Bogolyubov Institute for Theoretical Physics

ABSTRACT Recent optical surveys have identified a rare population of low-z ($z \sim 0.01 \!-\! 0.06$) extreme star-forming galaxies (xSFGs) characterized by very low metallicity, strong emission lines, extremely high specific star-formation rate, low stellar mass, and strong Ly $\alpha$ emission. Their global properties resemble recently discovered $z\gt 6$ reionization-era star-forming galaxies. We present new multifrequency radio continuum observations of eight xSFGs using the upgraded Giant Metrewave Radio Telescope at 1.25 GHz, the Karl G. Jansky Very Large Array at $1.5, 3.0, 6.0, 10.0$, and 15.0 GHz, along with archival LOw Frequency ARray data at 150 MHz for several sources. These data allow construction of the radio spectral energy distribution (radio-SED) from $\sim 1$ GHz (down to 150 MHz for some sources) to 15 GHz, spanning nearly two orders of magnitude in frequency. We find that xSFGs exhibit a flat spectral index between 6 and 15 GHz, while a subset shows spectral turnovers at $0.3 \!-\! 3$ GHz. Our Bayesian radio-SED modelling indicates that these features are consistent with a high thermal fraction combined with free–free absorption, requiring high emission measures in some systems. By comparing modelled thermal radio emission with observed H$\beta {}$ line flux density, we find evidence for dust in several xSFGs. Finally, we confirm a previously reported correlation between Lyman continuum escape fraction ($f_\mathrm{esc}^\mathrm{LyC}$), ionization state, and radio spectral index, particularly among strong leakers.

We investigated how a magnetic topological defect affects the vacuum polarization of a charged massive scalar field in a flat (3+1)-dimensional space-time. The defect was modeled as an impenetrable-to-matter-field, finite-thickness tube with magnetic flux inside. We implemented the most general form of the Robin boundary condition on the surface of the magnetic tube, which enables a fully general analysis of the problem. We found that in flat space-time, the total vacuum energy generated by a magnetic topological defect depends on the curvature (ξ), except for special cases corresponding to the Dirichlet and Neumann boundary conditions. By contrast, when Robin’s general boundary conditions are imposed, the induced vacuum energy acquires an explicit dependence on the curvature coupling (ξ), which is significant even in flat space-time. A detailed study of the dependence of the effect on the boundary-condition parameter was carried out. The obtained results highlight the nontrivial role played by boundary conditions in vacuum polarization phenomena.

We analyse the impact of the decaying magnetic turbulence of primordial magnetic fields (PMFs) and ambipolar diffusion on the ionisation and thermal history of the Dark Ages Universe (30 ≤ z ≤ 300), and its imprint on the spectral profile of the global signal in the redshifted 21 cm hydrogen line. The heating function caused by decaying magnetic turbulence monotonically decreases after cosmological recombination; its amplitude strongly depends on the strength of the PMFs’ B 0 and weakly depends on the spectral index of the initial power spectrum of the PMFs’ n B . The heating function caused by ambipolar diffusion, in contrast, noticeably depends on the spectral index in the range −3 ≲ n B ≲ 4 but is subdominant in the Dark Ages epoch for PMF models with B 0 ≲ 0.5 nG. We computed the ionisation and thermal history of intergalactic gas from the cosmological recombination up to the end of the Dark Ages epoch for a range of PMF parameters, 0.05 ≲ B 0 ≲ 0.5 nG, −2.9 ≲ n B ≲ 4, and show the essentially distinguished thermal evolution from one in the Lambda cold dark matter (ΛCDM) model. We also show that the profile of the redshifted 21 cm hydrogen line is very sensitive to the PMF parameters from this range and can be used for their constraints in conjunction with other observational data.

