Dissecting cosmic-ray electron-positron data with Occam's Razor: the role of known Pulsars

We argue that both the positron fraction measured by PAMELA and the peculiar spectral features reported in the total electron-positron (e+e-) flux measured by ATIC have a very natural explanation in electron-positron pairs produced by nearby pulsars. While this possibility was pointed out a long time ago, the greatly improved quality of current data potentially allow to reverse-engineer the problem: given the regions of pulsar parameter space favored by PAMELA and by ATIC, are there known pulsars that explain the data with reasonable assumptions on the injected e+e- pairs? In the context of simple benchmark models for estimating the e+e- output, we consider all known pulsars, as listed in the most complete available catalogue. We find that it is unlikely that a single pulsar be responsible for both the PAMELA e+ fraction anomaly and for the ATIC excess, although two single sources are in principle enough to explain both experimental results. The PAMELA excess e+ likely come from a set of mature pulsars (age ~ 10^6 yr), with a distance of 0.8-1 kpc, or from a single, younger and closer source like Geminga. The ATIC data require a larger (and less plausible) energy output, and favor an origin associated to powerful, more distant (1-2 kpc) and younger (age ~ 10^5$ yr) pulsars. We list several candidate pulsars that can individually or coherently contribute to explain the PAMELA and ATIC data. Although generally suppressed, we find that the contribution of pulsars more distant than 1-2 kpc could contribute for the ATIC excess. Finally, we stress the multi-faceted and decisive role that Fermi-LAT will play in the very near future by (1) providing an exquisite measurement of the e+e- flux, (2) unveiling the existence of as yet undetected pulsars, and (3) searching for anisotropies in the arrival direction of high-energy e+e-.Comment: revised version, references and new figures added, changes in the discussion and figure

Good NEWS for GeV Dark Matter Searches

The proposed NEWS apparatus, a spherical detector with a small central electrode sensor operating as a proportional counter, promises to explore new swaths of the direct detection parameter space in the GeV and sub-GeV Dark Matter particle mass range by employing very light nuclear targets, such as H and He, and by taking advantage of a very low (sub-keV) energy threshold. Here we discuss and study two example classes of Dark Matter models that will be tested with NEWS: GeV-scale millicharged Dark Matter, and a GeV-Dirac Fermion Dark Matter model with a light (MeV-GeV) scalar or vector mediator, and indicate the physical regions of parameter space the experiment can probe.Comment: 5 pages, 3 figures; accepted for publication in Physical Review

TASI 2012 Lectures on Astrophysical Probes of Dark Matter

What is the connection between how the dark matter was produced in the early universe and how we can detect it today? Where does the WIMP miracle come from, and is it really a "WIMP" miracle? What brackets the mass range for thermal relics? Where does come from, and what does it mean? What is the difference between chemical and kinetic decoupling? Why do some people think that dark matter cannot be lighter than 40 GeV? Why is b\bar b such a popular annihilation final state? Why is antimatter a good way to look for dark matter? Why should the cosmic-ray positron fraction decline with energy, and why does it not? How does one calculate the flux of neutrinos from dark matter annihilation in a celestial body, and when is that flux independent of the dark matter pair-annihilation rate? How does dark matter produce photons? Read these lecture notes, do the suggested 10 exercises, and you will find answers to all of these questions (and to many more on what You Always Wanted to Know About Dark Matter But Were Afraid to Ask).Comment: 41 pages, 6 figures, 10 exercise

Unraveling the origin of black holes from effective spin measurements with LIGO-Virgo

We investigate how to use information on the effective spin parameter of binary black hole mergers from the LIGO-Virgo gravitational wave detections to discriminate the origin of the merging black holes. We calculate the expected probability distribution function for the effective spin parameter for primordial black holes. Using LIGO-Virgo observations, we then calculate odds ratios for different models for the distribution of black holes' spin magnitude and alignment. We evaluate the posterior probability density for a possible mixture of astrophysical and primordial black holes as emerging from current data, and calculate the number of future merger events needed to discriminate different spin and alignment models at a given level of statistical significance.Comment: 22 pages, 10 figure