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.

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

The experimental search for CP violation in paramagnetic atomic and molecular systems has made impressive progress in recent years. This has led to strong upper limits on the electron electric dipole moment. The same measurements can also be used to constrain hadronic sources of CP violation through CP-violating interactions between the electrons and the nucleus. We employ heavy-baryon chiral perturbation theory to compute such CP-violating semileptonic electron-nucleus interactions arising from the QCD theta term. We sharpen earlier results by determining the relevant short-distance effects and by an explicit two-loop calculation of meson-photon diagrams. We derive a bound of $$ \left|\overline{\theta}\right| $$ < 1.5·10 at 90% confidence, based on HfF experiments at JILA. A further experimental improvement of one to two orders of magnitude would make paramagnetic molecular electric dipole moment experiments competitive with the neutron and diamagnetic atom program in constraining strong CP violation and higher-dimensional CP-odd quark-gluon operators.

Netherlands

Heleen Mulder

Rob Timmermans

Jordy Vries

Probing the QCD $$ \overline{\theta} $$ term with paramagnetic molecules

We introduce building blocks for the cluster hadronization model in light of a new structure, focusing on cluster fission and cluster decay. We propose theoretically motivated matrix elements for cluster fission and decay as building blocks and study some first phenomenological implications at different energies. In particular we develop a set of observables which can be used to dissect the hadronization history and have constraining power on the individual building blocks. Our analysis will be completed by including colour reconnection in a follow-up work.

Stefan Gieseke

Stefan Kiebacher

Austria

Simon Plätzer

Jan Priedigkeit

Phenomenological constraints of the building blocks of the cluster hadronization model

The photon sphere defines the unstable circular orbit of photons in a black hole spacetime. Photons emitted by a source located inside the photon sphere can be gravitationally lensed by the black hole and have time delays when reaching the observer. These delays may lead to light echoes produced in the light curve if an accretion event in the vicinity of the horizon can be observed. In this work, we present fully analytical formulas with high accuracy to describe the change of the azimuthal angle and the travel time of those photons. By employing the analytical approaches, we find that the time delay between photons emitted from the interior of the photon sphere has a typical time scale of $$2(\pi - \phi _\textrm{S}) u_\textrm{m}$$ with $$\phi _\textrm{S}$$ and $$u_\textrm{m}$$ being respectively the azimuthal angle of the source and the impact parameter evaluated at the photon sphere, which can provide some clues on the future search for gravitational lensing signatures in the accretion inflow event.

China

Yuan-Xing Gao

Analytical description for light propagation with the source inside the black hole photon sphere

The symmetry can be broken at high temperature and then restored at low temperature, which is the so-called <italic>high temperature symmetry breaking</italic>. It often appears in some theories such as the high scale electroweak baryogenesis mechanism. In this paper, we probe the high temperature <math altimg='si1.svg'><msub><mrow><mi mathvariant='double-struck'>Z</mi></mrow><mrow><mn>2</mn></mrow></msub></math> symmetry breaking with gravitational waves (GWs) from the melting domain walls. We first introduce a scalar with <math altimg='si1.svg'><msub><mrow><mi mathvariant='double-struck'>Z</mi></mrow><mrow><mn>2</mn></mrow></msub></math> symmetry and a few singlet fermions that interact with scalar through a five-dimension operator. This leads to that the scalar potential has a non-zero minimum at high temperature. At the early stage, the scalar is pinned at symmetric phase due to the large Hubble fraction. When the scalar field's thermal mass becomes comparable to the Hubble parameter, it can quickly roll down to the minimum of potential. Then the <math altimg='si1.svg'><msub><mrow><mi mathvariant='double-struck'>Z</mi></mrow><mrow><mn>2</mn></mrow></msub></math> symmetry is spontaneously broken and the domain walls will form. With the decrease of temperature, <math altimg='si1.svg'><msub><mrow><mi mathvariant='double-struck'>Z</mi></mrow><mrow><mn>2</mn></mrow></msub></math> symmetry will be restored. We find that if domain walls are formed at <math altimg='si2.svg'><mi mathvariant='script'>O</mi><mo stretchy='false'>(</mo><msup><mrow><mn>10</mn></mrow><mrow><mn>9</mn></mrow></msup><mo stretchy='false'>)</mo><mspace width='0.25em' /><mtext>GeV</mtext></math>, the GW produced by the melting domain walls is expected to be observed by BBO, CE and ET. In addition, we also discuss the relationships between this scenario and NANOGrav signal.

Xiu-Fei Li

Probing the high temperature symmetry breaking with gravitational waves from domain walls

We examine the sterile neutrino dark matter production in the primordial plasma with lepton asymmetry unequally distributed over different neutrino flavors. We argue that with the specific flavor fractions, one can mitigate limits from the Big Bang Nucleosynthesis on the sterile-active neutrino mixing angle and sterile neutrino mass. It happens due to cancellation of the neutrino flavor asymmetries in active neutrino oscillations, which is more efficient in the case of inverse hierarchy of active neutrino masses and does not depend on the value of CP-phase. This finding opens a window of lower sterile-active mixing angles. Likewise, we show that, with lepton asymmetry disappearing from the plasma at certain intermediate stages of the sterile neutrino production, the spectrum of produced neutrinos becomes much colder, which weakens the limits on the model parameter space from observations of cosmic small-scale structures (Ly- <italic>&#945;</italic> forest, galaxy counts, etc.). This finding reopens the region of lighter sterile neutrinos. The new region may be explored with the next generation of X-ray telescopes searching for the inherent peak signature provided by the dark matter sterile neutrino radiative decays in the Galaxy.

