stringent bounds from direct detection experiments, since ψ has no direct coupling to the Standard Model particles. Furthermore, the model can accommodate inflation in three different ways, one along the Standard Model Higgs direction, one along the dark Higgs direction, and one along the combination of the two. Considering the running of the parameters and various observational constraints, we perform a detailed numerical analysis and identify allowed parameter spaces that explain both dark matter and Higgs inflation in a unified manner. We discuss in detail how the imposition of Higgs inflation severely constrains the dark matter parameter space. The existence of the dark Higgs field is found to play a crucial role both in dark matter phenomenology and in generalised Higgs inflation.

Interplay between Higgs inflation and dark matter models with dark U(1) gauge symmetry

It has been known for some time that the cosmological bound on the invisible axion scale can be avoided by an early phase of strong QCD. While most approaches rely on theories where the strong coupling constant is determined through the expectation value of some scalar field, we show that this mechanism can also be implemented into the benchmark Kim-Shifman-Vainshtein-Zakharov and Dine-Fischler-Srednicki-Zhitnitsky models when the early phase of strong QCD emerges by the modification of the running coupling during inflation. For both models the physics that are responsible for making QCD strong do not displace the axions minimum by too much, so that the efficiency of the relaxation is controlled by parameters of the theory and the number of inflationary <math><mi>e</mi></math>-folds. In particular, we consider the case of very efficient relaxation where the axion abundance is dominated by inflationary quantum and postinflationary thermal fluctuations. Within this situation we identify the parameter space compatible with all cosmological constrains and derive conditions on the reheating temperature and the QCD scale during inflation that result in the axion making up all the dark matter. Because of duality below the Peccei-Quinn scale and a minor influence of the Kim-Shifman-Vainshtein-Zakharov and Dine-Fischler-Srednicki-Zhitnitsky fields on the running, our findings also apply to a minimal two-form implementation of the axion.

Emmanouil Koutsangelas

Removing the cosmological bound on the axion scale in the Kim-Shifman-Vainshtein-Zakharov and Dine-Fischler-Srednicki-Zhitnitsky models

We report the results of an axion dark matter search over an axion mass range of <math><mrow><mn>9.39</mn><mi>–</mi><mn>9.51</mn><mtext> </mtext><mtext> </mtext><mi>μ</mi><mi>eV</mi></mrow></math>. A flux-driven Josephson parametric amplifier (JPA) was added to the cryogenic receiver chain. A system noise temperature of as low as 200 mK was achieved, which is the lowest recorded noise among published axion cavity experiments with phase-insensitive JPA operation. In addition, we developed a two-stage scanning method which boosted the scan speed by 26%. As a result, a range of two-photon coupling in a plausible model for the QCD axion was excluded with an order of magnitude higher in sensitivity than existing limits.

Ohjoon Kwon

Çağlar Kutlu

Woohyun Chung

Andrei Matlashov

Arjan Ferdinand van Loo

HeeSu Byun

Danho Ahn

Near-Quantum-Noise Axion Dark Matter Search at CAPP around <math><mrow><mrow><mn>9.5</mn><mtext> </mtext><mtext> </mtext><mi>μ</mi></mrow><mi>eV</mi></mrow></math>

We report an axion dark matter search at Dine-Fischler-Srednicki-Zhitnitskii sensitivity with the CAPP-12TB haloscope, assuming axions contribute 100% of the local dark matter density. The search excluded the axion-photon coupling <math><msub><mi>g</mi><mrow><mi>a</mi><mi>γ</mi><mi>γ</mi></mrow></msub></math> down to about <math><mn>6.2</mn><mo>×</mo><msup><mn>10</mn><mrow><mo>−</mo><mn>16</mn></mrow></msup><mtext> </mtext><mtext> </mtext><mrow><msup><mrow><mi>GeV</mi></mrow><mrow><mo>−</mo><mn>1</mn></mrow></msup></mrow></math> over the axion mass range between 4.51 and <math><mrow><mn>4.59</mn><mtext> </mtext><mtext> </mtext><mi>μ</mi><mi>eV</mi></mrow></math> at a 90% confidence level. The achieved experimental sensitivity can also exclude Kim-Shifman-Vainshtein-Zakharov axion dark matter that makes up just 13% of the local dark matter density. The CAPP-12TB haloscope will continue the search over a wide range of axion masses.