We present observations of eleven compact star-forming galaxies in the redshift range z = 0.6145 -- 1.0053, with the Cosmic Origins Spectrograph (COS) on board the Hubble Space Telescope HST ). We aim to spectroscopically measure for the first time the Lyman continuum (LyC) over a wider rest-frame wavelength range of ∼ 600 -- 900Å compared to ∼ 850 -- 900Å in previous studies of galaxies at z ∼ 0.3 -- 0.4. The HST data are supplemented by SDSS spectra of all galaxies and by a VLT/Xshooter spectrum of one galaxy, J0232$+$0025. These data are used to derive the spectral energy distribution in the entire UV and optical range, the stellar mass, and the chemical composition from the nebular emission lines. We detect stellar LyC emission in seven out of eleven galaxies with escape fractions, f_ in the range of ∼ 2 -- 60%, and establish upper limits for f_ in the remaining galaxies. We discover for the first time nebular LyC emission as a bump just bluewards of the LyC limit at 912Å in two galaxies, J0232$+$0025 and J1021$+$0436. We find a similar bump among our earlier studies in a less distant galaxy J1243$+$4646 with z = 0.4317. We conclude that the use of the LyC continuum in the wavelength range close to the LyC limit, which contains both the stellar and nebular continua, requires special consideration to not overestimate the observed f_

Purpose To investigate synthesis of nuclei in pycnonuclear reactions in dense medium of neutron stars on the basis of understanding, how the compound nucleus is formed during collision of two nuclei. To implement microscopic formulation of nuclear interactions and fusion in pycnonuclear reactions in dense medium. Methods (1) Nuclei synthesis in pycnonuclear reaction in dense medium of neutron star is investigated in the folding approximation of the cluster model. (2) Formation of compound nucleus in dense medium is studied with the method of Multiple Internal Reflections. Results (1) Wave functions of resonance states of $^{24}$Mg are determined by interaction of two $^{12}$C nuclei. (2) Clear maxima of probability of formation of compound nucleus in dense stellar medium are established at first time. (3) Difference between quasibound energies for potential of Woods-Saxon type and folding potentials with the shell-model approximation for wave functions is essential. (4) Formation of the compound nucleus is much more probable in the quasibound states than in states of zero-point vibrations. (5) Only the first quasibound energies for $^{12}$C + $^{12}$Care smaller than the barrier maximums. At these energies compound nuclear system has barrier which prevents its decay going through tunneling phenomenon. This is the new excited nucleus $^{24}$Mg synthesised in the neutron star. \item[Conclusions] Cluster approach with folding potential provides significant modification of picture of formation of compound nucleus, previously obtained concerning the potential of Woods-Saxon type. The highest precision is provided by the folding potential, created by semi-realistic nucleon-nucleon potential and shell-model description of the internal structure of interacting $p$-shell nuclei.

The nature and structure of high-energy resonance states in Be8, located just below and above the p+Li7 threshold, are investigated in detail. A microscopic many-cluster and many-channel model is employed to study the formation of these resonances. This model includes three distinct three-cluster configurations: He4+H3+p, He4+He3+n, and He4+d+d, enabling a comprehensive treatment of all major binary decay channels of Be8, namely He4+He4, p+Li7, n+Be7, and d+Li6. The primary focus of our analysis is the structure and dominant decay channels of the twin 1+, 2+, 3+, and 4+ resonance states. Additionally, we propose and implement a model to clarify how the 2+ resonance states lying below the p+Li7 threshold are formed. We demonstrate that these resonances are Feshbach-type states arising due to coupling of the open He4+He4 channel with the closed channels p+Li7, n+Be7, and d+Li6 at these energies. Overall, the present approach provides a realistic description of the experimentally observed resonance spectrum near the Li7+p decay threshold, including negative-parity states 1− and 2−. Our results are consistent with other microscopic calculations but offer more detailed insight into the internal structure and decay pathways of these resonances.

We analytically solve the Landau-Lifshitz equations for the collective magnetization dynamics in a synthetic antiferromagnet (SAF) nanoparticle and uncover a regime of barrier-free switching under a short small-amplitude magnetic field pulse applied perpendicular to the SAF plane. We give examples of specific implementations for forming such low-power and ultra-fast switching pulses. For fully optical, resonant, barrier-free SAF switching we estimate the power per write operation to be ∼100 pJ, 10–100 times smaller than for conventional quasi-static rotation, which should be attractive for memory applications.

A dip-bump structure in the squared four-momentum transfer (t) distribution of proton’s single and double diffractive distributions is predicted around t ≈ −4 GeV2 for single diffractive distribution at LHC energies.