2,201 research outputs found
Too Hot, Too Cold or Just Right? Implications of a 21-cm Signal for Dark Matter Annihilation and Decay
Measurements of the temperature of the baryons at the end of the cosmic dark
ages can potentially set very precise constraints on energy injection from
exotic sources, such as annihilation or decay of the dark matter. However,
additional effects that lower the gas temperature can substantially weaken the
expected constraints on exotic energy injection, whereas additional radiation
backgrounds can conceal the effect of an increased gas temperature in
measurements of the 21-cm hyperfine transition of neutral hydrogen. Motivated
in part by recent claims of a detection of 21-cm absorption from a redshift of
17 by the EDGES experiment, we derive the constraints on dark matter
annihilation and decay that can be placed in the presence of extra radiation
backgrounds or effects that modify the gas temperature, such as dark
matter-baryon scattering and early baryon-photon decoupling. We find that if
the EDGES observation is confirmed, then constraints on light dark matter
decaying or annihilating to electrons will in most scenarios be stronger than
existing state-of-the-art limits from the cosmic microwave background,
potentially by several orders of magnitude. More generally, our results allow
mapping any future measurement of the global 21-cm signal into constraints on
dark matter annihilation and decay, within the broad range of scenarios we
consider.Comment: 22 pages with appendices, 12 figures, comments welcome; v2:
references added with comments, typos corrected, minor change to millicharged
DM limit
Reduced O diffusion through Be doped Pt electrodes
Using first principles electronic structure calculations we screen nine
elements for their potential to retard oxygen diffusion through
poly-crystalline Pt (p-Pt) films. We determine that O diffuses preferentially
as interstitial along Pt grain boundaries (GBs). The calculated barriers are
compatible with experimental estimates. We find that Be controls O diffusion
through p-Pt. Beryllium segregates to Pt GBs at interstitial (i) and
substitutional (s) sites. i-Be is slightly less mobile than O and it repels O,
thus stuffing the GB. s-Be has a high diffusion barrier and it forms strong
bonds to O, trapping O in the GB. Experiments confirm our theoretical
predictions.Comment: 3 pages, 2 figure
DarkHistory: A code package for calculating modified cosmic ionization and thermal histories with dark matter and other exotic energy injections
We present a new public Python package, DarkHistory, for computing the
effects of dark matter annihilation and decay on the temperature and ionization
history of the early universe. DarkHistory simultaneously solves for the
evolution of the free electron fraction and gas temperature, and for the
cooling of annihilation/decay products and the secondary particles produced in
the process. Consequently, we can self-consistently include the effects of both
astrophysical and exotic sources of heating and ionization, and automatically
take into account backreaction, where modifications to the
ionization/temperature history in turn modify the energy-loss processes for
injected particles. We present a number of worked examples, demonstrating how
to use the code in a range of different configurations, in particular for
arbitrary dark matter masses and annihilation/decay final states. Possible
applications of DarkHistory include mapping out the effects of dark matter
annihilation/decay on the global 21cm signal and the epoch of reionization, as
well as the effects of exotic energy injections other than dark matter
annihilation/decay. The code is available at
https://github.com/hongwanliu/DarkHistory with documentation at
https://darkhistory.readthedocs.io . Data files required to run the code can be
downloaded at https://doi.org/10.7910/DVN/DUOUWA .Comment: 40 pages, 17 figure
Setting Standards for Credible Compliance and Law Enforcement
This paper examines the setting of optimal legal standards to simultaneously induce parties to invest in care and to motivate law enforcers to detect violators of the law. The strategic interaction between care providers and law enforcers determines the degree of efficiency achieved by the standards. Our principal finding is that some divergence between the marginal benefits and marginal costs of providing care is required to control enforcement costs. Further, the setting of standards may effectively substitute for the setting of fines when penalties for violation are fixed. In particular, maximal fines may be welfare reducing when standards are set optimally.
Nous considĂ©rons dans cet article la dĂ©termination, en information incomplĂšte, de normes lĂ©gales optimales pour Ă la fois inciter les citoyens Ă faire preuve de diligence (prĂ©vention) et motiver les agents de la paix Ă veiller au respect des lois. L'interaction stratĂ©gique entre citoyens et agents de la paix dĂ©termine l'efficacitĂ© des normes choisies. Notre rĂ©sultat principal est Ă l'effet qu'un Ă©cart entre bĂ©nĂ©fices marginaux et coĂ»ts marginaux de la diligence est nĂ©cessaire afin de rĂ©duire les coĂ»ts d'application des lois. De plus, les normes peuvent ĂȘtre un substitut aux amendes lorsque les pĂ©nalitĂ©s pour infraction sont fixes. Des amendes maximales peuvent en particulier ĂȘtre contre-indiquĂ©es lorsque les normes sont optimalement dĂ©terminĂ©es.Law Enforcement, Legal Standards, Fines, Strategic Behavior, Normes lĂ©gales, amendes, respect des lois, comportement stratĂ©gique
Enabling Forbidden Dark Matter
The thermal relic density of dark matter is conventionally set by two-body
annihilations. We point out that in many simple models, annihilations
can play an important role in determining the relic density over a broad range
of model parameters. This occurs when the two-body annihilation is
kinematically forbidden, but the process is allowed; we call this
scenario "Not-Forbidden Dark Matter". We illustrate this mechanism for a vector
portal dark matter model, showing that for a dark matter mass of , processes not only lead to the observed relic
density, but also imply a self-interaction cross section that can solve the
cusp/core problem. This can be accomplished while remaining consistent with
stringent CMB constraints on light dark matter, and can potentially be
discovered at future direct detection experiments.Comment: 12 pages, 8 figures. Updated to match version to be published in PRD.
Minor corrections to the cross sections and the Boltzmann equations have been
made. More detailed discussions of the secluded case, the Boltzmann equations
and the computation of the cross sections have been include
An updated meta-analysis approach for genetic linkage
We present a meta-analysis procedure for genome-wide linkage studies (MAGS). The MAGS procedure combines genome-wide linkage results across studies with possibly distinct marker maps. We applied the MAGS procedure to the simulated data from the Genetic Analysis Workshop 14 in order to investigate power to detect linkage to disease genes and power to detect linkage to disease modifier genes while controlling for type I error. We analyzed all 100 replicates of the four simulated studies for chromosomes 1 (disease gene), 2 (modifier gene), 3 (disease gene), 4 (no disease gene), 5 (disease gene), and 10 (modifier gene) with knowledge of the simulated disease gene locations. We found that the procedure correctly identified the disease loci on chromosomes 1, 3, and 5 and did not erroneously identify a linkage signal on chromosome 4. The MAGS procedure provided little to no evidence of linkage to the disease modifier genes on chromosomes 2 and 10
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