Some of the dark matter parameter space can be ruled out because people aren't suddenly slammed great distances or killed by random particles of dark matter flying around on a regular basis.
Death by Dark Matter
(Submitted on 15 Jul 2019)Macroscopic dark matter refers to a variety of dark matter candidates that would be expected to (elastically) scatter off of ordinary matter with a large geometric cross-section. A wide range of macro massesMX and cross-sectionsσX remain unprobed. We show that over a wide region within the unexplored parameter space, collisions of a macro with a human body would result in serious injury or death. We use the absence of such unexplained impacts with a well-monitored subset of the human population to exclude a region bounded byσX≥10−8−10−7 cm2 andMX<50 kg. Our results open a new window on dark matter: the human body as a dark matter detector.
This is not really all that informative, however, as there is good reason to believe for a variety of reasons that the cross section of interaction between dark matter particles (if they exist), and ordinary matter, is less than 10^-40 per square centimeter (i.e. at least roughly as weak as the neutrino cross-section of interaction).
In other news, a dark matter annihilation explanation for certain cosmic ray signals in a particular case, as opposed to a more conventional explanation, is strongly disfavored although not quite ruled out, certain other kinds of dark matter annihilation signals are ruled out, and solar system bounds on dark matter halo effects are reconsidered.
In other news, a dark matter annihilation explanation for certain cosmic ray signals in a particular case, as opposed to a more conventional explanation, is strongly disfavored although not quite ruled out, certain other kinds of dark matter annihilation signals are ruled out, and solar system bounds on dark matter halo effects are reconsidered.
On the origin of the gamma-ray emission from Omega Centauri: Milisecond pulsars and dark matter annihilation
(Submitted on 15 Jul 2019)
We explore two possible scenarios to explain the observed gamma-ray emission associated with the atypical globular cluster Omega-Centauri: emission from millisecond pulsars (MSP) and dark matter (DM) annihilation. In the first case the total number of MSPs needed to produce the gamma-ray flux is compatible with the known (but not confirmed) MSP candidates observed in X-rays. A DM interpretation is motivated by the possibility of Omega-Centauri being the remnant core of an ancient dwarf galaxy hosting a surviving DM component. At least two annihilation channels, light quarks and muons, can plausibly produce the observed gamma-ray spectrum. We outline constraints on the parameter space of DM mass versus the product of the pair-annihilation cross section and integrated squared DM density (the so-called J-factor). We translate upper limits on the dark matter content of Omega-Centauri into lower limits on the annihilation cross section. This shows s-wave annihilation into muons to be inconsistent with CMB observations, while a small window for annihilation into light quarks is allowed. Further analysis of Omega-Centauri's internal kinematics, and/or additional information on the resident MSP population will yield much stronger constraints and shed light about the origin of this otherwise mysterious gamma-ray source.
Bounds on WIMP dark matter from galaxy clusters at low redshift
(Submitted on 16 Jul 2019)The study of the cross-correlation angular power spectrum between gravitational tracers and electromagnetic signals can be a powerful tool to constrain Dark Matter (DM) microscopic properties. In this work we correlate \Fermi\ diffuse \g-ray maps with catalogues of galaxy clusters. To emphasize the sensitivity to a DM signal, we select clusters at low-redshift0<z<0.2 and with large-halo massM500>1013M⊙ . The analysis is performed with four catalogues in different wavebands, including infrared, optical and X-rays. No evidence for a DM signal is identified. On the other hand, we derive competitive bounds: the thermal cross-section is excluded at 95\% C.L. for DM masses below 20 GeV and annihilation in theτ+−τ− channel.
Effect of the Solar dark matter wake on planets
(Submitted on 9 Jul 2019)
The Galaxy is conventionally thought to be surrounded by a massive dark matter (DM) halo. As the Sun goes through this halo, it excites a DM wake behind it. This local asymmetry in the DM distribution would gravitationally affect the motions of Solar System planets, potentially allowing the DM wake to be detected or ruled out. Hernandez (2019) recently calculated that the DM-induced perturbation to Saturn's position is 252 metres net of the effect on the Sun. No such anomaly is seen in Saturn's motion despite very accurate tracking of the Cassini spacecraft, which orbited Saturn for >13 years. Here, we revisit the calculation of how much Saturn would deviate from Keplerian motion if we fix its position and velocity at some particular time. The DM wake induces a nearly resonant perturbation whose amplitude grows almost linearly with time. We show that the Hernandez (2019) result applies only for an observing duration comparable to the≈250 million year period of the Sun's orbit around the Galaxy. Over a 100 year period, the perturbation to Saturn's orbit amounts to <1 cm, which is quite consistent with existing observations. Even smaller perturbations are expected for the terrestrial planets.
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Rapidly Rotating Neutron Stars And Black Holes – Millisecond Pulsars
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