Evidence from the BICEP2 experiment for a significant gravitational-wave background has focussed 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 wre. The canonical reheating scenario is then described by wre = 0. The simplest α = 2 models are consistent with wre = 0 for values of ns well within the current 1σ range. Models with α = 1 or α = 2/3 require a more exotic reheating phase, with −1/3 < wre < 0, unless ns falls above the current 1σ range. Likewise, models with α = 4 require a physically implausible wre > 1/3, unless ns 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 Tre/10 6 GeV ≃ 2000 (ns − 0.96) between the reheat temperature Tre and the scalar spectral index ns. Thus, if ns is close to its central value, then Tre 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 ns ≃ 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 ns should allow m 2 φ 2 , axion-monodromy, and φ 4 models to be distinguished, even without precise measurement of r, and to test the m 2 φ 2 expectation of ns ≃ 0.965. PACS numbers:Introduction. The imprint of inflationary gravitational waves in the cosmic microwave background polarization [1] reported by the BICEP2 collaboration [2] implies, if confirmed, that the inflaton field φ traversed a distance large compared with the Planck mass during inflation [3,4]. One particularly simple and elegant model for large-field inflation is "m 2 φ 2 " inflation [5, 6] (derived originally as a simple example of chaotic inflation [7]), in which the inflaton potential is simply a quadratic function of φ. Ref. [8] recently argued that this is perhaps the simplest and most elegant model. They then derived a consistency relation between the scalar spectral index (now constrained to be n s − 1 = −0.0397 ± 0.0073 [9]) and tensor-to-scalar ratio (roughly r ∼ 0.2 according to Ref. [2]) that can be tested with higher-precision measurements of n s and in particular of r. Another promising candidate large-field model, axion monodromy which suggests a potential V ∝ φ [10] or V ∝ φ 2/3 [11], has also been receiving considerable attention. We parametrize all these models by a power-law potential V ∝ φ α .

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.[1], and are above the detection thresholds as defined in Abbott et al. [2]. 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 χ eff . The most secure new event, GW170121 (pastro > 0.99), is also notable due to its inferred negative value of χ eff , 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 is nearly twice that of other pipelines. 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.

We report a new binary black hole merger in the publicly available LIGO First Observing Run (O1) data release. The event has a false alarm rate of one per six years in the detector-frame chirp-mass range M det ∈ [20, 40]M in a new independent analysis pipeline that we developed. Our best estimate of the probability that the event is of astrophysical origin is Pastro ∼ 0.71 . The estimated physical parameters of the event indicate that it is the merger of two massive black holes, M det = 31 +2 −3 M with an effective spin parameter, χ eff = 0.81 +0.15 −0.21 , making this the most highly spinning merger reported to date. It is also among the two highest redshift mergers observed so far. The high aligned spin of the merger supports the hypothesis that merging binary black holes can be created by binary stellar evolution.

We combine gravitational wave (GW) and electromagnetic (EM) data to perform a Bayesian parameter estimation of the binary neutron star (NS) merger GW170817. The EM likelihood is constructed from a fit to a large number of numerical relativity simulations which we combine with a lower bound on the mass of the remnant's accretion disk inferred from the modeling of the EM light curve. In comparison with previous works, our analysis yields a more precise determination of the tidal deformability of the binary, for which the EM data provide a lower bound, and of the mass ratio of the binary, with the EM data favoring a smaller mass asymmetry. The 90% credible interval for the areal radius of a 1.4 M NS is found to be 12.2 +1.0 −0.8 ± 0.2 km (statistical and systematic uncertainties). PACS. 97.60.Jd Neutron stars -04.30.Tv Gravitational-wave astrophysics -04.25.D-Numerical relativity arXiv:1810.12917v2 [astro-ph.HE]

