It is well established from various observational evidences that the relative abundance of baryonic matter in the Universe is less than 5%. The remaining 95% is made up of dark matter (DM) and dark energy. The physical implications of the Eddington luminosity and the mass-radius relation (for galaxies and galaxy clusters) gives a relative abundance of baryonic matter in the Universe which is similar to that established through observations. This need for an additional 85% of matter is attributed to the presence of non-baryonic invisible matter (DM) in the standard model. But, the existence of dark matter is yet to be confirmed by dark matter detection experiments running for decades.

In view of the negative results from dark matter detection experiments running for several years, we had earlier proposed alternate models (which do not require DM) by postulating a minimal field strength (analogous to minimal curvature) and a minimal acceleration. These postulates led naturally to the Modification of Newtonian Dynamics (MOND) and Modification of Newtonian Gravity (MONG) respectively. Here we discuss how the physical implication of the Eddington luminosity and the mass-radius relation can be accounted for from the results of MONG without invoking DM. We also explore the implications of Modifications to Newtonian Dynamics (MOND) as an alternate to dark matter.

In MONG we consider an additional gravitational self-energy term in the Poisson’s equation that gives rise to a logarithmic term in the solution. For a typical galaxy such as the Milky Way, beyond a distance of about 10kpc from the galactic centre, the gravitational self-energy term begins to dominate giving a force that increases logarithmically with distance thus accounting for the dynamics without requiring dark matter. A comparison of the Newtonian gravitational force and that obtained from MONG for various galaxy types is in accordance with observations (with MONG replacing DM). This argument can similarly be extended to larger scales like that of galaxy clusters and superclusters.

The presence of a neutron superflow in the inner crust and outer core of neutron stars can lead to a regime in which neutrons remain superfluid even though the energy spectrum of quasiparticle excitations exhibits no gap. For such gapless superfluidity, we have shown within the nuclear energy density functional theory that the neutron specific heat is comparable to that in the normal phase. We have studied the implication of gapless superfluidity for the thermal relaxation of transiently accreting neutron stars and compared our calculations with observations.

Space-based gravitational-wave detectors offer new prospects for probing the interior of white dwarfs in binary systems through the imprints of tidal effects on the gravitational-wave signal. Some of the binaries that will be observed could have evolved for long enough for the white dwarfs to be at least partially crystallized. The apsidal motion constant k2 (also called the second gravitoelectric Love number) of a cold crystallized white dwarf was computed in full general relativity considering different compositions. The elasticity of the crystallized core was found to systematically reduce the tidal deformability, especially for low-mass stars. Fully relativistic results were compared to those obtained in Newtonian gravity. It was shown that the relativistic correction to the observable tidal deformability k2*R^5 (where R is the stellar radius) is negligible for low-mass white dwarfs but becomes increasingly important for more massive white dwarfs. When approaching the maximum mass, the application of Newtonian theory instead of general relativity leads to dramatic errors. The case of eccentric binaries, for which the precession of the periastron causes a frequency splitting of the gravitational-wave signal depending on the apsidal motion constants of the two stars, was investigated. Future measurements of the precession rate by the Laser Interferometer Space Antenna, which is planned to be in operation within the next decade, could potentially provide estimates of the individual masses. It was found that the errors incurred by the neglect of the elasticity of the crystallized core could be very large, especially for low-mass white dwarfs. Gravitational-wave observations could thus provide a new way to study the crystallization of white dwarfs.

This work deals with the deconfinement phase transition from a hadronic gas (HG) phase consisting of massive pions, to a quark-gluon plasma QGP phase consisting of gluons, massless up and down quarks and massive strange quarks, in addition to their antiquarks. Based on the Bag and coexistence models, we study the variations of the pressure characterizing the HG and the QGP phases. For this latter, we calculate the partition function of the color-singlet QGP within the projection method, using a density of states containing curvature and area terms additionally to the volume term. We investigate the phase diagram of the strongly interacting matter, in the T-µ plane, in several cases: with 2 massless quarks then when adding massive strange quarks in the QGP phase.

