arXiv subjects

Maxim Lyutikov

Publications and source records attributed to Maxim Lyutikov.

At least 19 recordsLinked to original sources

arXiv2026

Chaotic cosmic ray acceleration in nonlinear Alfven waves

We demonstrate that motion of a particle in a single coherent linearly polarized (LP) Alfven wave with relative amplitude $\delta = B_w /B_0 \gtrsim 0.25 $ becomes chaotic. As a result, a sufficiently strong, near resonant Alfven waves ($r_L k_\parallel \sim 1$, $r_L $ is relativistic cyclotron radius, $k_\parallel$ is wavevector) can lead to transient trapping and phase mixing, imitating classical scattering. Evolution of pitch angle via Alfven chaos is non-diffusive - a particle on trapped trajectory can reverse its velocity in one scattering event. This both avoids the problem of the 90$^\circ$ barrier, and increases the acceleration rate for those special particle.

astro-ph.HE↗

arXiv2026

Electromagnetic Emission from a Black Hole Evaporating in External Magnetic Field

We describe a classical (non-quantum) radiation process: additional (to Hawking) emission by a black hole evaporating in an external magnetic field in vacuum. The electromagnetic radiation process is completely electric charge-free and bears some resemblance to the Gertsenshtein-Zel'dovich effect. The time evolution of the spacetime metric perturbs a static background magnetic field, inducing a radiative field that acts as an effective electromagnetic source even in the absence of physical charges or currents. To isolate the dynamic effects of the time-dependent spacetime on the external magnetic field, we approximate Hawking radiation as a spherically symmetric outflow of null fluid governed by the prescribed time-dependence of the central mass $M(t)$. We employ Laplace transform, which selects the retarded outgoing branch of the electromagnetic response, producing fields proportional to $\Theta(t-r)$ and thereby fixing a causal radiative arrow of emission. The emitted spectral energy is red-dominated, scaling as $d\mathcal{E}_B/d\omega \propto B_0^2 m_0^2 \tau_H^{-2/3} \omega^{-8/3}$, where $\tau_H$ is the Hawking evaporation timescale, and corresponds to a pure Transverse Electric (TE) mode. There is no final bright burst at the end of the evaporation. We offer classical analogues for this mechanism as transmission-line emission and, separately, as the displacement current emission from a medium with time-varying dielectric permittivity.

astro-ph.HE↗

arXiv2026

Particle dynamics in nonlinear electromagnetic waves: chaos onset, diffusive heating, and wave surfing

We investigate the dynamics of charged particles interacting with ultra-intense electromagnetic X-modes in strongly magnetized plasmas. We demonstrate that particle motion becomes chaotic for relative wave intensities $\delta = B_w/B_0 \gtrsim 0.25$ (not above the field reversal threshold $\delta \geq 1$). The transition to chaos occurs via the Chirikov resonance overlap mechanism and the related destruction of Kolmogorov-Arnold-Moser (KAM) tori. The maximum Lyapunov exponent increases logarithmically with $\delta$, even though the unmagnetized $\delta \to \infty$ limit is strictly integrable. In the $\delta \gg 1$ regime, incomplete re-laminarization of the phase space flow leads to two distinct populations: (i) the majority of particles undergoing stochastic diffusion, and (ii) a fraction of particles that become phase-locked with the wave, experiencing macroscopic intermittent surfing (L\'evy flights). The 1D Particle-In-Cell simulations using the EPOCH code in the highly magnetized ($\sigma \gg 1$) and under-dense regime are generally consistent with the Hamiltonian single-particle theory. The dissipation fraction of the initial EM energy remains mild.

physics.plasm-ph↗

arXiv2026

Long-period radio transient PSR J0901-4046 is not an Isolated White Dwarf Pulsar

We report the {\it Chandra} non-detection of PSR J0901$-$4046, a $P=75.89 $ seconds long-period radio transient (LPT). For a distance of 467 pc, the upper limit on X-ray luminosity is $L_X \leq$ few $\times 10^{28}$ erg s$^{-1}$. For the measured $P$ and $\dot{P}$, this upper limit, approximately 50 times lower than the previous {\it Swift} observations, is comparable to the spin-down luminosity of a neutron star, but would be approximately four orders of magnitude smaller than the spindown power of a white dwarf. Our results disfavor isolated WDs as the central star in PSR J0901$-$4046. We suggest that the isolated LPTs are powered by magnetic dissipation (not rotation), in a way similar to magnetars' radio emission.

astro-ph.HE↗

arXiv2026

Fast Radio Bursts produced during collapse of macroscopic X-mode in magnetized pair plasma

