ABSTRACT
We study light variability of gravitationally magnified high-redshift star clusters induced by a foreground population of microlenses. This arises as the incoherent superposition of light ...variations from many source stars traversing the random magnification pattern on the source plane. The light curve resembles a scale-invariant, Gaussian process on time-scales of years to decades, while exhibits rapid and frequent micro-caustic crossing flares of larger amplitudes on time-scales of days to months. For a concrete example, we study a young Lyman-continuum-leaking star cluster in the Sunburst Arc at z = 2.37. We show that one magnified image happens to be intervened by a foreground galaxy, and hence should exhibit a variable flux at the 1–$2{{\ \rm per\ cent}}$ level, which is measurable in space with ∼1–$3\,$ ks exposures on the Hubble Space Telescope and more easily with the James Webb Space Telescope, or even from the ground using a ∼4-m telescope without adaptive optics. Detailed measurement of this variability can help determine the absolute macro magnification and hence the intrinsic mass and length scales of the star cluster, test synthetic stellar population models, and probe multiplicity of massive stars. Furthermore, monitoring the other lensed images of the star cluster, which are free from significant intervention by foreground microlenses, can allow us to probe planetary to stellar mass compact objects constituting as little as a few per cent of the dark matter. Given the typical surface density of intracluster stars, we expect this phenomenon to be relevant for other extragalactic star clusters lensed by galaxy clusters.
We report the detection of new binary black hole merger events in the publicly available data from the second observing run of Advanced LIGO and Advanced Virgo (O2). The mergers were discovered using ...the new search pipeline described in Venumadhav et al. Phys. Rev. D 100, 023011 (2019) and are above the detection thresholds as defined in Abbott et al. (LIGO Scientific and Virgo Collaborations) Phys. Rev. X 9, 031040 (2019).. Three of the mergers (GW170121, GW170304, GW170727) have inferred probabilities of being of astrophysical origin pastro>0.98. The remaining three (GW170425, GW170202, GW170403) are less certain, with pastro ranging from 0.5 to 0.8. The newly found mergers largely share the statistical properties of previously reported events, with the exception of GW170403, the least secure event, which has a highly negative effective spin parameter χeff. The most secure new event, GW170121 (pastro>0.99), is also notable due to its inferred negative value of χeff, which is inconsistent with being positive at the ≈95.8% confidence level. The new mergers nearly double the sample of gravitational wave events reported from O2 and present a substantial opportunity to explore the statistics of the binary black hole population in the Universe. The number of detected events is not surprising since we estimate that the detection volume of our pipeline may be larger than that of other pipelines by as much as a factor of 2 (with significant uncertainties in the estimate). The increase in volume is larger when the constituent detectors of the network have very different sensitivities, as is likely to be the case in current and future runs.
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When a cosmic microwave background (CMB) photon travels from the surface of last scatter through spacetime metric perturbations, the polarization vector may rotate about its direction of propagation. ...This gravitational rotation is distinct from, and occurs in addition to, the lensing deflection of the photon trajectory. This rotation can be sourced by linear vector or tensor metric perturbations and is fully coherent with the curl deflection field. Therefore, lensing corrections to the CMB polarization power spectra as well as the temperature-polarization cross correlations due to nonscalar perturbations are modified. The rotation does not affect lensing by linear scalar perturbations, but needs to be included when calculations go to higher orders. We present complete results for weak lensing of the full-sky CMB power spectra by general linear metric perturbations, taking into account both deflection of the photon trajectory and rotation of the polarization. For the case of lensing by gravitational waves, we show that the B modes induced by the rotation largely cancel those induced by the curl component of deflection.
