arXiv subjects
Publications and source records attributed to R. Toldra.
We consider lepton-quark contact interactions in models with right-handed neutrinos, and find that observational data from SN1987A restricts the scale of such interactions to be at least $Λ>90$ TeV.
We reanalyse the limits on the gravitino mass $m_{3/2}$ in superlight gravitino scenarios derived from arguments on energy-loss during gravitational collapse. We conclude that the mass range $10^{-6}eV\leq m_{3/2}\leq2.3\times10^{-5}eV$ is excluded by SN1987A data. In terms of the scale of supersymmetry breaking $Λ$, the range $70GeV\leqΛ\leq 300GeV$ is not allowed.
We establish that forces mediated by the exchange of a pair of Majorana neutrinos differ from those due to Dirac neutrino exchange.
A light pseudoscalar coupled to two photons would be copiously emitted by the core of a supernova. Part of this flux would be converted to $γ-$rays by the galactic magnetic field. Measurements on the SN1987A $γ-$ray flux by the Gamma-Ray Spectrometer on the Solar Maximum Mission satellite already imply a bound on the coupling $g < 3 \times 10^{-12}$ GeV$^{-1}$. The improved generation of satellite-borne detectors, like EGRET or the project GLAST, could be able to detect a pseudoscalar-to-photon signal from a nearby supernova, for allowed values of $g$.
A pseudoscalar or scalar particle $ϕ$ that couples to two photons but not to leptons, quarks and nucleons would have effects in most of the experiments searching for axions, since these are based on the $a γγ$ coupling. We examine the laboratory, astrophysical and cosmological constraints on $ϕ$ and study whether it may constitute a substantial part of the dark matter. We also generalize the $ϕ$ interactions to possess $SU(2) \times U(1)$ gauge invariance, and analyze the phenomenological implications.
The discrepancy between the experimental decay rate of orthopositronium (o-Ps) and the QED theoretical prediction can be solved by invoking decays of o-Ps into exotic particles with branching ratios of the order of 10^{-3}. We show that considerations based on primordial nucleosynthesis and effective Lagrangians place a very stringent upper bound: B = Gamma(o-Ps -> ``exotic'' + ...)/Gamma(o-Ps) <= 2 x 10^{-15}, ruling out the exotic decay solution to the puzzle.