First results from the DEAP-3600 dark matter search with argon at SNOLAB [CEA]

This paper reports the first results of a direct dark matter search with the DEAP-3600 single-phase liquid argon (LAr) detector. The experiment was performed 2 km underground at SNOLAB (Sudbury, Canada) utilizing a large target mass, with the LAr target contained in a spherical acrylic vessel of 3600 kg capacity. The LAr is viewed by an array of PMTs, which would register scintillation light produced by rare nuclear recoil signals induced by dark matter particle scattering. An analysis of 4.7 days (fiducial exposure of 9.87 tonne-days) of data taken with the nearly full detector during the initial filling phase demonstrates the detector performance and the best electronic recoil rejection using pulse-shape discrimination in argon, with leakage $<1.2\times 10^{-7}$ (90% C.L.) between 16 and 33 keV$_{ee}$. No candidate signal events are observed, which results in the leading limit on WIMP-nucleon spin-independent cross section on argon, $<1.2\times 10^{-44}$ cm$^2$ for a 100 GeV/c$^2$ WIMP mass (90% C.L.).

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P. Amaudruz, M. Baldwin, M. Batygov, et. al.
Wed, 26 Jul 17

Comments: N/A

The dipole anisotropy of WISE x SuperCOSMOS number counts [CEA]

We probe the validity of the isotropy hypothesis of the Universe, one of the foundations of modern Cosmology, with the WISE $\times$ SuperCOSMOS data set. This is performed by searching for dipole anisotropy of galaxy number counts in different redshift shells in the $0.10 < z \leq 0.35$ range. We find that the dipole direction is in concordance with most of previous analyses in the literature, however, its amplitude is only consistent with $\Lambda$CDM-based mocks when we adopt the cleanest sample of this catalogue, except for the $z < 0.15$ data, which exhibits a persistently large dipole signal. Hence, we obtain no significant evidence against the large-scale isotropy assumption once the data are purified from stellar contamination, yet our results in the lowest redshift range are still inconclusive.

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C. Bengaly, C. Novaes, H. Xavier, et. al.
Wed, 26 Jul 17

Comments: 5 pages, 4 figures, 2 tables. Comments welcome!

Exploring the Potential of the Dark Matter Candidate from the Madala Hypothesis with Multi-frequency Indirect Detection [CEA]

The Madala hypothesis was proposed by members of the Wits-ATLAS group to account for several anomalies in both ATLAS and CMS data at the LHC. This hypothesis extends the standard model through the addition of two scalar bosons and a hidden sector that can provide a dark matter candidate. This hidden sector interacts with the standard model only through the mediation of one of these scalars S. The couplings of S are not amenable to investigation in current collider data and so are assumed to be Higgs-like to reduce the parameter space of the model. Our previous work (Beck & Colafrancesco 2016) has shown that these couplings can be limited via indirect dark matter detection experiments in gamma-rays (for resonant annihilations into S). Here we will treat the dark matter and S masses independently, and we generalise our previous work and examine what fraction of the cosmological dark matter abundance can be accounted for by particles in the hidden sector of the Madala hypothesis dark matter when these annihilate to standard model products via a Higgs-like S. We will also extend our gamma-ray analysis of Madala hypothesis dark matter to include the constraints of diffuse radio data from the Coma galaxy cluster in addition to the Fermi-LAT gamma-ray data from both this target and the Reticulum II dwarf galaxy.
Our analysis indicates that either the Madala hypothesis cannot provide the bulk of cosmological dark matter, or the S boson cannot be simply Higgs-like. These apply unless the candidate particle exceeds a mass of 200 GeV. Both these scenarios may reduce the attractiveness of the hypothesis as the second case will imply that many free parameters must be added to describe S, greatly weakening fits for the model. To investigate the full consequences of this further work will necessitate using larger astrophysical data sets to strongly constrain details about S.

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G. Beck and S. Colafrancesco
Wed, 26 Jul 17

Comments: 6 Pages, 2 figures, submitted to the proceedings of the South African Institute of Physics Conference 2017

What sets the central structure of dark matter haloes? [CEA]

Dark matter (DM) haloes forming near the thermal cut-off scale of the density perturbations are unique, since they are the smallest objects and form through monolithic gravitational collapse, while larger haloes contrastingly have experienced mergers. While standard cold dark matter simulations readily produce haloes that follow the universal Navarro-Frenk-White (NFW) density profile with an inner slope, $\rho \propto r^{-\alpha}$, with $\alpha=1$, recent simulations have found that when the free-streaming cut-off is resolved, the resulting haloes follow nearly power-law density profiles of $\alpha\sim1.5$. In this paper, we study the formation of density cusps in haloes using idealized $N$-body simulations of the collapse of proto-haloes. When the proto-halo profile is initially cored due to particle free-streaming at high redshift, we universally find $\sim r^{-1.5}$ profiles irrespective of the proto-halo profile slope outside the core and large-scale non-spherical perturbations. Quite in contrast, when the proto-halo has a power-law profile, then we obtain profiles compatible with the NFW shape when the density slope of the proto-halo patch is shallower than a critical value, $\alpha_{\rm ini} \sim 0.3$, while the final slope can be steeper for $\alpha_{\rm ini}\gtrsim 0.3$. We further demonstrate that the $r^{-1.5}$ profiles are sensitive to small scale noise, which gradually drives them towards an inner slope of $-1$, where they become resilient to such perturbations. We demonstrate that the $r^{-1.5}$ solutions are in hydrostatic equilibrium, largely consistent with a simple analytic model, and provide arguments that angular momentum appears to determine the inner slope.

