Abstract: We describe models in which dark matter is xenophobic, with significantly reduced signal strength in direct detection experiments using xenon as a target material. Such models alleviate tension between xenon-based constraints and possible signal at other direct detection experiments, and in particular regions of interest at CoGeNT and CDMS are largely below XENON100 bounds in the purely xenophobic limit. We also show the constraints from upcoming LUX results and orthogonal searches using Fermi-LAT results from line searches in dwarf spheroidals and monojet searches at CMS.

No.: 1604
ID: CaltechAUTHORS:20140707-080005855

]]>

Abstract: We provide a derivation of the Born Rule in the context of the Everett (Many-Worlds) approach to quantum mechanics. Our argument is based on the idea of self-locating uncertainty: in the period between the wave function branching via decoherence and an observer registering the outcome of the measurement, that observer can know the state of the universe precisely without knowing which branch they are on. We show that there is a uniquely rational way to apportion credence in such cases, which leads directly to the Born Rule. [Editors note: for a video of the talk given by Prof. Carroll at the Aharonov-80 conference in 2012 at Chapman University, see quantum.chapman.edu/talk-14.]

Publication: arXiv
ID: CaltechAUTHORS:20141216-203110170

]]>

Abstract: There is no direct evidence for radiation domination prior to big-bang nucleosynthesis, and so it is useful to consider how constraints to thermally-produced axions change in non-standard thermal histories. In the low-temperature-reheating scenario, radiation domination begins as late as ~1 MeV, and is preceded by significant entropy generation. Axion abundances are then suppressed, and cosmological limits to axions are significantly loosened. In a kination scenario, a more modest change to axion constraints occurs. Future possible constraints to axions and low-temperature reheating are discussed.

No.: 1274
ID: CaltechAUTHORS:20110318-145420435

]]>

Abstract: We explore the feasibility and astrophysical consequences of a new long-range U(1) gauge field ("dark electromagnetism") that couples only to dark matter, not to the Standard Model. The dark matter consists of an equal number of positive and negative charges under the new force, but annihilations are suppressed if the dark matter mass is sufficiently high and the dark fine-structure constant α is sufficiently small. The correct relic abundance can be obtained if the dark matter also couples to the conventional weak interactions, and we verify that this is consistent with particle-physics constraints. The primary limit on a comes from the demand that the dark matter be effectively collisionless in galactic dynamics, which implies α ≾ 10^(-3) for TeV-scale dark matter. These values are easily compatible with constraints from structure formation and primordial nucleosynthesis. We raise the prospect of interesting new plasma effects in dark matter dynamics, which remain to be explored. This proceedings is based on the work presented originally in.(1)

ID: CaltechAUTHORS:20100715-111557235

]]>

Abstract: There is no direct evidence for radiation domination prior to big-bang nucleosynthesis, and so it is useful to consider how constraints to thermally-produced axions change in non-standard thermal histories. In the low-temperature-reheating scenario, radiation domination begins as late as ~1 MeV, and is preceded by significant entropy generation. Axion abundances are then suppressed, and cosmological limits to axions are significantly loosened. In a kination scenario, a more modest change to axion constraints occurs. Future possible constraints to axions and low-temperature reheating are discussed.

No.: 1166
ID: CaltechAUTHORS:20100804-142905281

]]>