Munch: Monday, September 11, 2006
		usual time and place:  12:30, 6th floor conference room
FAQ What is Munch? Munch Archive --------- 05 Sep 2006 26June 2006 19 June 2006 12 June 2006 5 June 2006 22 May 2006 15 May 2006 8 May 2006 1 May 2006 24 Apr 2006 17 Apr 2006 10 Apr 2006 03 Apr 2006 27 Mar 2006 13 Mar 2006 6 Mar 2006	Next week:  tension between cosmological probes?  See the last paper for a teaser... The Compton-Getting effect on ultra-high energy cosmic rays of cosmological origin Authors: M. Kachelriess, P.D. Serpico Comments: v2: 5 pages, no figure. Minor changes, matches published version Report-no: MPP-2006-50 DOI: 10.1016/j.physletb.2006.08.006 Deviations from isotropy have been a key tool to identify the origin and the primary type of cosmic rays at low energies. We suggest that the Compton-Getting effect can play a similar role at ultra-high energies: If at these energies the cosmic ray flux is dominated by sources at cosmological distances, then the movement of the Sun relative to the cosmic microwave background frame induces a dipole anisotropy at the 0.6% level. The energy dependence and the orientation of this anisotropy provide important information about the transition between galactic and extragalactic cosmic rays, the charge of the cosmic ray primaries, the galactic magnetic field and, at the highest energies, the energy-loss horizon of cosmic rays. A 3-sigma detection of this effect requires around 10^6 events in the considered energy range and is thus challenging but not impossible with present detectors. As a corollary we note that the Compton-Getting effect allows one also to constrain the fraction of the diffuse gamma-ray background emitted by sources at cosmological distance, with promising detection possibilities for the GLAST satellite. Full-text: PostScript, PDF, or Other formats Primordial non-Gaussianity and Dark Energy constraints from Cluster Surveys Authors: Emiliano Sefusatti, Chris Vale, Kenji Kadota, Joshua Frieman Comments: 10 pages, 4 figures. Replaced Fig. 1 Report-no: FERMILAB-PUB-06-324-A Galaxy cluster surveys will be a powerful probe of dark energy. At the same time, cluster abundances is sensitive to any non-Gaussianity of the primordial density field. It is therefore possible that non-Gaussian initial conditions might be misinterpreted as a sign of dark energy or at least degrade the expected constraints on dark energy parameters. To address this issue, we perform a likelihood analysis of an ideal cluster survey similar in size and depth to the upcoming South Pole Telescope/Dark Energy Survey (SPT-DES). We analyze a model in which the strength of the non-Gaussianity is parameterized by the constant fNL; this model has been used extensively to derive Cosmic Microwave Background (CMB) anisotropy constraints on non-Gaussianity, allowing us to make contact with those works. We find that the constraining power of the cluster survey on dark energy observables is not significantly diminished by non-Gaussianity provided that cluster redshift information is included in the analysis. We also find that even an ideal cluster survey is unlikely to improve significantly current and future CMB constraints on non-Gaussianity. However, when all systematics are under control, it could constitute a valuable cross check to CMB observations. Full-text: PostScript, PDF, or Other formats Cosmic Superstring Scattering in Backgrounds Authors: Mark G. Jackson Comments: 12 pages, 2 figures Report-no: FERMILAB-PUB-06-288-A We generalize the calculation of cosmic superstring reconnection probability to non-trivial backgrounds. This is done by modeling cosmic strings as wound tachyon modes in the 0B theory, and the spacetime effective action is then used to couple this to background fields. Simple examples are given including trivial and warped compactifications. Generalization to $(p,q)$ strings is discussed. Full-text: PostScript, PDF, or Other formats Separating Dark Physics from Physical Darkness: Minimalist Modified Gravity vs. Dark Energy Authors: Dragan Huterer (KICP Chicago), Eric V. Linder (Lawrence Berkeley Lab) Comments: 9 pages, 4 figures The acceleration of the cosmic expansion may be due to a new component of physical energy density or a modification of physics itself. Mapping the expansion of cosmic scales and the growth of large scale structure in tandem can provide insights to distinguish between the two origins. Using Minimal Modified Gravity (MMG) - a single parameter gravitational growth index formalism to parameterize modified gravity theories - we examine the constraints that cosmological data can place on the nature of the new physics. For next generation measurements combining weak lensing, supernovae distances, and the cosmic microwave background we can extend the reach of physics to allow for fitting gravity simultaneously with the expansion equation of state, diluting the equation of state estimation by less than 25% relative to when general relativity is assumed, and determining the growth index to 8%. For weak lensing we examine the level of understanding needed of quasi- and nonlinear structure formation in modified gravity theories, and the trade off between stronger precision but greater susceptibility to bias as progressively more nonlinear information is used. Full-text: PostScript, PDF, or Other formats Probing Modified Gravity by Combining Supernovae and Galaxy Cluster Surveys Authors: Jia-Yu Tang, Jochen Weller, Alan Zablocki Comments: 5 pages, 3 figures Possible explanations of the observed accelerated expansion of the Universe are the introduction of a dark energy component or the modifications of gravity at large distances. A particular difference between these scenarios is the dynamics of the growth of structures. The redshift distribution of galaxy clusters will probe this growth of