We demonstrate that in highly magnetized pair plasma nonlinear long-wavelength X-modes experience wave collapse/breaking, whereby the wave undergoes severe spatial steepening, driven by nonlinear modifications of the refractive index and strong ponderomotive forces. The collapse/wave breaking occurs in a narrow parameter regime, when the fluctuating part of the magnetic field exceed the guide field, and plasma magnetization is close to the current starvation regime. This regime is naturally achieved in highly magnetized neutron stars, magnetars. Breaking during a fraction of the dynamic timescale, and quickly generates high-k modes. The initial EM energy, spread over large spatial scales, is squeezed into these highly localized, short-wavelength (yet macroscopic) singular pulses. The corresponding electromagnetic ``foam'' spectrum is red, $E_k \propto k^{-2}$, while the particles' spectrum is exceptionally hard, $f(\gamma) \propto \gamma^0$ The wave collapse produces short bright EM pulses - astrophysical Fast Radio Bursts. The highest energy particles may produce short contemporaneous high energy bursts.

astro-ph.HE↗

arXiv2026

Guitar Nebula: extreme accelerator in extreme environment

Guitar nebula is a prime example of a class of bow-shock pulsar wind nebulae (PWNe), powered by a wind of a supersonically moving neutron star. Bow-shock PWNe can probe particle acceleration processes in relativistic pulsar winds, as well as the structure of the interstellar medium (ISM). We demonstrate that the Guitar is an exceptional object in a number of ways. First, particles escaping the PWN and forming the X-ray ``kinetic jet'' need to be accelerated to the energies corresponding to the maximal electric potential of the neutron star $\eta_\text{acc}\gtrsim 3/4$ : it is another example of the class of extreme accelerators. Second, exceptionally bright H$_\alpha$ emission requires that the central pulsar PSR J2225+6535 passes through a dense, low ionization ISM region. Bright X-ray emission of the ``kinetic jet'' then also requires exceptionally high magnetic field, $\sim 100~\mu$G. We hypothesize that Guitar passes through the one of long-predicted, narrow dense shells of an old supernova remnant, currently in the ``pressure-driven snowplow'' regime.

astro-ph.HE↗

arXiv2026

Tearing of charged current layers

Astrophysical current layers, e.g., in pulsar winds, can be electrically charged, while the plasma is charge-symmetric, $e^\pm$. Using PIC simulations, we investigate dynamics and plasmoid formation (tearing instability) in charged Harris-type and rotational current layers. Electrically charged current layers, initially in global force-balance, are electrostatically unstable: the resulting dynamics is an intricate interplay between electrostatic Bernstein waves (BWs) and the current tearing mode. Besides overall density and magnetic field, plasma temperature is an important factor. In the charged Harris sheet set-up, the quickly generated BW are trapped within the layers (internally reflected at the upper hybrid resonance). BWs quickly redistribute the charge modifying the initial stage of tearing, but without strongly affecting overall plasmoid growth; resulting plasmoids are mildly charged. In rotational current layers: (i) even initially overall uncharged configurations develop large fluctuations of charge density; (ii) overall dynamics depends on the initial overall temperature; (iii) for certain combination of parameters tearing rate is greatly increased in the charged case.

astro-ph.HE↗

arXiv2026

Powerful parametric instability of Alfven waves in astrophysical pair plasma

We demonstrate that in highly magnetized pair plasmas, nonlinear Alfven waves with wave-number $k \leq k_0 = ω_p^2 /(δω_B)$ ($δ=( δB)/B_0$ are relative fluctuations of the magnetic field) experience powerful modulational instability. In the two-fluid approximation, we develop an analytic set-up for circularly polarized (CP) Alfven mode in its frame (where the initial configuration is stationary; it is moving with relativistic, amplitude-dependent Alfven velocity $v_A (σ, δ) $, while both charges experience different, amplitude-dependent, synchrotron gyration). PIC simulations using EPOCH code demonstrate that for Alfven waves with $k$ near $k_0$, large, parametrically-driven density fluctuations develop, and lead to fast modulational instability. Charge separation effects, for a CP wave in magnetized pair plasma, might be temporarily important; on longer time-scales the density fluctuations are charge neutral and in symmetric pair plasma quickly grow to large amplitudes. In highly magnetized plasma, $σ\gg 1$, high frequency modes $k / k_0 \sim (2-3 ) \times σ\gg 1 $ are quickly generated; for smaller plasma magnetization, the dominant mode is at the Bragg's condition $k = 2 k_0$. Long term behavior of CP and LP modes is similar. We discuss application of the results to the physics of Fast Radio Bursts generated/propagating in the magnetospheres of magnetars.

astro-ph.HE↗

arXiv2026

Complete reflection of nonlinear electromagnetic waves in underdense pair plasmas enabled by dynamically formed Bragg-like structures

