Extracts from the Internet

New constraints on the parameters of sterile neutrinos

1 February 2025

It is still unknown what the hidden mass of the Universe consists of, but one of the well theoretically motivated versions are sterile neutrinos &nu_s with masses of the order of keV [1, 2]. Researchers from IKI RAS, INR RAS, and MIPT undertook a new search for the decay path of ν_s in the data of space X-ray NuSTAR telescope for 11 years of observation [3]. Photons were selected that had come from angles of several degrees from the telescope optical axis (such illumination is called “stray light”) in the energy range of 3 to 20 keV and directions >3° from the galactic plane, where the contribution of astrophysical disc objects is small. The radiation spectrum turned out to be approximately exponential, and an additional maximum corresponding to ν_s decays was not revealed. This made it possible to obtain new rigid restrictions on the mixing angle of ν_s and the width of their decay. Although there still remains a small region of admissible parameters, constraints have already approached closely to closing the simplest models of ν_s as the main component of dark matter. [1] Gorbunov D S, Rubakov V A Introduction to the theory of the early Universe: Hot big bang theory (M.: LENAND, 2016) [2] Gorbunov D S Phys. Usp. 57 503 (2014); UFN 184 545 (2014) [3] Krivonos R A et al. Phys. Rev. Lett. 133 261002 (2024)

The joint analysis of neutrino oscillation data

1 February 2025

While some neutrino oscillation parameters have already been measured rather precisely, others now remain uncertain. The T2K and Super-Kamiokande collaborations have jointly analyzed their data in the common range of measured neutrino energies [4]. In the T2K (Tokai-to-Kamioka) experiment, neutrinos from the accelerator are recorded in the near detector and in the far (at a distance of 295 km), which is the Super-Kamiokande detector. The squared mass differences measured by T2K (depending on ordering) and the mixing angle δ_CP, responsible for CP violation make a similar contribution to the asymmetry of neutrino and antineutrino oscillations, which is responsible for the degeneracy. But this degeneracy can be broken with allowance for the Super-Kamiokande data for atmospheric neutrinos that passed through the Earth and experienced resonant amplification of oscillations. A similar complementary analysis of T2K and Super-Kamiokande showed that the CP invariance conservation in neutrino oscillations is excluded at a level of 1.9 σ and the inverse order of masses is excluded with 1.2 σ. The main error in the result is due to the uncertainty in the hadron production models. [4] Abe1 K et al. Phys. Rev. Lett. 134 011801 (2025)

Landau – Zener tunneling in an open system

1 February 2025

The tunneling theory formulated independently by L D Landau and S Zener in 1932 describes transitions between quantum energy levels, which, under external parameter (e.g., magnetic field) variation, first converge to a minimal gap distance Δ and then diverge. This type of the energy spectrum is realized in many physical systems. The tunneling regime is called weak or strong depending on the ratio of the characteristic noise energy, generated by the surroundings, to Δ. X Dai (University of Waterloo, Canada) and their co-authors performed an experiment with a superconducting tunable qubit, where transition from weak to strong Landau-Zener tunneling was demonstrated and a nonmonotonic behavior of the tunneling rate predicted theoretically was revealed for the first time [5]. The authors worked out a theoretical model of “spin bath” qualitatively reproducing their experimental results. [5] Dai X et al. Nature Communications 16 329 (2025)

Nonstandard quantum statistics

1 February 2025

As a rule, particles obey Fermi – Dirac or Bose – Einstein quantum statistics and, accordingly, are called fermions or bosons. An exception is enion statistics of quasiparticles in some two-dimensional systems. In their theoretical work [6], Z Wang and K R A Hazzard (Rice University, USA and Max Planck Institute of Quantum Optics, Germany) showed that for identical quasiparticles, the fourth version of quantum statistics (parastatistics) is possible for any number of measurements, which is in a sense intermediate between fermion and boson statistics, but not, however, reducible to either of them. In this case, an interchange of two particles makes the wavefunction undergo a more complex transformation than merely a change in sign. The hypothesized possibility of parastatistics was considered as far back as 1953, but then parastatistics was thought of as equivalent to the fermion or boson statistics. In paper [6], the rules of secondary quantization of paraparticles were formulated, a generalized exclusion principle was derived, and nontrivial thermodynamic properties of paraparticle systems were pointed out. Possibly, the quasiparticles that obey the rules of parastatistics can be identified in solid state physics, but such properties can also be inherent in now unknown elementary particles. [6] Wang Z, Hazzard K R A Nature Photonics 19 89 (2025)

