<p>This Letter presents the first search for dark matter axions with mass in the ranges <math xmlns="http://www.w3.org/1998/Math/MathML" display="inline"><mrow><mn>76.56</mn></mrow></math> to <math xmlns="http://www.w3.org/1998/Math/MathML" display="inline"><mn>76.82</mn><mtext> </mtext><mtext> </mtext><mrow><mi mathvariant="normal">μ</mi><mi>eV</mi></mrow></math> and <math xmlns="http://www.w3.org/1998/Math/MathML" display="inline"><mrow><mn>79.31</mn></mrow></math> to <math xmlns="http://www.w3.org/1998/Math/MathML" display="inline"><mn>79.53</mn><mtext> </mtext><mtext> </mtext><mrow><mi mathvariant="normal">μ</mi><mi>eV</mi></mrow></math> using a prototype setup for the MAgnetized Disk and Mirror Axion eXperiment (MADMAX). The experimental setup employs a dielectric haloscope consisting of three sapphire disks and a mirror to resonantly enhance the axion-induced microwave signal within the magnetic dipole field provided by the 1.6 T Morpurgo magnet at CERN. Over 14.5 days of data collection, no axion signal was detected. A 95% CL upper limit on the axion-photon coupling strength down to <math xmlns="http://www.w3.org/1998/Math/MathML" display="inline"><mrow><mo stretchy="false">|</mo><msub><mrow><mi>g</mi></mrow><mrow><mi>a</mi><mi>γ</mi></mrow></msub><mo stretchy="false">|</mo><mo>∼</mo><mn>2</mn><mo>×</mo><msup><mrow><mn>10</mn></mrow><mrow><mo>−</mo><mn>11</mn></mrow></msup><mtext> </mtext><mtext> </mtext><msup><mrow><mi>GeV</mi></mrow><mrow><mo>−</mo><mn>1</mn></mrow></msup></mrow></math> is set in the targeted mass ranges, surpassing previous constraints, assuming a local axion dark matter density <math xmlns="http://www.w3.org/1998/Math/MathML" display="inline"><msub><mi>ρ</mi><mi>a</mi></msub></math> of <math xmlns="http://www.w3.org/1998/Math/MathML" display="inline"><mrow><mn>0.3</mn><mtext> </mtext><mtext> </mtext><mi>GeV</mi><mo>/</mo><msup><mrow><mi>cm</mi></mrow><mrow><mn>3</mn></mrow></msup></mrow></math>. This study marks the first axion dark matter search using a dielectric haloscope.</p>

Germany

B. Ary dos Santos Garcia

D. Bergermann

A. Caldwell

France

V. Dabhi

C. Diaconu

J. Diehl

G. Dvali

J. Egge

E. Garutti

S. Heyminck

F. Hubaut

A. Ivanov

J. Jochum

United States

S. Knirck

M. Kramer

D. Kreikemeyer-Lorenzo

C. Krieger

C. Lee

D. Leppla-Weber

X. Li

A. Lindner

B. Majorovits

J.P.A. Maldonado

A. Martini

A. Miyazaki

E. Öz

P. Pralavorio

G. Raffelt

Spain

J. Redondo

A. Ringwald

J. Schaffran

A. Schmidt

F. Steffen

C. Strandhagen

I. Usherov

H. Wang

G. Wieching

First Search for Axion Dark Matter with a MADMAX Prototype

In this paper, we study the periodic orbits, characterized by zoom-whirl behavior, around a Schwarzschild-like black hole (BH) embedded within a Dehnen-type dark matter (DM) halo. We demonstrate how the DM halo modifies the gravitational dynamics of the black hole, influencing the energy and angular momentum of timelike particle geodesics and enhancing their interaction with the BH. We determine the radii of the marginally bound orbits (MBOs) and innermost stable circular orbits (ISCOs), showing that the DM halo increases both. This provides a deeper understanding of how the DM alters the behavior, energy, and angular momentum of timelike particle geodesics. Furthermore, we explore the gravitational waveforms emitted by a timelike particle in periodic orbits around a supermassive black hole (SMBH) within this BH-DM system. Using a semi-analytical approach, we calculate particle trajectories and derive the corresponding waveforms, demonstrating that the DM halo modifies the zoom-whirl orbital behavior, leading to distinct changes in the waveform structure. Our findings suggest that future gravitational wave (GW) observations could constrain the properties of DM halos surrounding BHs, providing new insights into the gravitational wave signatures arising from the interaction between BH gravity and DM.

