Andrzej K. Drukier, Sebastian Baum, Katherine Freese, Maciej Górski, Patrick Stengel

Recently, we proposed paleo-detectors as a method for the direct detection of Weakly Interacting Massive Particle (WIMP) dark matter. In paleo-detectors, one would search for the persistent traces left by dark matter-nucleon interactions in ancient minerals. Thanks to the large integration time of paleo-detectors, relatively small target masses suffice to obtain exposures, i.e. the product of integration time and target mass, much larger than what is feasible in the conventional direct detection approach. Here, we discuss the paleo-detector proposal in detail, in particular, a range of background sources. For low-mass WIMPs with masses $m_\chi\lesssim10\,$GeV, the largest contribution to the background budget comes from nuclear recoils induced by coherent scattering of solar neutrinos. For heavier WIMPs, the largest background source is nuclear recoils induced by fast neutrons created by heavy radioactive contaminants, particularly $^{238}$U; neutrons can arise in spontaneous fission or from $\alpha$-particles created in $^{238}$U decays. We also discuss the challenges of mineral optimization, specifically the determination of readily available minerals from rocks in deep boreholes which are able to record persistent damage from nuclear recoils. In order to suppress backgrounds induced by radioactive contaminants, we propose to use minerals found in marine evaporites or in ultra-basic rocks. We estimate the sensitivity of paleo-detectors to spin-independent and spin-dependent WIMP-nucleus interactions. In all interaction cases considered here, the sensitivity to low-mass WIMPs with masses $m_\chi\lesssim10\,$GeV extends to WIMP-nucleon cross sections many orders of magnitude smaller than current upper limits. For heavier WIMPs with masses $m_\chi\gtrsim30\,$GeV cross sections a factor of a few to $\sim100$ smaller than current upper limits can be probed by paleo-detectors. [Abridged]

Florian Kuhnel, Andrew Matas, Glenn D. Starkman, Katherine Freese

A significant fraction of cosmological dark matter can be formed by very dense macroscopic objects, for example primordial black holes. Gravitational waves offer a promising way to probe of these kinds of dark matter candidates, in a parameter space region that is relatively untested by electromagnetic observations. In this work we consider an ensemble of macroscopic dark matter with masses in the range $10^{-13}$ - $10^{3}\,M_{\odot}$ orbiting a super-massive black hole. While the strain produced by an individual dark matter particle will be very small, gravitational waves emitted by a large number of such objects will add incoherently and produce a stochastic gravitational-wave background. We show that LISA can be a formidable machine for detecting the stochastic background of such objects orbiting the black hole in the center of the Milky Way, Sgr$\mspace{2mu}$A$^{\!*}$, if a dark matter spike of the type originally predicted by Gondolo and Silk forms near the central black hole.

Tomohiro Nakama, Jun'ichi Yokoyama

High energy collisions of particles may have created tiny black holes in the early Universe, which might leave stable remnants instead of fully evaporating as a result of Hawking radiation. If the reheating temperature was sufficiently close to the fundamental gravity scale, which can be different from the usual Planck scale depending of the presence and properties of spatial extra-dimensions, the formation rate could have been sufficiently high and hence such remnants could account for the entire cold dark matter of the Universe.

Clay Cordova, G. Bruno De Luca, Alessandro Tomasiello

We find non-supersymmetric AdS$_8$ solutions of type IIA supergravity. The internal space is topologically an $S^2$ with a U(1) isometry. The only non-zero flux is $F_0$; an O8 sourcing it is present at the equator of the $S^2$. The warping function and dilaton are non-constant. It is also possible to add D8-branes on top of the O8. Possible destabilizing brane bubbles (whose presence would be suggested by the weak-gravity conjecture) are either absent or collapsing. Our solutions are candidate holographic duals to unitary interacting CFTs in seven dimensions with exceptional global symmetry. We also present analogous non-supersymmetric AdS$_{d}$ solutions for general $d$ which are supported only by $F_0$.