118590129
CMB anisotropy due to cosmic strings: Large angular scale
17612131
CBR Anisotropy from Primordial Gravitational Waves in Two-Component Inflationary Cosmology
We examine stochastic temperature fluctuations of the cosmic background radiation (CBR) arising via the Sachs-Wolfe effect from gravitational wave perturbations produced in the early universe. We consider spatially flat, perturbed FRW models that begin with an inflationary phase, followed by a mixed phase containing both radiation and dust. The scale factor during the mixed phase takes the form a(η) = c1η 2 + c2η + c3, where ci are constants. During the mixed phase the universe smoothly transforms from being radiation to dust dominated. We find analytic expressions for the graviton mode function during the mixed phase in terms of spheroidal wave functions. This mode function is used to find an analytic expression for the multipole moments 〈al 〉 of the two-point angular correlation function C(γ) for the CBR anisotropy. The analytic expression for the multipole moments is written in terms of two integrals, which are evaluated numerically. The results are compared to multipoles calculated for models that are completely dust dominated at last-scattering. We find that the multipoles 〈al 〉 of the CBR temperature perturbations for l > 10 are significantly larger for a universe that contains both radiation and dust at last-scattering. We compare our results with recent, similar numerical work and find good agreement. The spheroidal wave functions may have applications to other problems of cosmological interest. PACS numbers: 98.80.Cq, 98.80.C, 98.80.Es Typeset using REVTEX
32994345
The PALFA Survey: Going to great depths to find radio pulsars
The on-going PALFA survey is searching the Galactic plane (|b| < 5 ◦ , 32 ◦ < l < 77 ◦ and 168 ◦ < l < 214 ◦ ) for radio pulsars at 1.4 GHz using ALFA, the 7-beam receiver installed at the Arecibo Observatory. By the end of August 2012, the PALFA survey has discovered 100 pulsars, including 17 millisecond pulsars (P < 30 ms). Many of these discoveries are among the pulsars with the largest DM/P ratios, proving that the PALFA survey is capable of probing the Galactic plane for millisecond pulsars to a much greater depth than any previous survey. This is due to the survey's high sensitivity, relatively high observing frequency, and its high time and frequency resolution. Recently the rate of discoveries has increased, due to a new more sensitive spectrometer, two updated complementary search pipelines, the development of online collaborative tools, and access to new computing resources. Looking forward, focus has shifted to the application of artificial intelligence systems to identify pulsar-like candidates, and the development of an improved full-resolution pipeline incorporating more sophisticated radio interference rejection. The new pipeline will be used in a complete second analysis of data already taken, and will be applied to future survey observations. An overview of recent developments, and highlights of exciting discoveries will be presented.
7392737
Timing of a Young Mildly Recycled Pulsar with a Massive White Dwarf Companion
We report on timing observations of the recently discovered binary pulsar PSR J1952+2630 using the Arecibo Observatory. The mildly recycled 20.7-ms pulsar is in a 9.4-hr orbit with a massive, MW D > 0.93 M⊙, white dwarf (WD) companion. We present, for the first time, a phase-coherent timing solution, with precise spin, astrometric, and Keplerian orbital parameters. This shows that the characteristic age of PSR J1952+2630 is 77 Myr, younger by one order of magnitude than any other recycled pulsar–massive WD system. We derive an upper limit on the true age of the system of 150 Myr. We investigate the formation of PSR J1952+2630 using detailed modelling of the mass-transfer process from a naked helium star on to the neutron star following a common-envelope phase (Case BB Roche-lobe overflow). From our modelling of the progenitor system, we constrain the accretion efficiency of the neutron star, which suggests a value between 100 and 300% of the Eddington accretion limit. We present numerical models of the chemical structure of a possible oxygenneon-magnesium WD companion. Furthermore, we calculate the past and the future spin evolution of PSR J1952+2630, until the system merges in about 3.4 Gyr due to gravitational wave emission. Although we detect no relativistic effects in our timing analysis we show that several such effects will become measurable with continued observations over the next 10 years; thus PSR J1952+2630 has potential as a testbed for gravitational theories.
