On September 14, 2015 at 09:50:45 UTC the two detectors of the Laser Interferometer Gravitational-Wave Observatory simultaneously observed a transient gravitational-wave signal. The signal sweeps upwards in frequency from 35 to 250 Hz with a peak gravitational-wave strain of 1.0×10(-21). It matches the waveform predicted by general relativity for the inspiral and merger of a pair of black holes and the ringdown of the resulting single black hole. The signal was observed with a matched-filter signal-to-noise ratio of 24 and a false alarm rate estimated to be less than 1 event per 203,000 years, equivalent to a significance greater than 5.1σ. The source lies at a luminosity distance of 410(-180)(+160)  Mpc corresponding to a redshift z=0.09(-0.04)(+0.03). In the source frame, the initial black hole masses are 36(-4)(+5)M⊙ and 29(-4)(+4)M⊙, and the final black hole mass is 62(-4)(+4)M⊙, with 3.0(-0.5)(+0.5)M⊙c(2) radiated in gravitational waves. All uncertainties define 90% credible intervals. These observations demonstrate the existence of binary stellar-mass black hole systems. This is the first direct detection of gravitational waves and the first observation of a binary black hole merger.

/pdf/the-observation-of-gravitational-waves-from-a-binary-black-58srpupgg9.pdf

The Observation of Gravitational Waves from a Binary Black Hole Merger

We study the cosmological information content of the redshift-space galaxy bispectrum monopole at one-loop order in perturbation theory. We incorporate all effects necessary for comparison to data: fourth-order galaxy bias, infrared resummation (accounting for the non-linear evolution of baryon acoustic oscillations), ultraviolet counterterms, non-linear redshift-space distortions, stochastic contributions, projection, and binning effects. The model is implemented using FFTLog, and validated with the PT Challenge suite of N -body simulations, whose large volume allows for high-precision tests. Focusing on the mass fluctuation amplitude, σ8, and galaxy bias parameters, we find that including one-loop corrections allow us to significantly extend the range of scales over which the bispectrum can be modeled, and greatly tightens constraints on bias parameters. However, this does not lead to noticeable improvements in the σ8 errorbar due to the necessary marginalization over a large number of nuisance parameters with conservative priors. Analyzing a BOSS-volume likelihood, we find that the addition of the one-loop bispectrum may lead to improvements on primordial non-Gaussianity constraints by . 30% and on σ8 by ≈ 10%, though we caution that this requires pushing the analysis to short-scales where the galaxy bias parameters may not be correctly recovered; this may lead to biases in the recovered parameter values. We conclude that restrictive priors from simulations or higher-order statistics such as the bispectrum multipoles will be needed in order to realize the full information content of the galaxy bispectrum. ohep2@cantab.ac.uk ivanov@ias.edu, Einstein Fellow ar X iv :2 20 6. 02 80 0v 2 [ as tr oph .C O ] 1 3 Ju n 20 22

http://link.aps.org/pdf/10.1103/PhysRevD.106.043530

Cosmology with the redshift-space galaxy bispectrum monopole at one-loop order

We analyse the BOSS DR12 multipoles of the galaxy power spectrum jointly with measurements of the BAO scale for three different models of dark energy. We use recent measurements performed with a windowless estimator, and an independent and fast pipeline based on EFTofLSS modelling implemented via the FAST-PT algorithm to compute the integrals of the redshift-space loop corrections. We accelerate our analysis further by using the bacco linear power spectrum emulator instead of a Boltzmann solver. We perform two sets of analyses: one including 3σ Planck priors on As and ns , and another that is fully CMB-free, i.e., letting the primordial parameters vary freely. The first model we study is ΛCDM, within which we reproduce previous results obtained with the same estimator. We find a low value of the scalar amplitude in the CMB-free case, in agreement with many previous EFT-based full-shape analyses of the BOSS data. We then study wCDM, finding a lower value of the amplitude in the CMB-free run, coupled with a preference for phantom dark energy with w = -1.17+0.12 -0.11, again in broad agreement with previous results. Finally, we investigate the dark scattering model of interacting dark energy, which we label wACDM. In the CMB-free analysis, we find a large degeneracy between the interaction strength A and the amplitude As , hampering measurements of those parameters. On the contrary, in our run with a CMB prior, we are able to constrain the dark energy parameters to be w = -0.972+0.036 -0.029 and A = 3.9+3.2 -3.7, which show a 1σ hint of interacting dark energy. This is the first measurement of this parameter and demonstrates the ability of this model to alleviate the σ 8 tension. Our analysis can be used as a guide for the analysis of any model with scale-independent growth. Finally, we study the dependence of the results on the priors imposed on the nuisance parameters and find these priors to be informative, with their broadening generating shifts in the contours. We argue for an in depth study of this issue, which can affect current and forthcoming analyses of LSS data.

