Dark Matter Subhalos In the Fermi First Source Catalog

The Milky Way's dark matter halo is thought to contain large numbers of smaller subhalos. These objects can contain very high densities of dark matter, and produce potentially observable fluxes of gamma rays. In this article, we study the gamma ray sources in the Fermi Gamma Ray Space Telescope's recently published First Source Catalog, and attempt to determine whether this catalog might contain a population of dark matter subhalos. We find that, while approximately 20-60 of the catalog's unidentified sources could plausibly be dark matter subhalos, such a population cannot be clearly identified as such at this time. From the properties of the sources in the First Source Catalog, we derive limits on the dark matter's annihilation cross section that are comparably stringent to those derived from recent observations of dwarf spheroidal galaxies.Comment: 11 pages, 9 figures V2: Minor errors in Figure 3 correcte

Searching For Dark Matter Subhalos In the Fermi-LAT Second Source Catalog

The dark matter halo of the Milky Way is expected to contain an abundance of smaller subhalos. These subhalos can be dense and produce potentially observable fluxes of gamma rays. In this paper, we search for dark matter subhalo candidates among the sources in the Fermi-LAT Second Source Catalog which are not currently identified or associated with counterparts at other wavelengths. Of the nine high-significance, high-latitude (|b|>60 degrees), non-variable, unidentified sources contained in this catalog, only one or two are compatible with the spectrum of a dark matter particle heavier than approximately 50-100 GeV. The majority of these nine sources, however, feature a spectrum that is compatible with that predicted from a lighter (~5-40 GeV) dark matter particle. This population is consistent with the number of observable subhalos predicted for a dark matter candidate in this mass range and with an annihilation cross section of a simple thermal relic (sigma v~3x10^{-26} cm^3/s). Observations in the direction of these sources at other wavelengths will be necessary to either reveal their astrophysical nature (as blazars or other active galactic nuclei, for example), or to further support the possibility that they are dark matter subhalos by failing to detect any non-gamma ray counterpart.Comment: 8 pages, 4 figure

Implications of a 130 GeV Gamma-Ray Line for Dark Matter

Recent reports of a gamma-ray line feature at ~130 GeV in data from the Fermi Gamma-Ray Space Telescope have generated a great deal of interest in models in which dark matter particles annihilate with a sizable cross section to final states including photons. In this article, we take a model-independent approach, and discuss a number of possibilities for dark matter candidates which could potentially generate such a feature. While we identify several scenarios which could lead to such a gamma-ray line, these models are each fairly constrained. In particular, viable models require large couplings (g>1-3), and additional charged particles with masses in the range of approximately ~130-200 GeV. Furthermore, lower energy gamma-ray constraints from the Galactic Center force us to consider scenarios in which the dark matter annihilates in the early universe through velocity-suppressed processes, or to final states which yield relatively few gamma-rays (such as electrons, muons or neutrinos). An exception to these conclusions can be found in models in which the dark matter annihilates to heavy intermediate states which decay to photons to generate a line-like gamma-ray spectrum.Comment: 7 pages, 4 figure

Light Z' Bosons at the Tevatron

New gauge bosons with Standard Model-like couplings to leptons are constrained by collider searches to be heavier than approximately ~1 TeV. A Z' boson with suppressed couplings to leptons, however, could be much lighter and possess substantial couplings to Standard Model quarks. In this article, we consider a new leptophobic Z' gauge boson as a simple and well motivated extension of the Standard Model, and discuss several of its possible signatures at the Tevatron. We find that three of the recent anomalies reported from the Tevatron - in particular the top-quark forward-backward asymmetry and excesses in the 3b and W + 2 jets final states - could be explained by a new Z' with a mass of approximately 150 GeV, relatively large couplings to quarks, and suppressed couplings to electrons and muons. Moreover, we find that such a particle could also mediate the interactions of dark matter, leading to potentially interesting implications for direct detection experiments.Comment: 12 pages, 7 figures. v2, v3: updated references. v4: updated to match published version, including minor revisions to figures 1 and

UNPACKING THE SUBJECTIVE NORM: APPLYING STRUCTURATION THEORY TO TRADITIONAL MEASURES OF SOCIAL INFLUENCE

This study took place within the context of a larger project seeking to identify the factors that are associated with the acceptance and use of electronic recordkeeping systems in public sector organizations. This class of system relies on ordinary end-users to choose to select and file appropriate records into the system in order to comply with organizational and legislative recordkeeping requirements. The use of such a system necessarily includes a social or organizational context dimension to explain the intention to use. This paper focuses on the construct validity associated with social influence within the research model. This particular construct traces its roots back to the 1970s and appears in much of the technology acceptance literature as the subjective norm. The measures and techniques for identifying construct validity prior to the development of a survey instrument, and subsequent measures and techniques for detecting construct validity after gathering the detailed survey dataset, are discussed. The techniques used to group the measurement items by construct, and thus into a survey instrument, included card sorting and the use of cluster analyses and dendrograms. After the survey instrument data collection activity, the detailed construct validity analysis utilized the circle of correlations based on a principal component analysis.The research found that the traditional measures of social influence constructs cluster well, but are in fact multidimensional. Furthermore, the dimensionality revealed by the statistical analysis aligns with and supports the predicted interactions of society as put forward in Giddens’ Structuration Theory. This finding lends empirical support to Structuration Theory and underscores the importance of construct validity, particularly in the current push to increase the “social” aspects of technology