Uzbekistan

China

Mirzabek Alloqulov

Tursunali Xamidov

Azerbaijan

Sanjar Shaymatov

Bobomurat Ahmedov

Gravitational waveforms from periodic orbits around a Schwarzschild black hole embedded in a Dehnen-type dark matter halo

The Event Horizon Telescope (EHT) imaged black holes M87 $$^*$$ (angular diameter $$\theta _d = 42 \pm 3\,\upmu \text {as},$$ mass $$\sim 6.5 \times 10^9\,M_\odot )$$ and Sgr A $$^*$$ $$(\theta _d = 48.7 \pm 7\,\upmu \text {as},$$ shadow deviation $$\delta \approx -0.08^{+0.09}_{-0.09}$$ (VLTI), $$-0.04^{+0.09}_{-0.10})$$ (Keck). These observations enable tests of gravity in strong regimes. We propose a rotating non-commutative inspired Kiselev black hole (RNKBH), incorporating dark energy $$(\omega )$$ and non-commutative $$(\Theta )$$ parameters, extending Kerr solutions. Our analysis reveals that $$\omega = -2/3$$ allows larger $$\Theta $$ but requires $$a \ge 0.16M$$ to maintain horizons. Shadow calculations show significant deviations from Kerr predictions: for $$\Theta = 0.001-0.005M^2,$$ shadows shrink by 8-15% and distortion increases by 20-35% for rapidly spinning $$(a > 0.5M)$$ black holes. The $$\omega = -2/3$$ exhibits shadow squeezing near the cosmological horizon. We compute shadow observables and compare them with EHT data. For Sgr A $$^*$$ $$(50^\circ $$ inclination), the bounds are $$0.001497 \le \Theta \le 0.002868\,M^2$$ at $$a =0.9146$$ $$(\omega = -2/3)$$ . For M87 $$^*$$ $$(17^\circ )$$ , $$0 \le \Theta \le 0.004993 \,M^2$$ at $$a=0.0.6167$$ $$(\omega = -2/3)$$ . While EHT cannot yet distinguish RNKBH from Kerr BH, our results highlight its viability as an astrophysical candidate.

Fazlay Ahmed

India

Heena Ali

Qiang Wu

Tao Zhu

South Africa

Sushant Ghosh

Shadows of rotating non-commutative Kiselev black holes: constraints from EHT observations of M87* and Sgr A*

In this paper, we investigate a <math altimg='si1.svg'><mo stretchy='false'>(</mo><mn>1</mn><mo linebreak='badbreak' linebreakstyle='after'>+</mo><mn>3</mn><mo stretchy='false'>)</mo></math>-dimensional static Friedmann-Robertson-Walker (FRW) space-time, pierced by a cosmic string. Our analysis begins with a detail study of the geodesic motion of photon rays in this curved background, focusing on the behavior of the associated effective potential. This allows us to understand how the cosmic string and curvature of space-time influence the trajectories of light rays. Moving beyond ray optics, we explore wave optics by solving the covariant Helmholtz equation in this gravitational setting. By transforming the resulting radial equation into a Schr&#246;dinger-like form, we extract an effective potential and derive a frequency-dependent refractive index. This refractive index shows the combined effects of the cosmic string and the curvature parameter, showing their influence on the wave propagation. Furthermore, we extend our study to a <math altimg='si2.svg'><mo stretchy='false'>(</mo><mn>1</mn><mo linebreak='badbreak' linebreakstyle='after'>+</mo><mn>2</mn><mo stretchy='false'>)</mo></math>-dimensional space-time with disclinations, where we analyze the wave optics phenomena. Through the Helmholtz equation in this lower-dimensional case, we determine the refractive index and discuss how it is affected by the geometric parameters of this lower-dimensional space-time. Through both geometric and wave optics approaches, our work provides a comprehensive understanding of how topological defects and curvature impact geometric and physical optics in curved space-time of three- and four-dimensions.

Faizuddin Ahmed

Algeria

Abdelmalek Bouzenada

Ray and wave dynamics in a static FRW spacetime with conical singularity

<p>Atmospheric neutrino oscillations are important to the study of neutrino properties, including the neutrino mass ordering problem. A good capability to identify neutrinos’ flavor and neutrinos against antineutrinos is crucial in such measurements. In this paper, we present a machine-learning-based approach for identifying atmospheric neutrino events in a large homogeneous liquid scintillator detector. This method identifies features of photomultiplier tube waveforms that reflect event topologies and uses them as input to machine learning models. In addition, neutron-capture information is utilized to achieve neutrino vs antineutrino discrimination. Preliminary performances based on Monte Carlo simulations are presented, which demonstrate such a detector’s potential in future measurements of atmospheric neutrinos such as the one planned for the JUNO experiment.</p>

