Viscosity, pressure, and support of the gas in simulations of merging cool-core clusters [CEA]

Major mergers are considered to be a significant source of turbulence in clusters. We performed a numerical simulation of a major merger event using nested-grid initial conditions, adaptive mesh refinement, radiative cooling of primordial gas, and a homogeneous ultraviolet background. By calculating the microscopic viscosity on the basis of various theoretical assumptions and estimating the Kolmogorov length from the turbulent dissipation rate computed with a subgrid-scale model, we are able to demonstrate that most of the warm-hot intergalactic medium can sustain a fully turbulent state only if the magnetic suppression of the viscosity is considerable. Accepting this as premise, it turns out that ratios of turbulent and thermal quantities change only little in the course of the merger. This confirms the tight correlations between the mean thermal and non-thermal energy content for large samples of clusters in earlier studies, which can be interpreted as second self-similarity on top of the self-similarity for different halo masses. Another long-standing question is how and to which extent turbulence contributes to the support of the gas against gravity. From a global perspective, the ratio of turbulent and thermal pressures is significant for the clusters in our simulation. On the other hand, a local measure is provided by the compression rate, i.e. the growth rate of the divergence of the flow. Particularly for the intracluster medium, we find that the dominant contribution against gravity comes from thermal pressure, while compressible turbulence effectively counteracts the support. For this reason it appears to be too simplistic to consider turbulence merely as an effective enhancement of thermal energy.

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W. Schmidt, C. Byrohl, J. Engels, et. al.
Mon, 22 May 17

Comments: 16 pages, 16 figures, accepted for publication by MNRAS

Standard Model – Axion – Seesaw – H portal inflation [CL]

Extending the Standard Model with a new complex singlet scalar, right-handed neutrinos and a vector-like quark allows to simultaneously tackle several problems in particle physics and cosmology within a constrained framework that can be falsified by future probes of the cosmic microwave background, as well as by upcoming axion experiments. This Standard Model – Axion – Seesaw – H portal inflation theory (SMASH) provides predictive inflation and $H$ boson stabilization, and can explain baryogenesis, light neutrino masses, dark matter and the strong CP problem. The model contains a unique new mass scale which coincides with the axion decay constant, and also sets the scale for perturbative lepton-number violation processes. Testable predictions include a minimum value of the tensor-to-scalar ratio of $r\gtrsim 0.004$, a running of the spectral index $\alpha\gtrsim-8\times10^{-4}$, a change $\delta N_{\rm eff}\sim 0.03$ in the number of effective relativistic neutrinos, and an axion mass in the range $50\mu eV\leq m_A \leq 200 \mu eV$.

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C. Tamarit
Mon, 22 May 17

Comments: 8 pages, 2 figures, Contribution to the proceedings of the 52nd Rencontres de Moriond conference, Electroweak session, La Thuile (Italy) 2017

The first-year shear catalog of the Subaru Hyper Suprime-Cam SSP Survey [CEA]

We present and characterize the catalog of galaxy shape measurements that will be used for cosmological weak lensing measurements in the Wide layer of the first year of the Hyper Suprime-Cam (HSC) survey. The catalog covers an area of 136.9 deg$^2$ split into six fields, with a mean $i$-band seeing of 0.58 arcsec and $5\sigma$ point-source depth of $i\sim 26$. Given conservative galaxy selection criteria for first year science, the depth and excellent image quality results in unweighted and weighted source number densities of 24.6 and 21.8 arcmin$^{-2}$, respectively. Point-spread function (PSF) modeling is carried out on individual exposures, while galaxy shapes are measured on a linear coaddition. We define the requirements for cosmological weak lensing science with this catalog, characterize potential systematics in the catalog using a series of internal null tests for problems with PSF modeling, shear estimation, and other aspects of the image processing, and describe systematics tests using two different sets of image simulations. Finally, we discuss the dominant systematics and the planned algorithmic changes to reduce them in future data reductions.

