Spin of primordial black holes in the model with collapsing domain walls

The angular momentum (spin) acquisition by a collapsing domain wall at the cosmological radiation-dominated stage is investigated. During the collapses, primordial black holes and their clusters can be born in various mass ranges. Spin accumulation occurs under the influence of tidal gravitational perturbations from the surrounding density inhomogeneities at the epoch when the domain wall crosses the cosmological horizon. It is shown that the dimensionless spin parameter can have the small values aS < 1 only for primordial black holes with masses M > 10-3M☉, whereas less massive black holes receive extreme spins aS ≃ 1. It is possible that primordial black holes obtain an additional spin due to the vector mode of perturbations.

Electron acceleration by the lower-hybrid-drift instability at Mercury: an extended quasilinear model

&lt;p&gt;Density inhomogeneities are ubiquitous in space and astrophysical plasmas, in particular at contact boundaries between different media. They often correspond to regions that exhibits strong dynamics on a wide range of spatial and temporal scales. Indeed, density inhomogeneities are a source of free energy that can drive various plasma instabilities such as, for instance, the lower-hybrid-drift instability&lt;strong&gt; &lt;/strong&gt;which in turn transfers energy to the particles through wave-particle interactions and eventually heats the plasma. Here, we address the role of this instability in the Hermean plasma environment were kinetic processes of this fashion are expected to be crucial in the plasma dynamics and have so far eluded the measurements of past missions (Mariner-X and MESSENGER) to Mercury. &lt;br /&gt;The goal of our work is to quantify the efficiency of the lower-hybrid-drift instability to accelerate and/or heat electrons parallel to the ambient magnetic field.&lt;br /&gt;To reach this goal, we combine two complementary methods: full-kinetic and quasilinear models.&lt;br /&gt;We report self-consistent evidence of electron acceleration driven by the development of the lower-hybrid-drift instability using 3D-3V full-kinetic numerical simulations. The efficiency of the observed acceleration cannot be explained by standard quasilinear theory. For this reason, we develop an extended quasilinear model able to quantitatively predict the interaction between lower-hybrid fluctuations and electrons on long time scales, now in agreement with full-kinetic simulations results. Finally, we apply this new, extended quasilinear model to a specific inhomogeneous space plasma boundary: the magnetopause of Mercury, and we discuss our quantitative predictions of electron acceleration in support to future BepiColombo observations.&lt;/p&gt;

Studying the small-scale structure of a polarization jet during the April 20, 2018 geomagnetic storm

In this work, we study the small-scale structure of a polarization jet in the subauroral region during the April 20, 2018 geomagnetic storm. We report measurement results of plasma parameters inside the polarization jet with a maximum sampling rate of up to 1 kHz, obtained with Langmuir probes installed on the NorSat-1 microsatellite. The study establishes the presence of temperature and electron density inhomogeneities inside the polarization jet with spatial dimensions of tens to hundreds of meters. The previously known features of the polarization jet evolution have been confirmed. We have also found that the distribution of the electron temperature inside the jet forms two separate peaks as the geomagnetic activity develops during the storm.

Studying the small-scale structure of a polarization jet during the April 20, 2018 geomagnetic storm

In this work, we study the small-scale structure of a polarization jet in the subauroral region during the April 20, 2018 geomagnetic storm. We report measurement results of plasma parameters inside the polarization jet with a maximum sampling rate of up to 1 kHz, obtained with Langmuir probes installed on the NorSat-1 microsatellite. The study establishes the presence of temperature and electron density inhomogeneities inside the polarization jet with spatial dimensions of tens to hundreds of meters. The previously known features of the polarization jet evolution have been confirmed. We have also found that the distribution of the electron temperature inside the jet forms two separate peaks as the geomagnetic activity develops during the storm.

The effects of density inhomogeneities on the radio wave emission in electron beam plasmas

Type III radio bursts are radio emissions associated with solar flares. They are considered to be caused by electron beams travelling from the solar corona to the solar wind. Magnetic reconnection is a possible accelerator of electron beams in the course of solar flares since it causes unstable distribution functions and density inhomogeneities (cavities). The properties of radio emission by electron beams in an inhomogeneous environment are still poorly understood. We capture the nonlinear kinetic plasma processes of the generation of beam-related radio emissions in inhomogeneous plasmas by utilizing fully kinetic particle-in-cell code numerical simulations. Our model takes into account initial electron velocity distribution functions (EVDFs) as they are supposed to be created by magnetic reconnection. We focus our analysis on low-density regions with strong magnetic fields. The assumed EVDFs allow two distinct mechanisms of radio wave emissions: plasma emission due to wave–wave interactions and so-called electron cyclotron maser emission (ECME) due to direct wave–particle interactions. We investigate the effects of density inhomogeneities on the conversion of free energy from the electron beams into the energy of electrostatic and electromagnetic waves via plasma emission and ECME, as well as the frequency shift of electron resonances caused by perpendicular gradients in the beam EVDFs. Our most important finding is that the number of harmonics of Langmuir waves increases due to the presence of density inhomogeneities. The additional harmonics of Langmuir waves are generated by a coalescence of beam-generated Langmuir waves and their harmonics.

