Speaker: Pedro De la Torre Luque (Stockholm University)
The FLUKA cross sections for cosmic-ray propagation
While the accuracy of current cosmic-ray (CR) data allows us to carry out precise tests of our models of propagation of charged particles in the Galaxy, the precision of cross sections data for the production of secondary particles (secondary CRs, neutrinos, gamma rays) is very poor, considerably limiting these tests. Given that most of the calculations of these cross sections from fundamental models of particle interactions are in disagreement with data, we rely on parameterizations fitted to the very scarce and uncertain experimental data. In the last years, the FLUKA Monte Carlo nuclear toolkit has been optimized to be used in different kinds of CR studies and has been extensively tested against data. In this talk, we present new sets of spallation cross sections of CR interactions in the Galaxy, both inelastic and inclusive, computed with FLUKA. Furthermore, these cross sections have been implemented in the DRAGON2 code to characterize the spectra of CR nuclei up to Z=26 (Iron) and study the main propagation parameters predicted from the spectra of secondary CRs such as B, Be and Li. These results and their implications will be discussed in the talk.
Speaker: Akaxia Cruz (Washington U., Seattle)
Astrophysical Plasma Instabilities induced by Long-Range Interacting Dark Matter
If dark matter (DM) is millicharged or darkly charged, collective plasma processes may dominate momentum exchange over direct particle collisions. In particular, plasma streaming instabilities can couple the momentum of DM to counter-streaming baryons or other DM and result in the counter-streaming fluids coming to rest with each other, just as happens for baryonic collisionless shocks in astrophysical systems. While electrostatic plasma instabilities (such as the two stream) are highly suppressed by Landau damping in the cosmological situations of interest, electromagnetic instabilities such as the Weibel can couple the momenta. Their growth rates are slower than the prior assumption that they would grow at the plasma frequency of DM. We find that the streaming of DM in the pre-Recombination universe is affected more strongly by direct collisions than collective processes, validating previous constraints. However, when considering unmagnetized instabilities the properties of the Bullet Cluster merger would be substantially altered if [qχ/mχ]≳10−4[q_\chi/m_\chi] \gtrsim 10^{-4}[qχ/mχ]≳10−4, where [qχ/mχ][qχ/mχ]][qχ/mχ] is the charge-to-mass ratio of DM relative to that of the proton. When a magnetic field is added consistent with cluster observations, Weibel and Firehose instabilities result in the constraint [qχ/mχ]≳10−12−10−11[qχ/mχ]] \gtrsim10^{-12}-10^{-11}[qχ/mχ]≳10−12−10−11. The constraints are even stronger in the case of a dark U(1)U(1)U(1) charge, ruling out [qχ/mχ]≳10−14[qχ/mχ]] \gtrsim10^{-14}[qχ/mχ]≳10−14 in the Bullet Cluster system. The strongest previous limits on millicharged DM arise from considering the spin down of galactic disks. We show that plasma instabilities or tangled background magnetic fields could lead to diffusive propagation of DM, weakening these spin down limits. Thus, our constraints from considering plasma instabilities are the most stringent over much of the millicharged and especially dark-charged parameter space.