 |
RSS feeds |
|
|||||
| Issue 9, 2026 |
|
||||||
|
|
|
||||||
Extracts from the Internet | ||
Investigation of the gluon density in photonuclear reactions1 September 2026Deep inelastic scattering experiments have shown that the gluon density inside atomic nucleus nucleons is lower than that of free nucleons. Saturation and shadowing models have been proposed to explain this effect. In the case of saturation, the growth of the gluon number is restrained by recombination. The process of incoherent photonuclear production of J/ψ mesons is highly sensitive to local fluctuations in the gluon density. However, experiments with J/ψ have not yet been able to provide decisive arguments in favor of one or another model. New studies of J/ψ photoproduction in collisions of lead nuclei with a center-of-mass energy of 5 TeV have been carried out in the ALICE experiment at the Large Hadron Collider, [1]. During ultraperipheral flybys, the electric field of the nucleus can be represented as a flux of quasi-real photons causing the production of J/ψ. It was found with certainty of 3 σ that in the region of large transferred momenta the increase in the J/ψ photoproduction cross section ceases. The shadowing model is inconsistent with these data, whereas the saturation model qualitatively reproduces the observed dependence. Thus, the obtained results support the effect of gluon saturation in heavy nuclei. [1] Acharya S et al. Phys. Rev. Lett. 137 052301 (2026) Nonsphericity of vacuum decay near a black hole (BH)1 September 2026A new interesting effect [2] was discovered in the theoretical work of researchers from the Institute for Nuclear Research of the Russian Academy of Sciences (INR RAS), the Moscow Institute of Physics and Technology (MIPT) and the Institute of Theoretical and Mathematical Physics (ITMP) of M V Lomonosov Moscow State University, and the Physical Department of MSU. It is a known fact that the electroweak vacuum in the Standard Model is metastable (is a false vacuum), but the probability of its decay in the catastrophic transition to the state of true vacuum is extremely low, which provides stability of the observed Universe. Nevertheless, the theory predicts the possibility of such a transition between vacuum states with a possible acceleration (catalysis) around a BH. D S Gorbunov, D G Levkov, and V E Maslov considered the decay of vacuum in the model of Higgs type scalar field near a BH which is in thermal equilibrium with surroundings. A new unexpected discovery was that for a sufficiently large BH mass the vacuum decay is not spherically symmetric about the BH center, whereas the previous works always presumed spherical symmetry. Instead, the decay begins in a small local region near the BH horizon and continues as a bubble growing first on one side of the BH. The work is important as it provides insight into the mechanisms of vacuum decay in the Universe at various stages of its evolution. [2] Gorbunov D S, Levkov D G, Maslov V E, arXiv:2608.12469 [gr-qc] A search for oscillations of neutrons n into mirror n1 September 2026In elementary particle physics, the hypothesis of mirror matter is being discussed, where each particle has a mirror partner [3, 4]. The Standard Model particles, including n, might transform (oscillate), with a low probability, into corresponding mirror particles. The experiment on a change in the n lifetime in closed cavities was carried out earlier at the Laue – Langevin Institut (France). Although the results of the experiment, according to its authors, agree with the lack of oscillations, alternative interpretations pointed to a statistically significant insufficiency of n, which could be explained by n oscillation into mirror n and a free leakage of the latter through the cavity walls. New high-precision measurements of the lifetime of n in a cavity were performed at the Paul Sherrer Institute (Switzerland) by N J Ayres (Swiss Higher Technical School in Zurich) and their co-authors [5]. The neutrons were sent to a steel reservoir and in some time were released and detected. Measurements for opposite directions of the magnetic field allowed part of the n loss channels to be excluded. With a probability of 95 %, no evidence for deficiency of n was found. Although the effect of oscillations has not been confirmed, new restrictions were obtained on the lifetime of n relative to oscillations depending on the magnetic field. Mirror particles may constitute dark matter, and their oscillations may explain baryon asymmetry. [3] Okun L B Phys. Usp. 50 380 (2007) [4] Blinnikov S I Phys. Usp. 57 183 (2014) [5] Ayres N J et al. Phys. Rev. Lett. 137 051802 (2026) A perovskite-based polariton laser diode1 September 2026Polariton laser is a source of coherent light, whose operation is based not on stimulated radiation, but rather on Bose-Einstein condensation of exciton polaritons (systems of photons and electron-hole pairs). The first electrically pumped polariton laser was demonstrated in 2013. Owing to low energy consumption and small size, polariton lasers are promising for application in nanoelectronics. A P Pushkarev (Hybrid Photonics Laboratory in Skolkovo) and his colleagues from the ITMO University and National Research University Higher School of Economics (HSE) were the first to create an electrically controlled polariton laser diode on the basis of perovskite CsPbBr3 operating under direct electric pumping with constant current [6]. A CsPbBr3 microplate was grown in a solution and integrated into an optical microresonator with charges injected into it through thin-film electrodes from carbon nanotubes. The chemical inertness of nanotubes to perovskite prevented undesirable reactions and excluded ohmic heating. Charge carriers were injected in the course of two-stage device cooling down to 8 K, ensuring stability. The analysis of the electroluminescence spectrum revealed a transition to polariton laser operation at a low threshold current. [6] Pushkarev A P et al. Nature 656 80 (2026) Supermassive black hole (BH) in a gas cocoon1 September 2026The models of supermassive BH formation in the early Universe face difficulties due to the lack of time for the BH mass growth. A new interesting object of the kind, MoM-BH*-1, at z=7.8 (the age of the Universe is 660 million years) was discovered by the G Webb Space Telescope [7]. A distinctive feature of MoM-BH*-1 is a record-large Balmer jump in the spectrum. A broad Hβ line, absorption lines, and a variable emission component are also observed. MoM-BH*-1 is most likely a BH with a mass of (106-107)M☉ immersed in a dense turbulent gas cloud, and there are no stars or dust around it. It is also of interest that a stellar galaxy with a mass of 109.5M☉ is located near MoM-BH*-1. The ultraviolet radiation of this galaxy has possibly suppressed the H2 molecule formation in MoM-BH*-1, resulting in a direct gas collapse into a BH without fragmentation and star formation. [7] Naidu R P et al. Nature 656 329 (2026) |
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. | |
|
© 1918–2026 Uspekhi Fizicheskikh Nauk Email: ufn@ufn.ru Editorial office contacts About the journal Terms and conditions |