Extracts from the Internet

Searching for axions

Axions were initially proposed for solution to the problem of a strong CP violation (see, e.g., [1]). These hypothetical particles have not yet been discovered, but are being actively searched for. Axions and axionlike particles are one of the probable candidates for dark matter particles. For several years, T.S. Roussy (University of Colorado, USA) and her co-authors have carried out an experiment on measuring the electric dipole moment of 180Hf19F+ ions, which can be contributed by the effects beyond the Standard Model. Although they have not yet been found, the experiment provided a new constraint on axions [2]. The oscillating axion field, which constitutes dark matter, would provoke a shift of Stark sublevels in 180Hf19F+. Because of the absence of such a shift, a constraint on the axion-gluon coupling constant in the axion mass range of 10−22-10−15 eV was found at today’s precision level, this constraint having been reached for the first time for 10−17-10−15 eV. Stochasticity of axion field distribution was also taken into account for the first time. Another group of researchers, A. Basu (Karl Schwarzschild Observatory and Bielefeld University, Germany) and their co-authors devised a new prospective axion searching method from observations of strong gravitational quasar lensing [3]. Waves with different polarizationscan propagate at different velocities because of parity violation in the course of photon – axion field interaction. Observation of several lensed quasar images with time delay could reveal axion field oscillations from the difference in the radiation polarization plane rotation angle. The new method was applied to a quasar at the red shift z=1.019 lensed by a galaxy with z=0.439. New constraints on the axion-photon coupling constant g were obtained in the axion mass range of 3.6 × 10−21-4.6 × 10−18 eV. The new constraints are by 1–2 orders of magnitude stronger than thoseobtained previously. [1] Kazakov D I Phys. Usp. 62 364 (2019); UFN 189 387 (2019) [2] Roussy T S et al. Phys. Rev. Lett. 126 171301 (2021) [3] Basu A et al. Phys. Rev. Lett. 126 191102 (2021)

Landau damping in accelerator beams

The perturbation damping in collisionless plasma caused by a collective particle interaction (Landau damping) was predicted by L.D. Landau and A.A. Vlasov in 1945 and first confirmed experimentally in 1964 [4,5]. Landau damping plays the key role, in particular, in beam stabilization on accelerators, where active stabilization methods are also applied, namely, beam deformation is recorded and the beam is affected in the reverse direction. For design and exploitation of accelerators it is of importance to know the so-called stability diagram (SD) characterizing the beam stability limits. An SD was earlier found using indirect approximate methods. In a test experiment at the Large Hadron Collider, S.A. Antipov (CERN, Switzerland) and his co-authors proposed and demonstrated a new direct SD measurement method [6]. To this end, a regular transverse feedback system was used with opposite polarity to amplify occurring transverse beam deviations. Traced was the low-intensity proton beam behavior for different magnitudes and phases of the action, which made it possible to design an SD and, thus, measure the Landau damping. [4] Kadomtsev B B Sov. Phys. Usp. 11 328 (1968); UFN 95 111 (1968) [5] Rukhadze A A, Silin V P Phys. Usp. 62 691 (2019); UFN 189 739 (2019) [6] Antipov S A et al. Phys. Rev. Lett. 126 164801 (2021)