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R. Mandelbaum, H. Miyatake, T. Hamana, et. al.
Mon, 22 May 17

Comments: 23 figures, 4 tables, submitted to PASJ

Stability of Einstein static universe in Eddington-inspire Born-Infeld theory [CL]

By considering the realization of emergent universe scenario in Eddington-inspire Born-Infeld (EiBI) theory, we study the stability of Einstein static universe filled with perfect fluid in EiBI theory against both the homogeneous and inhomogeneous scalar perturbations in this work. We find that in both the spatially flat and closed cases, the emergent universe scenario is no longer viable, since Einstein static universe cannot be stable against both the homogeneous and inhomogeneous scalar perturbations simultaneously. However, the emergent universe scenario survives in the spatially open case, while Einstein static universe can be stable under some conditions.

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S. Li and H. Wei
Mon, 22 May 17

Comments: 10 pages, revtex4

New fitting formula for cosmic non-linear density distribution [CEA]

We have measured the probability distribution function (PDF) of cosmic matter density field from a suite of N-body simulations. We propose the generalized normal distribution of version 2 (Nv2) as an alternative fitting formula to the well-known log-normal distribution. We find that Nv2 provides significantly better fit than the log-normal distribution for all smoothing radii (2, 5, 10, 25 [Mpc/h]) that we studied. The improvement is substantial in the underdense regions. The development of non- Gaissianities in the cosmic matter density field is captured by continuous evolution of the skewness and shifts parameters of the Nv2 distribution. We present the redshift evolution of these parameters for aforementioned smoothing radii and various background cosmology models. All the PDFs measured from large and high-resolution N-body simulations that we use in this study can be obtained from a Web site at

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J. Shin, J. Kim, C. Pichon, et. al.
Mon, 22 May 17

Comments: Accepted for publication in ApJ

Bias to CMB Lensing Reconstruction from Temperature Anisotropies due to Large-Scale Galaxy Motions [CEA]

Gravitational lensing of the cosmic microwave background (CMB) is expected to be amongst the most powerful cosmological tools for ongoing and upcoming CMB experiments. In this work, we investigate a bias to CMB lensing reconstruction from temperature anisotropies due to the kinematic Sunyaev-Zel’dovich (kSZ) effect, that is, the Doppler shift of CMB photons induced by Compton-scattering off moving electrons. The kSZ signal yields biases due to both its own intrinsic non-Gaussianity and its non-zero cross-correlation with the CMB lensing field (and other fields that trace the large-scale structure). This kSZ-induced bias affects both the CMB lensing auto-power spectrum and its cross-correlation with low-redshift tracers. Furthermore, it cannot be removed by multifrequency foreground separation techniques because the kSZ effect preserves the blackbody spectrum of the CMB. While statistically negligible for current datasets, we show that it will be important for upcoming surveys, and failure to account for it can lead to large biases in constraints on neutrino masses or the properties of dark energy. For a Stage 4 CMB experiment, the bias can be as large as $\approx$ 15% or 12% in cross-correlation with LSST galaxy lensing convergence or galaxy overdensity maps, respectively, when the maximum temperature multipole used in the reconstruction is $\ell_{\rm max} = 4000$, and about half of that when $\ell_{\rm max} = 3000$. Similarly, we find that the CMB lensing auto-power spectrum can be biased by nearly 10%, although our numerical calculation includes only the expected dominant term. These biases are many times larger than the expected statistical errors. Reducing $\ell_{\rm max}$ can significantly mitigate the bias at the cost of a decrease in the overall lensing reconstruction signal-to-noise. Polarization-only reconstruction may be the most robust mitigation strategy.

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S. Ferraro and J. Hill
Mon, 22 May 17

Comments: 19 pages, 5 figures, comments are welcome

The nonspinning binary black hole merger scenario revisited [CL]

We present the results of 14 simulations of nonspinning black hole binaries with mass ratios $q=m_1/m_2$ in the range $1/100\leq q\leq1$. For each of these simulations we perform three runs at increasing resolution to assess the finite difference errors and to extrapolate the results to infinite resolution. For $q\geq 1/6$, we follow the evolution of the binary typically for the last ten orbits prior to merger. By fitting the results of these simulations, we accurately model the peak luminosity, peak waveform frequency and amplitude, and the recoil of the remnant hole for unequal mass nonspinning binaries. We verify the accuracy of these new models and compare them to previously existing empirical formulas. These new fits provide a basis for a hierarchical approach to produce more accurate remnant formulas in the generic precessing case. They also provide input to gravitational waveform modeling.

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J. Healy, C. Lousto and Y. Zlochower
Mon, 22 May 17

Comments: 8 pages, 4 figures