Vol 118, No 7-8 (10) (2023)

We discuss the process ℓ+ℓ−→NW±ℓ∓">${\ell }^{+}{\ell }^{-}\to N{W}^{\pm }{\ell }^{\mp }$, where N is a heavy Majorana neutrino and ℓ=e,μ">$\ell =e,\mu$. Large cross sections are expected for these processes at high center-of-mass energies, which can be reached at future lepton–lepton colliders. The Monte Carlo simulation of the studied processes is produced within the framework of the seesaw type-I model, where the Majorana neutrinos (or heavy neutral leptons, HNL), are introduced in the standard leptonic sector. Recently the possibility to search for the direct HNL production was studied in the ℓ+ℓ−→Nνℓ">${\ell }^{+}{\ell }^{-}\to N{\nu }_{\ell }$ process with the subsequent decay N→W±ℓ∓">$N\to W^{\pm }{\ell }^{\mp }$. In this paper we investigate an alternative process ℓ+ℓ−→NW±ℓ∓→W±W±ℓ∓ℓ∓">${\ell }^{+}{\ell }^{-}\to N{W}^{\pm }{\ell }^{\mp }\to W^{\pm }{W}^{\pm }{\ell }^{\mp }{\ell }^{\mp }$ with the lepton number violation by two units. The similar processes appear in collisions with the same-sign beams, e−e−→NW−e−→W−W−e+e−">$e^{-}{e}^{-}\to N{W}^{-}{e}^{-}\to W^{-}{W}^{-}{e}^{+}{e}^{-}$ or μ+μ+">${\mu }^{+}{\mu }^{+}$ →">$\to$ NW+μ+→W+W+μ+μ−">$N{W}^{+}{\mu }^{+}\to W^{+}{W}^{+}{\mu }^{+}{\mu }^{-}$. The cross sections of the processes under consideration are enhanced by the soft photon exchange in the t-channel. We calculate the cross sections for the signals and potential Standard Model backgrounds for the e+e−">$e^{+}{e}^{-}$ beam collisions at the 1 TeV center-of-mass energy and the μ+μ−">${\mu }^{+}{\mu }^{-}$ collisions at 3 and 10 TeV. Due to the diagrams with soft t-channel photons and respective interference the promptly emitted leptons are produced in the direction close to the corresponding beam. These leptons will be lost in the beam pipe or badly measured by forward detectors. However, the signal events can be well separated from backgrounds using the rest of the event containing the WWℓ">$WW\ell$ particles. Finally, the expected upper limits on the mixing parameters |VℓN|2">${\left|V_{\ell N}\right|}^2$ as a function of M(N) are calculated.

We have experimentally obtained two-dimensional distributions of terahertz radiation generated by one or four filaments formed by phase optical elements in air. It has been demonstrated that the use of the phase mask reduces the propagation angles of terahertz beam by approximately one and a half times, which is due to the interference of terahertz radiation from four sources. The use of the Dammann grating slightly enlarges these angles.

Two-dimensional materials are promising candidates for the creation of flat photonics devices. The main problem of using such materials for applied applications is the complexity of creating films of specified geometric parameters. The films of two-dimensional materials made by exfoliation or chemical deposition methods are usually randomly distributed over a large area and have a large thickness spread. In this paper, we use convolutional neural networks to predict the film thickness of a quasi-two-dimensional material based on optical microscopy data. Hexagonal boron nitride, which is actively used in the creation of flat electronic and optoelectronic devices, was chosen as a test material. Due to the high spatial resolution of microscopy, it is possible to achieve high accuracy in predicting the thicknesses of flat areas of the sample, which allows for rapid characterization of structures. In addition, using the example of the signal of the third optical harmonic, we show the possibility of predicting the magnitude of the nonlinear optical response of the film, which expands the scope of the method.

We compare the structure of the superconducting order parameter of overdoped BaFe_1.88Ni_0.12As₂ and underdoped BaFe_1.92Ni_0.08As₂ pnictides with similar Tc≈18.0−18.3">$T_c\approx 18.0-18.3$ K. Using incoherent multiple Andreev reflection effect spectroscopy, we directly determined the magnitudes of the two microscopic superconducting order parameters: the small superconducting gap and probably anisotropic large gap, their characteristic ratios and temperature dependences. We discuss similarity and difference in the gap structure, as well as possible influence of antiferromagnetic phase to superconducting properties.

