Dark matter theory
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Dark Matter Theory: An Overview of Current Research
Introduction to Dark Matter Theory
Dark matter is a fundamental component of the universe, constituting approximately 20% of its energy density and playing a crucial role in the formation and evolution of cosmic structures Nelson2011Strumia2010. Despite its significance, the exact nature of dark matter remains elusive, with various theories and models proposed to explain its properties and behavior.
Asymmetric Dark Matter (ADM)
Asymmetric Dark Matter (ADM) theories propose that the dark matter in the universe has a matter-antimatter asymmetry similar to that of visible matter. These models focus on mechanisms for generating and transferring this asymmetry between the dark and visible sectors. ADM theories also explore the hidden sectors, relic abundance calculations, and potential erasure of the DM asymmetry through oscillations at late times. Cosmological constraints from sources like the cosmic microwave background and neutron stars are considered, along with indirect and direct detection methods .
Technicolor Theories and Dark Matter
Technicolor theories introduce new dark matter candidates, specifically technibaryons, which emerge from these models. These candidates are analyzed for their relic density under weak thermal equilibrium and electric neutrality conditions. The impact of sphaleron processes, which violate baryon, lepton, and technibaryon numbers, is also examined. Both first and second-order electroweak phase transitions are considered, with technibaryons contributing to the dark matter content of the universe. Constraints from earth-based experiments are also discussed .
Non-Abelian Dark Matter
Non-Abelian dark matter theories propose that dark matter is charged with respect to "dark" gluons from a new non-Abelian gauge theory. These gluons constitute self-interacting dark radiation, leading to unique cosmological consequences and experimental signatures. This model suggests that dark matter could interact through a new force, distinct from the standard model interactions .
Atomic Dark Matter
The Atomic Dark Matter model posits that dark matter consists of two fermions oppositely charged under a new U(1) dark force. These fermions initially couple to a thermal bath of "dark photons" and eventually recombine into neutral atom-like bound states. This model predicts novel properties on small scales while retaining the success of cold dark matter on larger scales. The delayed kinetic decoupling in this scenario leads to unique imprints on the matter power spectrum and the cosmic microwave background (CMB) .
Dynamical Dark Matter
The Dynamical Dark Matter framework suggests a multi-component model where dark matter comprises a vast ensemble of interacting fields with varying masses, mixings, and abundances. Stability is not imposed on each field individually but is balanced against abundance. This leads to a dynamic scenario where cosmological quantities experience non-trivial time-dependences beyond the universe's expansion. This model can naturally arise from theories with large extra dimensions, such as certain limits of string theory .
Detection and Experimental Constraints
Various methods for detecting dark matter are explored, including underground direct detection and indirect detection in space. Direct detection involves dark matter scattering off target nuclei, while indirect detection looks for dark matter annihilation or decay in galaxies. Recent experimental developments focus on both low-mass and high-mass dark matter candidates, with specific techniques tailored to each .
Conclusion
The study of dark matter encompasses a wide range of theories and models, each offering unique insights into its nature and behavior. From asymmetric dark matter and technicolor theories to non-Abelian and atomic dark matter models, researchers continue to explore various possibilities. Experimental efforts to detect dark matter and constrain these theories are ongoing, with the hope of uncovering the true nature of this mysterious component of the universe.
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