structures with large precision. Here we will investigate how proposed galaxy cluster surveys will allow one to distinguish the modified gravity scenarios from dark energy models. We find that cluster counts can distinguish the Dvali-Gabadadze-Porrati model from a dark energy model, which has the same background evolution, as long as the amplitude of the primordial power spectrum is constrained by a CMB experiment like Planck. In order to achieve this, only a couple of hundred clusters in bins of width Delta-z = 0.1 are required. This should be easily achievable with forthcoming Sunyaev-Zel'dovich cluster counts, such as the South Pole Telescope in conjunction with the Dark Energy Survey. Full-text: PostScript, PDF, or Other formats Supernovae, Lensed CMB and Dark Energy Authors: Wayne Hu, Dragan Huterer, Kendrick M. Smith (KICP, UChicago) Comments: 4 pages, 4 figures, submitted to ApJL Supernova distance and primary CMB anisotropy measurements provide powerful probes of the dark energy evolution in a flat universe but degrade substantially once curvature is marginalized. We show that lensed CMB polarization power spectrum measurements, accessible to next generation ground based surveys such as SPTpol or QUIET, can remove the curvature degeneracy at a level sufficient for the SNAP and Planck surveys and allow a measurement of sigma(w_p)=0.03, sigma(w_a)=0.3 jointly with sigma(Omega_K)=0.0035. This expectation assumes that the sum of neutrino masses is independently known to better than 0.1 eV. This assumption is valid if the lightest neutrino is assumed to have negligible mass in a normal neutrino mass hierarchy and is potentially testable with upcoming direct laboratory measurements. Full-text: PostScript, PDF, or Other formats Cosmological Information from Lensed CMB Power Spectra Authors: Kendrick M. Smith, Wayne Hu (KICP, UChicago), Manoj Kaplinghat (UC Irvine) Comments: 19 pages, 16 figures, submitted to PRD Gravitational lensing distorts the cosmic microwave background (CMB) temperature and polarization fields and encodes valuable information on distances and growth rates at intermediate redshifts into the lensed power spectra. The non-Gaussian bandpower covariance induced by the lenses is negligible to l=2000 for all but the B polarization field where it increases the net variance by up to a factor of 10 and favors an observing strategy with 3 times more area than if it were Gaussian. To quantify the cosmological information, we introduce two lensing observables, characterizing nearly all of the information, which simplify the study of non-Gaussian impact, parameter degeneracies, dark energy models, and complementarity with other cosmological probes. Information on the intermediate redshift parameters rapidly becomes limited by constraints on the cold dark matter density and initial amplitude of fluctuations as observations improve. Extraction of this information requires deep polarization measurements on only 5-10% of the sky, and can improve Planck lensing constraints by a factor of ~2-3 on any one of the parameters w_0, w_a, Omega_K, sum(m_nu) with the others fixed. Sensitivity to the curvature and neutrino mass are the highest due to the high redshift weight of CMB lensing but degeneracies between the parameters must be broken externally. Full-text: PostScript, PDF, or Other formats teaser for next week:  tension is cosmological parameters?  See section 5.8 of Massey et al., below The Shear TEsting Programme 2: Factors affecting high precision weak lensing analyses Authors: Richard Massey, Catherine Heymans, Joel Berge, Gary Bernstein, Sarah Bridle, Douglas Clowe, Hakon Dahle, Richard Ellis, Thomas Erben, Marco Hetterscheidt, F. William High, Christopher Hirata, Henk Hoekstra, Patrick Hudelot, Mike Jarvis, David Johnston, Konrad Kuijken, Vera Margoniner, Rachel Mandelbaum, Yannick Mellier, Reiko Nakajima, Stephane Paulin-Henriksson, Molly Peeples, Chris Roat, Alexandre Refregier, Jason Rhodes, Tim Schrabback, Mischa Schirmer, Uros Seljak, Elisabetta Semboloni, Ludovic Van Waerbeke Comments: 27 pages, 10 figures, MNRAS submitted The Shear TEsting Programme (STEP) is a collaborative project to improve the accuracy and reliability of weak lensing measurement, in preparation for the next generation of wide-field surveys. We review sixteen current and emerging shear measurement methods in a common language, and assess their performance by running them (blindly) on simulated images that contain a known shear signal. We determine the common features of algorithms that most successfully recover the input parameters. We achieve previously unattained discriminatory precision in our analysis, via a combination of more extensive simulations, and pairs of galaxy images that have been rotated with respect to each other, thus removing noise from their intrinsic ellipticities. The robustness of our simulation approach is also confirmed by testing the relative calibration of methods on real data. Weak lensing measurement has improved since the first STEP paper. Several methods now consistently achieve better than 2% precision, and are still being developed. However, the simulations can now distinguish all methods from perfect performance. Our main concern continues to be the potential for a multiplicative shear calibration bias: not least because this can not be internally calibrated with real data. We determine which galaxy populations are responsible and, by adjusting the simulated observing conditions, we also investigate the effects of instrumental and atmospheric parameters. We have isolated several previously unrecognised aspects of galaxy shape measurement, in which focussed development could provide further progress towards the sub-percent level of precision desired for future surveys. [ABRIDGED] Full-text: PostScript, PDF, or Other formats