Cosmological consequences of the Poincare-Weyl gauge theory of gravity are considered. A generalized cosmological constant depending from the Dirac scalar field is introduced. The stage of a super-early (Harrison-Zel'dovich) scale invariant Universe is considered. It is shown that while the scale factor sharply increases and demonstrates inflationary behavior, the generalized cosmological constant decreases sharply from a huge value at the beginning of the Big Bang to an extremely small value in the modern era, which solves the well-known "cosmological constant problem".
We investigate the effect of the cosmological QCD transition on the evolution of primordial density perturbations. If the phase transition is first order, the sound speed vanishes during the transition and density perturbations fall freely. The Harrison-Zel'dovich spectrum of density fluctuations develops large peaks on scales below the Hubble radius at the transition. These peaks above the primordial spectrum grow with wavenumber and produce cold dark matter clumps of masses less than $10^{-10} M_\odot$. At the horizon scale the amplification of overdensities is of order unity, and thus no $1…
Primordial black holes are a popular candidate for dark matter. In the mass regime where their conjectured Hawking evaporation is significant, they have been subject to many constraints via X-rays, gamma-rays, and even radio emission. Previously the Sunyaev-Zel'dovich effect has been considered to place further limits on the M > 10M? primordial black hole abundance via the effects of their accretion of ambient gas. In this work, we will present a novel and robust means of placing abundance limits on low-mass black holes, using the Sunyaev-Zel'dovich effect induced by electrons produced via the…
In this paper we have considered a flat FLRW universe with bulk viscous Zel'dovich as the cosmic component. Being considered the bulk viscosity as per the Eckart formalism, we have analyzed the evolution of the Hubble parameter and constrained the model with the Type Ia Supernovae data thus extracting the constant bulk viscous parameter and present Hubble parameter. Further we have analyzed the scale factor, equation of state and deceleration parameter. The model predicts the late time acceleration and is also compatible with the age of the universe as given by the oldest globular clusters. We…
The quark-gluon to hadron transition affects the evolution of cosmological perturbations. If the phase transition is first order, the sound speed vanishes during the transition, and density perturbations fall freely. This distorts the primordial Harrison-Zel'dovich spectrum of density fluctuations below the Hubble scale at the transition. Peaks are produced, which grow at most linearly in wavenumber, both for the hadron-photon-lepton fluid and for cold dark matter. For cold dark matter which is kinetically decoupled well before the QCD transition clumps of masses below $10^{-10} M_\odot$ are p…
This Letter proposes a solution of the Vacuum Energy and the Cosmological Constant (CC) paradox based on the Zel'dovich's ansatz, which states that the observable contribution to the vacuum energy density is given by the gravitational energy of virtual particle-antiparticle pairs, continually generated and annihilated in the vacuum state. The novelty of this work is the use of an ultraviolet cut-off length based on the Holographic Principle, which is shown to yield current values of the CC in good agreement with experimental observations.
The problem of scattering of the background radiation on relic cosmological wormholes is considered. It is shown that static wormholes do not perturb the spectrum at all. The presence of peculiar velocities of wormholes results in a distortion of the CMB spectrum which is analogous to the kinematic Sunyaev-Zel'dovich effect. In the first order in $v/c$ the distortion of CMB cannot be separated from from the Compton scattering on electrons. In next orders the scattering on wormholes exhibits some difference from the Compton scattering. High-energy cosmic-ray particles spectrum does not change t…
We compare relativistic approximation methods, which describe gravitational instability in the expanding universe, in a spherically symmetric model. Linear perturbation theory, second-order perturbation theory, relativistic Zel'dovich approximation, and relativistic post-Zel'dovich approximation are considered and compared with the Lema\^ıtre-Tolman-Bondi solution in order to examine the accuracy of these approximations. We consider some cases of inhomogeneous matter distribution while the homogeneous top-hat model has been usually taken in the previous Newtonian works. It is found that the Ze…
Using a Green's function approach, we compare the trajectories of classical Hamiltonian point particles in an expanding space-time to the effectively inertial trajectories in the Zel'dovich approximation. It is shown that the effective gravitational potential accelerating the particles relative to the Zel'dovich trajectories vanishes exactly initially as a consequence of the continuity equation, and acts only during a short, early period. The Green's function approach suggests an iterative scheme for improving the Zel'dovich trajectories, which can be analytically solved. We construct these tr…
By using exclusively the Sunyaev-Zel'dovich effect and X-ray surface brightness data from 25 galaxy clusters in the redshift range 0.023< z < 0.784 we access cosmic acceleration employing a kinematic description. Such result is fully independent on the validity of any metric gravity theory, the possible matter-energy contents filling the Universe, as well as on the SNe Ia Hubble diagram.
