We present the first Advanced LIGO and Advanced Virgo search for ultracompact binary systems with component masses between 0.2 M -1.0 M using data taken between September 12, 2015 and January 19, 2016. We find no viable gravitational wave candidates. Our null result constrains the coalescence rate of monochromatic (delta function) distributions of non-spinning (0.2 M , 0.2 M ) ultracompact binaries to be less than 1.0 × 10 6 Gpc −3 yr −1 and the coalescence rate of a similar distribution of (1.0 M , 1.0 M ) ultracompact binaries to be less than 1.9 × 10 4 Gpc −3 yr −1 (at 90% confidence). Neither black holes nor neutron stars are expected to form below ∼ 1M through conventional stellar evolution, though it has been proposed that similarly low mass black holes could be formed primordially through density fluctuations in the early universe and contribute to the dark matter density. The interpretation of our constraints in the primordial black hole dark matter paradigm is highly model dependent, however, under a particular primordial black hole binary formation scenario we constrain monochromatic primordial black hole populations of 0.2 M to be less than 33% of the total dark matter density and monochromatic populations of 1.0 M to be less than 5% of the dark matter density. The latter strengthens the presently placed bounds from micro-lensing surveys of MAssive Compact Halo Objects (MACHOs) provided by the MACHO and EROS collaborations.

We describe detection methods for extensions of gravitational wave searches to sub-solar mass compact binaries. Sub-solar mass searches were previously carried out using Initial LIGO, and Advanced LIGO boasts a detection volume approximately 1000 times larger than Initial LIGO at design sensitivity. Low mass compact binary searches present computational difficulties, and we suggest a way to rein in the increased computational cost while retaining a sensitivity much greater than previous searches. Sub-solar mass compact objects are of particular interest because they are not expected to form astrophysically. If detected they could be evidence of primordial black holes (PBH). We consider a particular model of PBH binary formation that would allow LIGO/Virgo to place constraints on this population within the context of dark matter, and we demonstrate how to obtain conservative bounds for the upper limit on the dark matter fraction.

We examine the squeezed limit of the bispectrum when a light scalar with arbitrary non-derivative self-interactions is coupled to the inflaton. We find that when the hidden sector scalar is sufficiently light (m 0.1 H), the coupling between long and short wavelength modes from the series of higher order correlation functions (from arbitrary order contact diagrams) causes the statistics of the fluctuations to vary in sub-volumes. This means that observations of primordial non-Gaussianity cannot be used to uniquely reconstruct the potential of the hidden field. However, the local bispectrum induced by mode-coupling from these diagrams always has the same squeezed limit, so the field's locally determined mass is not affected by this cosmic variance.

We study statistical anisotropies generated in the observed two-point function of the cosmic microwave background (CMB) fluctuations if the primordial statistics are non-Gaussian. Focusing on the dipole modulations of the anisotropies, we find that the hemispherical power asymmetry observed in the CMB temperature fluctuations can be modeled by a local-type trispectrum with amplitude τNL(kp = 0.05 Mpc −1 ) ≈ 2 × 10 4 and a large red tilt n ≈ −0.68. We numerically evaluate the non-Gaussian covariance of the modulation estimators for both temperature and Emode polarization fluctuations and discuss the prospects of constraining the model using Planck satellite data. We then discuss other effects of the scale-dependent trispectrum that could be used to distinguish this scenario from other explanations of the power asymmetry: higher-order modulations of the two-point function and the non-Gaussian angular power spectrum covariance. As an important consequence of the non-Gaussian power spectrum covariance, we discuss how the CMB-inferred spectral index of primordial scalar fluctuations can be significantly biased in the presence of a scale-dependent local-type trispectrum.