Extracts from the Internet


Test of the equivalence principle

GRAVITY collaboration carried out a new test of the local position invariance (LPI) principle through observation of stars rotating around a supermassive black hole near the Galactic center. Being a part of the Einstein equivalence principle, this principle states that local non-gravitational measurements are independent of the space-time point at which they are performed. LPI violation would mean the effect of the gravitational potential on the fundamental physical constants. The VLT data on the motion of star S2 coming very close to the black hole were used. The star orbit was reconstructed to a high accuracy and the gravitational potential variations along the orbit were found. The gravitational frequency shifts in hydrogen and helium absorption lines were compared. The parameter characterizing a possible LPI violation is limited by the value (2.4 ± 5.1) × 10−2, which is compliant with zero value. Although in observations in the solar system and for stars – white dwarfs this parameter is limited stronger, the described work investigated the region of record large gravitational potential differences ΔΦ/c2=3.2 × 10−4. This result confirms once again the equivalence principle which is one of the bases of General Relativity. Source: arXiv:1902.04193 [astro-ph.GA]

Superscattering

The light scattering cross section by a system in a single channel is limited from above by a fundamental limit associated with the wavelength. The superscattering phenomenon predicted in the theoretical paper by Z. Ruan and S. Fan in 2010, when the cross section may exceed this limit, is based on the presence of many scattering channels contributing to the cross section. Superscattering could not be observed earlier because it was difficult to design a low-loss superscattering system. Superscattering in the microwave range was demonstrated for the first time in the experiment guided by H. Chen (Zhejiang University, China). Metasurfaces in the form of a periodic array of copper rings of subwavelength scale were created on three concentric cylinders. Electromagnetic TE type modes were localized on them. Different scattering channels were due to the excitation of electron oscillations with higher moments (quadrupole, octupole) at one and the same resonance frequency. The recording of radiation showed the existence of superscattering with cross section four times exceeding the single-channel limit. Superscattering can find application in various telecommunication devices and sensors. Superscattering is expected to be attainable in future in other wavelength ranges, too. Source: Phys. Rev. Lett. 122 201801 (2019)

Phonon spectroscopy

The creation of high-stable monochromatic electron beams paved the way for investigation of electron scattering by phonons (quanta of acoustic oscillations) in the THz range. The phonon spectroscopy method may have important applications in examining the structure of different substances. F.S. Hage (SuperSTEM laboratory, United Kingdom) with colleagues used phonon spectroscopy to scan a thin flake of a hexagonal boron nitride with spatial resolution higher by an order of magnitude than that attained in previous experiments. An electron transmission microscope registered phonon peaks due to electron-phonon inelastic scattering in the electron spectrum. The obtained images clearly show the periodic space structure of a crystal with resolution close to the atomic scale. Source: Phys. Rev. Lett. 122 016103 (2019)

Entropy growth in mesoscopic quantum systems

In recent years, the thermodynamic properties of systems have been actively examined at a quantum level, in particular, the entropic properties of systems and the fluctuation theorems have been studied. M. Brunelli (Cavendish Laboratory, University of Cambridge, United Kingdom) with colleagues examined two mesoscopic systems that consisted of a rather large number of atoms and were connected with heat reservoirs, and at the same time had quantum properties. In the former case, oscillations of a mechanical oscillator coupled to an electromagnetic resonator were investigated. The oscillations were excited by laser pulses. The radiation spectrum could be used to characterize the processes in a given optomechanical system and to calculate the entropy flows. The Bose-Einstein condensate of 105 rubidium atoms placed in an electromagnetic resonator was analyzed in the latter case. The irreversible entropy production under quantum fluctuations in the systems was equal to the entropy outflow, which maintained the steady state of the systems. Such experiments are important for clarification of the change from quantum to classical systems and may appear to help in construction of micromechanical setups. Source: Phys. Rev. Lett. 121 160604 (2018)

A second source of repeating fast radio bursts

Although already more than 60 fast radio bursts (bursts of cosmic radio emission of millisecond duration with a large dispersion measure) have been registered by now, only one source of recurrent bursts FRB 121102 has only been known. A second source of recurrent bursts FRB 180814.J0422+73 was discovered using the telescope CHIME with the field of vision of 250 square degrees. Six bursts with similar dispersion measures wereobserved from this source. Judging by the dispersion measure, the new source is located at a distance below 500 Mpc. No galaxies that might be candidates for the role of ghost galaxy were revealed in the source localization region. The bursts from the second source are very similar to those from FRB 121102, including multiple peaks and frequency downdrifts. Type II solar flares show an analogous drift, which may imply a similar generation mechanism, although the mechanism of fast radio burst formation has not yet been reliably established. The observation of the second source of recurrent bursts suggests a fairly large population of recurrent sources. For fast radio bursts see the review by S.B. Popov, K.A. Postnov, and M.S. Pshirkov in Physics-Uspekhi 61 965 (2018). Source: Nature 566 235 (2019)

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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.

It is compiled from a multitude of Internet sources.

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