We review theories of Asymmetric Dark Matter (ADM), their cosmological implications and detection. While there are many models of ADM in the literature, our review of existing models will center on ...highlighting the few common features and important mechanisms for generation and transfer of the matter–anti-matter asymmetry between dark and visible sectors. We also survey ADM hidden sectors, the calculation of the relic abundance for ADM, and how the DM asymmetry may be erased at late times through oscillations. We consider cosmological constraints on ADM from the cosmic microwave background, neutron stars, the Sun, and brown and white dwarves. Lastly, we review indirect and direct detection methods for ADM, collider signatures, and constraints.
Semiconductors are by now well-established targets for direct detection of MeV to GeV dark matter via scattering off electrons. We show that semiconductor targets can also detect significantly ...lighter dark matter via an absorption process. When the dark matter mass is above the band gap of the semiconductor (around an eV), absorption proceeds by excitation of an electron into the conduction band. Below the band gap, multiphonon excitations enable absorption of dark matter in the 0.01 eV to eV mass range. Energetic dark matter particles emitted from the sun can also be probed for masses below an eV. We derive the reach for absorption of a relic kinetically mixed dark photon or pseudoscalar in germanium and silicon, and show that existing direct detection results already probe new parameter space. With only a moderate exposure, low-threshold semiconductor target experiments can exceed current astrophysical and terrestrial constraints on sub-keV bosonic dark matter.
Superconducting targets have recently been proposed for the direct detection of dark matter as light as a keV, via elastic scattering off conduction electrons in Cooper pairs. Detecting such light ...dark matter requires sensitivity to energies as small as the superconducting gap of ScriptO(meV). Here we show that these same superconducting devices can detect much lighter DM, of meV to eV mass, via dark matter absorption on a conduction electron, followed by emission of an athermal phonon. We demonstrate the power of this setup for relic kinetically mixed hidden photons, pseudoscalars, and scalars, showing that the reach can exceed current astrophysical and terrestrial constraints with only a moderate exposure.
Spacetime fluctuations in AdS/CFT Verlinde, Erik; Zurek, Kathryn M.
The journal of high energy physics,
04/2020, Letnik:
2020, Številka:
4
Journal Article
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A
bstract
We compute fluctuations in the modular energy of the vacuum associated with a Rindler-wedge in AdS spacetime in the context of AdS/CFT. We discuss the possible effect of these energy ...fluctuations on the spacetime geometry, and on the traversal time of a light beam propagating from the boundary to the bulk and back.
Direct-detection experiments for light dark matter are making enormous leaps in reaching previously unexplored model space. Several recent proposals rely on collective excitations, where the ...experimental sensitivity is highly dependent on detailed properties of the target material, well beyond just nucleus mass numbers as in conventional searches. It is thus important to optimize the target choice when considering which experiment to build. We carry out a comparative study of target materials across several detection channels, focusing on electron transitions and single (acoustic or optical) phonon excitations in crystals, as well as the traditional nuclear recoils. We compare materials currently in use in nuclear recoil experiments (Si, Ge, NaI, CsI, CaWO4), a few of which have been proposed for light dark matter experiments (GaAs, Al2O3, diamond), as well as 16 other promising polar crystals across all detection channels. We find that target- and dark-matter-model-dependent reach is largely determined by a small number of material parameters: speed of sound, electronic band gap, mass number, Born effective charge, high-frequency dielectric constant, and optical phonon energies. We showcase, for each of the two benchmark models, an exemplary material that has a better reach than in any currently proposed experiment.
We compute the mass function of bound states of asymmetric dark matter-nuggets-synthesized in the early Universe. We apply our results for the nugget density and binding energy computed from a ...nuclear model to obtain analytic estimates of the typical nugget size exiting synthesis. We numerically solve the Boltzmann equation for synthesis including two-to-two fusion reactions, estimating the impact of bottlenecks on the mass function exiting synthesis. These results provide the basis for studying the late Universe cosmology of nuggets in a future companion paper.
Nuggets-very large stable bound objects arising in the presence of a sufficiently attractive and long-range force and in the absence of a dark Coulomb force-are a smoking gun signature for asymmetric ...dark matter (ADM). The cosmology of ADM nuggets is both generic and unique: nuggets feature highly exothermic fusion processes, which can impact the shape of the core in galaxies, as well as give rise to rare dark star formation. We find, considering the properties of nuggets in a generic extended nuclear model with both attractive and repulsive forces, that self-interaction constraints place an upper bound on nugget masses at the freeze-out of synthesis in the ballpark of Mfo≲1016 GeV. We also show that indirect detection strongly constrains models where the scalar mediator binding the nuggets mixes with the Higgs.
A
bstract
We present a unified theoretical framework for computing spin-independent direct detection rates via various channels relevant for sub-GeV dark matter — nuclear re- coils, electron ...transitions and single phonon excitations. Despite the very different physics involved, in each case the rate factorizes into the particle-level matrix element squared, and an integral over a target material- and channel-specific dynamic structure factor. We show how the dynamic structure factor can be derived in all three cases following the same procedure, and extend previous results in the literature in several aspects. For electron transitions, we incorporate directional dependence and point out anisotropic target materials with strong daily modulation in the scattering rate. For single phonon excitations, we present a new derivation of the rate formula from first principles for generic spin-independent couplings, and include the first calculation of phonon excitation through electron couplings. We also discuss the interplay between single phonon excitations and nuclear recoils, and clarify the role of Umklapp processes, which can dominate the single phonon production rate for dark matter heavier than an MeV. Our results highlight the complementarity between various search channels in probing different kinematic regimes of dark matter scattering, and provide a common reference to connect dark matter theories with ongoing and future direct detection experiments.
We study the reach of direct detection experiments for large bound states (containing 104 or more dark nucleons) of asymmetric dark matter. We consider ordinary nuclear recoils, excitation of ...collective modes (phonons), and electronic excitations, paying careful attention to the impact of the energy threshold of the experiment. Large exposure experiments with keV energy thresholds provide the best (future) limits when the dark matter is small enough to be treated as a point particle, but rapidly lose sensitivity for more extended dark bound states, or when the mediator is light. In those cases, low threshold, low exposure experiments (such as with a superfluid helium, polar material or superconducting target) are often more sensitive due to coherent enhancement over the dark nucleons. We also discuss indirect constraints on composite asymmetric dark matter arising from self-interaction, formation history, and the properties of the composite states themselves.
We propose a simple model of spacetime vacuum fluctuations motivated by AdS/CFT, where the vacuum is described by a thermal density matrix, ρ=e−KTr(e−K) with K the modular Hamiltonian. In AdS/CFT, ...both the expectation value of K and its fluctuations 〈ΔK2〉 have been calculated; both obey an area law identical to the Bekenstein-Hawking area law of black hole mechanics: 〈K〉=〈ΔK2〉=A4GN, where A is the area of an (extremal) entangling surface. It has also been shown that ΔK gravitates in AdS, and hence generates metric fluctuations. These theoretical results are intriguing, but it is not known how to precisely extend such ideas about holographic quantum gravity to ordinary flat space. We take the approach of considering whether experimental signatures in metric fluctuations could determine properties of the vacuum of quantum gravity in flat space. In particular, we propose a theoretical model motived by the AdS/CFT calculations that reproduces the most important features of modular Hamiltonian fluctuations; the model consists of a high occupation number bosonic degree of freedom. We show that if this theory couples through ordinary gravitational couplings to the mirrors in an interferometer with strain sensitivity similar to what will be available for gravitational waves, vacuum fluctuations could be observable.
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