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G. Ogiya and O. Hahn
Wed, 26 Jul 17

Comments: 22 pages, 20 figures, 2 tables, submitted to MNRAS, Figure 9 summarizes the main results

Probing the imprints of generalized interacting dark energy on the growth of perturbations [CEA]

We extensively study the evolution and distinct signatures of cosmological models, in which dark energy interacts directly with dark matter. We first focus on the imprints of these coupled models on the cosmic microwave background temperature power spectrum, in which we discuss the multipole peak separation together with the integrated Sachs-Wolfe effect. We also address the growth of matter perturbations, and disentangle the interacting dark energy models using the expansion history together with the growth history. We find that a disformal coupling between dark matter and dark energy induces intermediate-scales and time-dependent damped oscillatory features in the matter growth rate function, a unique characteristic of this coupling. Apart from the disformal coupling, we also consider conformally coupled models, together with models which simultaneously make use of both couplings.

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J. Mifsud and C. Bruck
Tue, 25 Jul 17

Comments: 30 pages, 13 figures

Cosmological parameter forecasts for HI intensity mapping experiments using the angular power spectrum [CEA]

HI intensity mapping is a new observational technique to survey the large-scale structure of matter using the 21 cm emission line of atomic hydrogen (HI). It can be used to constrain cosmological parameters, including the dark energy equation-of-state $w$. As our experimental setups we use BINGO (BAO from Integrated Neutral Gas Observations) and the SKA (Square Kilometre Array) phase-1 dish array operating in auto-correlation mode. We find that the use of the power spectrum is potentially more powerful than the BAO wiggles alone, even in the presence of extra nuisance parameters such as the HI bias and HI amplitude. For the optimal case of BINGO with no foregrounds, we find that the combination of the HI angular power spectrum with Planck results allows $w$ to be measured with a precision of $4\%$, while the combination of the BAO acoustic scale with Planck gives a precision of $7\%$. We consider a number of potentially complicating effects, including foregrounds and redshift dependent bias, which increase the uncertainty on $w$ but not dramatically; in all cases we find the final uncertainty to be $\Delta w < 8\%$ for BINGO. For the combination of SKA-MID in auto-correlation mode with Planck, we find that $w$ can be measured with a precision of $4\%$ for band 1 $(0.35 < z < 3)$ and $2\%$ for band 2 $(0 < z < 0.49)$. Extending the model to include the sum of neutrino masses yields a $95\%$ upper limit of $\sum m_\nu < 0.24$ eV for BINGO and $\sum m_\nu < 0.08$ eV for SKA phase 1, competitive with the current best constraints in the case of BINGO and significantly better than them in the case of SKA.

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L. Olivari, C. Dickinson, R. Battye, et. al.
Tue, 25 Jul 17

Comments: 17 pages, 7 figures, 6 tables. Submitted to MNRAS

Accelerating Approximate Bayesian Computation with Quantile Regression: Application to Cosmological Redshift Distributions [CEA]

Approximate Bayesian Computation (ABC) is a method to obtain a posterior distribution without a likelihood function, using simulations and a set of distance metrics. For that reason, it has recently been gaining popularity as an analysis tool in cosmology and astrophysics. Its drawback, however, is a slow convergence rate. We propose a novel method, which we call qABC, to accelerate ABC with Quantile Regression. In this method, we create a model of quantiles of distance measure as a function of input parameters. This model is trained on a small number of simulations and estimates which regions of the prior space are likely to be accepted into the posterior. Other regions are then immediately rejected. This procedure is then repeated as more simulations are available. We apply it to the practical problem of estimation of redshift distribution of cosmological samples, using forward modelling developed in previous work. The qABC method converges to nearly same posterior as the basic ABC. It uses, however, only 20\% of the number of simulations compared to basic ABC, achieving a fivefold gain in execution time for our problem. For other problems the acceleration rate may vary; it depends on how close the prior is to the final posterior. We discuss possible improvements and extensions to this method.

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T. Kacprzak, J. Herbel, A. Amara, et. al.
Tue, 25 Jul 17

Comments: 10 pages, 5 figures, prepared for submission to JCAP