arXiv subjects

E. V. Gorbar

Publications and source records attributed to E. V. Gorbar.

At least 19 recordsLinked to original sources

arXiv2026

Bound states, resonances, and their thermodynamic properties in pseudospin-1 systems with short-range impurities

Bound states and resonances induced by short-range impurities modeled by circular potential wells are analyzed in the vicinity of flat and dispersive bands in gapped and gapless pseudospin-1 systems. We find that the bound and resonant states derived from the flat band show unusual characteristics originating from the multicomponent structure of pseudospin-1 fermions, which are distinct from those for pseudospin-$\tfrac{1}{2}$ fermions. Contrary to gapped Dirac systems and unlike bound states in the vicinity of the upper dispersive band, the bound states derived from the flat band occur for any value of the total angular momentum. The energies of these bound states with higher angular momentum $j$ tend to decrease with $|j|$. In addition, it is found that their wave functions are localized at the potential well edge and the localization increases with $|j|$. The signatures of the impurity states in the local density of states are determined. Using the Anderson model for independent electrons in the disorder potential, the thermodynamic potential, entropy density, and heat capacity are obtained. In the regime dominated by bound states derived from the flat band, the entropy density monotonically increases with temperature and saturates, whereas the heat capacity exhibits a single maximum.

cond-mat.str-el↗

arXiv2026

Damping of dynamical friction force in self-interacting ultralight dark matter and Fornax timing problem

The dynamics of globular clusters in the Fornax dwarf galaxy pose a challenge for the standard cold dark matter and can be used to test other models of dark matter. We study this dynamics in the context of an ultralight bosonic dark matter model, accounting for the damping term in a generalized Gross-Pitaevskii equation. Employing analytic formulas for the dynamical friction force, the infall time and evolution of globular clusters are compared in the cases with and without the damping term. It is argued that the damping term plays an important role in the Fornax timing problem in ultralight dark matter (ULDM) models. We found that the ULDM model with repulsive self-interaction can solve the Fornax timing problem in the absence of or with very small self-interaction, even if the initial position of the globular cluster is not far from the center of the galaxy. Still, the problem is resolved for strongly interacting repulsive ULDM, even for the most pressing case of globular cluster GC3, if its starting position exceeds 1.5 kpc.

astro-ph.GA↗

arXiv2026

Nodal structure of bound-state wave functions for systems with quartic dispersion

The nodal structure of bound-state wave functions for one-dimensional quantum systems with quartic energy-momentum dispersion and polynomial potentials is analysed by using the semiclassical approximation and variational approach. For energies of bound states, we derive the quantization condition, obtained by using the complex Wentzel method, where we take into account perturbative (up to the fourth order) and nonperturbative in the Planck constant corrections. The bound-state energies and wave functions for the harmonic and quartic potentials are compared with those found by applying the variational approach utilizing the universal Gaussian basis. It is shown that the classical oscillation theorem, valid for systems with quadratic energy-momentum dispersion, breaks down in the classically forbidden region where wave functions also have nodes, while it still remains valid in the classically allowed region. These results are confirmed in addition via the solutions of the exactly solvable problem of the fourth-order Schrodinger equation with a square well potential.

cond-mat.str-el↗

arXiv2026

Velocity dispersion profiles of dwarf spheroidal galaxies with self-interacting ultralight dark matter

Dark-matter-dominated dwarf galaxies provide an excellent laboratory for testing dark matter models at small scale and, in particular, the ultralight dark matter (ULDM) class of models. Within the framework of self-interacting bosonic dark matter, we use the observed velocity-dispersion profiles of seven dwarf spheroidal galaxies to constrain the parameters of ULDM. In our modeling, we account for the impact of the baryonic component on the velocity dispersion and ULDM halo structure. We find that the repulsive self-interaction of ULDM, which fits the observations, is almost negligible, consistent with non-interacting ULDM with a boson mass of approximately $1.6 \times 10^{-22}\,\mathrm{eV}$. In contrast, for attractively interacting ULDM, the best fit corresponds to a smaller boson mass of about $1.3 \times 10^{-22}\,\mathrm{eV}$, with self-interaction playing a significant role in shaping the dark-matter halo and thereby influencing the interpretation of observations.

astro-ph.GA↗

arXiv2026

Electric and spin current vortices in altermagnets

Altermagnets constitute a class of collinear magnets with momentum-dependent spin splitting and vanishing net magnetization. Direct observation of the characteristic altermagnetic spin splitting, however, remains challenging. Indirect signatures can be obtained via transport studies, which so far have only considered homogeneous driving fields. We propose to leverage nonuniform electric fields and spin density gradients to probe the shape and the spin polarization of altermagnetic Fermi surfaces via transport measurements. By using both a semiclassical Boltzmann approach and a lattice Keldysh formalism, we show that altermagnets excite swirling electric and spin currents whose profiles depend on the relative orientation of altermagnetic lobes with respect to the sample boundaries. These currents can be measured via magnetometry techniques. Unlike previous proposals considering the hydrodynamic regime of transport, swirling currents are observed even in the Ohmic regime and rely exclusively on the altermagnetic spin splitting, with no swirls observed in ferromagnets. The electric and spin current vortices predicted here provide a different altermagnetic signature in an experimentally accessible setup.

