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| Issue 11, 2024 |
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Extracts from the Internet | ||
Hadronic contribution to the muon anomalous magnetic moment1 July 2024The results of the last measurements of an anomalous muon magnetic moment aμ=(gμ-2)/2 differ from the theoretical calculations by around 5 σ. The main uncertainty is due to the hadronic contribution – the hadronic polarization of vacuum [1]. The hadronic contribution is measured by the effect of pion production in electron-positron collisions e+e− → π+π−, but the data of different experiments differ considerably. The new measurements of the cross section of the process e+e− → π+π− were performed with the detector CMD-3 at the electron-positron collider VEPP-2000 at G I Budker Institute of Nuclear Physics SD RAS (Novosibirsk) with the center-of-mass energy of 0.32-2.0 GeV [2]. Thanks to the unique circular optics of the beam, the experiment achieves luminosities in the beam at the level of the maximum world values. CMD-3 includes a drift chamber, a superconducting solenoid, and calorimeters. The results of recording 209 events are presented in terms of a pion form factor containing a hadronic contribution to aμ. The obtained # value agrees with the calculations within the Standard Model at the level of 0.9 σ. The reason for the discrepancy with other measurements, including those at the CMD-2 detector, the predecessor of SMD-3, is not yet clear. [1] Logashenko I B, Eidel’man S I Phys. Usp. 61 480 (2018); UFN 188 540 (2018) [2] Ignatov F V et al. Phys. Rev. Lett. 132 231903 (2024) The phonon Stark effect1 July 2024The usual Stark effect discovered in hydrogen atoms in 1913 consists in the spectral line shift or splitting under the influence of an external electric field. In solid state physics, an analog of the Stark effect was only observed earlier for excitons (bound systems of electrons and holes). Z Huang (Institute of Physics, Chinese Academy of Sciences) and their co-authors were the first to discover the Stark effect for phonons – quasiparticles corresponding to acoustic oscillations of the crystal lattice of a solid body [3]. The two-layer compound MoS2 in 2H phase lay between layers of a hexagonal boron nitride h-BN, and multilayer graphene electrodes got connected with the sample. Photoluminescence as a function of the electric field value was measured. As a result, a giant linear Stark effect for phonons was found, in which the frequency shift reached ≈ 1 THz. The authors’ theoretical calculations explain the giant Stark effect by the strong coupling between the phonons and interlayer excitons. The Stark effect for phonons has broad prospects for practical applications, for instance, for ultrafast switching of magnetic and other properties of substances and for creation of phonon lasers. [3] Huang Z et al. Nature Communications 15 4586 (2024) Registration of Earth’s rotation with quantum-entangled photons1 July 2024Interferometers that use the property of quantum entanglement of particles, are of great interest for fundamental research, for they can give ahigh phase shift resolution. R Silvestri (University of Vienna, Austria) and their co-authors demonstrated a new quantum photon Sagnac interferometer, which can be used to record even a diurnal Earth’s rotation [4]. The interferometer included a 2-km optical fiber on an aluminum 1.5-m frame. The effective interferometer area was 700 m2. Entangled photons in N00N states, obtained by the mechanism of parametric down conversion, propagated in the optical fiber in different directions. For N=2, the sensitivity to rotation of 5 μrad s−1, the highest for optical quantum interferometers, was achieved, which surpasses the result of previous Sagnac quantum interferometers by three orders of magnitude. A further improvement of this methodology may result in achieving the sensitivity needed to record general-relativistic and, perhaps, quantum-gravitational effects. [4] Silvestri R et al. Science Advances 10 eado0215 (2024) New observations with J Webb telescope. 1. Galaxies at z ≈ 141 July 2024Three galaxies – candidates at redshifts z>14 were observed earlier with the J Webb space telescope (JWST), but their z were only estimated photometrically. New JWST observations using the NIRSpec spectrograph confirmed spectroscopically the redshifts z = 14.32+0.08−0.20 and z=13.90 ± 0.17 for two out of the three above-mentioned galaxies [5]. Although no lines are seen in their spectra, a clear Lyman-α-break of the spectrum exists in the UV continuum. The galactic radii are 260 and 160 pc, and the stellar mass of the first of them is estimated to be about 1 % of the stellar mass of our Galaxy. To determine z of the third galaxy is not yet possible because of weakness of its radiation. The redshift z ≈ 14 corresponds to the Universe age of only 300 mln years. According to the current theories, the number of galaxies in that epoch must have been an order of magnitude smaller than it is observed, and this divergency has not yet been reliably explained. [5] Carniani S et al., arXiv:2405.18485 [astro-ph.GA] 2. An excess of spiral galaxies at z = 0.5-41 July 2024Another JWST observation has revealed an unexpectedly large number of spiral galaxies at redshifts of 0.5 ≤ z ≤ 4, approximately twice as large as had been observed by Hubble space telescope [6]. 216 out of 873 galaxies observed by JWST were attributed by visual method to spiral galaxies. To estimate the efficiency of revealing spirals, the catalogues of modern spiral galaxies were modified to become a model set of galaxies in the early Universe, and the galaxies were counted. With allowance for the thus found efficiency of finding spirals it was obtained that at all studied z the fraction of spiral galaxies makes up ≈ 40 % and at z ≈ 3 they are at least ≈ 20 %. The observational data testify in favor of the evolutionary picture of galaxy formation, in which disc galaxies are formed at z > 4-5, and up to z ≈ 3, their discs become dynamically cold and thin. [6] Kuhn V et al. Astrophys. J. Lett. 968 L15 (2024) 3. A rapidly growing black hole1 July 2024A unique object LID-568 at z = 3.965, which is a black hole (BH) of mass 7.2 × 106 M☉, was also observed with JWST [7]. This active galactic nucleus, strongly shadowed by dust, had been discovered before in X-ray Chandra observations, but no star galaxy was seen in the optical range around LID-568. The gas outflow from a BH in the IR range was discovered using JWST and the IR spectrum was measured. The characteristics of emission testify to the fact that a BH accretes gas at a rate exceeding the Eddington accretion limit by two orders of magnitude. That is, LID-568 is an extremely rapidly accreting and growing black hole. The star formation was probably suppressed by a backreaction of radiation from accretion. The black hole could have accumulated most of its mass in the super-Eddington accretion mode within # years, and so the observation of the object LID-568 may be a clue to the emergence and rapid growth of supermassive BHs providing similar objects did exist in earlier epochs. [7] Suh H et al., arXiv:2405.05333 [astro-ph.GA] |
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. It is compiled from a multitude of Internet sources. | |
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