International Journal of Modern Physics D

The preface to the special issue of IJMPD “Challenging Problems of Particle physics and Astrophysics” briefly reviews some new ideas in the development of modern Astrophysics, Cosmology, Particle and Astroparticle physics inspired by discussions at the Fifth International Conference on Particle Physics and Astrophysics (ICPPA2020).

We consider some properties and possible observational manifestations of the very heavy primordial black holes (PBHs), with masses $\sim (10^9-10^{10})M_{\odot }$. These black holes should be surrounded by the dense dark matter and baryonic halos even at early cosmological epochs. There are mechanisms as for radiation emission in the centers due to accretion and for deep absorption of relic radiation at the periphery of the halos. We calculate the absorption profile in the 21cm line of atomic hydrogen by solving the equations of radiation transfer through the baryonic halo around a PBH. The calculations show that a spherical absorbing layer appears around the object, which can be observed with radio telescopes. Also, at some epochs, shock waves may form at the periphery of the objects. The accelerated charged particles can radiate in radio frequency band, so it is possible that these objects can explain the recently discovered radio circles.

The conventional Friedmann cosmology is known to be in tension with the existence of stable particles having interaction strength typical for supersymmetry and heavier than several TeV. A possible way to save life of such particles may be a modification of the standard cosmological expansion law in such a way that the density of these heavy relics would be significantly reduced. We study particle creation in the Starobinsky inflationary model for different decay channels of the scalaron. It is shown that the process of thermalization superheavy stable particles with the coupling strength typical for the GUT SUSY could be created with the density equal to the observed density of dark matter.

In the present investigation, compact stellar models are dealt with in the framework of the modified gravity theory, specifically of $f(𝕋,{𝒯})$ type. We have considered that the compact objects are following a spherically symmetric static metric and obtained the Einstein field equations in the spacetime of $f(𝕋,{𝒯})$. To make the Einstein equations solvable, we employ the methodology of conformal Killing vectors. Thereafter by using the MIT bag equation of state to the compact stars, considering that the stars are formed by strange quark, we find the solutions set. The solutions are examined via several physical testings which exhibit viability of the model.

In this paper, we discuss the mechanism for generating the lepton/baryon number and its subsequent conservation based on extra-dimensional evolution. The internal angular momentum of extra space is related to the lepton/baryon charge. Extra space metric is assumed to be initially asymmetric. Symmetries appear during inflation due to an increase in entropy. Using the multidimensional field toy model, we show that internal angular momentum can accumulate in fermions, which could explain the lepton/baryon asymmetry of the universe.

In this paper, we present some cosmological models with a hybrid scale factor (HSF) in the framework of general relativity (GR). The HSF fosters an early deceleration as well as a late-time acceleration and mimics the present Universe. The dynamical aspects of different cosmological models with HSF in the presence of different matter fields have been discussed.

In this paper, we analyze scenario with strongly interacting massive particles which follows from the Standard Model extension with singlet quark. The lightest new neutral hadron is stable, it can be interpreted as a candidate for hadronic dark matter. Here, we consider principal features of this scenario: large mass of new hadrons, fine and hyperfine splitting in the spectrum of hadron states, low-energy interaction with the standard particles. Both splitting effects lead to processes which can be registered in cosmic rays and deciphered as the hadronic dark matter manifestations. In this work, we reconsider and specify some results from our previous papers.

In this paper, we investigate the cosmological inflation in the context of a minimal matter–geometry coupling, which is based on the $f(R,T)$ gravity theory, where $f$ is a generic function of the curvature scalar $R$ and the trace $T$ of the energy–momentum tensor. Assuming that the slow-roll inflation conditions hold true in $f(R,T)$ gravity, we obtain the various inflation-related observables such as the tensor-to-scalar ratio $r$, the scalar spectral index $n_s$, the running ${\alpha }_s$ of the spectral index and the tensor spectral $n_T$ for two specific $f(R,T)$ models from the Hubble slow-roll parameters. To observe the viability of these models, a numerical analysis of such parameters has been done. The results showed that, by using the various values of free parameters, it is possible to obtain a viable compatible with the observational data.

When the vacuum like energy of the Higgs potential within the standard model undergoes electroweak phase transition, an influx of entropy into the primordial plasma can lead to a significant dilution of frozen out dark matter density that was already present before the onset of the phase transition. The same effect can take place if the early universe was dominated by primordial black holes of small mass, evaporating before the period of Big Bang Nucleosynthesis. In this paper, we calculate the dilution factor for the above-mentioned scenarios.

In this paper, vector hyperquark extension of the Standard Model with multicomponent dark matter scenario is analyzed. Due to the splitting of dark matter candidates masses, transitions between these components accompanied with final state photons radiation are possible. For these processes, we calculate cross-sections and expected gamma-ray fluxes from regions with an increased density of dark matter. Effect of possible luminescence induced by complex structure of dark matter sector is discussed.

Using GAIA EDR3 catalog, we present the detailed analysis of the two-component Milky Way stellar disk in the solar neighborhood. To determine the kinematical properties of the thin and of the Thick disks, we select the complete sample of about 278,000 evolved red giant branch (RGB) stars distributed in the cylinder of 1 kpc radius and 0.5 kpc height centered at the Sun. We measured the following mean velocities and dispersions for the thin and the Thick disks, respectively: $(V_R,V_{\varphi },V_Z)=(-1,-239,0)$km s${}^{-1}$ with $({\sigma }_R,{\sigma }_{\varphi },{\sigma }_Z)=(31,20,11)$km s${}^{-1}$, and $(V_R,V_{\varphi },V_Z)=(+1,-225,0)$km s${}^{-1}$ with $({\sigma }_R,{\sigma }_{\varphi },{\sigma }_Z)=(49,35,22)$km s${}^{-1}$. Errors in mean velocities and dispersions are all less than 1km s${}^{-1}$. Same values were computed on much smaller subsamples of our Gaia data with RAVE DR5 [Fe/H] values, from which a metallicity selection was added. Results are basically the same. We find that up to 500 pc height above/below the galactic plane, Thick disk stars comprise about half the stars of the disk. We also find evidence of a substructure in $Z$ versus $V_Z$ in the thick disk population mostly that would give support to the accretion scenario for the formation of the thick disk.

Extended theories of gravity are considered as a new approach for solving the infrared and ultraviolet scale problems; the standard theory of gravity (general relativity) and observational evidence of gravitational waves and subsequent identification of the number of existing polarizations are an effective tool for testing general relativity and extended theories of gravity. The Newman–Penrose method is used to characterize the polarization modes for specific forms of $f(R)$ in the present study. Both the forms of the $f(R)$ theory belong to far more general variational class of gravitational waves, capable of presenting up to six separate polarizations states. We have introduced a new $f(R)$ gravity model as an attempt to have a theory with more parametric regulations so that the model can be used to describe existing issues and discover different directions in gravity physics. The primary goal of this research is to look into the properties of gravitational waves with new cases. The model shows the existence of scalar degrees of freedom in $f(R)$ gravity metric notation.