The Subject-centered Integrative Learning Model: A New Model for Teaching Occupational Therapy’s Distinct Value

The concept of occupation-centered education has been used to describe what programs do when they infuse occupation throughout an occupational therapy curriculum. In describing occupation-centered education, educators often describe the strategies they use to help students learn occupation, including courses about occupation, direct experience with occupation, cases and questions that connect biomedical sciences and health conditions to occupation, assignments that require students to infuse occupation into therapy, curriculum threads related to occupation, and many others. While each of these strategies is important, no conceptual model exists that defines occupation-centered education, elaborates its concepts and principles, and guides the development of curriculum and instructional strategies, uniting them within a whole theoretical approach to teaching occupational therapy. Research has consequently demonstrated that occupation can remain hidden and implied in these and similar teaching and learning strategies. Further, the number of topics students must learn continues to explode and many are not profession-specific. Thus, students and educators alike need a learning framework that helps them intentionally relate multi-disciplinary topics to the distinct value of occupational therapy. The Subject-centered Integrative Learning Model (SCIL-OT) is a conceptual model that outlines the theoretical foundations, elements, and principles of occupation-centered education. This model thus offers a roadmap for curriculum and instructional design that seeks to place the concept of occupation at the center of all aspects of education

Factors Influencing Employees\u27 Intention to Use an Electronic Recordkeeping System: Development of a Valid Survey Instrument

This study seeks to identify the factors that are associated with the acceptance and use of electronic recordkeeping systems in public sector organisations. These systems rely on ordinary end-users (rather than trained recordkeepers) to select and file appropriate records to comply with organisational and legislative recordkeeping requirements; however, current acceptance and utilisation rates of these systems are often mixed. The selected methodology is a mixed-methods approach, with this paper focusing on the development of a valid survey instrument. A theoretical model was initially derived from the literature covering three logical areas (and consisting of their supporting and pre-validated constructs): Technology Acceptance (performance expectancy, effort expectancy); Organizational Context (social influence, perceived power security), and Knowledge Interpretation. A new construct – perceived value of records – is introduced in this study to provide a construct in support of Knowledge Interpretation. The derived measurement items are then checked for construct validity before forming a suitable survey instrument

The Sensitivity of the IceCube Neutrino Detector to Dark Matter Annihilating in Dwarf Galaxies

In this paper, we compare the relative sensitivities of gamma-ray and neutrino observations to the dark matter annihilation cross section in leptophilic models such as have been designed to explain PAMELA data. We investigate whether the high energy neutrino telescope IceCube will be competitive with current and upcoming searches by gamma-ray telescopes, such as the Atmospheric Cerenkov Telescopes (ACTs) (HESS, VERITAS and MAGIC), or the Fermi Gamma Ray Space Telescope, in detecting or constraining dark matter particles annihilating in dwarf spheroidal galaxies. We find that after ten years of observation of the most promising nearby dwarfs, IceCube will have sensitivity comparable to the current sensitivity of gamma-ray telescopes only for very heavy (m_X > 7 TeV) or relatively light (m_X < 200 GeV) dark matter particles which annihilate primarily to mu+mu-. If dark matter particles annihilate primarily to tau+tau-, IceCube will have superior sensitivity only for dark matter particle masses below the 200 GeV threshold of current ACTs. If dark matter annihilations proceed directly to neutrino-antineutrino pairs a substantial fraction of the time, IceCube will be competitive with gamma-ray telescopes for a much wider range of dark matter masses.Comment: 7 pages, 3 figures. v2: references added and minor revisions. v3: as published in PRD

High-Energy Neutrino Signatures of Dark Matter Decaying into Leptons

Decaying dark matter has previously been proposed as a possible explanation for the excess high energy cosmic ray electrons and positrons seen by PAMELA and the Fermi Gamma-Ray Space Telescope (FGST). To accommodate these signals however, the decays must be predominantly leptonic, to muons or taus, and therefore produce neutrinos, potentially detectable with the IceCube neutrino observatory. We find that, with five years of data, IceCube (supplemented by DeepCore) will be able to significantly constrain the relevant parameter space of decaying dark matter, and may even be capable of discovering dark matter decaying in the halo of the Milky Way.Comment: 4 pages, 1 figur