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| Issue 4, 2024 |
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Extracts from the Internet | ||
A search for relic neutrinos in KATRIN experiment1 August 2022Our Universe is filled with neutrino ν gas that remained from early cosmological epochs. It has been impossible to register these relic ν because of their low energy and concentration. Nevertheless, a search for new detection methods and a design of next-generation neutrino telescopes to register these neutrinos are under way. The currently available detectors would be able to register relic ν, if near our Galaxy their density and their number increased for a not yet clear reason by many orders of magnitude compared to the average cosmological concentration. Such an increase, although no more than η = 1.2-20 times, must actually take place due to gravitation. The new search for relic ν was undertaken using the KATRIN detector aimed mainly at measuring the ν mass [1]. The KATRIN experiment, with a participation of Russian researchers from the Institute for Nuclear Research, is a larger-scale version of the “Troitsk nu-mass” experiment, which was performed under the guidance of academician V.M. Lobashev [2]. In KATRIN, the spectrum of electrons from the beta-decay of tritium nuclei 3H → 3H++e-+anti-&nue is measured using silicon detector and electrostatic filtration and the ν mass is determined from the spectrum specific features near the maximum energy dependent on the decay kinematics [3]. By the present time, the constraint mν < 0.8 eV has been obtained. Relic ν must with some probability be captured by tritium nuclei, excite them, and thus affect the beta-decay spectrum. In the 2019 KATRIN observations, such an effect was not revealed with the currently available precision, suggesting the conclusion that η < 9.7×1010. This constraint is several times better than those obtained earlier in Los-Alamos and Troitsk experiments. [1] Aker M et al. Phys. Rev. Lett. 129 011806 (2022) [2] Kravchuk L V Phys. Usp. 64 1186 (2021); UFN 191 1249 (2021) [3] Simkovic F Phys. Usp. 64 1238 (2021); UFN 191 1307 (2021) Relativistic particles in Bohm interpretation of quantum mechanics1 August 2022In the nonlocal Bohm interpretation of quantum mechanics (in the de Broglie – Bohm theory), the concepts of a pilot wave and real particle trajectories are introduced [4]. The predictions of probabilistic Copenhagen and deterministic Bohm interpretations are consistent for nonrelativistic particles. However, the Bohm interpretation could not earlier be extended to the relativistic case. A conclusion was drawn of impossibility to introduce in that case the concept of photon as a particle. J. Foo (University of Queensland, Australia) and his co-authors developed a new approach considering relativistic particles with the help of weak quantum measurements [5]. The authors managed to construct a Bohm velocity field having a relativistic form of dispersion and the velocity addition rule. It is also of importance that the developed theory has a usual nonrelativistic limit for low particle velocities. [4] Belinsky A V Phys. Usp. 62 1268 (2019); UFN 189 1352 (2019) [5] Foo J et al. Nature Communications 13 4002 (2022) Rotation of deuterium molecules in helium nanodroplets1 August 2022J. Qiang (East China Normal University) and their co-authors investigated rotation of D2 molecules inside superfluid helium nanodroplets [6]. Nanodroplets consisting of ≈2000 4He atoms were formed through helium ejection from a nozzle and were doped with D2 molecules. Rotational degrees of freedom of D2 molecules were excited by laser pulses, and after some time they were ionized and dissociated. The momentum distribution of the produced HeD+ ions was measured at the output. The obtained spectrum has shown that D2 were in superposition of rotational quantum states. The D2 molecules made over 500 revolutions inside nanodroplets. That is, the lifetime of a rotational level with J=2 exceeds 100 ps – almost like it is for free molecules in a gaseous medium. Thus, a rotating molecule experiences almost no resistance similarly to macroscopic bodies in a superfluid liquid. [6] Qiang J et al. Phys. Rev. Lett. 128 243201 (2022) Vortices in an electron liquid1 August 2022In some systems, electrons can interact with one another stronger than with the crystal lattice and behave as a viscous liquid. However, it is only laminar motion of electron liquid (in graphene and WTe2) that was earlier directly observed. A. Aharon-Steinberg (Weizmann Institute, Israel) and their co-authors were the first to directly observe turbulent vortices in a hydrodynamic electron flow [7]. The research tool was a superconducting contact (SQID) assembled on a needle at a distance of 50 nm from the examined sample surface. This device measured the magnetic field generated by an electron flow. Vortices were observed in an ultrapure Weyl semimetal WTe2 in the form of a current-conducting strip between two semicircles. A whirl-like electron motion occurred for a small isthmus size. The pulse diffusion length measured by the vortex stability diagram turned out to be 30 times smaller than given theoretically. [7] Aharon-Steinberg A et al. Nature 607 74 (2022) First observations with the James Webb Space Telescope1 August 2022The James Webb Space Telescope working in the IR range was launched on December 25, 2021 and was located at the Lagrange point L2 at a distance of 1.5 mln km from the Earth. The telescope has a segmented mirror 6.5 m in diameter, a shield, and a low detector temperature of 7 K (a low intrinsic noise). The James Webb Space Telescope excels all IR telescopes in the congenital combination of light sensitivity and resolution. Among its scientific tasks is investigation of exoplanets in our Galaxy and early galaxies in the late epoch of “Dark Ages”. The optical radiation of these galaxies is shifted towards the IR range owing to the cosmological redshift. The first full-value (not test) scientific data were obtained on July 12, 2022 after calibration and tuning of the telescope [8]. Images of the galaxies that had experienced gravitational lensing on massive galactic clusters were obtained. Among them is the galaxy with low metallicity and a small dust content, which was observed only 286 mln years after the Big Bang (z ≈ 14.3). An unexpected result was the fact that at redshifts z = 3-6, disc galaxies made up half of all the galaxies [9]. This is larger by an order of magnitude than follows from the previous estimates and may indicate that a coalescence of galaxies played a smaller role in their evolution than it was considered before. An image of the compact group of interacting galaxies – the Stephan’s Quintet was obtained. A photo of the Carina Nebula with young stars was taken. Of interest is also the image of the planetary nebula 0.5 light years in diameter and consisting of several shells. The spectrum of the star with the exoplanet WASP-96 b was measured. Its atmosphere contains water gas and clouds. Further observations with the James Webb Telescope may give valuable information on the Universe evolution and even change some of the conventional views. [8] https://webb.nasa.gov/; arXiv:2207.13067 [astro-ph.IM] [9] Ferreira L et al. arXiv:2207.09428 [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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