1,721,057 research outputs found
Recommended from our members
DECIPHERING CONTRIBUTIONS TO THE EXTRAGALACTIC GAMMA-RAY BACKGROUND FROM 2 GeV TO 2 TeV
Full text linkAstrophysical sources outside the Milky Way, such as active galactic nuclei and star-forming galaxies, leave their imprint on the gamma-ray sky as nearly isotropic emission referred to as the extragalactic gamma-ray background (EGB). While the brightest of these sources may be individually resolved, their fainter counterparts contribute diffusely. In this work, we use a recently developed analysis method, called the Non-Poissonian Template Fit, on up to 93 months of publicly available data from the Fermi Large Area Telescope to determine the properties of the point sources (PSs) that comprise the EGB. This analysis takes advantage of photon-count statistics to probe the aggregate properties of these source populations below the sensitivity threshold of published catalogs. We measure the source-count distributions and PS intensities, as a function of energy, from ~2 GeV to 2 TeV. We find that the EGB is dominated by PSs, likely blazars, in all seven energy sub-bins considered. These results have implications for the interpretation of IceCube's PeV neutrinos, which may originate from sources that contribute to the non-blazar component of the EGB. Additionally, we comment on implications for future TeV observatories such as the Cherenkov Telescope Array. We provide sky maps showing locations most likely to contain these new sources at both low (≲50 GeV) and high (≳50 GeV) energies for use in future observations and cross-correlation studies.United States. Department of Energy (DE-SC00012567
Directional Antineutrino Detection
Full text linkWe propose the first event-by-event directional antineutrino detector using inverse beta decay (IBD) interactions on hydrogen, with potential applications including monitoring for nuclear nonproliferation, spatially mapping geoneutrinos, characterizing the diffuse supernova neutrino background and searching for new physics in the neutrino sector. The detector consists of adjacent and separated target and capture scintillator planes. IBD events take place in the target layers, which are thin enough to allow the neutrons to escape without scattering elastically. The neutrons are detected in the thicker boron-loaded capture layers. The location of the IBD event and the momentum of the positron are determined by tracking the positron’s trajectory through the detector. Our design is a straightforward modification of existing antineutrino detectors; a prototype could be built with existing technology.MIT Department of Physics Pappalardo ProgramUnited States. Dept. of Energy (Grant DE-SC00012567
Broadband and Resonant Approaches to Axion Dark Matter Detection
Full text linkWhen ultralight axion dark matter encounters a static magnetic field, it sources an effective electric current that follows the magnetic field lines and oscillates at the axion Compton frequency. We propose a new experiment to detect this axion effective current. In the presence of axion dark matter, a large toroidal magnet will act like an oscillating current ring, whose induced magnetic flux can be measured by an external pickup loop inductively coupled to a SQUID magnetometer. We consider both resonant and broadband readout circuits and show that a broadband approach has advantages at small axion masses. We estimate the reach of this design, taking into account the irreducible sources of noise, and demonstrate potential sensitivity to axionlike dark matter with masses in the range of 10[superscript -14]-10[superscript -6] eV. In particular, both the broadband and resonant strategies can probe the QCD axion with a GUT-scale decay constant.Massachusetts Institute of Technology. Pappalardo FellowshipUnited States. Dept. of Energy (Cooperative Research Agreement DE-SC- 00012567)United States. Dept. of Energy (Early Career Research program DE-SC-0006389)Alfred P. Sloan Foundation (Sloan Research Fellowship
Recommended from our members
Modulation effects in dark matter-electron scattering experiments
Full text linkOne of the next frontiers in dark-matter direct-detection experiments is to explore the MeV to GeV mass regime. Such light dark matter does not carry enough kinetic energy to produce an observable nuclear recoil, but it can scatter off electrons, leading to a measurable signal. We introduce a semianalytic approach to characterize the resulting electron-scattering events in atomic and semiconductor targets, improving on previous analytic proposals that underestimate the signal at high recoil energies. We then use this procedure to study the time-dependent properties of the electron-scattering signal, including the modulation fraction, higher-harmonic modes and modulation phase. The time dependence can be distinct in a nontrivial way from the nuclear scattering case. Additionally, we show that dark-matter interactions inside the Earth can significantly distort the laboratory-frame phase-space distribution of sub-GeV dark matter.MIT Department of Physics Pappalardo Program (Fellowship
Comments on the diphoton excess: critical reappraisal of effective field theory interpretations