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Evidence from the BICEP2 experiment for a significant gravitational-wave background has focused attention on inflaton potentials V(ϕ)∝ϕ(α) with α = 2 ("chaotic" or "m(2)ϕ(2)" inflation) or with ...smaller values of α, as may arise in axion-monodromy models. Here we show that reheating considerations may provide additional constraints to these models. The reheating phase preceding the radiation era is modeled by an effective equation-of-state parameter w(re). The canonical reheating scenario is then described by w(re) = 0. The simplest α = 2 models are consistent with w(re) = 0 for values of n(s) well within the current 1σ range. Models with α = 1 or α = 2/3 require a more exotic reheating phase, with -1/3 < w(re) < 0, unless n(s) falls above the current 1σ range. Likewise, models with α = 4 require a physically implausible w(re) > 1/3, unless n(s) is close to the lower limit of the 2σ range. For m(2)ϕ(2) inflation and canonical reheating as a benchmark, we derive a relation log(10)(T(re)/10(6) GeV) ≃ 2000(n(s)-0.96) between the reheat temperature T(re) and the scalar spectral index n(s). Thus, if n(s) is close to its central value, then T(re) ≲ 10(6) GeV, just above the electroweak scale. If the reheat temperature is higher, as many theorists may prefer, then the scalar spectral index should be closer to n(s) ≃ 0.965 (at the pivot scale k = 0.05 Mpc(-1)), near the upper limit of the 1σ error range. Improved precision in the measurement of n(s) should allow m(2)ϕ(2), axion monodromy, and ϕ(40) models to be distinguished, even without precise measurement of r, and to test the m(2)ϕ(2) expectation of n(s) ≃ 0.965.
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A novel three‐dimensional micromechanical model describing frequency‐ and temperature‐dependent viscoelastic behavior of short fiber‐reinforced polymers (SFRPs) with graded interphase and slightly ...weakened interfaces are established. Elastic‐viscoelastic correspondence approach, time‐temperature superposition principle and Rao and Dai's (Compos. Struct. 2017; 168: 440) modification on the calculation of interface damage tensors are applied for dynamic thermo viscoelasticity prediction of the composite with the consideration of interphase/interface conditions. Certain parameters like filler content, interphase property, the aspect ratio of inclusions, frequency, and temperature were thoroughly analyzed to see their effect on the dynamic behavior of unidirectional SFRPs. Some valuable conclusions are made, which constitutes a valuable contribution to the theoretical prediction of SFRPs' mechanical properties.
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Axions are a viable candidate for cold dark matter, which should generically form minihalos of subplanetary masses from white-noise isocurvature density fluctuations if the Peccei-Quinn phase ...transition occurs after inflation. Despite being denser than the larger halos formed out of adiabatic fluctuations from inflation, axion minihalos have surface densities much smaller than the critical value required for gravitational lensing to produce multiple images or high magnification, and hence are practically undetectable as lenses in isolation. However, their lensing effect can be enhanced when superposed near critical curves of other lenses. We propose a method to detect them through photometric monitoring of recently discovered caustic transiting stars behind cluster lenses, under extreme magnification factors 103-104 as the lensed stars cross microlensing caustics induced by intracluster stars. For masses of the first gravitationally collapsed minihalos in the range ∼10−15-10−8 h−1 M , we show that axion minihalos in galaxy clusters should collectively produce subtle surface density fluctuations of amplitude ∼10−4-10−3 on projected length scales of ∼10-104 au, which imprint irregularities on the microlensing lightcurves of caustic transiting stars. We estimate that, inside a cluster halo and over the age of the universe, most of these minihalos are likely to avoid dynamic disruption by encounters with stars or other minihalos.
