Galaxy Cluster Astrophysics and Cosmology: Questions and Opportunities for the Coming Decade
We are learning much about how structure forms, in particular how clusters as nodes in the cosmic web evolve and accrete matter, and about the physical processes within these objects. In the next decade, the study of clusters will enable us to tackle important questions regarding the nature of Dark Matter and Dark Energy, how clusters co-evolve with super-massive black holes at their centers, and to advance our knowledge about fundamental plasma astrophysics. This science white paper outlines the key questions and research opportunities in cluster astrophysics that are emerging in the coming decade and beyond, and serves as an overview to other cluster related white papers.

title: DARK MATTER HALO PROFILES OF MASSIVE CLUSTERS: THEORY VERSUS OBSERVATIONS
abstract: Dark-matter-dominated cluster-scale halos act as an important cosmological probe and provide a key testing ground for structure formation theory. Focusing on their mass profiles, we have carried out (gravity-only) simulations of the concordance ΛCDM cosmology, covering a mass range of 2 × 1012 to 2 × 1015 h –1 M ☉ and a redshift range of z = 0-2, while satisfying the associated requirements of resolution and statistical control. When fitting to the Navarro-Frenk-White profile, our concentration-mass (c-M) relation differs in normalization and shape in comparison to previous studies that have limited statistics in the upper end of the mass range. We show that the flattening of the c-M relation with redshift is naturally expressed if c is viewed as a function of the peak height parameter, ν. Unlike the c-M relation, the slope of the c-ν relation is effectively constant over the redshift range z = 0-2, while the amplitude varies by ~30% for massive clusters. This relation is, however, not universal: using a simulation suite covering the allowed wCDM parameter space, we show that the c-ν relation varies by about ±20% as cosmological parameters are varied. At fixed mass, the c(M) distribution is well fit by a Gaussian with σ c /c 1/3, independent of the radius at which the concentration is defined, the halo dynamical state, and the underlying cosmology. We compare the ΛCDM predictions with observations of halo concentrations from strong lensing, weak lensing, galaxy kinematics, and X-ray data, finding good agreement for massive clusters (M vir > 4 × 1014 h –1 M ☉), but with some disagreements at lower masses. Because of uncertainty in observational systematics and modeling of baryonic physics, the significance of these discrepancies remains unclear.

title: CHAOS IN TIME-DEPENDENT VARIATIONAL APPROXIMATIONS TO QUANTUM DYNAMICS
abstract: Dynamical chaos has recently been shown to exist in the Gaussian approximation in quan-tum mechanics and in the self-consistent mean ﬁeld approach to studying the dynamics ofquantum ﬁelds. In this study, we ﬁrst show that any variationalapproximationto the dynam-ics of a quantum system based on the Dirac action principle leads to a classical Hamiltoniandynamics for the variational parameters. Since this Hamiltonian is generically nonlinearand nonintegrable, the dynamics thus generated can be chaotic, in distinction to the exactquantum evolution. We then restrict attention to a system of two biquadratically coupledquantum oscillators and study two variational schemes, the leading order large N (fourcanonical variables) and Hartree (six canonical variables) approximations. The chaos seenin the approximate dynamics is an artifact of the approximations: this is demonstrated bythe fact that its onset occurs on the same characteristic time scale as the breakdown of theapproximations when compared to numerical solutions of the time-dependent Schr¨odingerequation.PACS numbers: 05.45. +b, 03.65. Sq, 2.30 Wd,

title: COMPUTATIONAL CHALLENGES IN HIGH INTENSITY ION BEAM PHYSICS

title: COSMIC EMULATION: THE CONCENTRATION-MASS RELATION FOR wCDM UNIVERSES
abstract: The concentration-mass relation for dark matter-dominated halos is one of the essential results expected from a theory of structure formation. We present a simple prediction scheme, a cosmic emulator, for the concentration-mass (c-M) relation as a function of cosmological parameters for wCDM models. The emulator is constructed from 37 individual models, with three nested N-body gravity-only simulations carried out for each model. The mass range covered by the emulator is 2 × 1012 M ☉ < M < 1015 M ☉ with a corresponding redshift range of z = 0-1. Over this range of mass and redshift, as well as the variation of cosmological parameters studied, the mean halo concentration varies from c ~ 2 to c ~ 8. The distribution of the concentration at fixed mass is Gaussian with a standard deviation of one-third of the mean value, almost independent of cosmology, mass, and redshift over the ranges probed by the simulations. We compare results from the emulator with previously derived heuristic analytic fits for the c-M relation, finding that they underestimate the halo concentration at high masses. Using the emulator to investigate the cosmology dependence of the c-M relation over the currently allowable range of values, we find—not surprisingly—that σ8 and ω m influence it considerably, but also that the dark energy equation-of-state parameter w has a substantial effect. In general, the concentration of lower-mass halos is more sensitive to changes in cosmological parameters as compared to cluster mass halos. The c-M emulator is publicly available from http://www.hep.anl.gov/cosmology/CosmicEmu.

title: Joint Efficient Dark-energy Investigation (JEDI): a Candidate Implementation of the NASA-DOE Joint Dark Energy Mission (JDEM)
abstract: JEDI will probe dark energy in three independent ways by measuring the expansion history of the universe: (1) using type Ia supernovae as cosmological standard candles over a range of distances, (2) using baryon oscillations as a cosmological standard ruler over a range of cosmic epochs, (3) mapping the weak gravitational lensing distortion by foreground galaxies of the images of background galaxies at different distances. JEDI will unravel the nature of dark energy with accuracy and precision. 
JEDI is a 2m-class space telescope with the unique ability of simultaneous wide-field imaging (0.8-4.2 micron in five bands) and multi-slit spectroscopy (0.8-3.2 micron) with a field of view of 1 square degree. What makes JEDI efficient is its ability to simultaneously obtain high signal-to-noise ratio, moderate resolution slit spectra for all supernovae and ~ 5000 galaxies in its wide field of view, and to combine imaging and spectroscopy so that the appropriate balance of time is devoted to each. 
JEDI will measure the cosmic expansion history H(z) as a free function to 10^9 galaxies to H \~ 25.