Dark matter in the Milky Way is explained by the F-type of vacuum
polarization [1], which could be considered as representing dark
radiation. A nonsingular solution for dark radiation exists in the
presence of eicheon (i.e., black hole in old terminology) in the center
of the galaxy [1]. The model is spherically symmetric, but
a surface density of a baryonic galaxy disk is taken into account
approximately by smearing the disk over a sphere.

[1] S.L. Cherkas, V. L. Kalashnikov, Universe -2022. -Vol.8. -P.456.

The observations of the G2 gas cloud motion and the scarcity of observations on the event horizon-scale distances have challenged the comprehensiveness of the central supermassive black hole model. In addition, the Planck Legacy 2018 release has preferred a positively curved early Universe with a confidence level higher than 99%. This study investigates the impact of the background curvature and its evolution over the conformal time on the formation and morphological evolution of central compact objects and the consequent effect on their host galaxies. The formation of a galaxy from the collapse of a supermassive gas cloud in the early Universe is modelled based on interaction field equations as a 4D relativistic cloud-world that flows and spins through a 4D conformal bulk of a primordial positive curvature considering the preference of the Planck release. Owing to the curved background, this scenario of galaxy formation reveals that the core of the galaxy undergoes a forced vortex formation with a central event horizon leading to opposite vortices that spatially shrink while evolving in the conformal time. It indicates that the galaxy and its core are formed in the same process where the surrounding gas clouds form the spiral arms due to the frame-dragging induced by the fast-rotating core. Consequently, it shows that the accretion flow onto the central supermassive compact object only occurs at the central event horizon of the two opposite vortices while their other ends eject the relativistic jets. The background evolution from a preferred positively curved in the early Universe into present flatness deprives the gravitational potential of bulk which could lead to galaxy quenching. These findings could elucidate the relativistic jet formation and explain the G2 gas cloud motion if its orbit is around one of the vortices but at a distance from the central event horizon while the formation of a galaxy and its core simultaneously could explain the supermassive compact galaxy core growth to a mass of ~10⁹ M_⊙ at just 6% of the current Universe age.

In the present work, we have investigated the role of deceleration parameter in the evolution of the Brans-Dicke (BD) parameter. We have considered the generalized Brans-Dicke (GBD) theory where the BD parameter is assumed to be evolving with the the BD scalar field. We have shown that, the GBD theory with a cosmological constant can suitably be expressed as as an effective cosmic fluid within general relativity. We The BD parameter contains two terms one of which may be non-evolving and the other part bears the time evolution. Also, we have shown that, for anisotropic cosmological models within the GBD theory, for the time-independent deceleration parameter, the cosmic anisotropy will not contribute to the evolution of the Brans-Dicke parameter. However, for models with a time-dependent deceleration parameter, the cosmic anisotropy affects the BD parameter as a whole.

Here we discuss the possibility of admixture of baryons to the DM primordial planets with the DM particles varying in mass from 20GeV to 100 GeV. We have considered different fractions of admixture particles to form the planet. The mass of the primordial planet made completely of DM, ranges from asteroid mass to Neptune mass. Whereas, the mass of primordial planets (admixed with DM and baryonic matter) is found to increase with the fraction of baryonic matter in the planets and the mass of these objects can go well beyond the mass of Jupiter (around 40 times Jupiter mass) and can also approach sub stellar mass (Brown dwarf mass). So far, thousands of exoplanets have been discovered by the Kepler mission and more will be found by NASA’s Transiting Exoplanet Survey Satellite (TESS) mission, which is observing the entire sky to locate planets orbiting the nearest and brightest stars. Many exoplanets (Exo Jupiters) discovered so far fall in this mass range and we are not very sure whether these exoplanets are entirely made of baryons. Some of the exoplanets with mass several times Jupiter mass could be possible signatures of the presence of primordial planets with an admixture of baryonic and DM particles. It is also found that some of these planets could reach even sub stellar mass (10³²g) like that of a brown dwarf. Also, even if a small fraction of DM particles is trapped in these objects, the flux of ambient DM particles would be reduced significantly. This could be one of the many reasons for not detecting the DM particles in various experiments like XENON1T experiment etc. as suggested earlier. If two such primordial planets (in a binary system) merge, they will release a lot of energy. The energy released in gravitational waves and the time scale of merger of these objects is found to increase with the mass of primordial objects. The frequency of gravitational waves emitted in these systems is matching within the range of LIGO. The objects near the galactic center could consist of such primordial objects, planets, comets etc. We also discuss the possibility of tidal break up of these primordial objects in the presence of a BH. The mass of BH required for tidal break up is calculated and it is found that the mass of BH required for tidal break up increases with the DM particle mass and also with the increase in fraction of baryons in these objects. The energy released during tidal breakup will be emitted as Gravitational waves. The energy released as well as the frequency of waves is tabulated and again the frequency is in the sensitivity range of LIGO.

