O. S. Sazhina

Cosmic Microwave Background Anisotropy Induced by a Moving Straight Cosmic String

A method of searching for cosmic strings based on an analysis of the cosmic microwave background (CMB) anisotropy is presented. A moving straight cosmic string is shown to generate structures of enhanced and reduced brightness with a distinctive shape. The conditions under which a string can be detected by both CMB anisotropy and gravitational lensing in optical surveys are analyzed. For a relativistic string with a deficit angle of ∼1″–2″, the amplitude of the generated anisotropy is shown to be ∼15–30 μK.

The scale factor in a Universe with dark energy

The solution of the Friedmann cosmological equations for the scale factor in a model of the Universe containing matter having the equation of state of dust and dark energy is considered. The equation-of-state parameter of the dark energy is taken to be an arbitrary constant w = −1.006 ± 0.045, whose value is constrained by the current observational limits. An exact solution for the scale factor as a function of physical time and conformal time is obtained. Approximate solutions have been found for the entire admissible conformal time interval with an accuracy better than 1%, which exceeds the accuracy of the determined global parameters of our Universe. This is the first time an exact solution for the scale factor describing the evolution of the Universe in a unified way, beginning with the matter-dominated epoch and ending with the infinitely remote future, has been obtained.

Gravitational Lens Images Generated by Cosmic Strings

In this review paper the current understanding on the properties of cosmic strings is shortly outlined with spe- cial emphasis on the observational signatures which can be expected both in the optical, through gravitational lensing, and in the radio, through anisotropies in the cosmic microwave background. The experience gathered during the long term in- vestigation of the former candidate CSL-1 is also shortly summarized.

Apparent motions of quasars due to microlensing

The effect of weak microlensing on the apparent velocities of extragalactic sources is considered; in particular, the apparent motions of sources from the ICRF list are discussed. We expect from two to seven cases of apparent motions of extragalactic sources due to weak microlensing by stars or dark bodies in our Galaxy to be detected over the next 30 years.

CMB Anisotropy Induced by Tachyonic Perturbations of Dark Energy

We consider the effects of possible tachyonic perturbations of dark energy on the CMB anisotropy. Such perturbations emerge, in particular, in models with phantom dark energy violating Lorentz invariance. Therefore, we discuss tachyonic perturbations with a Lorentz-violating dispersion relation. We show that the corresponding contribution to the CMB anisotropy can have an appreciable amplitude, while the angular spectrum has a distinct maximum. These predictions are compared with observational data. The tachyonic contribution slightly improves the agreement between the theory and observations, but this improvement is statistically insignificant and our analysis gives constraints on the tachyonic perturbation amplitude.

CMB anisotropy induced by tachyonic perturbations of dark energy

We consider the effects of possible tachyonic perturbations of dark energy on the CMB anisotropy. Such perturbations emerge, in particular, in models with phantom dark energy violating Lorentz invariance. Therefore, we discuss tachyonic perturbations with a Lorentz-violating dispersion relation. We show that the corresponding contribution to the CMB anisotropy can have an appreciable amplitude, while the angular spectrum has a distinct maximum. These predictions are compared with observational data. The tachyonic contribution slightly improves the agreement between the theory and observations, but this improvement is statistically insignificant and our analysis gives constraints on the tachyonic perturbation amplitude.

Physical origins for variations in the apparent positions of quasars

The physical origins of the apparent motion of radio sources in the ICRF are considered. The sources can be divided into four groups, according to the characteristics of their motion. Here, we consider the model for the motion of the first group of sources—those displaying uniform linear motion. Since the apparent speeds of the radio sources are close to, and sometimes exceeding, the speed of light, it is natural to suppose that these sources are relativistic jets or plasma clouds moving with speeds close to the speed of light. Uniform linear motion can be explained by a model invoking precession of the jet. We consider the physical characteristics of a number of selected sources of the ICRF in the proposed model.

Observational constraints on the types of cosmic strings

This paper is aimed at setting observational limits to the number of cosmic strings (Nambu–Goto, Abelian-Higgs, semilocal) and other topological defects (textures). Radio maps of CMB anisotropy, provided by the space mission Planck for various frequencies, were filtered and then processed by the method of convolution with modified Haar functions (MHF) to search for cosmic string candidates. This method was designed to search for solitary strings, without additional assumptions as regards the presence of networks of such objects. The sensitivity of the MHF method is

Cosmic string detection in radio surveys

\delta T \approx 10~\upmu \hbox {K}