Full text linkWe consider the diphoton excess observed by ATLAS and CMS using the most up-to-date data and estimate the preferred enhancement in the production rate between 8 TeV and 13 TeV. Within the framework of effective field theory (EFT), we then show that for both spin-0 and spin-2 Standard Model (SM) gauge-singlet resonances, two of the three processes S --> ZZ, S --> Zγ, and S --> W W must occur with a non-zero rate. Moreover, we demonstrate that these branching ratios are highly correlated in the EFT. Couplings of S to additional SM states may be constrained and differentiated by comparing the S production rates with and without the vector-boson fusion (VBF) cuts. We find that for a given VBF to inclusive production ratio there is maximum rate of S to gauge bosons, bb[overbar], and lighter quark anti-quark pairs. Simultaneous measurements of the width and the VBF ratio may be able to point towards the existence of hidden decays.Slovenian Research Agency (SRA) (Research core funding No. P1-0035)National Science Foundation (U.S.) NSF CAREER Grant PHY-1151392)United States. Dept. of Energy (Contract Number DE-SC0012567)Massachusetts Institute of Technology. Department of Physics (Pappalardo Fellowship
Rényi entropy, stationarity, and entanglement of the conformal scalar
Full text linkWe extend previous work on the perturbative expansion of the Rényi entropy, Sq , around q = 1 for a spherical entangling surface in a general CFT. Applied to conformal scalar fields in various spacetime dimensions, the results appear to conflict with the known conformal scalar Rényi entropies. On the other hand, the perturbative results agree with known Rényi entropies in a variety of other theories, including theories of free fermions and vector fields and theories with Einstein gravity duals. We propose a resolution stemming from a careful consideration of boundary conditions near the entangling surface. This is equivalent to a proper treatment of total-derivative terms in the definition of the modular Hamiltonian. As a corollary, we are able to resolve an outstanding puzzle in the literature regarding the Rényi entropy of N=4 super-Yang-Mills near q = 1. A related puzzle regards the question of stationarity of the renormalized entanglement entropy (REE) across a circle for a (2+1)-dimensional massive scalar field. We point out that the boundary contributions to the modular Hamiltonian shed light on the previously-observed non-stationarity. Moreover, IR divergences appear in perturbation theory about the massless fixed point that inhibit our ability to reliably calculate the REE at small non-zero mass.National Science Foundation (U.S.) (grant PHY-1314198
High-energy tail of the Galactic Center gamma-ray excess
Full text linkObservations by the Fermi-LAT have uncovered a bright, spherically symmetric excess surrounding the center of the Milky Way Galaxy. The spectrum of the γ-ray excess peaks sharply at an energy ∼2 GeV, exhibiting a hard spectrum at lower energies, and falls off quickly above an energy ∼5 GeV. The spectrum of the excess above ∼10 GeV is potentially an important discriminator between different physical models for its origin. We focus our study on observations of the γ-ray excess at energies exceeding 10 GeV, finding: (1) a statistically significant excess remains in the energy range 9.5–47.5 GeV, which is not degenerate with known diffuse emission templates such as the Fermi bubbles, (2) the radial profile of the excess at high energies remains relatively consistent with data near the spectral peak (3) the data above ∼5 GeV prefer a slightly greater ellipticity with a major axis oriented perpendicular to the Galactic plane. Using the recently developed non-Poissonian template fit, we find mild evidence for a point-source origin for the high-energy excess, although given the statistical and systematic uncertainties we show that a smooth origin of the high-energy emission cannot be ruled out. We discuss the implication of these findings for pulsar and dark matter models of the γ-ray excess. Finally we provide a number of updated measurements of the γ-ray excess, utilizing novel diffuse templates and the Pass 8 data set.United States. Department of Energy (contract DE-SC00012567)United States. Department of Energy (contract DE-SC0013999
Recommended from our members
Evidence for Unresolved γ-Ray Point Sources in the Inner Galaxy
Full text linkWe 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 γ-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 γ-ray background in the energy range ∼1.9 to 11.9 GeV. Within 10° of the Galactic Center with |b| ≥ 2°, we find that ∼5%–10% of the flux can be accounted for by a population of unresolved PSs distributed consistently with the observed ∼GeV γ-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.MIT Department of Physics Pappalardo Program (Fellowship)United States. Dept. of Energy (Grant DE-SC00012567)United States. Dept. of Energy (Grant DE-SC0013999)United States. Dept. of Energy (Grant DE-SC0007968
Recommended from our members
Constraining axion dark matter with Big Bang Nucleosynthesis
Full text linkAbstractWe show that Big Bang Nucleosynthesis (BBN) significantly constrains axion-like dark matter. The axion acts like an oscillating QCD θ angle that redshifts in the early Universe, increasing the neutron–proton mass difference at neutron freeze-out. An axion-like particle that couples too strongly to QCD results in the underproduction of He4 during BBN and is thus excluded. The BBN bound overlaps with much of the parameter space that would be covered by proposed searches for a time-varying neutron EDM. The QCD axion does not couple strongly enough to affect BBN
- …