Over the past two decades much effort was put into the search for dark matter. To the present moment many models were proposed to describe the phenomena, yet there are no observations of the elementary particles that are capable of giving a proper explanation for this phenomenon. This fact gave rise to many attempts to describe dark matter as a purely gravitational effect. Most known model of this kind is Modified Newton Dynamics (MOND), proposed by M. Milgrom in 1981. Though the idea was not only elegant but also accurate in explaining many observations regarding dark matter, it has severe problem in describing the dynamics of the dark matter halo in the Bullet Cluster.

Fairly recently many new novel MOND-like models were proposed, that overcomes this problem. Most notable example is mimetic gravity proposed by A. Chamseddine and V. Mukhanov in 2014. The key idea is to use degenerate conformal transformation in Einstein-Hilbert action to isolate conformal mode of metric into new scalar field:
$$
g_{\mu\nu} = \bar{g}_{\mu\nu}\bar{g}^{\alpha\beta}\partial_\alpha\varphi\partial_\beta\varphi,
$$
where $\bar{g}_{\alpha\beta}$ is auxiliary metric. Because the scalar field enters the change through derivatives, the equations of motion are no longer Einstein but have a new terms that can be treated as effective energy-momentum tensor for dark matter. In the original formulation this matter is just pressureless dust, however its $4$-velocity must be gradient of the scalar, i.e. it is moving potentially. Most importantly, this type of effective dark matter has its own equations of motion and can exist on its own bypassing MOND problems with Bullet Cluster.

The original mimetic gravity and its numerous modifications were extensively studied during the last few years. Most of them rely on the addition of potential to the Lagrange multiplier formulation of the original theory or on the introduction new fields with possibly higher derivatives. In the present talk we are interested in one such modification - $p$-form mimetic gravity. Previously it was shown that it can be dualized in the same manner as the usual $p$-form electrodynamics. Dual theory appears to describe the fluid consisting of $(p+1)$-branes embedded in the spacetime. In the present report we will cover several exact solutions for these models in case of $d = 4$ such as FLRW universes and spherically symmetric cases. Using this formalism we recover the exact solutions $p = 1$ - mimetic gravity, that were previously obtained in the literature and also present the results for the new case $p = 2$, that was thought equivalent to $p = 0$. Finally, we discuss the stability of the obtained solutions are their cosmological implications.

Ideas often have unexpected sources, for example, a randomly appeared viral video, unwittingly found during a short break while working on the detailed geological mapping of a certain region on Dione, one of the icy satellites of Saturn. The target area of the study is located on the trailing hemisphere of the satellite. Following the analysis of Voyager images, it was named Wispy Terrain, referring to the frequent appearance of wispy streaks, markings, or lineas. The higher resolution images of Cassini spacecraft revealed that the Wispy Terrain and the so-called chasmata or chasm system consist of quasi-parallel graben, troughs, in parts with horsts, indicating extensional and shear stresses in Dione`s icy crust. Besides the basic, satellite-scale geological mapping and very general definition of the phenomenon, there are only a few studies with a focus on the Wispy Terrain and the chasmata, mostly targeting e.g., the timing of its formation. This study aims to fill this gap by providing a detailed geological and cryotectonic facies analysis in the surroundings of Eurotas and Palatine Chasmata, and proposing additional cryotectonic processes and formation model, an analog of stacking lake ice, observed e.g. at Lake Superior. The study of the relationship between impact craters and tectonic features (supposed fault systems) revealed the “lost” of half of some crosscut craters, indicating additional horizontal movements, the appearance of accretion prism-like phenomenon, and theoretically, subsumption-like processes. Such observation provides new information about surface renewal processes around Dione`s one of the youngest and probably still active regions.