In contrast to relativistically induced transparency in electron--ion plasmas, where nonlinear electromagnetic waves render initially opaque plasmas transparent, we show using kinetic simulations that such waves can instead make initially transparent pair plasmas fully reflective. The difference is mass symmetry, which eliminates charge-separation electric fields. As the wave compresses the pair plasma, weak reflection seeds density spikes that form a moving Bragg-like grating. Enhanced reflection enables a transition to a regime where the plasma--vacuum interface sustains complete reflection.

physics.plasm-ph↗

arXiv2026

Alfven-winged pulsar

Detecting possible electromagnetic precursors to the gravitational signal from merging compact objects is challenging, but it can reveal intricate physical properties of the merging stars through their gravitational and electromagnetic interactions. We demonstrate, using 3D Particle-In-Cell simulations, that a neutron star moving through the magnetosphere of a merging companion generates a complicated system of dissipative currents, a relativistic analogue of planetary Alfven wings. Generated electric currents carry a large fraction of the electromagnetic power intersected by the neutron star. These currents may lead to the generation of beamed, pulsar-like coherent radio and high-energy emission. Orbital modulation will produce a nearly periodic signal, an Alfven-winged pulsar.

astro-ph.HE↗

arXiv2026

Relativistically-strong electromagnetic waves in magnetized plasmas

Using a two-fluid approach, we consider the properties of relativistically nonlinear (arbitrary $a_0$), circularly polarized \EM\ waves propagating along magnetic field in electron-ion and pair plasmas. Dispersion relations depend on how wave intensity scales with frequency, $a_0 (ω)$. For superluminal branches, the nonlinear effects reduce the cut-off frequency, while the general form of the dispersion relations $ω(k)$ remains similar to the linear case. For subluminal waves, whistlers and Alfven, a new effect appears: dispersion curves effectively terminate at finite $ω^\ast - k^\ast$, where the group velocity becomes zero. Qualitatively, subluminal modes with fluctuating electric field larger than the guide field, $E_w (ω) \geq B_0$, cannot propagate. In extended systems, e.g., within magnetospheres of neutron stars, this leads to opening of the magnetosphere by a strong wave.

astro-ph.HE↗

arXiv2026

Dynamics and stability of magnetized AGN-blown bubbles in clusters of galaxies

We perform MHD simulations of AGN-blown bubbles in the Intercluster Medium (ICM) containing large-scale coherent magnetic fields. We assume that bubbles, created by the intermittent jets from Active Galactic Nuclei, quickly relax to the Woltjer-Taylor spheromak-like state, with internal plasma beta-parameter $\sim 1$. We demonstrate that such bubbles rising through hydrostatically-stratified atmosphere are magnetically stabilized against fluid interface instabilities, remaining coherent for a long time. Typical velocity is $ v /c_s \sim \sqrt{R/H} \leq 1 $ ($c_s$ is sound speed, $R$ is the bubble size, $H$ is the scale height). Current-driven instabilities (internal kinks) lead to bubble's tilting, but develop on long time scales, and remain unimportant, leading to minor modifications of the internal structure. Our results explain apparent long-term stability of ICM cavities. Subsonically rising stable bubbles dissipate in their wake approximately the energy initially injected by the jet, and may efficiently reheat the clusters cores in a ``gentle'' way.

astro-ph.GA↗

arXiv2026

Production of Jets before Neutron Star Mergers

We demonstrate that magnetospheric interactions between merging neutron stars (NSs) generate dual-jetted current outflows, analogous to the Alfv\'{e}n wings observed during planetary interactions in the Solar System. Using 3D relativistic MHD simulations, we model the interaction as a conducting sphere moving through a highly magnetized plasma of the companion's magnetosphere. Unusually, the interaction operates in a regime that is relativistic yet sub-Alfv\'{e}nic. Electromagnetic draping amplifies magnetic fields in a narrow layer near the stellar surface, leading to the generation of electric currents along the local magnetic field. The generation of beamed outflows enhances the instantaneous power of the pulsar-like radio and high-energy emission, produces spin/orbital modulations, and is likely to lead to observable precursor emission preceding the main gravitational wave event.

astro-ph.HE↗

arXiv2026

Electromagnetic ghosts in pair plasmas

Collisions of two weakly nonlinear, $a_0 \ll 1$, counter-propagating EM pulses in pair plasma leave behind a long-surviving collection of localized waves, {\it an electromagnetic ghost}. Waves are trapped (localized) by the random large density fluctuations created by the beat between the pulses. The process is similar to random plasma density grating and/or Anderson-like wave localization. Structures survive for long, mesoscale times, while the EM energy slowly bleeds through high density walls of the density trap. Large guide magnetic field, $ω_B \geq $ few $ω$, suppresses the formation of the ghosts.