The possibility that part of the dark matter is made of massive compact halo objects (MACHOs) remains poorly constrained over a wide range of masses, and especially in the 20 − 100 M window. We show that strong gravitational lensing of extragalactic fast radio bursts (FRBs) by MACHOs of masses larger than ∼ 20 M would result in repeated FRBs with an observable time delay. Strong lensing of a FRB by a lens of mass ML induces two images, separated by a typical time delay ∼ few ×(ML/30 M ) milliseconds. Considering the expected FRB detection rate by upcoming experiments, such as CHIME, of 104 FRBs per year, we should observe from tens to hundreds of repeated bursts yearly, if MACHOs in this window make up all the dark matter. A null search for echoes with just 10 4 FRBs would constrain the fraction fDM of dark matter in MACHOs to fDM 0.08 for ML 20 M .Although observations indicate that dark matter accounts for a significant share of the energy density of our Universe [1], we do not know its composition. Longtime candidates to make up the dark matter are massive compact halo objects (MACHOs) [2]. They were originally proposed to be as light as 10 −7 M and as heavy as the first stars (∼ 10 3 M ) [3]. Over the years, different experiments have progressively constrained the fraction f DM of dark matter that can reside in MACHOs with a given mass, placing tight upper bounds over most of the vast range above. High-mass ( 100 M ) MACHOs, for example, are constrained by the fact that they would perturb wide stellar binaries in our Galaxy [4]. Meanwhile, lower-mass ( 20M ) MACHOs are effectively ruled out as the sole component of Galactic dark matter, as they would create artificial variability in stars, due to gravitational microlensing [5][6][7].However, there remains a window of masses between 20 and 100 M , where the constraints are weaker, and in which arguably all the cosmological dark matter could be in the form of MACHOs [6][7][8][9][10]. This is a particularly interesting window, as it has been recently argued in Ref.[11] that if primordial black holes (PBHs) [12,13] in the ∼ 30 M mass range are the constituents of dark matter, they form binaries in halos, coalesce, and emit observable gravitational waves, with an event rate consistent with the published LIGO detection [14].In this Letter we propose to use the strong lensing of fast radio bursts (FRBs) to probe MACHOs of masses 20 M , including PBHs, and either confirm that they make up the dark matter or close this window. FRBs are strong radio bursts with a very short duration, which makes them ideal as microlensing targets. Their temporal width is increased by the dispersion measure (DM), which measures the time delay of photons with different radio frequencies due to scattering by free electrons on their way to Earth. All detected FRBs to date possess high DMs, which yield burst widths of ∼ 1 − 10 ms [15][16][17][18][19][20][21][22][23][24]. These values of the DM are several times larger than the expected contribution from free electrons within the Milky Way ...

Abstract. The separate universe conjecture states that in General Relativity a density perturbation behaves locally (i.e. on scales much smaller than the wavelength of the mode) as a separate universe with different background density and curvature. We prove this conjecture for a spherical compensated tophat density perturbation of arbitrary amplitude and radius in ΛCDM. We then use Conformal Fermi Coordinates to generalize this result to scalar perturbations of arbitrary configuration and scale in a general cosmology with a mixture of fluids, but to linear order in perturbations. In this case, the separate universe conjecture holds for the isotropic part of the perturbations. The anisotropic part on the other hand is exactly captured by a tidal field in the Newtonian form. We show that the separate universe picture is restricted to scales larger than the sound horizons of all fluid components. We then derive an expression for the locally measured matter bispectrum induced by a long-wavelength mode of arbitrary wavelength, a new result which in standard perturbation theory is equivalent to a relativistic second-order calculation. We show that nonlinear gravitational dynamics does not generate observable contributions that scale like local-type non-Gaussianity f loc NL , and hence does not contribute to a scale-dependent galaxy bias ∆b ∝ k −2 on large scales; rather, the locally measurable long-short mode coupling assumes a form essentially identical to subhorizon perturbation theory results, once the long-mode density perturbation is replaced by the synchronous-comoving gauge density perturbation. Apparent f loc NL -type contributions arise through projection effects on photon propagation, which depend on the specific large-scale structure tracer and observable considered, and are in principle distinguishable from the local mode coupling induced by gravity. We conclude that any observation of f loc NL beyond these projection effects signals a departure from standard single-clock inflation.

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 non-stationary nature of the detector noise, the signal-quality vetoes at the singledetector 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.

Physical models for the hemispherical power asymmetry in the cosmic microwave background (CMB) reported by the Planck Collaboration must satisfy CMB constraints to the homogeneity of the Universe and quasar constraints to power asymmetries. We survey a variety of models for the power asymmetry and show that consistent models include a modulated scale-dependent isocurvature contribution to the matter power spectrum or a modulation of the reionization optical depth, gravitational-wave amplitude, or scalar spectral index. We propose further tests to distinguish between the different scenarios.