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| Issue 11, 2025 |
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Extracts from the Internet | ||
A longitudinally polarized W boson1 October 2025The prediction of the Standard Model of elementary particles concerning the possibility of production of longitudinally polarized W bosons was confirmed in an LHC experiment [1]. W bosons may have a longitudinal polarization with spin along momentum owing to a nonzero mass occurring by the Higgs mechanism. Particles were born in proton-proton collisions at a center-of-mass energy of 13 TeV, and the ATLAS detector was used to examine effects with two same-sign leptons and two jets in the final state. Same-sign W± boson pairs, one of which was longitudinally polarized, were discovered for the first time. The significance of recording such events is 3.3 σ, and the cross section of the process, 0.88±0.30 fb, agrees with calculations within the Standard Model. Observation of this process paves the way for searching for the effects beyond the Standard Model. The described experiment also gave the most stringent constraint on the possibility of production of two single-signed longitudinally polarized W bosons. [1] Aad G et al. Phys. Rev. Lett. 135 111802 (2025) Investigation of the islands of inversion of atomic nuclei1 October 2025In the nuclide table there are regions – “islands of inversion”, where the shape of the nucleus in the ground and excited states differ strongly. Experiments revealed four such islands near nuclides with filled neutron shells. A spin in the ground state and the magnetic dipole moment of 61Cr nuclei having N=37 neutrons were measured for the first time using laser spectroscopy at the CERN-ISOLDE installation [2]. Spin-parity of Cr# nuclei in the ground state was considered earlier to be Iπ=5/2, but the measurement showed that actually Iπ=1/2. Such a refinement made it possible to improve the scheme of 61Cr levels and to determine the boundary of the island of inversion near N=40. The results of measurements were interpreted in the framework of the new theoretical models LSSM and DNO-SM. According to these calculations, the ground state of 61Cr nuclei has a triaxial shape with prevalence of the neutron configuration 2p-2h connected with an unpaired neutron, and the change in the neutron shape is due to the wavefunction reconstruction upon quantum phase transition. [2] Lalanne L et al. Phys. Rev. C 112 L031301 (2025) Neutrino laser1 October 2025In 1954, R Dikke predicted the possibility of superradiation, i.e., a collective spontaneous radiation of an ensemble of atoms [3 – 5], and for photons, this effect had already been realized in experiments. In their theoretical work [6], B J P Jones (University of Texas at Arlington, USA) and J A Formaggio (Massachusetts Institute of Technology, USA) showed that it is in principle possible to use superradiation to create a powerful directed neutrino beam. Although in the case of neutrino the laser effect of stimulated radiation is missing, the coherent properties of the beam allow calling the device under discussion a “neutrino laser”. Neutrino superradiation must take place in collective spontaneous beta-decays with an electron trapping in a Bose-Einstein condensate of radioactive atoms. Atoms in a condensate have a common wavefunction, and therefore in decays, quantum probability amplitudes are summed, and decays accelerate proportionally to the number of particles squared. According to calculations, a condensate of ≈ 106 83Rb atoms already suffices to create a neutrino laser, and the 83Rb half-decay time will decrease from 86.2 days to 2.5 minutes. If neutrino lasers appear, they may find application in fundamental studies and for neutrino communication. Furthermore, the inverse effect of neutrino capture in a Bose-Einstein condensate can be used to register relic (cosmological) neutrinos. [3] Andreev A V, Emel’yanov V I, Il’inskii Yu A Sov. Phys. Usp. 23 493 (1980); UFN 131 653 (1980) [4] Men’shikov L I Phys. Usp. 42 107 (1999); UFN 169 113 (1999) [5] Vasil’ev P P Phys. Usp. 68 525 (2025); UFN 195 557 (2025) [6] Jones B J P, Formaggio J A Phys. Rev. Lett. 135 111801 (2025) Testing the area law for black holes (BH)1 October 2025On January 14, 2025, two gravitational-wave LIGO detectors recorded a gravitational-wave burst GW250114 with a record signal-to-noise ratio, equal to 80, which made it possible to reach the level of BH spectroscopy and investigate various horizon oscillation modes [7]. Two BHs with masses 33.6+1.2−0.8M☉ and 32.2+0.8−1.3M☉ and small spins merged in this event. Observed was a gravitational wave emission upon BH approach, radiation during coalescence, as well as radiation upon oscillations of the BH, which was formed upon coalescence (the ringdown phase). In the analysis, several strongest oscillations upon coalescence were excluded, and so, for the remaining time interval, the linear perturbation theory was applicable. The resultant BH had a dominant oscillation mode and its first overtone. The frequencies and times of damping are indicative of the formation of a rotating BH described by a perturbed Kerr solution. It also appeared possible to test S Hawking’s prediction of a non-decrease of the horizon area upon BH merging more precisely than before (at the 4.4 credibility level). [7] Abac A G et al., Phys. Rev. Lett. 135 111403 (2025) Unusual cosmological objects1 October 2025Recent J Webb space telescope observations revealed a new class of compact (with a radius of ≈ 150 pc) bright red shaded galaxies within the first milliard years of the Universe life (z ≥ 6). Such objects were called “little red dots” (LRD). LRD radiation is generated either by stars or by active galactic nuclei. In the latter case, the central supermassive black holes (SMBH) must have masses larger by 2 – 3 orders of magnitude than follows from the known relations in the modern Universe. It is still unknown what is the nature of LRD, how they formed, and what they later transformed into. New J Webb observations revealed an LRD at a record-high z = 9.288 [8]. This galaxy has a broad Balmer emission line, a stellar mass ≤ 109M☉, and the SMBH mass makes up > 5% of the star masses. Observations of another LRD revealed a large amount of hot dust [9]. An object resembling an LRD was also discovered at z = 3.55 [10]. It may be not a star galaxy, but rather a SMBH immersed in a dense gas cloud and accreting in the super-Eddington regime. In paper [11], LRDs were hypothesized to be rare galaxies with a small angular momentum L. The small L simultaneously explains compactness of LRDs (a high concentrations of stars) and their observed number. [8] Taylor A J et al. The Astrophysical Journal Letters 989 L7 (2025) [9] Delvecchio I et al., arXiv:2509.07100 [astro-ph.GA] [10] de Graaff A et al. Astron. & Astrophys. 701 A168 (2025) [11] Pacucci F, Loeb A Astrophys. J. Lett. 989 L19 (2025) |
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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