54002264
The SU(5) potential in desitter space
Abstract The one-loop effective potential for a minimal SU (5) theory is calculated on a curved DeSitter background spacetime. The stability of its extrema in the following subgroups is investigated: SU (4) × U (1), SU (3) × SU (2) × U (1), SU (3) × U (1) × U (1), SU (2) × SU (2) × U (1) × U (1). A combination of analytic and numerical methods is used to obtain phase diagrams for the model. In the inflationary universe, the curvature effects do not prevent a slide into the SU (4) × U (1) extremum.
13728005
Large Angular Scale CMB Anisotropy Induced by Cosmic Strings
B. Allen, R. R. Caldwell, E. P. S. Shellard, A. Stebbins, and S. Veeraraghavan Department of Physics, University of Wisconsin – Milwaukee, P.O. Box 413, Milwaukee, Wisconsin 53201, U.S.A. University of Cambridge, D.A.M.T.P. Silver Street, Cambridge CB3 9EW, U.K. NASA/Fermilab Astrophysics Center, P.O. Box 500, Batavia, Illinois 60510, U.S.A. NASA/Goddard Space Flight Center, Greenbelt, Maryland 20771
35408696
WITNESS BUNCH ACCELERATION IN A MULTI-BUNCH PWFA ∗
We present initial experimental results showing the excitation of plasma wakefields by a train of two drive bunches. These wakefields are experienced by a trailing witness bunch that gains energy while retaining a finite energy spread. These well controlled plasma wakefield accelerator (PWFA) experiments are important to test the theory of the PWFA and serve as a testbed for techniques that will be used in high energy experiments.
138041514
GENERATION AND CHARACTERIZATION OF 5-MICRON ELECTRON BEAM FOR PROBING OPTICAL SCALE STRUCTURES
In recent years advanced acceleration technologies have progress toward combination of electron beam, laser and optical scale dielectric structures. In present paper described generation of the electron beam probe with parameters satisfied to perform test of such optical structures.
119196181
The REgolith X-Ray Imaging Spectrometer (REXIS) for OSIRIS-REx: identifying regional elemental enrichment on asteroids
The OSIRIS-REx Mission was selected under the NASA New Frontiers program and is scheduled for launch in September of 2016 for a rendezvous with, and collection of a sample from the surface of asteroid Bennu in 2019. 101955 Bennu (previously 1999 RQ36) is an Apollo (near-Earth) asteroid originally discovered by the LINEAR project in 1999 which has since been classified as a potentially hazardous near-Earth object. The REgolith X-Ray Imaging Spectrometer (REXIS) was proposed jointly by MIT and Harvard and was subsequently accepted as a student led instrument for the determination of the elemental composition of the asteroid's surface as well as the surface distribution of select elements through solar induced X-ray fluorescence. REXIS consists of a detector plane that contains 4 X-ray CCDs integrated into a wide field coded aperture telescope with a focal length of 20 em for the detection of regions with enhanced abundance in key elements at 50 m scales. Elemental surface distributions of approximately 50-200 m scales can be detected using the instrument as a simple collimator. An overview of the observation strategy of the REXIS instrument and expected performance are presented here.
121348159
Measurement of the Crab spectrum with Milagro
Through use of new algorithms for estimating γ-ray and cosmic ray primary energies of events in Milagro we determine the energy spectra of gamma rays from the Crab nebula and spectra of Milagro background triggers have been determined in the energy range 1 to 100 TeV. The measured spectra are compared with those measured by ACT techniques and direct measurements of cosmic ray spectra.
122963493
Neutron-Capture Cross Sections of the Stable Lead Isotopes
Neutron-capture yields for several samples of separated lead isotopes were obtained at the Oak Ridge electron linear accelerator, in the neutron energy range above 2.5 keV. These were analyzed for resonance-capture areas and parameters. The data are included in a new evaluation of lead cross-section data.