The L. D. Landau Institute for Theoretical Physics (Russian: Институт теоретической физики имени Л. Д. Ландау (ИТФ)) of the Russian Academy of Sciences is a research institution, located in the small town of Chernogolovka near Moscow (there is also a subdivision in Moscow, on the territory of the P. L. Kapitza Institute for Physical Problems).
Topologically nontrivial localized 2D magnetic states with high topological charge (|Q| > 1) have attracted significant attention in the last decade, driven by their experimental and numerical discovery. In this work, we propose an analytical ansatz capable of describing both axially symmetric kπ-skyrmions and Cg-symmetric skyrmion bags, with a straightforward extension to a wide range of other multi-skyrmion textures. By comparing with numerical micromagnetic simulations, we show that the proposed ansatz describes skyrmion bags with accuracy sufficient for practical applications.
We investigate numerically correlation functions of the phase of light waves that propagate through turbulent media. Special attention is paid to the off-diagonal component of the correlation function of the phase gradients which is insensitive to the outer scale of turbulence. The results of our simulations are in a good agreement with the analytical expressions obtained in the work (I. V. Kolokolov, V. V. Lebedev, and F. A. Starikov, JOSA A 42(11), 1654 (2025)). Thus, we numerically confirm expectations based on uniformity of the perturbation theory for the logarithm of the envelope.
We study multipoint Virasoro conformal blocks on the sphere in the comb channel. We arrive at the asymptotic expression for these blocks at large intermediate dimensions, applying WKB method for "classical BPZ equation", which is used to study (classical) Virasoro blocks via monodromy method. Several applications of this asymptotic are discussed, such as the possibility to generalize Zamolodchikov's elliptic recursion and numerical evaluation of amplitudes in minimal string theory. Our expressions pass nontrivial checks, such as agreement with known exact expressions for 5-point blocks in special cases and the usual series expansion of Virasoro blocks computed using AGT correspondence.
We construct the Orlov–Schulman symmetries for the Manakov–Santini (MS) hierarchy. We give an explicit proof of the compatibility of additional symmetries with the basic flows of the MS hierarchy, and consider several simple examples, including the Galilean transformation and scalings. We also present a picture of the Orlov–Schulman symmetries in terms of the dressing scheme based on the Riemann–Hilbert problem.
In this paper we theoretically discuss thermal Hall effect of magnons in insulating N & eacute;el ordered antiferromagnets at zero external magnetic field. We show that for compensated N & eacute;el order the nonzero thermal Hall effect will occur in the absence of any symmetry between the two magnetic sublattices, thus making the system ferrimagnetic. We then show that collinear Dzyaloshinskii's weak ferromagnets, in which there is a symmetry connecting the magnetic sublattices, also show magnon thermal Hall effect. The thermal Hall effect of magnons will be nonzero by a virtue of the spin-momentum splitting of the magnon spectrum due to the Dzyaloshinskii-Moriya interaction as well as second-nearest exchange interaction different in the two magnetic sublattices, both corresponding to the broken symmetries that lead to the Dzyaloshinskii's invariant. We construct a theoretical model in which an external electric field may change the symmetry of the antiferromagnetic system thus altering the thermal Hall effect of magnons.
