A Bound on the Flux of Magnetic Monopoles from Catalysis of Nucleon Decay in White Dwarfs

Catalysis of nucleon decay in white dwarfs is used to constrain the abundance of magnetic monopoles arising from Grand Unified Theories. Recent discoveries of the dimmest white dwarf ever observed, WD 1136-286 with $L = 10^{-4.94} L_{\odot}$, place limits on the monopole flux. An abundance of monopoles greater than the new bound would heat this star to a luminosity higher than what is observed. The new bound is $(F/$cm $^{-2}$ s$^{-1}$ sr$^{-1}$) $(\sigma \upsilon/10^{-28} cm^2) < 1.3 \times 10^{-20} (\upsilon/10^{-3}c)^2$, where $\upsilon $ is the monopole velocity. The limit is improved by including the monopoles captured by the main-sequence progenitor of the white dwarf: $(F/$cm $^{-2}$ s$^{-1}$ sr$^{-1}$) $(\sigma \upsilon /10^{-28} cm^2) < 3.5(26) \times 10^{-21}$ for $10^{17}$ ($10^{16}$) GeV monopoles. We also note that the dependence on monopole mass of flux bounds due to catalysis in neutron stars with main sequence accretion has previously been calculated incorrectly (previously the bound has been stated as $F (\sigma \upsilon/10^{-28} cm^2) < 10^{-28} $ cm $^{-2}$ s$^{-1}$ sr$^{-1}$). We show that the correct bounds are somewhat weaker for monopole mass other than $10^{17}$ GeV.