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| Issue 11, 2024 |
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Extracts from the Internet | ||
Proton polarizability1 January 2023One of the enigmas in elementary particle physics is the problem of proton electric polarizability αE determined by the complicated quark-gluon interaction. According to theoretical calculations, αE must decrease monotonically with increasing transferred momentum squared. In measurements, however, a local maximum was discovered near Q2=0.33 GeV2, and the existence of this anomaly could have been neither confirmed nor refuted for two decades. In the new independent experiment [1], carried out at T. Jefferson National Laboratory (USA), the maximum is revealed with a still higher fidelity than before. The measurement accuracy was increased by the study of excited intermediate states of the proton, measurement of the azimuthal asymmetry of scattering, and investigation of ep → epπ0 reactions simultaneously with ep → epγ. An electron beam with an energy of 4.56 GeV met liquid hydrogen, the ep → epγ reaction products were registered, and the cross section of virtual Compton scattering containing information on polarizability was measured. The found position of the local maximum of αE coincides with that obtained in the previous measurements, but the maximum turned out to be a little lower. The characteristic radius of proton electric polarizability exceeds greatly the charge radius [2]. Thus, the presence of anomaly in αE has been confirmed, although the available theories fail to present an explanation. The above-mentioned problem is planned to be solved in the near future through new calculations using the “lattice QCD” method at high computational capacities and in new experiments. [1] Li R et al. Nature 611 265 (2022) [2] Khabarova K Yu, Kolachevsky N N Phys. Usp. 64 1038 (2021); UFN 191 1095 (2021) The mechanism of superconductivity in Bi2Sr2CaCu2O8+x1 January 2023In 1934, H. Kramers predicted the possibility of so-called superexchange interaction of electrons and in 1950, F. Anderson improved this model. It was hypothesized that this mechanism can be responsible for electron pairing in some superconductors (cuprates), where superexchange is due to quantum tunneling (virtual jumps) of electrons between copper atoms in neighboring atomic layers through intermediate oxygen atoms. In particular, this can occur in Bi2Sr2CaCu2O8+x, the compound that becomes a high-temperature hole-doped superconductor. Using a modified superconducting-needle tunnel microscope, S.M. O’Mahony (National University of Ireland in Cork) and their co-authors studied the relation between the charge exchange energy (the value of the energy barrier) and the electron pair density in hole-doped i2Sr2CaCu2O8+x [3]. The obtained dependences suggest that the superexchange interaction is the cause of electron paring in Bi2Sr2CaCu2O8+x. [3] O’Mahony, S M et al. PNAS 119 e2207449119 (2022) Light amplification in a topological waveguide1 January 2023Topological photon devices based on the properties of radiation edge modes can find an important application, including a topological quantum generation of light, topological lasers, and photon routing. B.-U. Sohn (Singapore University of Technology and Design) and their co-authors worked out and demonstrated experimentally a new device, namely, a topological nonlinear parametric amplifier [4]. Its work is described by a topological Su – Schrieffer – Heeger model. The device consists of 199 parallel film waveguides with a total width of 0.6 mm, of which 9 play the role of domain wall localizing edge modes of transmitted radiation. A parametric amplification of a signal (up to 12.8 dB) propagating together with the pumping radiation is due to nonlinearity of the silicon nitride enriched in silicon of which the waveguides are fabricated. This waveguide maintains the data transmission rate of 54 Gbit$/$s and can realize a nonlinear wavelength conversion. [4] Sohn B-U et al. Nature Communications 13 7218 (2022) Laboratory modeling of earthquakes1 January 2023The problem of earthquake prognosis is rather topical, but the earthquake shock mechanisms are largely unclear [5-7]. Along with full-scale observations and mathematical simulations, important is laboratory modeling. S.B.L. Cebry (Cornell University, USA) and her co-authors investigated quartz powder under pressure between immobile and moving polymer blocks serving a model of tectonic plates [8]. In the powder, a creeping front was propagating, from time to time inducing abrupt skipping (earthquakes) transforming to complex successions of aftershocks with a great role of the prehistory of these events. The obtained results may possibly provide insight into some processes proceeding in real earthquakes. Solution of the complicated problem of predicting earthquakes may require allowance for a whole complex of factors, such as electromagnetic perturbations in atmosphere, aerosol and radon ejections, etc. [5] Buchachenko A L Phys. Usp. 57 92 (2014); UFN 184 101 (2014) [6] Guglielmi A V Phys. Usp. 60 319 (2017); UFN 187 343 (2017) [7] Stakhovsky I R Phys. Usp. 60 472 (2017); UFN 187 505 (2017) [8] Cebry S B L et al. Nature Communications 13 6839 (2022) A local cosmological expansion1 January 2023Although gravitationally bound systems, in particular, galaxies and binary stars do not expand together with the surrounding Universe, the cosmological effects can still affect their inner dynamics at a very low level. This effect is due to the boundary conditions in the region of matching of the expanding cosmological reference frame with the local rigid reference frame [9] and also to dark energy gravitation. In observation of the motion of the binary pulsars PSR B1534+12 and PSR B1913+16 at 2.5 σ, corrections were revealed before that may correspond to the effect of local cosmological expansion. K. Agatsuma (University of Birmingham, Great Britain) discovered its signatures for two more systems [10]. In the pair of a pulsar and the white dwarf PSR J1012-5307, the emission of gravitational waves leading to orbit compression is compensated by the effect of local cosmological expansion, and therefore the orbital motion almost exactly obeys the Keplerian law. The second system is the binary pulsar PSR J1906+0746. As a result, the total statistical significance increased to 3.6 σ, although the level of 5 σ has not yet been attained. [9] Cooperstock F I, Faraoni V, Vollick D N, ``The Influence of the Cosmological Expansion on Local Systems'', Astrophys. J. 503 61 (1998) [10] Agatsuma K Physics of the Dark Universe 38 101134 (2022) |
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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