Modern Physics Letters A

The double-beta decay process has been widely investigated in the last two decades due to the possible lepton number nonconservation decay modes that may occur. An experimental evidence of these modes would lead to the conclusion that neutrino is a massive Majorana particle. At present, when the nonzero neutrino mass is convincingly proved by neutrino oscillation experiments, the double-beta decay investigations are the most promising for determining the absolute value of the neutrino mass. In this paper we give a brief review of some recent nuclear double-beta decay investigations in connection with neutrino mass. We discuss the potential of this process to search for beyond standard model physics, the QRPA-based methods for computing the relevant nuclear matrix elements and the derivation of neutrino masses both from double-beta decay and neutrino oscillation data and in agreement with the present cosmological constraints.

A closed analytic expression is given for the spectrum of low energy photons in the annihilation of orthopositronium, which expression sums all the effects of the Coulomb interaction between the electron and the positron. The applicability of the formula is limited only by the condition ω_γ ≪ m_e. In the region ω_γ ≫ m_eα² the Coulomb interaction term gives the leading at low energy one-loop correction, proportional to , to the decay spectrum. The constant in ω_γ radiative term in the one-loop correction to the spectrum is also presented here in an analytic form.

We analyze the effects of flavor-changing Z_L penguin diagrams on rare kaon decays in a left–right supersymmetric model (LRSUSY). Using the mass-insertion approximation and including up to second-order effects, we show that the constraints obtained on up-sector flavor violating parameters can be stronger than previous bounds. These effects present a sensitive test of an extended gauge sector in supersymmetry and can be used to distinguish LRSUSY from other supersymmetric models.

We study Sorkin's proposal of a generalization of quantum mechanics and find that the theories proposed derive their probabilities from kth order polynomials in additive measures, in the same way that quantum mechanics uses a probability bilinear in the quantum amplitude and its complex conjugate. Two complementary approaches are presented, a C* and a Hopf-algebraic one, illuminating both algebraic and geometric aspects of the problem.

The effective gravitational mass as well as the energy and momentum distributions of a radiating charged particle in Einstein's universe are evaluated. The Møller's energy–momentum complex is employed for this computation. The spacetime under study is a generalization of Bonnor and Vaidya spacetime in the sense that the metric is described in the cosmological background of Einstein's universe in lieu of the flat background. Several spacetimes are limiting cases of the one considered here. In particular for the Reissner–Nordström black hole background, our results are exactly the same as those derived by Cohen and Gautreau using Whittaker's theorem and by Cohen and de Felice using Komar's mass. Furthermore, the power output for the spacetime under consideration is obtained.

The current algebra for gauge theories like QCD at finite temperature and density is studied. We start considering, the massless Thirring model at finite temperature and density, finding an explicit expression for the current algebra. The central charge only depends on the coupling constant and there are not new effects due to temperature and density. From this calculation, we argue how to compute the central charge for QCD₄ and we argue why the central charge in four dimensions could be modified by finite temperature and density.

We study the massless scalar wave propagation in the time-dependent Schwarzschild black hole background. We find that the Kruskal coordinate is an appropriate framework to investigate the time-dependent spacetime. A time-dependent scattering potential is derived by considering dynamical black hole with parameters changing with time. It is shown that in the quasinormal ringing both the decay time-scale and oscillation are modified in the time-dependent background.