Measurements of the absolute temperature of the relic radiation observations at0.6, 0.82 and2.5 GHz from Alpe Gera and the South Pole

Summary In spite of the very accurate results obtained by the Cosmic Background Explorer (COBE), the existence of deviations from a Planckian distribution in the spectrum of the relic or cosmic background radiation (CBR) at frequencies near and below 1 GHz is still an open question. The detection of distortions would be very important for the cosmological implications they can have. We present results from a program of measurements of the absolute temperature of the CBR at low frequencies carried out by a Milano-Berkeley collaboration. Future programs are also discussed. Paper presented at the V Cosmic Physics National Conference, S. Miniato, November 27–30, 1990.     

Polarization of the cosmic microwave background radiation

In re-ionized models, the measurement of polarization of CMBR can be a good criterion to narrow down the parameter space for cosmological models. A Vishniac-type effect in second order polarization over arc minute scales has been calculated. It has been shown that while the effect is very small (∼10⁻² μK) for CDM models, it can be significant (∼0.3μK) for some isocurvature models.     

Response of photomultiplier tubes to background cosmic radiation

The properties of photomultiplier tubes (PMTs) have been investigated experimentally. The flux of cosmic rays has been used as a source of signals detected directly by a PMT (without a scintillator). The number of detected events versus the size of the PMT’s transparent front window has been studied. To this end, modified FEU-167 multipliers (FEU-167M) have been fabricated in which all parameters have been kept unchanged except for the size of the front window, which has been decreased. It has been found that the number of detected signals is roughly proportional to the surface area of the window. Hence, a signal induced by background cosmic rays arises in the glass of the PMT’s front screen. This circumstance should be taken into consideration when operating with different PMTs.     

Dark energy and the cosmic microwave background radiation

We find that current cosmic microwave background anisotropy data strongly constrain the mean spatial curvature of the Universe to be near zero, or, equivalently, the total energy density to be near critical-as predicted by inflation. This result is robust to editing of data sets, and variation of other cosmological parameters (totaling seven, including a cosmological constant). Other lines of argument indicate that the energy density of nonrelativistic matter is much less than critical. Together, these results are evidence, independent of supernovae data, for dark energy in the Universe.     

The cosmic x-ray background

As the sky in the microwave band is dominated by a cosmic background, so too is the X-ray sky. In this report, the experimental approach used for measuring the X-ray background is explained and evaluated. The Compton-Getting interpretation of the dipole anisotropy in the microwave background is presented as a diagnostic of the weak asymmetry exhibited by the cosmic X-ray background. Spectral characteristics and spatial fluctuations of this X-ray background are described and then discussed within the context of what is known about individual extragalactic sources. It is concluded that the bulk of the cosmic X-ray background is yet to be understood. The critical apparatus of modern cosmology is reviewed and applied to this problem, providing constraints and indicating possible avenues for achieving a solution. The outlook for obtaining the new data called for is examined in terms of experiments now in preparation.     

Interactions of high-energy cosmic rays with extragalactic infrared radiation background

We consider the modification of the extragalactic cosmic-ray spectrum caused by cosmic-ray interactions with infrared background photons which are present in extragalactic space together with relic photons. It is assumed that cosmic-ray spectrum at superhigh energies has extragalactic origin and is proton dominated. The text was submitted by the authors in English.     

Gauge-invariant variations in the redshift and cosmic background radiation anisotropies

The gauge-invariance of the calculations determining anisotropics in the cosmic microwave background radiation (the Sachs-Wolfe effect) is re-examined. It is shown that the results obtained are gauge-invariant only if a physically-based definition of the surface of last scattering is implemented, in a context where perturbations of the surface of last scattering as well as of the space-time are taken into account. Any physical interpretation of the results based on their splitting into scalar, vector, and tensor parts, is unique only if non-local (unverifiable) conditions are imposed; locally, any such interpretation is non-unique. The physical meaning of the Sachs-Wolfe potentialB and associated redshift formula depends on implementing a very specific gauge, without a clear physical or geometric meaning; its implications do not extend to other, more usual, gauges.     

Cosmological production of vector bosons and cosmic microwave background radiation

An intensive cosmological production of vector W and Z bosons is considered within a cosmological model that involves a relative scale of measurement. Field-theory models are studied in which cosmic microwave background radiation and baryon matter may appear as products of the decay of such primordial bosons.     

Superconducting cosmic strings and the spectrum of microwave background radiation

We analyse distortions of the spectrum of microwave background radiation caused by heating of cosmic plasma by the population of superconducting cosmic string loops. We find that the effect in the Rayleigh-Jeans part of the spectrum is at the observational level and may be used to constrain the parameters of the cosmological model by Ostriker, Thompson and Witten.     

Relic photon temperature versus redshift and the cosmic neutrino background

Presuming that CMB photons are described by the deconfining phase of an SU(2) Yang‐Mills theory with the critical temperature for the deconfining‐preconfining phase transition matching the present CMB temperature K (SU(2)_CMB), we investigate how CMB temperature T connects with the cosmological scale factor a in a Friedmann‐Lemaître‐Robertson‐Walker Universe. Owing to a violation of conformal scaling at late times, the tension between the (instantaneous) redshift of reionisation from CMB observation () and quasar spectra () is repealed. Also, we find that the redshift of CMB decoupling moves from to which questions ΛCDM cosmology at high redshifts. Adapting this model to the conventional physics of three flavours of massless cosmic neutrinos, we demonstrate inconsistency with the value N_eff ～ 3.36 extracted from Planck data. Interactions between cosmic neutrinos and the CMB implies a common temperature T of (no longer separately conserved) CMB and neutrino fluids. N_eff ～ 3.36 then entails a universal, temperature induced cosmic neutrino mass with . Our above results on z_re and z_dec, derived from SU(2)_CMB alone, are essentially unaffected when including such a neutrino sector.

     

Large-scale anisotropies of the cosmic background radiation in generalized inflationary cosmologies

We calculate the dipole and quadropole moments, (ΔT/T)_l l=1, 2, of the cosmic background radiation anisotropy due to scalar and tensor waves with power-law spectra, produced by quantum processes during a “generalized” inflationary era of the early universe. The observational bounds on (ΔT/T)_l are used to give constraints on the parameters of the cosmological models.