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ABSTRACT A possibility of DM being multicomponent has a strong implication on resolving decades-long known cosmological problems on small scale. In addition to elastic scattering, the model allows for inelastic interactions, which can be characterized by a ‘velocity kick’ parameter. The simplest 2cDM model with cross-section $0.01\lesssim \sigma /m\lt 1\, \textrm {cm}^{2}{ \rm g}^{-1}$ and the kick velocity $V_{\mathrm{ k}}\simeq 100\, \rm {km\, s}^{-1}$ have been shown to robustly resolve the missing satellites, core-cusp, and too-big-to-fail problems in N-body cosmological simulations tested on Milky Way (MW)-like haloes of a virial mass ${\sim}5 \times 10^{11}\, {\rm M_{\odot }}$ (Papers I & II). With the aim of further constraining the parameter space available for the 2cDM model, we extend our analysis to dwarf and galaxy cluster haloes with their virial mass of ∼107−108 and ${\sim}10^{13} - 10^{14}\, {\rm M_{\odot }}$, respectively. We find that σ0/m ≳ 0.1 cm2g−1 is preferentially disfavoured for both dwarfs and galaxy cluster haloes in comparison with observations, while σ0/m = 0.001 cm2g−1 causes little perceptible difference from that of the CDM counterpart for most of the cross-section’s velocity dependence studied in this work. Our main result is that within the reasonable set of parameters, the 2cDM model can successfully explain themore »observational trends seen in dwarf galaxy and galaxy cluster haloes, and the model leaves us an open window for other possible alternative DM models.« less

In a collisionless plasma, the energy distribution function of plasma particles can be strongly affected by turbulence. In particular, it can develop a nonthermal power-law tail at high energies. We argue that turbulence with initially relativistically strong magnetic perturbations (magnetization parameterσ≫ 1) quickly evolves into a state with ultrarelativistic plasma temperature but mildly relativistic turbulent fluctuations. We present a phenomenological and numerical study suggesting that in this case, the exponentαin the power-law particle-energy distribution function,f(γ)dγ∝γ^−αdγ, depends on magnetic compressibility of turbulence. Our analytic prediction for the scaling exponentαis in good agreement with the numerical results.

The Cosmic Ray Extremely Distributed Observatory (CREDO) pursues a global research strategy dedicated to the search for correlated cosmic rays, so-called Cosmic Ray Ensembles (CRE). Its general approach to CRE detection does not involve any a priori considerations, and its search strategy encompasses both spatial and temporal correlations, on different scales. Here we search for time clustering of the cosmic ray events collected with a small sea-level extensive air shower array at the University of Adelaide. The array consists of seven one-square-metre scintillators enclosing an area of 10 m × 19 m. It has a threshold energy ~0.1 PeV, and records cosmic ray showers at a rate of ~6 mHz. We have examined event arrival times over a period of over 2.5 years in two equipment configurations (without and with GPS timing), recording ~300 k events and ~100 k events. We determined the event time spacing distributions between individual events and the distributions of time periods which contained specific numbers of multiple events. We find that the overall time distributions are as expected for random events. The distribution which was chosen a priori for particular study was for time periods covering five events (four spacings). Overall, these distributions fit closelymore »with expectation, but there are two outliers of short burst periods in data for each configuration. One of these outliers contains eight events within 48 s. The physical characteristics of the array will be discussed together with the analysis procedure, including a comparison between the observed time distributions and expectation based on randomly arriving events.« less