Bulletin of the Lebedev Physics Institute最新文献

In the ({{E}_{6}}) composite Higgs model (({{E}_{6}})CHM) the candidate for asymmetric dark matter (DM) is a Dirac composite fermion (chi ), possessing a baryon number that ensures its stability. It is shown that in the ({{E}_{6}}) CHM there exist parameter regions not excluded by experimental constraints on the cross section for (chi ) interactions with nucleons, as well as regions in which efficient annihilation of the symmetric component of (chi ) is achieved.

We report the status of an ongoing measurement of the branching-fraction ratio (mathcal{B})(B^– → ({{D}^{{*0}}}{{pi }^{ - }}){text{/}}mathcal{B}({{B}^{ - }} to {{D}^{0}}{{pi }^{ - }})) using (711{kern 1pt} ,{text{f}}{{{text{b}}}^{{ - 1}}}) of Belle data and (362,{kern 1pt} {text{f}}{{{text{b}}}^{{ - 1}}}) of Belle II data collected at the (Upsilon (4S)) resonance. The signal yields are extracted with an inclusive recoil-mass method: one B meson (the tag-B) is fully reconstructed in hadronic modes, and only the charged pion from the signal B is reconstructed. A deep neural-network classifier is used for background suppression. The invariant mass of the remaining unreconstructed particles, referred to as the recoil mass, is calculated using the known initial ({{e}^{ + }}{{e}^{ - }}) state and the reconstructed tag-B and charged pion, and is fit to extract the (Dpi ) and (D{text{*}}pi ) yields. The fit uses separate signal shapes for correctly and incorrectly reconstructed tag-(B) candidates. The branching-fraction ratio remains blinded while the analysis procedure is finalized; we obtain a statistical uncertainty of (1.7% ). For comparison, the world-average PDG relative uncertainties are 2.2% for ({{B}^{ - }} to {{D}^{0}}{{pi }^{ - }}) and (2.9% ) for ({{B}^{ - }} to {{D}^{{*0}}}{{pi }^{ - }}). The ({{B}^{ - }} to {{D}^{{(*)0}}}{{pi }^{ - }}) fits also determine tag-mode-dependent corrections to the ({{B}_{{{text{tag}}}}}) reconstruction efficiency and good-tag fractions. These corrections are used in the inclusive measurement of the branching fraction of ({{B}^{ - }} to X(3872){{K}^{ - }}).

Within the relativistic quark model based on the quasipotential approach and QCD, tetraquarks containing two heavy flavors (charm c, bottom b) are studied. The tetraquark is considered as a bound state of a diquark and an antidiquark. The interaction potential in the relativistic quasipotential equation includes all spin-dependent and spin-independent relativistic contributions. The finite size of the diquark is taken into account. The calculated tetraquark masses are compared with the strong fall-apart decay thresholds into a pair of mesons and with experimental data. The states that could be observed as narrow resonances in other decay modes are identified.

Cation-based memristors are promising candidates for applications in next-generation computing due to their low power consumption, high scalability, and analogue switching capability. However, Si-based memristors typically require relatively high electroforming voltages, which negatively affect reliability and energy efficiency. In this work, we investigate the effect of Ti incorporation into α-Si on the electrical properties of α-Si:Ti/Ag memristors by varying the Ti concentration up to 27.4%. The electroforming voltage is reduced from 5.0 V in undoped devices to 1.1 V for the samples with the highest Ti concentration, while high ON/OFF resistance ratios (~10⁶), stable retention for at least 12 h, and multilevel resistance states (>10³) are preserved. These improvements can be attributed to the immobile sites in α-Si created by Ti that serve as the foundation for Ag filament formation. The results open new ways for optimising the performance of Si-based memristors by engineering the bulk switching medium.