Andrew K. Yi

Saebyeok Ahn

JinMyeong Kim

Byeong Rok Ko

Boris I. Ivanov

SeongTae Park

Sergey V. Uchaikin

Jihoon Choi

Soohyung Lee

MyeongJae Lee

Yun Chang Shin

Doyu Lee

SungJae Bae

Jiwon Lee

Violeta Gkika

Ki Woong Lee

DongMin Kim

Axion Dark Matter Search around <math><mrow><mn>4.55</mn><mtext> </mtext><mtext> </mtext><mi>μ</mi><mi>eV</mi></mrow></math> with Dine-Fischler-Srednicki-Zhitnitskii Sensitivity

We consider an extension of the Standard Model that explains the neutrino masses and has a rich dark matter phenomenology. The model has two dark matter candidates, a vector WIMP and a fermion FIMP, and the sum of their relic densities matches the total dark matter abundance. We extensively study the dark matter production mechanisms and its connection with the neutrino sector, together with various bounds from present and future experiments. The extra scalar field in the model may induce a first-order phase transition in the early Universe. We study the production of stochastic gravitational waves associated with the first-order phase transition. We show that the phase transition can be strong, and thus the model may satisfy one of the necessary conditions for a successful electroweak baryogenesis. Detectability of the phase transition-associated gravitational waves is also discussed.

Francesco Costa

CERN

A two-component vector WIMP — fermion FIMP dark matter model with an extended seesaw mechanism

We consider an extension of the Standard Model that accounts for the muon g − 2 tension and neutrino masses and study in detail dark matter phenomenology. The model under consideration includes a WIMP and a FIMP scalar dark matter candidates and thus gives rise to two-component dark matter scenarios. We discuss different regimes and mechanisms of production, including the novel freeze-in semi-production, and show that the WIMP and FIMP together compose the observed relic density today. The presence of the extra scalar fields allows phase transitions of the first order. We examine the evolution of the vacuum state and discuss stochastic gravitational wave signals associated with the first-order phase transition. We show that the gravitational wave signals may be probed by future gravitational wave experiments which may serve as a complementary detection signal.

A two-component dark matter model and its associated gravitational waves

Multi-component dark matter scenarios are studied in the model with U(1) X  dark gauge symmetry that is broken into its product subgroup Z 2 × Z 3 á la Krauss-Wilczek mechanism. In this setup, there exist two types of dark matter fields, X and Y, distinguished by different Z 2 × Z 3 charges. The real and imaginary parts of the Z 2-charged field, X  R  and X  I , get different masses from the U(1) X  symmetry breaking. The field Y, which is another dark matter candidate due to the unbroken Z 3 symmetry, belongs to the Strongly Interacting Massive Particle (SIMP)-type dark matter. Both X  I  and X  R  may contribute to Y’s 3 → 2 annihilation processes, opening a new class of SIMP models with a local dark gauge symmetry. Depending on the mass difference between X  I  and X  R , we have either two-component or three-component dark matter scenarios. In particular two- or three-component SIMP scenarios can be realised not only for small mass difference between X and Y, but also for large mass hierarchy between them, which is a new and unique feature of the present model. We consider both theoretical and experimental constraints, and present four case studies of the multi-component dark matter scenarios.

Soo-Min Choi

Jinmian Li

A multi-component SIMP model with U(1) X  → Z 2 × Z 3

In the gravitational effective theories including higher curvature terms, cosmological solutions can have nontrivial de Sitter fixed points. We study phenomenological implications of such points, focusing on a theory in which a massive scalar field is nonminimally coupled to the Euler density. We first analyze the phase portrait of the dynamical system and show that the fixed point can be a sink or a saddle, depending on the strength of the coupling. Then, we compute the perturbation spectra generated in the vicinity of the fixed point in order to investigate whether the fixed point may be considered as cosmic inflation. We find parameter regions that are consistent with the cosmological data, given that the anisotropies in the cosmic microwave background are seeded by the fluctuations generated near the fixed point. Future observation may be used to further constrain the coupling function of this model. We also comment briefly on the swampland conjecture.

Shinsuke Kawai

CMB from a Gauss-Bonnet-induced de Sitter fixed point