Dynamics of Primordial Hydrogen Recombination with Allowance for a Recoil for Scattering in the Ly-alpha Line

It is shown that taking into account a recoil for radiation scattering in the Ly-alpha line can lead to a noticable acceleration of primordial hydrogen recombination. Thus for LambdaCDM model a decrease of ionization degree exceeds 1% for redshifts z in a range 800 - 1050 achieving approximately 1.3% at z=900. Corresponding corrections to the cosmic microwave background power spectra can achieve 1.1% for TT spectra and 1.7% for EE ones. Radiative transfer in these calculations was treated in a quasistationary approximation. Numerical solutions are also obtained in diffusion approximation for a nonstationary problem of Ly-alpha line radiative transfer under partial frequency redistribution with a recoil. An evolution of a local line profile is traced to as well as an evolution of a relative number of uncompensated transitions from 2p state down to 1s one. It is shown that taking into account nonstationarity of Ly-alpha line radiative transfer can lead to an additional acceleration of primordial hydrogen recombination.Comment: 9 pages, 5 figures; accepted for publication in Astronomy Letter

Continuous families of isospectral Heisenberg spin systems and the limits of inference from measurements

We investigate classes of quantum Heisenberg spin systems which have different coupling constants but the same energy spectrum and hence the same thermodynamical properties. To this end we define various types of isospectrality and establish conditions for their occurence. The triangle and the tetrahedron whose vertices are occupied by spins 1/2 are investigated in some detail. The problem is also of practical interest since isospectrality presents an obstacle to the experimental determination of the coupling constants of small interacting spin systems such as magnetic molecules

EPR studies of manganese centers in SrTiO3: Non-Kramers Mn3+ ions and spin-spin coupled Mn4+ dimers

X- and Q-band electron paramagnetic resonance (EPR) study is reported on the SrTiO3 single crystals doped with 0.5-at.% MnO. EPR spectra originating from the S = 2 ground state of Mn3+ ions are shown to belong to the three distinct types of Jahn-Teller centres. The ordering of the oxygen vacancies due to the reduction treatment of the samples and consequent formation of oxygen vacancy associated Mn3+ centres are explained in terms of the localized charge compensation. The EPR spectra of SrTiO3: Mn crystals show the presence of next nearest neighbor exchange coupled Mn4+ pairs in the directions.Comment: 17 pages, 8 figure