cond-mat.mes-hall↗

arXiv2025

Bound states of quasiparticles with quartic dispersion in an external potential: WKB approach

The Wentzel-Kramers-Brillouin semiclassical method is formulated for quasiparticles with quartic-in-momentum dispersion which presents the simplest case of a soft energy-momentum dispersion. It is shown that matching wave functions in the classically forbidden and allowed regions requires the consideration of higher-order Airy-type functions. The asymptotics of these functions are found by using the method of steepest descents and contain additional exponentially suppressed contributions known as hyperasymptotics. These hyperasymptotics are crucially important for the correct matching of wave functions in vicinity of turning points for higher-order differential equations. A quantization condition for bound state energies is obtained, which generalizes the standard Bohr-Sommerfeld quantization condition for particles with quadratic energy-momentum dispersion and contains non-perturbative in $\hbar$ correction. This non-perturbative correction, usually associated with tunneling effects or the presence of complex turning points, occurs even for the harmonic potential with quartic dispersion where complex turning points and tunneling are absent. The quantization condition is used to find bound state energies in the case of quadratic and quartic potentials.

cond-mat.str-el↗

arXiv2025

Internal kinematics of dwarf galaxies orbitally moving in ultralight dark matter

For dwarf galaxies modeled as deformed Plummer spheres and orbitally moving in ultralight dark matter halo of the Milky Way, the torque induced by the dynamical friction force is determined. The impact of this torque, as well as the torque produced by the gravitational force of the Milky Way, on the internal kinematics of dwarf galaxies is studied. Possible oscillations of dwarf galaxies caused by the tidal torque and misalignment of dwarf galaxies with respect to their equilibrium position are investigated and the corresponding frequencies and periods of oscillations are found.

astro-ph.GA↗

arXiv2025

Analytic calculation of dynamical friction for Plummer sphere in ultralight dark matter

The dynamical friction force acting on a spatially extended probe (globular clusters and dwarf galaxies) moving in the environment of ultralight bosonic dark matter in the state of the Bose-Einstein condensate is determined. Modeling the probe as a Plumer sphere of radius $l_p$, the radial and tangential components of the dynamic friction force are found in an analytic form, which reduce in the limit $l_p \to 0$ to the corresponding analytic expressions obtained in the literature in the case of a point probe. The dependence of the dynamical friction force on boson particle mass $m$ was analyzed and found to be non-monotonous in the interval $10^{-23} - 10^{-21}$eV.

astro-ph.GA↗

arXiv2025

Surface states and finite size effects in triple-fold semimetals

Triple-fold or pseudospin-1 semimetals belong to a class of multi-fold materials in which linearly dispersive bands and flat bands intersect at the same point, forming triple-fold crossing points. We conduct an analytical investigation of topologically protected Fermi arc surface states and finite-size effects in three-dimensional (3D) triple-fold and doubly degenerate triple-fold semimetals in continuum low-energy models. Higher topological charge of the triple-fold crossing points leads to two Fermi arcs connecting the nodes. For a single triple-fold crossing point, we found that no term in the Hamiltonian with momentum-independent elements can open a gap, prompting us to consider doubly-degenerate triple-fold fermions, where the gap can be opened by mixing the degenerate copies. Thin films of triple-fold semimetals allow for mixing between the surface and bulk states in addition to the discretization of energy levels of the latter.

cond-mat.mes-hall↗

arXiv2025

Viscoelastic tensor and hydrodynamics of altermagnets

We calculate the viscoelasticity tensor for altermagnets and formulate the corresponding hydrodynamic equations. The anisotropy of altermagnetic Fermi surfaces allows for additional terms in the viscoelasticity tensor and is manifested in transport properties, including electron and spin flows in a channel and nonlocal responses. In the channel geometry, the altermagnetic spin splitting leads to nontrivial spin density and spin current. Like the electric current, the spin current acquires a Poiseuille profile for no-slip boundary conditions. In nonlocal responses, the altermagnetic anisotropy affects current streamlines and electric potential distributions in the viscous regime. Our results provide signatures of the hydrodynamic transport regime in altermagnets, potentially facilitating its experimental studies and discovery.

cond-mat.str-el↗

arXiv2025

Dynamical friction in ultralight dark matter: Plummer sphere perspective

In models of dark matter composed of feebly interacting ultralight bosons in the state of Bose-Einstein condensate, the dynamical friction force acting on circularly moving globular clusters modelled as Plummer spheres is determined. Analytic expressions for both radial and tangential components of the dynamical friction force are given. We reveal that the dynamical friction force for the Plummer sphere deviates from that for a point probe of the same mass for a significantly large ratio of the Plummer sphere radius to its orbital radius, as well as for large values of the Mach number.

astro-ph.GA↗

arXiv2025

Vortex Lines in Ultralight Bosonic Dark Matter around Rotating Supermassive Black Holes