Driven-dissipative protocols are proposed to control and create nontrivial quantum many-body correlated states. Protocols conserving the number of particles stand apart. As well-known, in quantum systems with the unitary dynamics the particle number conservation and random scattering yield diffusive behavior of two-particle excitations (diffusons and cooperons). Existence of diffusive modes in the particle-number-conserving dissipative dynamics is not well studied yet. We explicitly demonstrate the existence of diffusons in a paradigmatic model of a two-band system, with dissipative dynamics aiming to empty one fermion band and to populate the other one. The studied model is generalization of the model introduced in F. Tonielli, J.C. Budich, A. Altland, and S. Diehl, Phys. Rev. Lett. 124, 240404 (2020). We find how the diffusion coefficient depends on details of a model and the rate of dissipation. We discuss how the existence of diffusive modes complicates engineering of macroscopic many-body correlated states.

The deflection of a 1-GeV proton beam by a bent silicon crystal 1 mm long by an angle of (3.0 ± 0.1) mrad with an efficiency of (32 ± 3)% for end-face capture into the channeling regime has been observed for the first time in the presented experiment. The developed crystal deflector makes it possible to increase the beam deflection angle and can be used to produce low-intensity beams at intermediate energies.

We study GRB 221009A, the brightest gamma-ray burst in the history of observations, using Fermi data. To calibrate them for large inclination angles, we use the Vela X gamma-ray source. Light curves in different spectral ranges demonstrate a 300 s overlap of afterglow and delayed episodes of soft prompt emission. We demonstrate that a relatively weak burst precursor that occurs 3 min before the main episode has its own afterglow, i.e., presumably, its own external shock. This is the first observation of such phenomenon which rules out some theoretical models of GRB precursors. The main afterglow is the brightest one, includes a photon with an energy of 400 GeV 9 h after the burst, we show that it is visible in the LAT data for up to two days.

A nonideal helium plasma has been compressed to a density of ρ ≈ 14 g/cm³ at a pressure of P≈20">$P\approx 20$ TPa (200 Mbar) in a spherical two-cascade device. The design of the device has been presented and the thermodynamic parameters of the helium plasma reached in it have been estimated. Data on the dynamics of the external and internal cascades in the device used to choose the calculation method have been obtained in a preliminary experiment with a hemispherical prototype. The experiment has been performed on the X-ray complex at the Russian Federal Nuclear Center All-Russian Research Institute of Experimental Physics, which includes BIM 234.3000 betatrons with a boundary energy of 60 MeV used in the multipulse bremsstrahlung generation regime with a multichannel optoelectronic system of recording X-ray images. A high-current linear accelerator LIU-R-T and an image detector assembly consisting of photochromic ADC screens have been used in addition to betatrons to detect the compressed shell cavity.

Systematic studies of second-generation high-temperature superconducting wires with Gd excess relative to the stoichiometric GdBa₂Cu₃O₇ composition are reported. It has been revealed that filamentary defects in the form of non-superconducting Gd₂CuO₄ phase located along the ab plane are formed during film growth. These inclusions lead to a change in the pinning mechanism of the vortex structure, due to which the peak of the critical current at +15% Gd is clearly observed.

The influence of the thermally induced magnetoelastic effect on the magnetization reversal field in 0.9 × 0.3 × 0.03-μm Ni particles formed on a single crystalline lithium triborate (LiB₃O₅) substrate has been studied. It has been shown experimentally that this substrate can reduce the magnetization reversal field of particles by a factor of more than 1.5 as the temperature of the sample increases from 30 to 45°C. This reduction of the reversal field is due to magnetoelastic anisotropy induced in the particles by the difference between the thermal expansion coefficients of the substrate along different crystallographic axes.

The excitation of a magnon Bose−Einstein condensate in an yttrium iron garnet film due to acoustic coupling with the condensate in the second sample is experimentally studied. A nonlinear nature of this excitation is demonstrated. The formation of a phonon Bose−Einstein condensate in the substrate is assumed. This experiment opens the possibility of creating qubits based on acoustically interacting Bose−Einstein condensates.