Dark-Matter Harmonics Beyond Annual Modulation

The count rate at dark-matter direct-detection experiments should modulate annually due to the motion of the Earth around the Sun. We show that higher-frequency modulations, including daily modulation, are also present and in some cases are nearly as strong as the annual modulation. These higher-order modes are particularly relevant if (i) the dark matter is light, O(10) GeV, (ii) the scattering is inelastic, or (iii) velocity substructure is present; for these cases, the higher-frequency modes are potentially observable at current and ton-scale detectors. We derive simple expressions for the harmonic modes as functions of the astrophysical and geophysical parameters describing the Earth's orbit, using an updated expression for the Earth's velocity that corrects a common error in the literature. For an isotropic halo velocity distribution, certain ratios of the modes are approximately constant as a function of nuclear recoil energy. Anisotropic distributions can also leave observable features in the harmonic spectrum. Consequently, the higher-order harmonic modes are a powerful tool for identifying a potential signal from interactions with the Galactic dark-matter halo.Comment: 40 pages, 10 figures; v2 refs added, minor improvements; v3 refs added, minor improvements, JCAP versio

Distinguishing Dark Matter from Unresolved Point Sources in the Inner Galaxy with Photon Statistics

Data from the Fermi Large Area Telescope suggests that there is an extended excess of GeV gamma-ray photons in the Inner Galaxy. Identifying potential astrophysical sources that contribute to this excess is an important step in verifying whether the signal originates from annihilating dark matter. In this paper, we focus on the potential contribution of unresolved point sources, such as millisecond pulsars (MSPs). We propose that the statistics of the photons---in particular, the flux probability density function (PDF) of the photon counts below the point-source detection threshold---can potentially distinguish between the dark-matter and point-source interpretations. We calculate the flux PDF via the method of generating functions for these two models of the excess. Working in the framework of Bayesian model comparison, we then demonstrate that the flux PDF can potentially provide evidence for an unresolved MSP-like point-source population.Comment: 27 pages, 8 figures; v2, reference added and other minor change

The Mitochondrial Calcium Uniporter Is Autoregulated by Cation Binding to the β-Grasp-Like Matrix Domain

Mitochondrial calcium (Ca2+) uptake plays fundamental roles in various signaling processes. Entry of Ca2+ into the mitochondrial matrix is tightly controlled by the mitochondrial Ca2+ uniporter (MCU) in a higher order complex regulated by inter- and intra-molecular protein-protein interactions. However, the precise mechanisms controlling MCU function and regulation remain largely unknown. I identified a well-folded N-terminal MCU region from residues 72-189, and its crystal structure revealed a β-grasp-like fold with a cluster of acidic residues that facilitates interactions with dibasic cations. Binding of Ca2+ or Mg2+ destabilize this fold and shift the protein towards monomer. Single mutants disrupting the acidic face reduced the cation sensitivity in vitro. Together, my data reveal that the β-grasp-like matrix region of MCU harbors a distinct acidic patch that modulates stability and protein-protein interaction equilibria in response to Mg2+ and Ca2+ binding, suggesting that these matrix cations play an important role in controlling MCU activity

Nonlinear preferential rewiring in fixed-size networks as a diffusion process

We present an evolving network model in which the total numbers of nodes and edges are conserved, but in which edges are continuously rewired according to nonlinear preferential detachment and reattachment. Assuming power-law kernels with exponents alpha and beta, the stationary states the degree distributions evolve towards exhibit a second order phase transition - from relatively homogeneous to highly heterogeneous (with the emergence of starlike structures) at alpha = beta. Temporal evolution of the distribution in this critical regime is shown to follow a nonlinear diffusion equation, arriving at either pure or mixed power-laws, of exponents -alpha and 1-alpha

Missing Lensed Images and the Galaxy Disk Mass in CXOCY J220132.8-320144

The CXOCY J220132.8-320144 system consists of an edge-on spiral galaxy lensing a background quasar into two bright images. Previous efforts to constrain the mass distribution in the galaxy have suggested that at least one additional image must be present (Castander et al. 2006). These extra images may be hidden behind the disk which features a prominent dust lane. We present and analyze Hubble Space Telescope (HST) observations of the system. We do not detect any extra images, but the observations further narrow the observable parameters of the lens system. We explore a range of models to describe the mass distribution in the system and find that a variety of acceptable model fits exist. All plausible models require 2 magnitudes of dust extinction in order to obscure extra images from detection, and some models may require an offset between the center of the galaxy and the center of the dark matter halo of 1 kiloparsec. Currently unobserved images will be detectable by future James Webb Space Telescope (JWST) observations and will provide strict constraints on the fraction of mass in the disk.Comment: 10 pages, 8 figures, 6 tables. Minor changes, version accepted for publication in Ap

Evidence for Unresolved Gamma-Ray Point Sources in the Inner Galaxy

We present a new method to characterize unresolved point sources (PSs), generalizing traditional template fits to account for non-Poissonian photon statistics. We apply this method to Fermi Large Area Telescope gamma-ray data to characterize PS populations at high latitudes and in the Inner Galaxy. We find that PSs (resolved and unresolved) account for ~50% of the total extragalactic gamma-ray background in the energy range ~1.9 to 11.9 GeV. Within 10$^\circ$ of the Galactic Center with $|b| \geq 2^\circ$, we find that ~5-10% of the flux can be accounted for by a population of unresolved PSs, distributed consistently with the observed ~GeV gamma-ray excess in this region. The excess is fully absorbed by such a population, in preference to dark-matter annihilation. The inferred source population is dominated by near-threshold sources, which may be detectable in future searches.Comment: 7+22 pages, 4+18 figures; v2, minor changes, new Pass 8 data analyzed (conclusions unchanged); v3, PRL version, substantive improvements and additional checks (conclusion unchanged