Fractional quantum Hall effect

1 February 2025

In the case of fractional quantum Hall effect observed in two-dimensional electron systems, quasiparticles only carry a part of a unit electric charge. It was predicted that in layered systems, interlayer excitons (bound states of electrons and holes) can be fermions or enions due to pairing between the components carrying fractional charges, but this effect has never been demonstrated experimentally. N J Zhang (Brown University, USA) and their co-authors were the first to perform a corresponding experiment to discover new interesting properties of excitons [7]. Two graphene layers in Corbino geometry, separated by hexagonal boron nitride, were included in independent electric circuits, and a condensate of interlayer excitons appeared in a strong magnetic field. Two classes of states of the fractional quantum Hall effect with nonintegral occupation numbers were revealed, namely, a fractional analog of exciton condensates and a two-layer generalization of fermion Jane states. Their properties are explained by the presence of exciton quasiparticles with fractional statistics, called “fractional excitons”. [7] Zhang N J et al. Nature 637 327 (2025)

Long-lived quantum Schrodinger cat state (SCS)

1 February 2025

Coherent states such as quantum entanglement state or SCS are of great interest for quantum information devices, quantum metrology, and for fundamental research, including the search for effects beyond the Standard Model [8, 9]. However, the common problem of nonclassical states is decoherence leading to their short lifetime. In their experiment with ¹⁷³Yb atom in an optical lattice, Y A Yang (University of Science and Technology of China) and their co-authors could reach a record large SCS coherence time ≈ 1.4×10³ s [10]. SCS was realized on two oppositely directed nucleus spins with projections m = + 5/2 and m = - 5/2. The necessary nonlinearity was due to the effect of Stark shift. With the help of a special sequence of laser pulses, the system was brought to the region of Hilbert state space, where the influence of noises is very weak. The Ramsay interferometry showed that in this region the indicated SCS with m = ± 5/2 is long-lived. [8] Rubakov V A Phys. Usp. 42 1193 (1999); UFN 169 1299 (1999) [9] Boos E E et al. Phys. Usp. 68 (2) (2025); UFN 195 (2025) [10] Yang Y A et al. Nature Photonics 19 89 (2025)

Spectroscopy of nuclear quadrupole resonance of individual nuclei

1 February 2025

Spectroscopy of nuclear quadrupole resonance based on recording the interaction between the electric quadrupole moment of nuclei and electric field gradients is being widely used in practice to reveal and identify various substances. But this method earlier helped to detect only resonance from large macroscopic ensembles of nuclei. S A Breitweiser (University of Pennsylvania, USA) and their co-authors were the first to demonstrate the method of nuclear quadrupole resonance for singe nitrogen nuclei in nitrogen-substituted vacancies in diamond (in NV-centers) [11]. The experiment was performed at room temperature by the method of dynamic-decoupling spectroscopy. The NV-centers served there as quantum sensors and studied systems. The measurements revealed significant differences in quadrupole and hyperfine parameters between different NV-centers, as well as a yet unknown term in the Hamiltonian of NV-centers, which arose as a result of symmetry breaking. The developed method can be applied to create hypersensitive nuclear sensors. [11] Breitweiser S A et al. Nano Letters 24 16253 (2024)