While (Bbar {B}) pairs from (Upsilon ) decays are predominantly in a C-odd state, soft photon emission introduces a C-even admixture, modifying the time-dependent CP-asymmetry. Using the two-particle wave function formalism, we derive the CP-asymmetry for pure C-even, C-odd and mixed C-parity states and highlight the characteristic ({text{|}}Delta t{text{|}}) dependence of the C-even contribution. We analyze the magnitude of the effect for (Upsilon (4S)) and (Upsilon (5S)) resonances. At (Upsilon (5S)) the admixture is large ((chi simeq 0.4)), while at (Upsilon (4S)) it is negligible on the peak but grows dramatically with a small shift of the center-of-mass energy.

We report the first observation of a bistable regime upon focusing pulsed laser radiation into a cuvette filled with a colloidal solution of gold nanoparticles in ethanol.

Multiscale simulation has shown that the formation of structurally modified tracks of swift heavy ions in GaN critically depends on the mechanism of dynamic screening of target atomic charges, which affects the efficiency of energy transfer from the excited electron subsystem to the atomic lattice. Using lead ion irradiation as an example, the formation of extended tracks with an amorphous core containing nanoscale cavities filled with nitrogen is demonstrated, in agreement with experimental results. In the defect halo surrounding the core, stable edge dislocations are formed, preventing recrystallization of the amorphous region during track cooling.

We report the experimental measurement of the optical damage threshold of the BaGa₂GeS₆ crystal surface irradiated with laser pulses with a wavelength of 1.03 μm and pulse durations ranging from 0.3 to 10 ps. Under single-pulse irradiation, the threshold energy density for optical damage was approximately 0.6 J/cm² (intensity ∼1.8 TW/cm²) for 0.3 ps pulses and increased gradually to 2.2 J/cm² (intensity ∼0.22 TW/cm²) for 10 ps pulses. The optical damage threshold of the BaGa₂GeS₆ crystal surface is found to exhibit a weak dependence on the pulse repetition rate: as the frequency increases from 1 Hz to 100 kHz, the optical damage threshold decreases from 0.6 to 0.45 J/cm². Analysis of literature data shows that the optical damage threshold for BaGa₂GeS₆ irradiated by femto- and picosecond laser pulses with a wavelength of 1 μm is an order of magnitude higher than that of traditional nonlinear crystals such as AgGaS₂ and LiGaS₂.

This paper investigates the reduction of optical losses in optical elements using specially designed nanostructured antireflective coatings consisting of densely packed homogeneous glass nanospheres or an array of air nanopores. Based on full-wave numerical simulation of the spatial distribution of optical fields using the finite element method, we report a detailed analysis of the influence of the thickness and structural design of a nanoporous layer on the transmission properties of a glass optical element. It is found that coatings consisting of air nanopores are, in most cases, more efficient at transmitting the incident optical radiation in the spectral range of sunlight than nanostructured layers formed by an ordered microassembly of homogeneous nanospheres. Practical recommendations for fabricating optimal antireflective coatings based on optical glass are presented.

We report a technique for the two-dimensional diagnostics of flames using laser-induced fluorescence in the saturated regime; the method involves measuring the absolute concentration of hydroxyl radicals (OH). A spatial resolution on the order of 50 μm is achieved, which is significantly smaller than the thermal flame thickness and the characteristic scales of heat-release zones. The technique is validated using a methane–air flame stabilized on a flat porous burner. It is shown that for rich mixtures, the combustion front structure is two-dimensional due to the formation of a secondary conical diffusion flame at the interface between the unreacted fuel and the surrounding air. It is found that the use of a nitrogen shielding stream co-flowing at the same linear velocity as the exiting fuel–air mixture from the burner completely suppresses the secondary flame and ensures a one-dimensional flame front structure in the central part of the burner, extending up to approximately 20 mm from its surface. It is demonstrated experimentally for the first time that, for pore diameters up to 400 μm, flow nonuniformities at the scale of the porous structure do not deform the combustion front. The developed technique enables the high-precision determination of laminar burning velocity based on critical flame blowoff conditions and can also be used to verify detailed kinetic mechanisms and validate numerical combustion models.