Dark matter distributions around massive black holes: A general relativistic analysis

The cold dark matter at the center of a galaxy will be redistributed by the presence of a massive black hole. The redistribution may be determined using an approach pioneered by Gondolo and Silk: begin with a model distribution function for the dark matter, and ``grow'' the black hole adiabatically, holding the adiabatic invariants of the motion constant. Unlike the approach of Gondolo and Silk, which adopted Newtonian theory together with ad hoc correction factors to mimic general relativistic effects, we carry out the calculation fully relativistically, using the exact Schwarzschild geometry of the black hole. We find that the density of dark matter generically vanishes at r=2R_S, not 4R_S as found by Gondolo and Silk, where R_S is the Schwarzschild radius, and that the spike very close to the black hole reaches significantly higher densities. We apply the relativistic adiabatic growth framework to obtain the final dark matter density for both cored and cusped initial distributions. Besides the implications of these results for indirect detection estimates, we show that the gravitational effects of such a dark matter spike are significantly smaller than the relativistic effects of the black hole, including frame dragging and quadrupolar effects, for stars orbiting close to the black hole that might be candidates for testing the black hole no-hair theorems.Comment: 18 pages, 5 figures, submitted to Phys. Rev

Search for CP Violating Signature of Intergalactic Magnetic Helicity in the Gamma Ray Sky

The existence of a cosmological magnetic field could be revealed by the effects of non-trivial helicity on large scales. We evaluate a CP odd statistic, $Q$, using gamma ray data obtained from Fermi satellite observations at high galactic latitudes to search for such a signature. Observed values of $Q$ are found to be non-zero; the probability of a similar signal in Monte Carlo simulations is $\sim 0.2\%$. Contamination from the Milky Way does not seem to be responsible for the signal since it is present even for data at very high galactic latitudes. Assuming that the signal is indeed due to a helical cosmological magnetic field, our results indicate left-handed magnetic helicity and field strength $\sim 10^{-14}~{\rm G}$ on $\sim 10~{\rm Mpc}$ scales.Comment: 5 pages. Matches published MNRAS Lett. version. For analysis tools see http://sites.physics.wustl.edu/magneticfields/wiki/index.php/Search_for_CP_violation_in_the_gamma-ray_sk

Dark matter spikes in the vicinity of Kerr black holes

The growth of a massive black hole will steepen the cold dark matter density at the center of a galaxy into a dense spike, enhancing the prospects for indirect detection. We study the impact of black hole spin on the density profile using the exact Kerr geometry of the black whole in a fully relativistic adiabatic growth framework. We find that, despite the transfer of angular momentum from the hole to the halo, rotation increases significantly the dark matter density close to the black hole. The gravitational effects are still dominated by the black hole within its influence radius, but the larger dark matter annihilation fluxes might be relevant for indirect detection estimates.Comment: Published version plus corrected typo in Fig 1

Dark matter in natural supersymmetric extensions of the Standard Model

We explore the dark matter sector in extensions of the Minimal Supersymmetric Standard Model (MSSM) that can provide a good fit to the PAMELA cosmic ray positron excess, while at the same time addressing the little hierarchy problem of the MSSM. Adding a singlet Higgs superfield, S, can account for the observed positron excess, as recently discussed in the literature, but we point out that it requires a fine-tuned choice for the parameters of the model. We find that including an additional singlet allows both a reduction of the weak-scale fine-tuning, and an interpretation of the cosmic ray observations in terms of dark matter annihilations in the galactic halo. Our setup contains a light axion, but does not require light CP-even scalars in the spectrum.Comment: 26 pages, 8 figures, references adde