13600969
Weighing neutrinos with galaxy cluster surveys.
Large future galaxy cluster surveys, combined with cosmic microwave background observations, can achieve a high sensitivity to the masses of cosmologically important neutrinos. We show that a weak lensing selected sample of > or approximately 100,000 clusters could tighten the current upper bound on the sum of masses of neutrino species by an order of magnitude, to a level of 0.03 eV. Since this statistical sensitivity is below the best existing lower limit on the mass of at least one neutrino species, a future detection is likely, provided that systematic errors can be controlled to a similar level.
119629909
Is modified gravity required by observations? An empirical consistency test of dark energy models
We apply the technique of parameter splitting to existing cosmological data sets, to check for a generic failure of dark energy models. Given a dark energy parameter, such as the energy density {omega}{sub {lambda}} or equation of state w, we split it into two meta-parameters with one controlling geometrical distances, and the other controlling the growth of structure. Observational data spanning Type Ia Supernovae, the cosmic microwave background (CMB), galaxy clustering, and weak gravitational lensing statistics are fit without requiring the two meta-parameters to be equal. This technique checks for inconsistency between different data sets, as well as for internal inconsistency within any one data set (e.g., CMB or lensing statistics) that is sensitive to both geometry and growth. We find that the cosmological constant model is consistent with current data. Theories of modified gravity generally predict a relation between growth and geometry that is different from that of general relativity. Parameter splitting can be viewed as a crude way to parametrize the space of such theories. Our analysis of current data already appears to put sharp limits on these theories: assuming a flat universe, current data constrain the difference {delta}{omega}{sub {lambda}}={omega}{sub {lambda}}(geom)-{omega}{sub {lambda}}(grow) to be -0.0044{sub -0.0057-0.0119}{sup +0.0058+0.0108} (68%more » and 95% C.L. respectively); allowing the equation of state w to vary, the difference {delta}w=w(geom)-w(grow) is constrained to be 0.37{sub -0.36-0.53}{sup +0.37+1.09}. Interestingly, the region w(grow)>w(geom), which should be generically favored by theories that slow structure formation relative to general relativity, is quite restricted by data already. We find w(grow)<-0.80 at 2{sigma}. As an example, the best-fit flat Dvali-Gabadadze-Porrati model approximated by our parametrization lies beyond the 3{sigma} contour for constraints from all the data sets.« less
119405677
Constraining the evolution of dark energy with a combination of galaxy cluster observables
We show that the abundance and redshift distribution (dN/dz) of galaxy clusters in future high-yield cluster surveys, combined with the spatial power spectrum [P{sub c}(k)] of the same clusters, can place significant constraints on the evolution of the dark energy equation of state, w=w(a). We evaluate the expected errors on w{sub a}=-dw/da and other cosmological parameters using a Fisher matrix approach, and simultaneously including cluster structure evolution parameters in our analysis. We study three different types of forthcoming surveys that will identify clusters based on their x-ray emission (such as DUO, the Dark Universe Observatory), their Sunyaev-Zel'dovich (SZ) decrement (such as SPT, the South Pole Telescope), or their weak-lensing shear (such as LSST, the Large Synoptic Survey Telescope). We find that combining the cluster abundance and power spectrum significantly enhances constraints from either method alone. We show that the weak-lensing survey can deliver a constraint as tight as {delta}w{sub a}{approx}0.1 on the evolution of the dark energy equation of state, and that the x-ray and SZ surveys each yield {delta}w{sub a}{approx}0.4 separately, or {delta}w{sub a}{approx}0.2 when these two surveys are combined. For the x-ray and SZ surveys, constraints on dark energy parameters are improved by a factor of 2 bymore » combining the cluster data with cosmic microwave background anisotropy measurements by Planck, but degrade by a factor of 2 if the survey is required to solve simultaneously for cosmological and cluster structure evolution parameters. The constraint on w{sub a} from the weak-lensing survey is improved by {approx}25% with the addition of Planck data.« less
119228934
Cosmological information in weak lensing peaks
Recent studies have shown that the number counts of convergence peaks N(kappa) in weak lensing (WL) maps, expected from large forthcoming surveys, can be a useful probe of cosmology. We follow up on this finding, and use a suite of WL convergence maps, obtained from ray-tracing N-body simulations, to study (i) the physical origin of WL peaks with different heights, and (ii) whether the peaks contain information beyond the convergence power spectrum P_ell. In agreement with earlier work, we find that high peaks (with amplitudes >~ 3.5 sigma, where sigma is the r.m.s. of the convergence kappa) are typically dominated by a single massive halo. In contrast, medium-height peaks (~0.5-1.5 sigma) cannot be attributed to a single collapsed dark matter halo, and are instead created by the projection of multiple (typically, 4-8) halos along the line of sight, and by random galaxy shape noise. Nevertheless, these peaks dominate the sensitivity to the cosmological parameters w, sigma_8, and Omega_m. We find that the peak height distribution and its dependence on cosmology differ significantly from predictions in a Gaussian random field. We directly compute the marginalized errors on w, sigma_8, and Omega_m from the N(kappa) + P_ell combination, including redshift tomography with source galaxies at z_s=1 and z_s=2. We find that the N(kappa) + P_ell combination has approximately twice the cosmological sensitivity compared to P_ell alone. These results demonstrate that N(kappa) contains non-Gaussian information complementary to the power spectrum.