Cosmology with the EFTofLSS and BOSS: dark energy constraints and a note on priors

The 21cm emission of neutral hydrogen is a potential probe of the matter distribution in the Universe after reionisation. Cosmological surveys of this line intensity will be conducted in the coming years by the SKAO and HIRAX experiments, complementary to upcoming galaxy surveys. We present the first forecasts of the cosmological constraints from the combination of the 21cm power spectrum and bispectrum. Fisher forecasts are computed for the constraining power of these surveys on cosmological parameters, the BAO distance functions and the growth function. We also estimate the constraining power on dynamical dark energy and modified gravity. Finally we investigate the constraints on the 21cm clustering bias, up to second order. We take into account the effects on the 21cm correlators of the telescope beam, instrumental noise and foreground avoidance, as well as the Alcock-Paczynski effect and the effects of theoretical errors in the modelling of the correlators. We find that, together with Planck priors, and marginalising over clustering bias and nuisance parameters, HIRAX achieves sub-percent precision on the ΛCDM parameters, with SKAO delivering slightly lower precision. The modified gravity parameter γ is constrained at 1% (HIRAX) and 5% (SKAO). For the dark energy parameters w 0, wa , HIRAX delivers percent-level precision while SKAO constraints are weaker. HIRAX achieves sub-percent precision on the BAO distance functions DA, H, while SKAO reaches 1 - 2% for 0.6 ≲ z ≲ 1. The growth rate f is constrained at a few-percent level for the whole redshift range of HIRAX and for 0.6 ≲ z ≲ 1 by SKAO. The different performances arise mainly since HIRAX is a packed inteferometer that is optimised for BAO measurements, while SKAO is not optimised for interferometer cosmology and operates better in single-dish mode, where the telescope beam limits access to the smaller scales that are covered by an interferometer.

/pdf/cosmological-constraints-from-the-power-spectrum-and-1pt62r3s.pdf

Cosmological constraints from the power spectrum and bispectrum of 21cm intensity maps


 Interacting dark energy models have been suggested as alternatives to the standard cosmological model, ΛCDM. We focus on a phenomenologically interesting class of dark scattering models that is characterised by pure momentum exchange between dark energy and dark matter. This model extends the parameter space with respect to ΛCDM by two parameters, w and A, which define the dark energy equation of state and the strength of the coupling between dark energy and dark matter, respectively. In order to test non-standard cosmologies with Stage-IV galaxy clustering surveys, it is crucial to model mildly nonlinear scales and perform precision vs accuracy tests. We use the Effective Field Theory of Large-Scale Structure, and we perform validation tests by means of an MCMC analysis using a large set of N-body simulations. We find that adding the bispectrum monopole to the power spectrum multipoles improves the constraints on the dark energy parameters by $\sim 30 {{\ \rm per\ cent}}$ for $k_{\mathrm{max}, B}^{l=0} = 0.11$h Mpc−1, without introducing biases in the parameter estimation. We also find that the same improvement can be achieved with more moderate scale cuts and the use of bias relations, or with the addition of the bispectrum quadrupole. Finally, we study degeneracies between the dark energy parameters and the scalar amplitude As and discuss the corresponding projection effects, as well as degeneracies with other cosmological parameters.

https://academic.oup.com/mnras/article-pdf/520/2/2611/49161060/stad260.pdf

Interacting dark energy from the joint analysis of the power spectrum and bispectrum multipoles with the EFTofLSS