Electromagnetic electron hole generation: theory and PIC simulations

&lt;div&gt; &lt;div&gt; &lt;div&gt; &lt;p&gt;Recent MMS observations (&lt;em&gt;e.g.&lt;/em&gt; [Holmes et al, 2018, Steinvall et al., 2019]) exploring various regions of the magnetosphere have found solitary potential structures call Electron phase-space Hole (EH). These structures have kinetic scale (dozens of Debye lengths) and persist during long time (dozens of plasma frequency periods). EH are characterized by a bipolar electric field parallel to ambient magnetic field and fastly propagate along this latter (a few tenths of speed light). We have created a 3D Bernstein-Greene-Kruskal (BGK) model (as [Chen et al, 2004]) adapted to various magnetospheric ambient magnetic fields. BGK model results depend on choice of potential shape and passing distribution function at infinity (before EH potential interaction).&lt;/p&gt; &lt;p&gt;2D-3V Particle-In-Cell simulations have been developed with the fully kinetic code Smilei [Derouillat et al, 2017], using real magnetosphere plasma parameters. Solitary waves in the magnetotail are three-dimensional potentials which can be generated through nonlinear evolution of an electron beam instability (or bump on tail). The simulated EH are comparable to the EH observed in the magnetosphere with the same parameters.&lt;/p&gt; &lt;p&gt;We have also investigated the EH formation with density inhomogeneities using a BGK stability model we have developed. Indeed, density inhomogeneities exist notably in interplanetary plasmas. As a result taking into account the background density inhomogeneities, significantly alters the stability criteria. We have performed 2D-3V PIC simulations with realistic inhomogeneous density background (smaller than 10% of mean density) to understand such a type of EH formation.&lt;/p&gt; &lt;p&gt;&lt;strong&gt;References:&lt;/strong&gt;&lt;/p&gt; &lt;ul&gt;&lt;li&gt;Holmes et al., J. Geophys. Res. Space Phys. 123, 9963, 2018&lt;/li&gt; &lt;li&gt;Steinvall et al., Phys. Rev. Lett. 123, 255101, 2019&lt;/li&gt; &lt;li&gt;Chen et al., Phys. Rev. E 69, 055401, 2004&lt;/li&gt; &lt;li&gt;Derouillat et al., Comput. Phys. Commun. 222, 351, 2017&lt;/li&gt; &lt;/ul&gt;&lt;div&gt; &lt;div&gt; &lt;div&gt; &lt;div&gt; &lt;div&gt; &lt;div&gt; &lt;div&gt; &lt;div&gt; &lt;div&gt;&amp;#160;&lt;/div&gt; &lt;/div&gt; &lt;/div&gt; &lt;/div&gt; &lt;/div&gt; &lt;/div&gt; &lt;/div&gt; &lt;/div&gt; &lt;/div&gt; &lt;/div&gt; &lt;/div&gt; &lt;/div&gt;

Influence of plasma inhomogeneity with allowance for bremsstrahlung on absorption of an Alfvén wave by a dissipative plasma

The paper investigates a mathematical model of the absorption of an Alfvén wave in an inhomogeneous incompressible dissipative plasma using the equations of two-fluid electromagnetic hydrodynamics. It is shown that a consequence of taking into account bremsstrahlung is the finiteness of the penetration depth of the Alfvén wave into an inhomogeneous plasma and a steady quasi-stationary regime of the Alfvén wave absorption. Density inhomogeneities of two types are considered – hump and hollows, which are distributed according to the Gaussian law. The dependences on the value of the hump of the penetration depth of the Alfvén wave into the inhomogeneous plasma and the maximum temperatures of electrons and ions are obtained. The study showed that an increase in the amplitude of the incident wave leads to an increase in the maximum values of the electron and ion temperatures, as well as the depth of penetration of the Alfvén wave into an inhomogeneous dissipative plasma.

Velocity structure and density inhomogeneities of the White Sea crust

The study area is the White Sea basin and adjacent territories. The relevance of the work carried out here is determined by active geodynamics, kimberlite magmatism, and prospects for the hydrocarbon search. The authors set the goal to model the velocity structure of the region’s crust using data from instrumental observations and the Integro software package. A comprehensive interpretation of gravimetric, magnetometric, seismic, petrophysical and geological data has been carried out. With the help of 2D models based on the DSZ profiles and digital maps of geophysical fields, refined density structures of local sections of the earth’s crust have been specified. The developed 3D density model gives a general picture of the deep structure of the region’s crust. Within its framework, the spatial positions of the layers of the velocity reference model are determined and their connections with density inhomogeneities and geophysical anomalies are established.

Neutrino Cooling of Primordial Hot Regions

The effect of neutrino cooling of possible primary regions filled by hot matter is discussed. Such regions could be obtained from the primordial density inhomogeneities and survive up to the modern epoch. The inhomogeneities could be caused by a symmetry breaking during the inflationary stage. We show that the final temperature of such region should be ∼10 keV provided that the initial temperature is within the interval 10 keV ÷ 100 MeV. The cooling is realized due to the weak nuclear reactions containing n−p transition. The lower limit 10keV is accounted for by suppression of the reactions rates because of the threshold effect and particle concentration decrease.