Jiaxi Liu

Fanrui Zeng

Hongyue Duyang

Wanlei Guo

Xinhai He

Teng Li

Zhen Liu

Wuming Luo

Wing Yan Ma

Xiaohan Tan

Liangjian Wen

Zekun Yang

Yongpeng Zhang

Neutrino type identification for atmospheric neutrinos in a large homogeneous liquid scintillation detector

We study a strongly anisotropic self-organized critical system coupled to an isotropic random fluid environment. The former is described by a continuous (coarse-grained) model due to Hwa and Kardar. The latter is modelled by the Navier—Stokes equation with a random stirring force of a rather general form that includes, in particular, the overall shaking of the system and a non-local part with power-law spectrum <math altimg='si1.svg'><mo>&#8764;</mo><msup><mrow><mi>k</mi></mrow><mrow><mn>4</mn><mo linebreak='badbreak' linebreakstyle='after'>&#8722;</mo><mi>d</mi><mo linebreak='badbreak' linebreakstyle='after'>&#8722;</mo><mi>y</mi></mrow></msup></math> that describes, in the limiting case <math altimg='si2.svg'><mi>y</mi><mo stretchy='false'>&#8594;</mo><mn>4</mn></math>, a turbulent fluid. The full problem of the two coupled stochastic equations is represented as a field theoretic model which is shown to be multiplicatively renormalizable and logarithmic at <math altimg='si3.svg'><mi>d</mi><mo linebreak='goodbreak' linebreakstyle='after'>=</mo><mn>4</mn></math>. Due to the interplay between isotropic and anisotropic interactions, the corresponding renormalization group (RG) equations reveal a rich pattern of possible infrared (large scales, long times) regimes of asymptotic behaviour of various Green's functions. The attractors of the RG equations in the five-dimensional space of coupling parameters include a two-dimensional surface of Gaussian (free) fixed points, a single fixed point that corresponds to the plain advection by the turbulent fluid (the Hwa&#8211;Kardar self-interaction is irrelevant) and a one-dimensional curve of fixed points that corresponds to the case where the Hwa&#8211;Kardar nonlinearity and the uniform stirring are simultaneously relevant. The character of attractiveness is determined by the exponent <italic>y</italic> and the dimension of space <italic>d</italic>; the most interesting case <math altimg='si4.svg'><mi>d</mi><mo linebreak='goodbreak' linebreakstyle='after'>=</mo><mn>3</mn></math> and <math altimg='si2.svg'><mi>y</mi><mo stretchy='false'>&#8594;</mo><mn>4</mn></math> is described by the single fixed point. The corresponding critical dimensions of the frequency and the basic fields are found exactly.

Russia

N.V. Antonov

P.I. Kakin

N.M. Lebedev

A.Yu. Luchin

Renormalization group analysis of a continuous model with self-organized criticality: Effects of randomly moving environment

Among the three known types of static solutions proposed within the Hamiltonian constraint approach to effective quantum gravity (EQG), the first two have been extensively investigated, whereas the third type-which preserves general covariance, is free of Cauchy horizons, and was only recently obtained-remains relatively unexplored. This solution can describe a black hole with an event horizon for certain parameter ranges, or a horizonless compact object beyond those ranges. In this paper, we focus on the third type and show that its light rings feature both stable and unstable branches, and that the black hole shadow size grows with the quantum parameter-unlike in the first two types. However, when we account for both the shadow and the lensing ring, the overall behavior closely resembles that of the second type, in which an increasing quantum parameter leads to a larger portion of the lensing ring being occupied by the shadow. This feature can serve as a hallmark of black holes in EQG, offering a potential way to distinguish them from their GR counterparts. Remarkably, the parameter ranges under which the solution remains a black hole are highly consistent with the current observational constraints on black hole shadows, lending strong support to the classification of the third type of compact object in EQG as a black hole endowed with an event horizon.

