U-boson production in e+e annihilations, ψ and Υ decays, and light dark matter

摘要: We recall how a new light gauge boson emerged in supersymmetric extensions of the standard model with an extra singlet chiral superfield, and it could often behave very much as pseudoscalar, corresponding symmetry broken at scale higher than electroweak. (I) The possible existence such $U$, weakly coupled, allows for dark matter particles, which be origin 511 keV line from galactic bulge. Could found directly ${e}^{+}{e}^{\ensuremath{-}}$ annihilations? Not so easily, fact, due to various constraints limiting size its couplings, especially axial ones, leading axionlike behavior or parity-violation effects. In particular, searches decay $\ensuremath{\Upsilon}\ensuremath{\rightarrow}\ensuremath{\gamma}+\mathrm{\text{invisible}}\text{ }\text{ }U$ may used constrain severely coupling $U$ electron, ${f}_{eA}={f}_{bA}$, less about ${10}^{\ensuremath{-}6}{m}_{U}(\mathrm{MeV})$, 50 times smaller $\ensuremath{\simeq}5\text{ }{10}^{\ensuremath{-}5}{m}_{U}(\mathrm{MeV})$ that otherwise have been allowed ${g}_{e}\ensuremath{-}2$. (II) vector electron principle larger, but is also limited size. Even under favorable circumstances (no couplings quarks charged leptons, small neutrinos), taking into account $Z\mathrm{\text{\ensuremath{-}}}U$ mixing effects, we find ${g}_{\ensuremath{\mu}}\ensuremath{-}2$, reasonable assumptions cancellation effect, lepton universality), can most large $\ensuremath{\simeq}1.3\text{ }{10}^{\ensuremath{-}3}$, ${m}_{U}l{m}_{\ensuremath{\mu}}$. Such muon order ${10}^{\ensuremath{-}3}$ responsible somewhat value measured compared expectations, should this effect turn out real. (III) electrons are likely smaller, e.g. $\ensuremath{\lesssim}3\text{ }{10}^{\ensuremath{-}6}{m}_{U}(\mathrm{MeV})$, if neutrinos similar. This restricts significantly possibility detecting ${e}^{+}{e}^{\ensuremath{-}}\ensuremath{\rightarrow}\ensuremath{\gamma}U$, making search quite challenging. Despite smallness these exchanges provide annihilation cross sections (LDM) particles appropriate size, even require relatively strongly self-interacting.