M. V. Sazhin

Graviton creation in the inflationary universe and the grand unification scale

The creation of gravitons in the inflationary universe and their effects on the 3K photon background are considered. It is shown that the inflationary universe scenario is compatible with existing experimental data on the large scale anisotropy of relic photons only if the energy density of the symmetric vacuum is much less than the Planck energy density, ϵV < 3 × 10−8 Mpl4. This implies an upper bound on the grand unification scale.

CSL-1: chance projection effect or serendipitous discovery of a gravitational lens induced by a cosmic string?

CSL-1 (Capodimonte–Sternberg–Lens Candidate, No.1) is an extragalactic double source detected in the OACDF (Osservatorio Astronomico di Capodimonte - Deep Field). It can be interpreted either as the chance alignment of two identical galaxies at z = 0.46 or as the first case of gravitational lensing by a cosmic string. Extensive modeling shows in fact that cosmic strings are the only type of lens which (at least at low angular resolution) can produce undistorted double images of a background source. We propose an experimentum crucis to disentangle between these two possible explanations. If the lensing by a cosmic string should be confirmed, it would provide the first measurements of energy scale of symmetry breaking and of the energy scale of Grand Unified Theory (GUT).

TianQin: a space-borne gravitational wave detector

TianQin is a proposal for a space-borne detector of gravitational waves in the millihertz frequencies. The experiment relies on a constellation of three drag-free spacecraft orbiting the Earth. Inter-spacecraft laser interferometry is used to monitor the distances between the test masses. The experiment is designed to be capable of detecting a signal with high confidence from a single source of gravitational waves within a few months of observing time. We describe the preliminary mission concept for TianQin, including the candidate source and experimental designs. We present estimates for the major constituents of the experiments error budget and discuss the projects overall feasibility. Given the current level of technology readiness, we expect TianQin to be flown in the second half of the next decade.

Gravitational lensing by cosmic strings: what we learn from the CSL-1 case

Cosmic strings were postulated by Kibble in 1976 and, from a theoretical point of view, their existence finds support in modern superstring theories, both in compactification models and in theories with extended additional dimensions. Their eventual discovery would lead to significant advances in both cosmology and fundamental physics. One of the most effective ways to detect cosmic strings is through their lensing signatures which appear to be significantly different from those introduced by standard lenses (i.e. compact clumps of matter). In 2003, the discovery of the peculiar object CSL-1 raised the interest of the physics community since its morphology and spectral features strongly argued in favour of it being the first case of gravitational lensing by a cosmic string. In this paper we provide a detailed description of the expected observational effects of a cosmic string and show, by means of simulations, the lensing signatures produced on background galaxies. While high angular resolution images obtained with Hubble Space Telescope, revealed that CSL-1 is a pair of interacting ellipticals at redshift 0.46, it represents a useful lesson to plan future surveys.

The Sky Polarization Observatory

Abstract The Sky Polarization Observatory (SPOrt) is an ASI-funded experiment specifically designed to measure the sky polarization at 22, 32 and 90 GHz, which was selected in 1997 by ESA to be flown on the International Space Station. Starting in 2006 and for at least 18 months, it will be taking direct and simultaneous measurements of the Stokes parameters Q and U at 660 sky pixels, with FWHM=7°. Due to development efforts over the past few years, the design specifications have been significantly improved with respect to the first proposal. Here we present an up-to-date description of the instrument, which now warrants a pixel sensitivity of 1.7 μK for the polarization of the cosmic background radiation, assuming two years of observations. We discuss SPOrt scientific goals in the light of WMAP results, in particular in connection with the emerging double-reionization cosmological scenario.

Microarcsecond instability of the celestial reference frame.

The fluctuation of the angular positions of reference extragalactic radio and optical sources under the influence of the irregular gravitational field of visible Galactic stars is considered. It is shown that these angular fluctuations range from a few up to hundreds of microarcseconds. This leads to a small rotation of the celestial reference frame. The nondiagonal coefficients of the rotation matrix are of the order of a microarcsecond. The temporal variation of these coefficients due to the propermotion of the foreground stars is of the order of one microsecond per 20 years. Therefore, the celestial reference frame can be considered inertial and homogeneous only to microarcsecond accuracy. Astrometric catalogues with microarcsecond accuracy will be unstable, and must be reestablished every 20 years.

Image reconstruction technique and optical monitoring of the QSO2237+0305 from Maidanak Observatory in 2002-2003

We have observed the gravitational lens system Q2237+0305 from the Maidanak Observatory over the period from 2002 August to 2003 November. Here we report the results of our observations. We implemented a two-stage technique that has been developed specifically for the purpose of gravitational lens image reconstruction. The technique is based on the Tikhonov regularization approach and allows one to obtain astrometric and photometric characteristics of the gravitational lens system. Light curves with 78 data points for the four quasar components are obtained. Slow brightness variations over the observational period are found in all components. Images A, C and D have a tendency to decrease in brightness. Image B does not vary more than 0.05 mag. The observations did not reveal evidence for large variations in brightness of the components due to microlensing effects. To provide an overall picture of the photometry behaviour, our data are combined with the Maidanak observations published for 1995-2000.

ANALYSIS OF TWO QUINTESSENCE MODELS WITH TYPE Ia SUPERNOVA DATA

The Type Ia supernovae data are used to analyze two general exact solutions for quintessence models. The best-fit values for Ωm0 are smaller than in the Λ-term model, but still acceptable. With present-day data, it is not possible to discriminate among the various situations.

Black-hole relics in string gravity: last stages of Hawking evaporation

The endpoint of black-hole evaporation is a very intriguing problem of modern physics. Based on the Einstein-dilaton-Gauss–Bonnet four-dimensional string gravity model, we show that black holes do not disappear and should become relics at the end of the evaporation process. The possibility of experimental detection of such remnant black holes is investigated. If they really exist, these objects could form a considerable part of the non-baryonic dark matter in our universe.

The Gravitational Wave Contribution to the Cosmic Microwave Background Anisotropies

We study the possible contribution of a stochastic gravitational wave background to the anisotropy of the cosmic microwave background (CMB) in cold and mixed dark matter models. We test this contribution against recent detections of CMB anisotropy at large and intermediate angular scales. Our likelihood analysis indicates that models with blue power spectra (n 1.2) and a tensor-to-scalar quadrupole ratio of R = CT2/CS2 ~2 are most consistent with the anisotropy data considered here. We find that by including the possibility of such a background in the CMB data analysis, it can drastically alter the conclusion of the remaining cosmological parameters.