Theoretical analysis of the interaction between superfluid dark matter and rotating supermassive black holes offers a promising framework for probing quantum effects in ultralight dark matter and its role in galactic structure. We study how black hole rotation influences the state of ultralight bosonic dark matter, focusing on the stability and dynamics of vortex lines. The gravitational effects of both dark matter and the black hole on the physical properties of these vortex lines, including their precession around the black hole, are analyzed.

hep-ph↗

arXiv2024

Dynamical friction in rotating ultralight dark matter galactic cores

Dynamical friction and stellar orbital motion in spiral galaxies with dark matter composed of ultralight bosons in the state of rotating Bose-Einstein condensate (BEC) are studied. It is found that the dynamical friction force is significantly affected by the topological charge of the vortex structure of the BEC core with the strongest effect at distances near the galactic center. It is also shown that the ultralight dark matter self-interaction plays an important role in studying the dynamical friction.

astro-ph.GA↗

arXiv2024

Viscoelastic response and anisotropic hydrodynamics in Weyl semimetals

We study viscoelastic response in Weyl semimetals with broken time-reversal symmetry. The principal finding is that topology and anisotropy of the Fermi surface are manifested in the viscoelasticity tensor of the electron fluid. In the dynamic (interband) part of this tensor, the anisotropy leads to a qualitatively different, compared with isotropic models, scaling with frequency and the Fermi energy. The components of the viscosity tensor determined by the Fermi-surface properties agree in the Kubo and kinetic formalisms; the latter, however, misses the anomalous Hall viscosity originating from filled states below the Fermi surface. The anisotropy of the dispersion relation is also manifested in the acceleration and relaxation terms of the hydrodynamic equations providing means to probe the anisotropy in transport experiments.

cond-mat.mes-hall↗

arXiv2024

Reduced QED with few planes and fermion gap generation

The formalism of reduced quantum electrodynamics is generalized to the case of heterostructures composed of few atomically thick layers and the corresponding effective (2+1)-dimensional gauge theory is formulated. This dimensionally reduced theory describes charged fermions confined to $N$ planes and contains $N$ vector fields with Maxwell`s action modified by non-local form factors whose explicit form is determined. Taking into account the polarization function, the explicit formulae for the screened electromagnetic interaction are presented in the case of two and three layers. For a heterostructure with two atomically thick layers and charged fermions described by the massless Dirac equation, the dynamical gap generation of the excitonic type is studied. It is found that additional screening due to the second layer increases the value of the critical coupling constant for the gap generation compared to that in graphene.

cond-mat.str-el↗

arXiv2024

Electron binding energy of a donor in bilayer graphene with gate-tunable gap

In gapped bilayer graphene, similarly to conventional semiconductors, Coulomb impurities (such as nitrogen donors) may determine the activation energy of its conductivity and provide low temperature hopping conductivity. However, in spite of the importance of Coulomb impurities, nothing is known about their electron binding energy $E_b$ in the presence of gates. To close this gap, we study numerically the electron binding energy $E_b$ of a singly charged donor in BN-enveloped bilayer graphene with the top and bottom gates at distance $d$ and gate-tunable gap $2Δ$. We show that for $10 < d < 200$ nm and $1 < Δ< 100$ meV the ratio $E_b/Δ$ changes from 0.4 to 1.5. The ratio $E_b/Δ$ stays close to unity because of the dominating role of the bilayer polarization screening which reduces the Coulomb potential well depth to values $\sim Δ$. Still the ratio $E_b/Δ$ somewhat decreases with growing $Δ$, faster at small $Δ$ and slower at large $Δ$. On the other hand, $E_b/Δ$ weakly grows with $d$, again faster at small $Δ$ and slower at large $Δ$. We also studied the effect of trigonal warping and found only a small reduction of $E_b/Δ$.

cond-mat.mes-hall↗

arXiv2023

Hydrodynamical approach to chirality production during axion inflation

We study chirality production in the pseudoscalar inflation model of magnetogenesis taking into account the Schwinger effect and particle collisions in plasma in the relaxation time approximation. We consider the Schwinger production of one Dirac fermion species by an Abelian gauge field in two cases: (i) the fermion carries only the weak charge with respect to the U(1) group and (ii) it is also charged with respect to another strongly coupled gauge group. While the gradient-expansion formalism is employed for the description of the evolution of gauge field, plasma is described by hydrodynamical approach which allows us to determine the number, energy density, and chirality of produced fermions. It is found that while chirality production is very efficient for both, weakly and strongly interacting fermions, the resulting gauge field is typically stronger in the case of strongly interacting fermions due to suppression of the Schwinger conductivity by particle collisions.

hep-ph↗

arXiv2023

Magnetogenesis in non-local models during inflation

The generation of magnetic fields during inflation in an electromagnetic model with a non-local form factor in Maxwell`s action is studied. The equations of motion for the electromagnetic field are derived and solved. It is found that the conformal symmetry breaking due to the non-local form factor does not lead to the generation of magnetic fields during inflation in the absence of interaction with the inflaton field. If such a coupling takes place, then the presence of the form factor inhibits the generation of primordial magnetic fields compared to the case where the non-local form factor is absent.

gr-qc↗