An Improved Limit on Invisible Decays of Positronium

The results of a new search for positronium decays into invisible final states are reported. Convincing detection of this decay mode would be a strong evid ence for new physics beyond the Standard Model (SM): for example the existence of extra--dimensions, of milli-charged particles, of new light gauge bosons or of mirror particles. Mirror matter could be a relevant dark matter candidate. In this paper the setup and the results of a new experiment are presented. In a collected sample of about $(6.31\pm0.28) \times 10^6$ orthopositronium decay s, no evidence for invisible decays in an energy window [0,80] keV was found and an upper limit on the branching ratio of orthopositronium \invdecay could be set: \binvdecay<4.2\times 10^{-7} (90% C.L.) Our results provide a limit on the photon mirror-photon mixing strength $\epsilon \leq 1.55\times 10^{-7}$ (90% C.L.) and rule out particles lighter than the electron mass with a fraction $Q_x \leq 3.4 \times 10^{-5}$ of the electron charge. Furthermore, upper limits on the branching ratios for the decay of parapositronium $Br(p-Ps\to invisible)\leq 4.3 \times 10^{-7}$ (90% C.L.) and the direct annihilation $Br(e^+e^-\to invisible)\leq 2.1 \times 10^{-8}$ (90% C.L.) could be set.Comment: 17 pages, 7 figures, added references, fixed limit on millicharged particles and changed two plots accordingl

Light Curve Models of Supernovae and X-ray spectra of Supernova Remnants

We compare parameters of well-observed type II SN1999em derived by M.Hamuy and D.Nadyozhin based on Litvinova-Nadyozhin (1985) analytic fits with those found from the simulations with our radiative hydro code Stella. The difference of SN parameters is quite large for the long distance scale. The same code applied to models of SN1993J allows us to estimate systematic errors of extracting foreground extinction toward SN1993J suggested by Clocchiatti et al. (1995). A new implicit two-temperature hydro code code Supremna is introduced which self-consistently takes into account the kinetics of ionization, electron thermal conduction, and radiative losses for predicting X-ray spectra of young supernova remnants such as Tycho and Kepler.Comment: 7 pages, 10 figures, Supernovae as Cosmological Lighthouses, Padua, June 16- 19, 2004, eds. M.Turatto et al., ASP Conference Serie

Supernova Ia: a Converging Delayed Detonation Wave

A model of a carbon-oxygen (C--O) presupernova core with an initial mass 1.33 M_\odot, an initial carbon mass fraction 0.27, and with an average mass growth-rate 5 x 10^{-7} M_\odot/yr due to accretion in a binary system was evolved from initial central density 10^9 g/cm^3, and temperature 2.05 x 10^8 K through convective core formation and its subsequent expansion to the carbon runaway at the center. The only thermonuclear reaction contained in the equations of evolution and runaway was the carbon burning reaction 12C + 12C with an energy release corresponding to the full transition of carbon and oxygen (with the same rate as carbon) into 56Ni. As a parameter we take \alpha_c - a ratio of a mixing length to the size of the convective zone. In spite of the crude assumptions, we obtained a pattern of the runaway acceptable for the supernova theory with the strong dependence of its duration on \alpha_c. In the variants with large enough values of \alpha_c=4.0 x 10^{-3} and 3.0 x 10^{-3} the fuel combustion occurred from the very beginning as a prompt detonation. In the range of 2.0 x 10^{-3} >= \alpha_c >= 3.0 x 10^{-4} the burning started as a deflagration with excitation of stellar pulsations with growing amplitude. Eventually, the detonation set in, which was activated near the surface layers of the presupernova (with m about 1.33 M_\odot) and penetrated into the star down to the deflagration front. Excitation of model pulsations and formation of a detonation front are described in detail for the variant with \alpha_c=1.0 x 10^{-3}.Comment: 13 pages, 11 figures, to appear in Astronomy Letter