1108.1793
Scale-dependent growth from a transition in DE dynamics
Amin, Zukin, Bertschinger
If the quintessence field rolls and oscillates near a minimum in its potential at z<0.2, what is the observational consequence? Can lead to a rapid growth of field fluctuations and gravitational potential on subhorizon scales for a certain class of models, at a timescales << Hubble. Present when quintessence parameters are chosen to reproduce the expansion history consistent with observations. For linearized fluctuations, the DM/galaxy power spectrum is not significantly affected. Best constraint of the transition of quintessence field is provided via the ISW effect on CMB. Beyond the linearized regime, the quintessence field can fragment into large, localized, long-lived excitations (oscillons) with sizes comparable to galaxy clusters; this can provide observational constraints.
Two "signatures" of modified gravity are scale-dependent growth of the gravitational potential, and a difference between the matter power spectrum inferred from measurement of lensing and galaxy clustering. Both effects are achieved in the above scenario by a minimally coupled scalar field in GR with a canonical kinetic term.
* I fail to see why this is important. I guess it's interesting because there is an observational signal in the ISW.
1108.1981
Weak lensing measurement of galaxy cluster in the CFHTLS wide survey
Shan, Kneib, Tao, Fan, Jauzac, Limousin, Massey, Rhodes, Thanjavur
WL analysis of the CFHTLS: 72 sq deg of W1 field, generate largest contiguous WL convergence "mass map". Galaxy shapes measured in i-band, sub-arcsecond seeing, KSB pipeline verified with HST imaging that overlaps with CFHTLS and consistent with r-band. Contains 301 peaks with S/N > 3.5, which is consistent with LCDM. 126 of the peaks lie within 3' of a BCG. Identify 7 counterparts for massive clusters in X-ray emission w/in 6 sq deb of the XMM-LSS survey. With photo-z estimates, use tomographic lensing method to fit the redshift and mass of each convergence peak. Match to optical observations, and confirm 85 groups/clusters with chisq < 3.0, at a mean redshift z=0.36 and velocity dispersion sigma_v = 658.8 km/s. Determine empirical relation between the cluster mass and galaxy velocity dispersion; in reasonable agreement with predictions from N-body LCDM simulations.
1108.1985
Non-Gaussianity in LSS and Minkowski Functionals
Pratten, Munshi
* Minkowski Functionals: [functional analysis] given a linear space X, a Minkowski functional is a device that uses the linear structure to introduce a topology on X. (e.g., define a surface of a sphere in 3d space)
MFs are morphological statistics commonly used in cosmology (e.g., study departure from Gaussianity in various context): CMB observations, WL maps, and LSS surveys (really? where?). At the lowest order, the MFs depend on three generalized skewness parameters that probe the bispectrum with varying weights. Review motivations for studying non-Gaussianity and emphasize importance of the shape of higher order correlators in investigating inflationary models before introducing the skew-spectra applied to galaxy surveys as a tool to investigate primordial non-Gaussianity.
* Might want to read this paper if we want to study primoridal non-gaussianity for inflationary models.
UCB Astro TAC seminar
Double-diffusive magnetic buoyancy, shear dynamics, and the Solar tachocline
Geoffrey Vasil
* tachocline: transition region of the Sun between the radiative interior and the differentially rotating outer convective zone. It is the outer third of the sun (by radius).
Sun's magnetic field: well-ordered cyclic global-scale dynamo--the seat of this global dynamo has been thought to lie in the tachocline. Present work that find difficulties with the tachocline's expected role in the Sun's global dynamo machine, and some novel ways to get around these difficulties. Simple estimates and numerical calculations show difficulty for tachocline to build magnetic fields that are buoyant enough to transit from the internal depths to surface without feedbacks disrupting the tachocline itself. But simple estimates do not consider small diffusion on the dynamics; even small dissipation can have dramatic consequences if magnetic field diffuses much slower than heat (which is hard to calculate numerically). This regime allows for the mechanism of double-diffusive magnetic buoyancy, overcoming the strong stable stratification present in the tachocline. Present some theory and calculations focusing on shear-generated double-diffusive magnetic buoyancy; discuss the role of these physics in the sun and other stars.
LBL INPA
Beyond the standard cosmological model: neutrinos and non-Gaussianity
Tristan Smith
* central limit theorem (CLT): conditions under which the mean of a sufficiently large number of independent random variables, each with finite mean and variance, will be approximately normally distributed. CLT justifies the approximation of large-sample statistics to the normal distribution in controlled experiments.
* even if the initial single-measurement PDF is mot smooth, the probability of measuring the sum of "two independent variables" is the convolution of the above density with itself. Continuous convolution of many independent variables results in a normal distribution. (why??)
* fine print: for CLT to hold true, moments of the parent distribution must exist.
* even if the initial single-measurement PDF is mot smooth, the probability of measuring the sum of "two independent variables" is the convolution of the above density with itself. Continuous convolution of many independent variables results in a normal distribution. (why??)
* fine print: for CLT to hold true, moments of the parent distribution must exist.
Assumption of standard cosmological model need to be tested. (1) Small-scale CMB hints at a presence of extra relativistic energy density within the universe. Constrain clustering properties of the extra relativistic energy density; show that current observations disfavor the interpretation that any extra relativistic energy consists of standard neutrinos. (2) Primordial non-gaussianity use estimators constructed from either the CMB 3-pt or 4-pt correlation functions. Usually an estimator constructed from data to have Gaussian PDF as a result of the central limit theorem. In this case, the central limit theorem does not apply, since the number of terms tha appear in these estimators are much greater than the number of measurements (really? then is the measurement meaningful?). A complete knowledge of the shape of the PDF is necessary in order to properly assign confidence limits to any constraint (duh, if it's not Gaussian, then of course. Oh, I see, so if we assume non-Gaussian, then we can't trust the estimators, which assumes Gaussian PDF). Discuss how Monte Carlo simulations show that PDF for the estimators are nighly non-Gaussian themselves, necessitating more care in using these estimators, especially for future observations with the Planck satellite. Constraining power of these estimators may be improved by using a realization-dependent normalization.
* Oooh, this would have been an interesting talk to attend, especially the neutrino part.
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