119383884
Upper limits on the strength of periodic gravitational waves from PSR J1939+2134
The first science run of the LIGO and GEO gravitational wave detectors presented the opportunity to test methods of searching for gravitational waves from known pulsars. Here we present new direct upper limits on the strength of waves from the pulsar PSR J1939+2134 using two independent analysis methods, one in the frequency domain using frequentist statistics and one in the time domain using Bayesian inference. Both methods show that the strain amplitude at Earth from this pulsar is less than a few times 10−22.
28973038
Cosmic string loops and large-scale structure
We investigate the contribution made by small loops from a cosmic string network as seeds for large-scale structure formation. We show that cosmic string loops are highly correlated with the long-string network on large scales and therefore contribute significantly to the power spectrum of density perturbations if the average loop lifetime is comparable to or above one Hubble time. This effect further improves the large-scale bias problem previously identified in earlier studies of cosmic string models. @S0556-2821~99!01614-8# Quantitative predictions for the large-scale structure induced by cosmic strings have taken some time to crystallize as the understanding of cosmic string physics has improved @1#. In particular, the role of small loops produced by the string network has evolved from a potential one-to-one correspondence between loops and cosmological objects @2# through to a completely subsidiary role relative to the wakes swept out by long strings @3#. This dethronement of loops was a result of numerical studies which showed that the average loop size l ¯ 5at was much smaller than the horizon,
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.
121426208
Vacuum Energy in Gauged Extended Supergravity
Abstract The one loop vacuum energy in gauged extended supergravity is calculated in anti de Sitter space using zeta function regularisation. It vanishes for N ⩾ 5. The energy zeta function has no poles for N ⩾ 3.
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.
119876695
Gravitons in de sitter space
What has been shown in this talk is that the graviton propagator in de Sitter space is OK. If one makes a bad choice of gauge (-fixing term) then the propagator is infra-red divergent. However this is not a problem. You can either make a better choice of gauge (of which there are an infinite number), for which the propagator is completely, finite, or else you can go right ahead and use the infra-red divergent one. We demonstrated that it doesn't matter. Gauge-invariance is the over-riding principle, and it ensures that even if the propagator has an infra-red divergence, the physical scattering amplitudes are finite.
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.
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.
30677291
EXPERIMENTAL PROGRESS: CURRENT FILAMENTATION INSTABILITY STUDY *
Current Filamentation Instability, CFI, is of central importance for the propagation of relativistic electron beams in plasmas. CFI has potential relevance to astrophysics, magnetic field and radiation generation in the afterglow of gamma ray bursts, and inertial confinement fusion, energy transport in the fast-igniter concept. An experimental study of this instability is underway at the Brookhaven National Laboratory - Accelerator Test Facility. We use the particle-in-cell code QuickPIC to study phenomena observed in the experiment. These include merging of filaments and the dependence of the growth rate of the instability on plasma density and beam emittance.
68858618
Targeted cancer therapy: The Potential role of Tb-149
29439632
PROGRESS IN EXPERIMENTAL STUDY OF CURRENT FILAMENTATION INSTABILITY
Current Filamentation Instability, CFI, is of central importance for the propagation of relativistic electron beams in plasmas. CFI could play an important role in the generation of magnetic fields and radiation in the afterglow of gamma ray bursts and also in energy transport for the fast-igniter inertial confinement fusion concept. Simulations were conducted with the particle-in-cell code QuickPIC for e beam and plasma parameters at the Brookhaven National Laboratory – Accelerator Test Facility, BNL-ATF. Results show that for a 2cm plasma the instability reaches near saturation. An experimental program was proposed and accepted at the BNL-ATF and an experiment is currently underway. There are three components to the experimental program: 1) imaging of the filaments, beam density, at the exit from the plasma, 2) measurement and imaging of the transverse plasma density gradient and measurement of the magnetic field and 3) identifying the radiation spectrum of the instability. Preliminary results from phase one will be presented along with the progress and diagnostic design for the following phases of the experiment.