We perform a statistical inference of the astrophysical population of binary black hole (BBH) mergers observed during the first two observing runs of Advanced LIGO and Advanced Virgo, including ...events reported in the GWTC-1 and IAS catalogs. We derive a novel formalism to fully and consistently account for events of arbitrary significance. We carry out a software injection campaign to obtain a set of mock astrophysical events subject to our selection effects, and use the search background to compute the astrophysical probabilities pastro of candidate events for several phenomenological models of the BBH population. We emphasize that the values of pastro depend on both the astrophysical and background models. Finally, we combine the information from individual events to infer the rate, spin, mass, mass-ratio and redshift distributions of the mergers. The existing population does not discriminate between random spins with a spread in the effective spin parameter, and a small but nonzero fraction of events from tidally torqued stellar progenitors. The mass distribution is consistent with one having a cutoff at ... M⊙ , while the mass ratio favors equal masses; the mean mass ratio q > 0.67 . The rate shows no significant evolution with redshift. We show that the merger rate restricted to BBHs with a primary mass between 20–30 M , and a mass ratio q > 0.5 , and at z ~ 0.2 , is 1.5–5.3 Gpc−3 yr−1 (90% c.l.); these bounds are model independent and a factor of ∼ 3 tighter than that on the local rate of all BBH mergers, and hence are a robust constraint on all progenitor models. Including the events in our catalog increases the Fisher information about the BBH population by ∼ 47 % , and tightens the constraints on population parameters. (ProQuest: ... denotes formula omitted.)
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ABSTRACT
BACKGROUND
Children from disadvantaged backgrounds are more apt to experience lower availability of nutritious foods, lack opportunities to exercise, and lack access to recreational ...facilities, and thus, are more likely to be obese and at greater risk for developing chronic diseases. We review school health education programs' impact on physical activity behaviors among disadvantaged students.
METHODS
The inclusion criteria of the study were articles: published in English with full text between 2011 and 2017; focused on school health education programs for disadvantaged school‐aged students; assessed programs including a physical activity component; examined school‐aged children and adolescents' physical activity behaviors; and assessed programs with comparison groups.
RESULTS
There were 13 studies matching inclusion criteria in this review. The results of this review indicated that school‐based health education programs which included culturally appropriate physical activity, parent involvement, and enhanced student motivation and choice of activities appeared to increase physical activity levels among disadvantaged school‐aged students. Health education programs should also emphasize behavioral change skills, such as goal setting and self‐motivation, to positively impact on students' physical activity behaviors.
CONCLUSIONS
School‐based health education programs may help increase access to physical activity among disadvantaged populations.
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Given the possible repetitive nature of fast radio bursts (FRBs), their cosmological origin, and their high occurrence, detection of strongly lensed sources due to intervening galaxy lenses is ...possible with forthcoming radio surveys. We show that if multiple images of a repeating source are resolved with VLBI, using a method independent of lens modeling, accurate timing could reveal non-uniform motion, either physical or apparent, of the emission spot. This can probe the physical nature of FRBs and their surrounding environments, constraining scenarios including orbital motion around a stellar companion if FRBs require a compact star in a special system, and jet-medium interactions for which the location of the emission spot may randomly vary. The high timing precision possible for FRBs (∼ms) compared with the typical time delays between images in galaxy lensing ( 10 days) enables the measurement of tiny fractional changes in the delays ( ) and hence the detection of time-delay variations induced by relative motions between the source, the lens, and the Earth. We show that uniform cosmic peculiar velocities only cause the delay time to drift linearly, and that the effect from the Earth's orbital motion can be accurately subtracted, thus enabling a search for non-trivial source motion. For a timing accuracy of ∼1 ms and a repetition rate (of detected bursts) of ∼0.05 per day of a single FRB source, non-uniform displacement 0.1-1 au of the emission spot perpendicular to the line of sight is detectable if repetitions are seen over a period of hundreds of days.
In this paper, we report on the construction of a new and independent pipeline for analyzing the public data from the first observing run of Advanced LIGO for mergers of compact binary systems. The ...pipeline incorporates different techniques and makes independent implementation choices in all its stages including the search design, the method to construct template banks, the automatic routines to detect bad data segments ("glitches") and to insulate good data from them, the procedure to account for the nonstationary nature of the detector noise, the signal-quality vetoes at the single-detector level and the methods to combine results from multiple detectors. Our pipeline enabled us to identify a new binary black hole merger GW151216 in the public LIGO data. This paper serves as a bird's eye view of the pipeline's important stages. Full details and derivations underlying the various stages will appear in accompanying papers.
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