18834437
Challenges to the DGP model from horizon-scale growth and geometry
We conduct a Markov Chain Monte Carlo study of the Dvali-Gabadadze-Porrati (DGP) selfaccelerating braneworld scenario given the cosmic microwave background (CMB) anisotropy, supernovae and Hubble constant data by implementing an effective dark energy prescription for modified gravity into a standard Einstein-Boltzmann code. We find no way to alleviate the tension between distance measures and horizon scale growth in this model. Growth alterations due to perturbations propagating into the bulk appear as excess CMB anisotropy at the lowest multipoles. In a flat
9414980
Combination of CDF and D0 measurements of the W boson helicity in top quark decays
We report the combination of recent measurements of the helicity of the W boson from top quark decay by the CDF and D0 collaborations, based on data samples corresponding to integrated luminosities of 2.7-5.4 fb(-1) of p (p) over bar collisions collected during Run II of the Fermilab Tevatron collider. Combining measurements that simultaneously determine the fractions of W bosons with longitudinal (f(0)) and right-handed (f(+)) helicities, we find f(0) = 0.722 +/- 0.081[+/- 0.062(stat) +/- 0.052(syst)] and f(+) = -0.033 +/- 0.046[+/- 0.034(stat) +/- 0.031(syst)]. Combining measurements where one of the helicity fractions is fixed to the value expected in the standard model, we find f(0) = 0.682 +/- 0.057[+/- 0.035(stat) +/- 0.046(syst)] for fixed f(+) and f(+) = -0.015 +/- 0.035[+/- 0.018(stat) +/- 0.030(syst)] for fixed f(0). The results are consistent with standard model expectations.
117498892
First Flare-related Rapid Change of Photospheric Magnetic Field Observed by Solar Dynamics Observatory
Photospheric magnetic field not only plays important roles in building up free energy and triggering solar eruptions, but also has been observed to change rapidly and permanently responding to the coronal magnetic field restructuring due to coronal transients. The Helioseismic and Magnetic Imager instrument (HMI) on board the newly launched Solar Dynamics Observatory (SDO) produces seeing-free full-disk vector magnetograms at consistently high resolution and high cadence, which finally makes possible an unambiguous and comprehensive study of this important back-reaction process. In this study, we present a near disk-center, GOES-class X2.2 flare occurred at NOAA AR 11158 on 2011 February 15 using the magnetic field measurements made by HMI. We obtained the first solid evidence of an enhancement in the transverse magnetic field at the flaring magnetic polarity inversion line (PIL) by a magnitude of 70%. This rapid and irreversible field evolution is unequivocally associated with the flare occurrence, with the enhancement area located in between the two chromospheric flare ribbons. Similar findings have been made for another two major flare events observed by SDO. These results strongly corroborate our previous suggestion that the photospheric magnetic field near the PIL must become more horizontal after eruptions. 
In-depth studies will follow to further link the photospheric magnetic field changes with the dynamics of coronal mass ejections, when full Stokes inversion is carried out to generate accurate magnetic field vectors.
118478627
Predicting the Configuration of a Planetary System: KOI-152 Observed by Kepler
The recent Kepler discovery of KOI-152 reveals a system of three hot super-Earth candidates that are in or near a 4:2:1 mean motion resonance. It is unlikely that they formed in situ; the planets probably underwent orbital migration during the formation and evolution process. The small semimajor axes of the three planets suggest that migration stopped at the inner edge of the primordial gas disk. In this paper, we focus on the influence of migration halting mechanisms, including migration "dead zones," and inner truncation by the stellar magnetic field. We show that the stellar accretion rate, stellar magnetic field, and the speed of migration in the protoplanetary disk are the main factors affecting the final configuration of KOI-152. Our simulations suggest that three planets may be around a star with low star accretion rate or with high magnetic field. On the other hand, slow type I migration, which decreases to one-tenth of the linear analysis results, favors forming the configuration of KOI-152. Under such a formation scenario, the planets in the system are not massive enough to open gaps in the gas disk. The upper limits of the planetary masses are estimated to be about 15, 19, and 24M(circle plus), respectively. Our results are also indicative of the near Laplacian configurations that are quite common in planetary systems.
3923904
Top-quark mass measurement using events with missing transverse energy and jets at CDF.
We present a measurement of the top-quark mass using a sample of t ̄t events in 5.7 fb(-1) of integrated luminosity from p ̄p collisions at the Fermilab Tevatron with √s=1.96 TeV and collected by the CDF II Detector. We select events having large missing transverse energy, and four, five, or six jets with at least one jet tagged as coming from a b quark, and reject events with identified charged leptons. This analysis considers events from the semileptonic t ̄t decay channel, including events that contain tau leptons. The measurement is based on a multidimensional template method. We fit the data to signal templates of varying top-quark masses and background templates, and measure a top-quark mass of M(top)=172.32±2.4(stat)±1.0(syst)  GeV/c(2).
1205802
Search for the standard model Higgs boson decaying to a bb pair in events with no charged leptons and large missing transverse energy using the full CDF data set.
We report on a search for the standard model Higgs boson produced in association with a vector boson in the full data set of proton-antiproton collisions at sqrt[s]=1.96  TeV recorded by the CDF II detector at the Tevatron, corresponding to an integrated luminosity of 9.45  fb(-1). We consider events having no identified charged lepton, a transverse energy imbalance, and two or three jets, of which at least one is consistent with originating from the decay of a b quark. We place 95% credibility level upper limits on the production cross section times standard model branching fraction for several mass hypotheses between 90 and 150  GeV/c(2). For a Higgs boson mass of 125  GeV/c(2), the observed (expected) limit is 6.7 (3.6) times the standard model prediction.