We present a method to perform the exact convolution of the model prediction for bispectrum multipoles in redshift space with the survey window function. We extend a widely applied method for the power spectrum convolution to the bispectrum, taking advantage of a 2D-FFTlog algorithm. As a preliminary test of its accuracy, we consider the toy model of a spherical window function in real space. This setup provides an analytical evaluation of the 3-point function of the window, and therefore it allows to isolate and quantify possible systematic errors of the method. We find that our implementation of the convolution in terms of a mixing matrix shows differences at the percent level in comparison to the measurements from a very large set of mock halo catalogs. It is also able to recover unbiased constraints on halo bias parameters in a likelihood analysis of a set of numerical simulations with a total volume of 100 h -3 Gpc3. For the level of accuracy required by these tests, the multiplication with the mixing matrix is performed in the time of one second or less.

Bispectrum-window convolution via Hankel transform

We present the analysis of the halo bispectrum in redshift-space in terms of its multipoles, monopole, quadrupole and hexadecapole, measured from a large set of simulations. We fit such measurements with a tree-level model in perturbation theory that depends on linear and nonlinear bias parameters as well as on the growth rate f of density fluctuations. The likelihood analysis takes advantage of a very large set of mock catalogs, enabling a robust estimation of the covariance properties for all multipoles. We compare the numerical estimate of the covariance matrix to its Gaussian prediction finding discrepancies of 10% or less for all configurations with the sole exception of the squeezed triangles in the monopole case. We find the range of validity of the tree-level model, for the total simulation volume of about 1000 h -3Gpc3, reaches a maximum wavenumber of 0.08 h Mpc-1 for the monopole, while it is limited to 0.06 and 0.045 h Mpc-1 respectively for quadrupole and hexadecapole. Despite this, the addition of the quadrupole to the analysis allows for significant improvements on the determination of the model parameters and specifically on f, similarly to the power spectrum case. Finally, we compare our numerical estimate for the full covariance with its theoretical prediction in the Gaussian approximation and find the latter to work remarkably well in the context of simulation boxes with periodic boundary condition.

/pdf/the-halo-bispectrum-multipoles-in-redshift-space-3ulje0cm.pdf

The halo bispectrum multipoles in redshift space

Modified Friedmann equations in braneworld scenario

Primordial non-Gaussianities (PNG) leave unique signatures in the bispectrum of the large-scale structure. With upcoming galaxy surveys set to improve PNG constraints by at least one order of magnitude, it is important to account for any potential contamination. In our work we show how to include wide-angle effects into the 3-dimensional observed galaxy bispectrum. We compute the leading wide-angle corrections to the monopole, finding that they could mimic local PNG with an amplitude of $f_{\rm NL} = \mathcal{O}\left( 0.1 \right)$. We also compute the dipole induced by wide-angle effects, whose amplitude is a few-percent of the flat-sky monopole. Our formalism can be readily adapted to realistic survey geometries and to include relativistic effects, which may become relevant at high redshifts.

Wide-angle effects in the galaxy bispectrum

A five dimensional braneworld cosmological model in general scalar-tensor action comprises of various Horndeski Lagrangian is considered. The Friedmann equations in the case of the strongly and weakly coupled $\mathcal{L}_5$ Horndeski Lagrangian have been obtained. The strongly coupled $\mathcal{L}_5$ model produces the Cardassian term $\rho^n$ with $n=\pm 1/2$, which can served as alternative explanation for the accelerated expansion phase of the universe. Furthermore, the latest combined observational facts from BAO, CMB, SNIa, $f_{\sigma_8}$, and $H_0$ value observation suggest that the $n=-1/2$ term lies quite close to the constrained value. On the other hand, the weakly coupled $\mathcal{L}_5$ case has several new correction terms which are omitted in the braneworld Einstein-Hilbert model, e.g. the cubic $\rho^3$ and the dark radiation-matter interaction term $ \chi a^{-4}\rho$. Furthermore, this model provides a cosmological constant constructed from the bulk scalar field, requires no brane tension, and supports the big bang nucleosynthesis (BBN) constraint naturally.

Kevin F. S. Pardede

Papers

Bispectrum-window convolution via Hankel transform

The halo bispectrum multipoles in redshift space

Modified Friedmann equations in braneworld scenario

Wide-angle effects in the galaxy bispectrum

Nonlinear matter terms in general scalar-tensor braneworld cosmology