title: A precision measurement of the inclusive ep scattering cross section at HERA
abstract: A measurement of the inclusive deep inelastic neutral current e+p scattering cross section is reported in the region of four-momentum transfer squared, 12 GeV2≤Q2≤150 GeV2, and Bjorken x, 2×10−4≤x≤0.1. The results are based on data collected by the H1 Collaboration at the ep collider HERA at positron and proton beam energies of Ee=27.6 GeV and Ep=920 GeV, respectively. The data are combined with previously published data, taken at Ep=820 GeV. The accuracy of the combined measurement is typically in the range of 1.3–2%. A QCD analysis at next-to-leading order is performed to determine the parton distributions in the proton based on H1 data.

title: Low Mass WIMP Searches with a Neutrino Experiment: A Proposal for Further MiniBooNE Running
abstract: A proposal submitted to the FNAL PAC is described to search for light sub-GeV WIMP dark matter at MiniBooNE. The possibility to steer the beam past the target and into an absorber leads to a significant reduction in neutrino background, allowing for a sensitive search for elastic scattering of WIMPs off nucleons or electrons in the detector. Dark matter models involving a vector mediator can be probed in a parameter region consistent with the required thermal relic density, and which overlaps the region in which these models can resolve the muon g-2 discrepancy. Estimates of signal significance are presented for various operational modes and parameter points. The experimental approach outlined for applying MiniBooNE to a light WIMP search may also be applicable to other neutrino facilities.

title: Letter of Intent: A new investigation of $\nu_\mu\rightarrow\nu_e$ oscillations with improved sensitivity in an enhanced MiniBooNE experiment

title: Search for dark matter and large extra dimensions in monojet events in pp collisions at $ \sqrt {s} = {7} $ TeV
abstract: A bstractA search has been made for events containing an energetic jet and an imbalance in transverse momentum using a data sample of pp collisions at a center-of-mass energy of 7 TeV. This signature is common to both dark matter and extra dimensions models. The data were collected by the CMS detector at the LHC and correspond to an integrated luminosity of 5.0 fb−1. The number of observed events is consistent with the standard model expectation. Constraints on the dark matter-nucleon scattering cross sections are determined for both spin-independent and spin-dependent interaction models. For the spin-independent model, these are the most constraining limits for a dark matter particle with mass below 3.5 GeV/c2, a region unexplored by direct detection experiments. For the spin-dependent model, these are the most stringent constraints over the 0.1–200 GeV/c2 mass range. The constraints on the Arkani-Hamed, Dimopoulos, and Dvali model parameter MD determined as a function of the number of extra dimensions are also an improvement over the previous results.

title: A Combined Three-Phase Signal Extraction of the Sudbury Neutrino Observatory Data Using Markov Chain Monte Carlo Technique
abstract: Neutrino physics has entered an era of precision, after proving that the Standard Solar Model is a viable theory and going beyond the current Standard Model of particle physics by proving that neutrinos possess nonzero masses. The Sudbury Neutrino Observatory (SNO) experiment, along with other experiments, has restricted neutrino mixing angle (θ12) and the mass square difference (∆m21) to lie within the large mixing solution area. SNO, located 2 km underground in Sudbury, Canada, was an ultraclean heavy-water (D2O) imaging detector for observing neutrinos produced by fusion reactions in the Sun. Neutrino interactions with heavy water resulted in flashes of light called C̆erenkov radiation which was detected by an array of photomultiplier tubes. SNO took data from November 1999 to November 2006, totalling 1082 days of data taking. This work describes an improved measurement of the mixing parameters from a combined fit of all the data. For the signal extraction fit on the data consisting of 4 observable of an event – radial position, recoil electron energy, direction relative to the Sun and event isotropy – Markov Chain Monte Carlo (MCMC) method based on Metropolis algorithm was employed. The nuisance parameters (systematics), weighted by external constraints, were allowed to vary in the fit. The goal of the thesis was to extract the survival probabilities of electron neutrinos and determine the total flux of active-flavour neutrinos from B decay in the Sun measured through the neutral current interactions of neutrinos on deuterium. The B flux from the fit is (5.24 ± 0.02) × 10 cm−2 s−1; uncertainty from statistics and systematics is 3.56%. Along with B flux, the fit extracted energy spectra of charged current interactions of neutrinos on deuterium and elastic scattering interactions of neutrinos on electrons. The fit described the energy-dependent day survival probability of solar neutrinos as a quadratic equation and asymmetry on the day survival probability as a linear equation. Four polynomial coefficients of the survival probability were extracted from the fit: constant coefficient as 0.3206± 0.0197, linear coefficient as 0.005± 0.008 and quadratic coefficient as −0.0014± 0.0033. There are two coefficients on the day-night asymmetry: constant coefficient as 0.0496 ± 0.0347 and the linear coefficient as −0.018 ± 0.028. The day-night asymmetry (0.0496) observed is 1.4σ away from zero. Using these findings, the oscillation space in terms of ∆m21 and θ12 will be further constrained. Compared to the previous published SNO results, the uncertainty on B went down from 3.83% to 3.56% and average B νe survival probability (p0) went down from 6.57% to 6.14%. If the data were analysed with the same assumptions, the decrease in uncertainties would have been approximately twice as big; however, more conservative systematic uncertainties were assigned in some cases.