Thermal conductivity oscillations in α-RuCl3

Quantum spin liquids have quantum spin coherence but have no long-range magnetic ordering. These states attract great attention owing to their unusual properties. Experiments have shown that the quantum spin-liquid state is probably realized in a layered insulator α-RuCl3 in the range of magnetic fields H=7.3-11 T. The indicated interval # is located between the paramagnetic and zig-zag states. P. Czajka (Pakistan University, USA) and his co-authors have performed a new investigation of α-RuCl3 to reveal an unexpected effect of periodic thermal conductivity oscillations with increasing 1/H, and it is only the component H along the layer plane that plays the role [7]. These oscillations resemble Shubnikov-de Haas oscillations in metals, but here, they occur in an insulator and must be excited by another mechanism. The oscillations are strongest in the rage H=7.3–11 T and are suppressed otherwise. Therefore, they can be associated with the state of quantum spin liquid. The authors of the paper suggest that the oscillations can be due to spin Fermi surface quantization. For some topical issues of solid-state physics, see [8–10]. [7] Czajka P arXiv:2102.11410 [cond-mat.str-el] [8] Lider V V Phys. Usp. 63 907 (2020); UFN 190 971 (2020) [9] Kvon Z D et al. Phys. Usp. 63 629 (2020); UFN 190 673 (2020) [10] Dolgopolov V T Phys. Usp. 62 633 (2019); UFN 189 673 (2019)

Quantum entanglement of macroscopic membranes

S. Kotler (National Institute of Science and Technology and University of Colorado, USA) and their co-authors have demonstrated quantum entanglement of two 70-pg aluminum membranes [11]. Quantum states of the membranes have been measured efficiently, which could not be done in previous experiments. The space between the membranes formed a microwave cavity with resonance frequency dependent on the membrane position. In this hybrid system, entanglement occurs in mechanical degrees of freedom and control is realized in electric ones, which makes the requirement of system’s isolation from the environment not so strict. The membranes were cooled to lower vibrational levels with the help of microwave pulses. Then pulses at side frequency bands transferred the membranes into quantum entangled states. And finally, quantum tomography, namely, a quantum-state measurement, was implemented through recording signals reflected from the cavity. The Simon-Duan criterion has shown that the membranes were in quantum entangled state even without noise filtration. Observation of quantum entanglement of macroscopic bodies is of importance for investigation of the fundamental basis of quantum mechanics. For the state-of-the-art of quantum technology, see [12,13]. [11] Kotler S et al. Science 372 622 (2021) [12] Trushechkin A S et al. Phys. Usp. 64 (1) (2021); UFN 191 93 (2021) [13] Arbekov I M, Molotkov S N Phys. Usp. 64 (6) (2021) UFN 191 651 (2021)

Neutron star radius

Measurement of neutron star (NS) radiiis of importance for investigation of the properties of nuclear matter at extreme densities. The X-ray telescope NICER on board ISS is intended for NS observation and testing new pulsar-based space navigation technologies. With the help of NICER, the radius of a comparatively light (≈ 1.4M) NS has already been determined. More massive NSs must have a higher central density, and therefore their study is of great interest. The radius of NS PSR J0740+6620 entering in the binary system with an ordinary star and having a mass of 2.08 ± 0.07M is measured though combination of the new NICER and XMM-Newton telescope data [14]. NS pulses modulate companion-star radiation with a modulation depth depending on NS compactness. This effect suggests that the NS equatorial radius is 13.7+2.6−1.5 km. Making use of the information on other NSs and the LIGO/Virgo data on the absence of observed tidal NS deformation in gravitational wave effects, one can fix the radius of PSR J0740+6620 in the interval of 12.35 ± 0.75 km and specify the nuclear matter equation of state [15]. For NSs, see [16–18]. [14] Miller M C et al., arXiv:2105.06979 [astro-ph.HE] [15] Raaijmakers G et al., arXiv:2105.06981 [astro-ph.HE] [16] Beskin V S Phys. Usp. 61 353 (2018); UFN 188 377 (2018) [17] Shakura N I et al. Phys. Usp. 62 1126 (2019); UFN 189 1202 (2019) [18] Tutukov A V, Cherepashchuk A M Phys. Usp. 63 209 (2020); UFN 190 225 (2020)

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The Extracts from the Internet is a section of Uspekhi Fizicheskih Nauk (Physics Uspekhi) — the monthly rewiew journal of the current state of the most topical problems in physics and in associated fields. The presented News is devoted to the fundamental discoveries of physics and astrophysics.

Permanent editor is Yu.N. Eroshenko.

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