Wentao Liu

Di Wu

Jieci Wang

Light rings and shadows of static black holes in effective quantum gravity II: A new solution without Cauchy horizons

We study the thermal behavior of quarkonia and fully-heavy tetraquark states associated to the charmonium, bottomonium and bottom-charmonium mass spectra. The starting point is the Schrödinger formalism with a vacuum Cornell-like potential. The spin-spin, spin-orbit and tensor contributions are also considered to describe the structure of the vacuum quarkonia $$Q\bar{Q}$$ spectra ($\textit{Q}$ denoting $\textit{c}$, $\textit{b}$ quarks). The parameters of the model are fixed using the experimental data of the $$Q\bar{Q}$$ states. After that, this formalism is extended to the fully-heavy tetraquark states within the $$1^3 S_1$$ axial diquark– $$1^3 S_1$$ axial antidiquark configuration $$[QQ] [\bar{Q} \bar{Q}]$$ , and their vacuum mass spectra are obtained and compared to the experimental data recently obtained. Our predictions support the interpretation of the $\textit{X}$(6600) (or $\textit{X}$(6552)), $\textit{X}$(6900) and $\textit{X}$(7200) states as the radially-excited $$T_{4c}(n^1S_0)$$ configurations with $$n=2,3,4$$ . In the sequence, we evaluate the mass spectra behavior in a thermal medium, by introducing a modified temperature-dependent Cornell potential. As a consequence, this formalism enables us to get some insight into the dissociation mechanism of $$[QQ] [\bar{Q} \bar{Q}]$$ states caused by a thermal medium, and into the temperature range at which the tetraquark states might be formed. We find that these structures cannot be formed in the thermal medium when the system has a temperature higher than about twice the critical temperature. These findings may be useful to better understand the features of the exotics in heavy-ion collisions.

Brazil

Vinícius Silva

Cássio Pigozzo

Luciano Abreu

Fully-heavy tetraquarks in the vacuum and in a hot environment

The late-time cosmological expansion within a flat Friedmann–Lemaître–Robertson–Walker (FLRW) spacetime is studied using a model characterized by bulk viscous dark matter (bulk viscosity $$\zeta = \zeta _0 \rho _m H^{-1}+\zeta _1 H $$ , $$\zeta _0$$ & $$\zeta _1$$ are constants, and $\textit{H}$, the Hubble parameter) interacting with a decaying vacuum density $$\rho _{\Lambda } = \mathcal {C}_0 + 3\nu H^2$$ , where $$\mathcal {C}_0$$ and $$\nu $$ are constants. The bulk viscous pressure is described by Eckart’s theory. The interaction term is defined as $$ Q=3H\alpha (\rho _m+\rho _\Lambda )$$ , where $$\alpha $$ , the interaction parameter. Analytical solutions for the Hubble parameter and the scale factor have been derived. The validity of the models is evaluated by constraining their free parameters using observational data from $\textit{Cosmic Chronometer}$, the $\textit{Pantheon}$, and a combination of both datasets. The goodness of fit is assessed by minimizing the $$\chi ^2$$ function utilizing the Markov Chain Monte Carlo (MCMC) method. Selection information criteria, namely AIC and BIC, have been obtained to analyze the models’ stability. Additionally, several essential cosmological parameters characterizing the evolution dynamics are estimated and discussed analytically, and compared with the $$\Lambda $$ CDM model. The proposed model suggests a transition from the deceleration to the acceleration phase, indicating thermodynamic equilibrium in the distant future, aligning with the $$\Lambda $$ CDM model. The model shows a slight deviation from $$\Lambda $$ CDM model and effectively reduces the $$H_0$$ tension between local measurements by $\textit{R}$21 and global measurements by Planck 2018. The model is consistent with thermodynamic laws and upholds the second law of thermodynamics. Finally, Phase-space analysis supports the same evolutionary transitional phases.

Tanmay Nandi

Amitava Choudhuri

Bulk viscous matter interacting with decaying vacuum energy density: a model for late-time evolution of the Universe

Searching for dark matter at high-energy colliders and direct detection experiments can effectively cover nearly the entire mass range from the MeV to the TeV scale. In this paper, we focus on four-fermion contact interactions formulated within the framework of Effective Field Theory. Specifically, we present a detailed analysis of mono-lepton production at the LHC. Our results demonstrate that tensor operators exhibit superior sensitivity in the mono-lepton channel, constraining energy scales up to 3 TeV for a nearly massless dark fermion using current LHC data. Moreover, these operators mediate both spin-independent and spin-dependent absorption processes in nuclear targets. A systematic comparison of constraints between direct detection experiments and collider measurements reveals the LHC's distinct advantage in exploring sub-GeV dark matter candidates while maintaining competitive sensitivity at the TeV scale. Notably, direct detection experiments such as Super-Kamiokande and Borexino achieve complementary constraints in the 10-100 MeV mass range through their unique capabilities: utilization of light nuclei targets, large exposure volumes, and distinctive features of the recoil energy spectra.

Kai Ma

Lin-Yun He

Mono-lepton signature of a neutrino-philic dark fermion at hadron colliders