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Start date: 2022Subject: search.filters.subject.Dark Matter

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    The culprit for the termination of Mars’ magnetic field: Dark Matter
    (University of the Witwatersrand, Johannesburg, 2024) Makda, Javeria
    The reason for a significant change in the heat flux of the interior of Mars, leading to the termination of its magnetic dynamo, is not yet known. We present the idea that interaction of dark matter particles with the elements constituting the core of Mars is the cause for this significant heat flux change. We include resonant enhancements in the determining of the capture rate of dark matter particles by a planet, using more recent formulations. The exclusion limits for the interaction cross-sections in our work are more stringent than previous limits. We demonstrate, using Xenon1T limits, that the density of dark matter in our solar neighbourhood is insufficient to induce significant heating. However, encounters with low-mass ultra-compact mini-halos or very massive conventional sub-halos could both produce significant heating effects within terrestrial planets. We find that in 1 Gyr, there is a possibility of up to ∼ 860 interactions of Mars with an ultra-compact mini-halo, that would have the sufficient density and mass to alter the workings of the convective core of Mars, such that it would lead to the cessation of the Martian geodynamo. The interaction of Earth with these halos would not result in the cessation of its magnetic field due to mechanisms such as tectonic activity, crust recycling and the subsequent motion of molten iron in its outer core, which result in the continuous functioning of the geodynamo
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    Multi-messenger Indirect Dark Matter Searches in Milky Way Satellites
    (University of the Witwatersrand, Johannesburg, 2023-09) Noorbhai, Raees Mubeen; Beck, Geoffrey
    First suggested 90 years ago, the Dark Matter (DM) mystery has been deepened by a range of astronomical observations, from the galactic to the cosmological scale, demonstrating anomalous gravitational phenomena which necessitate the existence of some unknown DM. In the 1970s, particle DM models, including the WIMP hypothesis considered in this work, were proposed and have subsequently been subjected to empirical scrutiny. Over the past 2 decades, all DM direct detection experiments, collider searches and indirect detection searches have failed to detect a DM signal, placing stringent constraints upon WIMP parameters and ruling out WIMP-Hadron interactions. Following the detection of an excess e−/e + flux at approximately 1.4 TeV by DAMPE in 2017, a number of Massive Leptophilc Majorana Particle (MLMP) WIMP hypotheses were proposed to explain the flux. To conduct a model-independent test of these hypotheses, Leptophilic WIMPs in the 1-2 TeV mass-energy range are considered, accounting for self-Annihilation along all leptonic channels, as well as the 3l democratic case. The dwarf spheroidal galaxies orbiting the Milky Way (MW), particularly the Ultrafaints, are DM-dominated and are thus strong candidates for indirect DM searches using next-generation telescopes - such as CTA in gamma, KM3NeT in neutrinos and MeerKAT in radio, with sensitivities that dwarf those of prior telescopes like LHAASO. Accounting for the respective fields-of-view of these telescopes, 6 dwarf spheroidals, 4 Ultrafaints and 2 Classicals, are chosen as potential target environments for the multi-messenger analysis. Equations are also derived for the Mean Free Path (MFP) and Mean Annihilation Period (MAP) of the WIMPs in the respective DM Halos, for the case of both an arbitrary Halo boundary and at the virial radius boundary. Utilising conservative estimates of telescope sensitivities, non-detection upper bounds are placed upon the Annihilation cross-section ⟨σv⟩ψ and Decay rate Γψ. These bounds are taken in comparison to the bounds imposed by the Super-amiokande neutrino search in the MW Halo and centre, the ATCA radio search in Reticulum II and the ASKAP/EMUradio search in the LMC. In all cases, the non-detection bounds imposed by observations of the Ultra faints are more stringent, but with greater error margins than is the case with the Classicals. For CTA, non-detection bounds in the case of all Ultrafaints are competitive with those imposed by the ASKAP/EMU search and stronger than those imposed by both the ATCA and the Super-Kamiokande searches. For KM3NeT, no novel non-detection bounds are imposed for observations of all 6 dwarf spheroidals. For MeerKAT, in the case of the µ −/µ + channel, observations of Reticulum II are competitive with the ASKAP/EMU bounds. From the multi-messenger analysis, it is concluded that the strongest non-detection bounds are imposed by CTA observations of Segue 1 and MeerKAT observations of Reticulum II. In the Decay case, the bounds are compared to those imposed by the Fermi indirect search in the IGRB. In the case of all next-generation telescopes, no novel non-detection constraints can be imposed upon Γψ . In the case of the MFP and MAP results, the non-detection lower limits are often many orders of magnitude greater the Hubble time. At the relic density limit, the Halo-independent MAP at the virial limit is 14 orders of magnitude greater than the age of the Universe. This illustrates the severe extent to which the Annihilation channel for WIMPs has been suppressed, since successive instances of non-detection have placed tight bounds on ⟨σv⟩ψ . In light of this, proposed astrophysical explanations for the DAMPE flux are favourable, as they do not require the presupposition of WIMP Dark Matter.