physics.plasm-ph↗

arXiv2025

Anderson self-localization of light in pair plasmas

We demonstrate that in pair plasma weakly nonlinear electromagnetic waves, $a_0 \leq 1$, experience Anderson self-localization. The beat between the driver and a back-scattered wave creates charge-neutral, large random, {yet correlated} density fluctuations $\delta n/n_0 \gg 1$, and corresponding fluctuations of the dielectric permittivity $\epsilon$ (random plasma density grating). Propagating in quasi-1D, waves in a medium with spatially random self-created fluctuations of dielectric permeability experience localization. In the linear regime, the instability can be classified as Induced Brillouin Scattering; it is described by the parameter $\rho _L = \left( a_0 { \omega_{p}/ }{\omega}\right)^{2/3} \ll 1 $, related to the Pierce parameter of Free Electron Lasers. In the cold case, {the growth rate is $\Gamma \approx \rho _{L} \omega \ll 1 $} ($a_0 $ is laser nonlinearity parameter, $\omega_p$ is plasma frequency, $\omega$ is the laser frequency). Anderson self-localization of light leads to (i) reflection of EM waves by the under-dense pair plasma; (ii) a wave already present inside the plasma separates into bright trapped pockets and dark regions. Mild initial thermal spread with $\Theta \equiv k_B T/(m_e c^2) \approx a_0^2$, restores wave propagation by suppressing the seeds of parametrically unstable density fluctuations. A circularly polarized driver produces linearly polarized structures, with position angle varying randomly between the bright pulses. {Time-variability of the resulting density structures does not suppress localization due to remaining correlations (not white noise)}. We discuss possible applications to astrophysical Fast Radio Bursts.

physics.plasm-ph↗

arXiv2025

Relativistic van Allen belts in magnetospheres of pulsars and white dwarfs

We consider dynamics and multi-frequency emission patterns of relativistic van Allen belts - particles trapped in the magnetosphere of neutron stars and white dwarths. We account for synchrotron radiative losses and effects of relativistic beaming of radiation. The system is non-Hamiltonian (non-energy conserving): this results in a wide non-scalable variety of spectral and temporal behaviors. There are three types of trapped particles' trajectories: (i) oscillating (particles experience multiple bounces between magnetic bottles); (ii) precipitating (particles fall onto the star with finite transverse momentum); (iii) freezing (particles lose their transverse motion before falling onto the star). The separation between regimes (i) and (ii) depends both on the ratio of the bounce time to cooling time at magnetic equator $τ_{ 0} $, $η_0 = R_0/( c τ_0) \leq 1$, as well as the initial pitch angle $α_0$; regimes (i) and (ii) are separated at $ α_{0, crit} \sim η_0^{3/10}$. Resulting emission patterns show large variety: single or double peaked, and/or flat hat with sharp walls. Multi-frequency profiles - in optical and X-ray bands - can be used to get information about physical (magnetic field strength, injection point) and geometrical (dipolar angle and the line of sight) properties.

astro-ph.HE↗

arXiv2025

Multi-Messenger Windows on the Universe: detecting precursor emission to compacts' mergers

We provide an overview of various mechanisms, and corresponding powers, of precursor emission to compacts' mergers to be detected by LIGO-Virgo-KAGRA (LVK) collaboration. Expected peak powers, $\leq 10^{43}$ erg s$^{-1}$, are not sufficiently high to be detected by all-sky high-energy satellites (unless beamed). The best chance is the detection of possible coherent radio emission, producing observable signals up to $\sim$ Jansky of flux density. Low-frequency phased array telescopes like LOFAR, the MWA and DSA-2000 are best suited due to their large instantaneous sky coverage. Time-wise, in addition to LIGO early warning alerts up to a minute before the merger, the dispersive delay at lower frequencies of $\sim$ 300 MHz can be of the order of minutes. Optical detections are the most challenging.

astro-ph.HE↗

arXiv2025

Cherenkov emission by a fast-moving uncharged Schwarzschild black hole

We demonstrate that, in the presence of an external magnetic field, an uncharged classical Schwarzschild black hole moving superluminally in a dielectric with permittivity $ε> 1$ produces Cherenkov emission. This is a new physical effect: classical (non-quantum) emission of electromagnetic waves by a completely charge-neutral ``particle.'' The governing equations (involving general relativity, electromagnetism, and the physics of continuous media) have no external electromagnetic source -- it is the distortion of the initial electromagnetic fields by the gravity of the black hole that plays the role of a superluminally moving source. The effect relies on nonzero values of both the magnetic field and the gravitational radius, as well as on the usual Cherenkov condition on the velocity, $v/c > 1/\sqrtε$. Unlike Cherenkov emission by a point charge, the effective source in this case is spatially distributed, with emission generated along the single Cherenkov emission cone. The emitted spectrum is red-dominated, with power $\propto dk_z /|k_z|$ for wave numbers $|k_z| \leq 1/R_G$, where $R_G$ is the Schwarzschild radius. We comment on possible observability of this process during black hole -- neutron star mergers.

hep-th↗