We show how the Zel'dovich approximation and the second order displacement field of Lagrangian perturbation theory can be obtained from a general relativistic gradient expansion in ΛCDM cosmology. The displacement field arises as a result of a second order non-local coordinate transformation which brings the synchronous/comoving metric into a Newtonian form. We find that, with a small modification, the Zel'dovich approximation holds even on scales comparable to the horizon. The corresponding density perturbation is not related to the Newtonian potential via the usual Poisson equation but via a…
The initial conditions for Newtonian $N$-body simulations are usually generated by applying the Zel'dovich approximation to the initial displacements of the particles using an initial power spectrum of density fluctuations generated by an Einstein-Boltzmann solver. We show that in most gauges the initial displacements generated in this way receive a first-order relativistic correction. We define a new gauge, the $N$-body gauge, in which this relativistic correction vanishes and show that a conventional Newtonian $N$-body simulation includes all first-order relativistic contributions (in the ab…
The gravitational instability of inhomogeneities in the expanding universe is studied by the relativistic second-order approximation. Using the tetrad formalism we consider irrotational dust universes and get equations very similar to those given in the Lagrangian perturbation theory in Newtonian cosmology. Neglecting the cosmological constant and assuming a flat background model we give the solutions of the nonlinear dynamics of cosmological perturbations. We present the complete second-order solutions, which extend and improve earlier works.
Beginning with a relativistic action principle for the irrotational flow of collisionless matter, we compute higher order corrections to the Zel'dovich approximation by deriving a nonlinear Hamilton-Jacobi equation for the velocity potential. It is shown that the velocity of the field may always be derived from a potential which however may be a multi-valued function of the space-time coordinates. In the Newtonian limit, the results are nonlocal because one must solve the Newton-Poisson equation. By considering the Hamilton-Jacobi equation for general relativity, we set up gauge-invariant equa…
We consider circular motion of a heavy object in an atomic Bose-Einstein condensate (BEC) at $T=0{\rm K}$. Even if the linear velocity of the object is smaller than the Landau critical velocity, the object may radiate quasiparticles and thus experience the quantum friction. The radiation process is similar to Zel'dovich-Starobinskii (ZS) effect -- the radiation by a rotating black hole. This analogy emerges when one introduces the effective acoustic metric for quasiparticles. In the rotating frame this metric has an ergosurface, which is similar to the ergosurface in the metric of a rotating b…
We investigate the effect of modified gravity on cluster abundance and the Sunyaev-Zel'dovich angular power spectrum. Our modified gravity is based on a phenomenological extension of the Dvali-Gabadadze-Porrati model which includes two free parameters characterizing deviation from Lambda-CDM cosmology. Assuming that Birkhoff's theorem gives a reasonable approximation, we study the spherical collapse model of structure formation and show that while the growth function changes to some extent, modified gravity gives rise to no significant change in the linear density contrast at collapse time. Th…
Degenerate higher-order scalar-tensor (DHOST) theories are considered the most general class of scalar-tensor theories so that any constraints on them apply to the full set of scalar-tensor models. DHOST theories modify the laws of gravity even at galaxy clusters scale hence affecting the weak lensing (WL), X-ray and Sunyaev-Zel'dovich observables. We derive the theoretical expression for the lensing convergence $κ$, and the pressure profile $P$, of clusters in the framework of DHOST theories, and quantify how much they deviate from their General Relativity (GR) counterparts. We argue that com…
The kinetic Sunyaev Zel'dovich (kSZ) and polarized Sunyaev Zel'dovich (pSZ) effects are temperature and polarization anisotropies induced by the scattering of CMB photons from structure in the post-reionization Universe. In the case of the kSZ effect, small angular scale anisotropies in the optical depth are modulated by the cosmic microwave background (CMB) dipole field, i.e. the CMB dipole observed at each spacetime point, which is sourced by the primordial dipole and especially the local peculiar velocity. In the case of the pSZ effect, similar small-scale anisotropies are modulated by the …
It is shown that in non-linear electrodynamics (in particular, Born-Infeld one) in the framework of general relativity there exist "weakly singular" configurations such that (i) the proper mass M is finite in spite of divergences of the energy density, (ii) the electric charge q and Schwarzschild mass m ~ q can be made as small as one likes, (iv) all field and energy distributions are concentrated in the core region. This region has an almost zero surface area but a finite longitudinal size L=2M. Such configurations can be viewed as a new version of a classical analogue of an elementary partic…
Inertial motion superradiance, the emission of radiation by an initially unexcited system moving inertially but superluminally through a medium, has long been known. Rotational superradiance, the amplification of radiation by a rotating rigid object, was recognized much later, principally in connection with black hole radiances. Here we review the principles of inertial motion superradiance and prove thermodynamically that the Ginzburg--Frank condition for superradiance coincides with the condition for superradiant amplification of already existing radiation. Examples we cite include a new typ…