Icelike shells around nanoparticles in water

1 February 2025

In 2010, A F Bunkin and S M Pershin (IGP RAS) revealed the existence of an icelike structure of water molecules around large protein molecules in water solution. In the new experiment [12], the measurement of the shift of the “gravitational center” of the Raman OH-band as well as Mandelstam-Brillouin resonances showed the formation of an icelike structurer around quartz nanoparticles in water suspension at room temperature. A laser beam was directed to the suspension located in a quartz cuvette. The scattered radiation was recorded by a Raman spectrometer and Fabry – Perot interferometer. An OH-band shift towards the ice component was revealed and the known water line with a shift of 7.5 GHz and a new line of 14.3 GHz were observed in the spectrum. The latter shift of the line of Stokes component gives the velocity of sound of ≈ 2900 m s⁻¹ in the medium around nanoparticles. This value is much larger than the velocity of sound in water and is close to the velocity of sound in the ice, which confirms the formation of icelike hydrate shells around quartz nanoparticles. This study, as a continuation of the series of studies by the winners of the competition of scientific papers of RAS, performed jointly with NAS of Belarus, is of importance, in particular, for cryogen biotechnologies. [12] Pershin S M et al. Pisma ZhETF 121 93 (2025)

Localization of the fast radio burst (FRB) source

1 February 2025

The mechanism of generation of millisecond cosmic radio pulses coming from intergalactic distances is not yet clear. According to one of the theories, such FRBs occur near magnetars – neutron stars with strong magnetic fields [13]. But it remained unclear how far the region of radio emission generation is from the compact stellar remnant. K Nimmo (Massachusetts Institute of Technology, USA) and their co-authors managed to localize this region by observing scintillations of FRB 20221022A10 [14]. Scintillations occur upon radiation scattering by stochastic inhomogeneities of space on the line of sight. In the 20221022A10 spectrum, obtained with the CHIME telescope, two scintillation regions were revealed: one in the FRB galaxy and the other in our Galaxy. The position of these regions and the constraints on the electron number density indicate that the size of the generation region is ≤ 3×10⁴ km and it is located within the magnetosphere or near its boundary. This excludes non-magnetospheric models of FRB generation at a large distance from the compact object, for example, in a propagating shock wave. In 2024, R Mckinven et al. arrived at a similar conclusion for FRB 20221022A10 from observation of changes of the radiation polarization angle. [13] Popov S B, Postnov K A, Pshirkov M S Phys. Usp. 61 965 (2018); UFN 188 1063 (2018) [14] Nimmo K et al. Nature 637 48 (2025)

Evolution of dark energy (DE)

1 February 2025

Inhomogeneities in the distribution of galaxies (large-scale structure of the Universe) contain valuable information on the spectrum of initial perturbations and the Universe composition determining the dynamics of its expansion [15]. Furthermore, the data on the inhomogeneities can be used to verify the gravitation theory for seeking differences from the Einstein General Theory of Relativity (GTR) [16 - 18]. The DESI (Dark Energy Spectroscopic Instrument) project is aimed at investigating clasterization of galaxies and quasars, as well as lines Ly_α in the quasar spectra using specially configurated surveillance telescopes. The DESI collaboration presented new results of five years of observation [19]. They contain the spectra and correlation functions of 40 mln galaxies and quasars at 0 < z < 4, and the measured position of the peak corresponding to baryon acoustic oscillations. The obtained value of the Hubble constant is close to the results of Planck satellite measurements, and the restriction on the sum of neutrino masses has the form ≈ m_ν < 0.071 eV. With the existing precision, all the data agree with GTR predictions. An interesting new result is that the parameter of the equation of DE state probably differs from -1 (at the present time w = - 0.761 ± 0.065) and increases with expanding Universe. Then the DE density can evolve with time and is not a cosmological constant (for DE, see [20, 21]). [15] Silchenko O K Phys. Usp. 68 (2) (2025); UFN 195 (2025) [16] Rubakov V A, Tinyakov P G Phys. Usp. 51 759 (2008); UFN 178 785 (2008) [17] Mironov S A, Volkova V E ; 68 (2) (2025); UFN 195 (2025) [18] Postnov K A, Porayko N A, Pshirkov M S Phys. Usp. 68 (2) (2025); UFN 195 (2025) [19] DESI Collaboration: Adame A G et al. arXiv:2411.12022 [astro-ph.CO] [20] Lukash V N, Rubakov V A Phys. Usp. 51 283 (2008); UFN 178 301 (2008) [21] Rubakov V A Phys. Usp. 57 128 (2014); UFN 184 137 (2014)

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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.