Russia

Dmitry Gorbunov

Dmitry Kalashnikov

George Krugan

Playing with lepton asymmetry at the resonant production of sterile neutrino dark matter

The Event Horizon Telescope's 2024 observations report a shift in the position angle of the brightness asymmetry in M87*, revealing time variability in the black hole's image. In this analysis, we investigate the time-dependent of a Vaidya black hole. By introducing a mass function that increases linearly with time, along with a conformal transformation, we derive the conformal Vaidya metric and define a new time coordinate <math altimg='si1.svg'><msub><mrow><mi>t</mi></mrow><mrow><mi>c</mi></mrow></msub></math>. Using the semi-analytical approach, we analyze the ray trajectories and radiation flux of the Vaidya black hole in the background of a thin accretion disk. We discuss how the observed flux in the Vaidya spacetime evolves as a function of the new time coordinate <math altimg='si1.svg'><msub><mrow><mi>t</mi></mrow><mrow><mi>c</mi></mrow></msub></math>. The results show that the facula on the observable plane undergoes radial displacement as <math altimg='si1.svg'><msub><mrow><mi>t</mi></mrow><mrow><mi>c</mi></mrow></msub></math> increases, revealing the time-dependent evolution of black hole images.

Yu Liang

Sen Guo

Brazil

Kai Lin

Yu-Hao Cui

Yu-Xiang Huang

Tao Yu

Image of the time-dependent black hole

In analogue gravity studies, the goal is to replicate black hole phenomena, such as Hawking radiation, within controlled laboratory settings. In the realm of condensed matter systems, this may happen in 2D tilted Dirac cone materials based on honeycomb lattices. In particular, we compute the entropy of this system, and find it has the same form as black hole Bekenstein-Hawking entropy, if an analogue horizon forms. Hence, these systems can be potential analogues of quantum black holes. We show that this entropy is primarily concentrated in the region where the tilt parameter is close to one, which corresponds to the location of the analogue black hole horizon. Additionally, when nonlinear effects are taken into account, the entropy is peaked in a small pocket of the Fermi sea that forms behind the analogue event horizon, which we call the $\textit{Fermi puddle}$. We further refer to this new type of analogue black hole as a $\textit{smart hole}$, since, in contrast to dumb holes, it can simulate both the correct temperature $\textit{and}$ entropy of general relativistic black holes. These results provide an opportunity to illuminate various quantum facets of black hole physics in a laboratory setting.

Canada

Jiayue Yang

Niayesh Afshordi

Mahdi Torabian

Seyed Jafari

India

G. Baskaran

Smart holes: analogue black holes with the right temperature and entropy

We investigate the volume and lifetime of the high-baryon-density matter created in heavy-ion collisions and estimate the optimal collision-energy range to realize the high-baryon-density region over a large space-time volume. We simulate central collisions of gold ions for the center-of-mass energy per nucleon pair <math xmlns="http://www.w3.org/1998/Math/MathML"><mrow><msqrt><msub><mi>s</mi><mrow><mi>N</mi><mi>N</mi></mrow></msub></msqrt><mo>=</mo><mn>2.4</mn><mo>−</mo><mn>19.6</mn><mspace width="0.28em"></mspace><mi>GeV</mi></mrow></math> with a microscopic transport model JAM. We discover that the optimal range is around <math xmlns="http://www.w3.org/1998/Math/MathML"><mrow><msqrt><msub><mi>s</mi><mrow><mi>N</mi><mi>N</mi></mrow></msub></msqrt><mo>=</mo><mn>3</mn><mo>−</mo><mn>5</mn><mspace width="0.28em"></mspace><mi>GeV</mi></mrow></math>, where a baryon density exceeding three times the normal nuclear density is realized with a substantially large space-time volume. Higher and lower energies are disfavored due to short lifetime and low density, respectively. We also point out that event-by-event fluctuations of the space-time density profile are large, indicating the importance of the event selection in the experimental analysis.

Japan

Hidetoshi Taya

Asanosuke Jinno

Masakiyo Kitazawa

Yasushi Nara

Optimal collision-energy range for realizing macroscopic high-baryon-density matter

The pseudorapidity density distributions of charged particles and the transverse-momentum spectra of identified particles in proton-proton (<math xmlns="http://www.w3.org/1998/Math/MathML"><mrow><mi>p</mi><mi>p</mi></mrow></math>) collisions at the center-of-mass energies ranging from <math xmlns="http://www.w3.org/1998/Math/MathML"><mrow><msqrt><mi>s</mi></msqrt><mo>=</mo><mn>200</mn></mrow></math> GeV to 13 TeV have been systematically studied using the newly released parton and cascade model paciae 4.0 based on pythia 8.3. The available experimental data are well reproduced across all analyzed aspects. This theoretical method can be easily extended to anywhere the experimental data for <math xmlns="http://www.w3.org/1998/Math/MathML"><mrow><mi>p</mi><mi>p</mi></mrow></math> collisions are currently unavailable. Furthermore, since <math xmlns="http://www.w3.org/1998/Math/MathML"><mrow><mi>p</mi><mi>p</mi></mrow></math> collisions serve as the baseline for heavy-ion collisions, our results can provide a valuable resource for both experimentalists and theorists.

Zhen Xie

An-Ke Lei

Hua Zheng

Wenchao Zhang

Dai-Mei Zhou

Zhi-Lei She

Yu-Liang Yan

Ben-Hao Sa

Pseudorapidity density distributions of charged particles and transverse-momentum spectra of identified particles in <math xmlns="http://www.w3.org/1998/Math/MathML"><mrow><mi>p</mi><mi>p</mi></mrow></math> collisions in the PACIAE 4.0 model