Detecting a stochastic gravitational wave background requires that we first understand and model any astrophysical foregrounds. In the millihertz frequency band, the predominate foreground signal will be from unresolved white dwarf binaries in the galaxy. We build on our previous work to show that a stochastic gravitational wave background can be detected in the presence of both instrument noise and a galactic confusion foreground. The key to our approach is accurately modeling the spectra for each of the various signal components. We simulate data for a gigameter Laser Interferometer Space Antenna operating in the millihertz frequency band with both six and four links. We obtain posterior distribution functions for the instrument noise parameters, the galaxy level and modulation parameters, and the stochastic background energy density. We find that we are able to detect a scale-invariant stochastic background with energy density as low as Ω gw ¼ 2 × 10 −13 for a six-link interferometer and Ω gw ¼ 5 × 10 −13 for a four-link interferometer with one year of data.
The detection of a stochastic background of gravitational waves could significantly impact our understanding of the physical processes that shaped the early Universe. The challenge lies in separating the cosmological signal from other stochastic processes such as instrument noise and astrophysical foregrounds. One approach is to build two or more detectors and cross correlate their output, thereby enhancing the common gravitational wave signal relative to the uncorrelated instrument noise. When only one detector is available, as will likely be the case with the Laser Interferometer Space Antenna (LISA), alternative analysis techniques must be developed. Here we show that models of the noise and signal transfer functions can be used to tease apart the gravitational and instrument noise contributions. We discuss the role of gravitational wave insensitive ''null channels'' formed from particular combinations of the time delay interferometry, and derive a new combination that maintains this insensitivity for unequal arm-length detectors. We show that, in the absence of astrophysical foregrounds, LISA could detect signals with energy densities as low as gw ¼ 6 Â 10 À13 with just one month of data. We describe an endto-end Bayesian analysis pipeline that is able to search for, characterize and assign confidence levels for the detection of a stochastic gravitational wave background, and demonstrate the effectiveness of this approach using simulated data from the third round of Mock LISA Data Challenges.
Theoretical studies in gravitational wave astronomy have mostly focused on the information that can be extracted from individual detections, such as the mass of a binary system and its location in space. Here we consider how the information from multiple detections can be used to constrain astrophysical population models. This seemingly simple problem is made challenging by the high dimensionality and high degree of correlation in the parameter spaces that describe the signals, and by the complexity of the astrophysical models, which can also depend on a large number of parameters, some of which might not be directly constrained by the observations. We present a method for constraining population models using a hierarchical Bayesian modeling approach which simultaneously infers the source parameters and population model and provides the joint probability distributions for both. We illustrate this approach by considering the constraints that can be placed on population models for galactic white dwarf binaries using a future space-based gravitational wave detector. We find that a mission that is able to resolve $5000 of the shortest period binaries will be able to constrain the population model parameters, including the chirp mass distribution and a characteristic galaxy disk radius to within a few percent. This compares favorably to existing bounds, where electromagnetic observations of stars in the galaxy constrain disk radii to within 20%.
Please be advised that this information was generated on 2018-05-13 and may be subject to change.Erratum: Measurement of the electron charge asymmetry in pp → W þ X → eν þ X decays in pp collisions at ffiffi s p ¼ 1. The recent paper on the charge asymmetry for electrons from W boson decay has an error in Tables VII-XI that shows the correlation coefficients of systematic uncertainties. The correlation matrix elements shown in the original publication were the square roots of the calculated values.The corrected correlation matrices are shown in Tables VII-XI. The table numbers used here correspond directly to those in the paper. The results of the paper are unchanged except for these tables. PHYSICAL REVIEW D 91, 079901(E) (2015) 1550-7998=2015=91 (7)=079901 (3) 079901-1
We present a quantitative, direct comparison of constraints on sterile neutrinos derived from neutrino oscillation experiments and from Planck data, interpreted assuming standard cosmological evolution. We extend a $$1+1$$1+1 model, which is used to compare exclusion contours at the 95% Cl derived from Planck data to those from $$\nu _{e}$$νe-disappearance measurements, to a $$3+1$$3+1 model. This allows us to compare the Planck constraints with those obtained through $$\nu _{\mu }\rightarrow \nu _{e}$$νμ→νe appearance searches, which are sensitive to more than one active-sterile mixing angle. We find that the cosmological data fully exclude the allowed regions published by the LSND, MiniBooNE and Neutrino-4 collaborations, and those from the gallium and rector anomalies, at the 95% Cl. Compared to the exclusion region from the Daya Bay $$\nu _{e}$$νe-disappearance search, the Planck data are more strongly excluding above $$|\Delta m^{2}_{41}|\approx 0.1\,\mathrm {eV}^{2}$$|Δm412|≈0.1eV2 and $$m_\mathrm {eff}^\mathrm {sterile}\approx 0.2\,\mathrm {eV}$$meffsterile≈0.2eV, with the Daya Bay exclusion being stronger below these values. Compared to the combined Daya Bay/Bugey/MINOS exclusion region on $$\nu _{\mu }\rightarrow \nu _{e}$$νμ→νe appearance, the Planck data is more strongly excluding above $$\Delta m^{2}_{41}\approx 5\times 10^{-2}\,\mathrm {eV}^{2}$$Δm412≈5×10-2eV2, with the exclusion strengths of the Planck data and the Daya Bay/Bugey/MINOS combination becoming comparable below this value.
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