Munch: Monday, December 04, 2006

                               


 

    usual time and place:  12:30, 6th floor conference room

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 


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       Munch Archive

Cosmological solutions of supercritical string theory (suggested by Mark)

Authors: Simeon Hellerman, Ian Swanson
Comments: 34 pages, 9 figures
We study quintessence-driven, spatially flat, expanding FRW cosmologies that arise naturally from string theory formulated in a supercritical number of spacetime dimensions. The tree-level potential of the string theory produces an equation of state at the threshold between accelerating and decelerating cosmologies, and the resulting spacetime is globally conformally equivalent to Minkowski space. We demonstrate that exact solutions exist with a condensate of the closed-string tachyon, the simplest of which is a Liouville wall moving at the speed of light. We rely on the existence of this solution to derive constraints on the couplings of the tachyon to the dilaton and metric in the string theory effective action. In particular, we show that the tachyon dependence of the Einstein term must be nontrivial.

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Search of Axions at the Kuo-Sheng Nuclear Power Station with a High-Purity Germanium Detector (suggested by Aaron)

Authors: C.M. Chang, et al, TEXONO Collaboration
Comments: 4 pages, 2 tables, 4 figures
Report-no: AS-TEXONO/06-05
A search of axions produced in nuclear transitions was performed at the Kuo-Sheng Nuclear Power Station with a high-purity germanium detector of mass 1.06 kg at a distance of 28 m from the 2.9 GW reactor core. The experimental signatures were mono-energetic lines produced by their Primakoff or Compton conversions at the detector. No evidence of axion emissions were observed and model-independent constraints on the axion mass $m_a$, branching ratio $\braxion$, and couplings $\gagg$, $\gaee$ were placed. Limits on $\gagg ^2 \braxion$$<$$5.2 \times 10^{-17}$ GeV$^{-2}$ at $m_{a}$$<$50 keV and $\gaee ^2$$\braxion$$<$$1.5 \times 10^{-20}$ at $m_{a}$$<$2.2 MeV at 90% confidence level were derived. In particular, the sensitivities in $\gaee$ for $\braxion$$>$$10^{-9}$ improve over previous results and provide a unique probe to the window $10^4$ eV$<$$m_a$$<$$10^6$ eV not covered by other studies.

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Search of Neutrino Magnetic Moments with a High-Purity Germanium Detector at the Kuo-Sheng Nuclear Power Station (suggested by Aaron)

Authors: H. T. Wong, et al, TEXONO Collaboration
Comments: 16 pages, 15 figures, 9 tables
Report-no: AS-TEXONO/06-03
A search of neutrino magnetic moments was carried out at the Kuo-Sheng Nuclear Power Station at a distance of 28 m from the 2.9 GW reactor core. With a high purity germanium detector of mass 1.06 kg surrounded by scintillating NaI(Tl) and CsI(Tl) crystals as anti-Compton detectors, a detection threshold of 5 keV and a background level of 1 $\cpd$ near threshold were achieved. Details of the reactor neutrino source, experimental hardware, background understanding and analysis methods are presented. Based on 570.7 and 127.8 days of Reactor ON and OFF data, respectively, at an average Reactor ON electron anti-neutrino flux of $\rm{6.4 \times 10^{12} cm^{-2} s^{-1}}$, the limit on the neutrino magnetic moments of $\rm{\munuebar < 7.4 \times 10^{-11} \mub}$ at 90% confidence level was derived. Indirect bounds on the $\nuebar$ radiative decay lifetimes were inferred.

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Evidence for merging or disruption of red galaxies from the evolution of their clustering

Authors: Martin White, Zheng Zheng, Michael J.I. Brown, Arjun Dey, Buell T. Jannuzi
Comments: 4 pages, 3 figures
The formation and evolution of massive red galaxies form a crucial test of theories of galaxy formation based on hierarchical assembly. In this letter we use observations of the clustering of luminous red galaxies from the Bootes field and N-body simulations to argue that about 1/3 of the most luminous satellite galaxies appear to undergo merging or disruption within massive halos between z~0.9 and z~0.5.

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LeMoMaF: Lensed Mock Map Facility

Authors: Jaime E. Forero-Romero, Jeremy Blaizot, Julien Devriendt, Ludovic Van Waerbeke, Bruno Guiderdoni
Comments: 14 pages, 11 figures, submitted to MNRAS
We present the Lensed Mock Map Facility (LeMoMaF), a tool designed to perform mock weak lensing measurements on numerically simulated chunks of the universe. Coupling N-body simulations to a semi-analytical model of galaxy formation, LeMoMaF can create realistic lensed images and mock catalogues of galaxies, at wavelengths ranging from the UV to the submm. To demonstrate the power of such a tool we compute predictions of the source-lens clustering effect on the convergence statistics, and quantify the impact of weak lensing on galaxy counts in two different filters. We find that the source-lens clustering effect skews the probability density function of the convergence towards low values, with an intensity which strongly depends on the redshift distribution of galaxies. On the other hand, the degree of enhancement or depletion in galaxy counts due to weak lensing is independent of the source-lens clustering effect. We discuss the impact on the two-points shear statistics to be measured by future missions like SNAP and LSST. The source-lens clustering effect would bias the estimation of sigma_8 from two point statistics by 2% -5%. We conclude that accurate photometric redshifts for individual galaxies are necessary in order to quantify and isolate the source-lens clustering effect.

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Gravitational lensing by cosmic strings: what we learn from the CSL-1 case

Authors: M.V. Sazhin (1), O.S. Khovanskaya (1), M. Capaccioli (2,3), G. Longo (3,4,5), M. Paolillo (3,5,6), G. Covone (4), N.A. Grogin (7), E.J. Schreier (7,8) ((1) Sternberg Astronomical Institute, Moscow State University, Moscow, RUSSIA; (2) VSTceN-INAF, Napoli, ITALY; (3) Universita' di Napoli Federico II, Dip. di Scienze Fisiche, ITALY; (4) INAF-Osservatorio Astronomico di Capodimonte, Napoli, ITALY; (5) INFN-Napoli Unit, ITALY; (6) Space Telescope Science Institute, Baltimore, USA; (7) Dep. of Physics and Astronomy, The Johns Hopkins University, Baltimore, USA; (8) Associated Universities Inc., Washington DC, USA)
Comments: 12 pages, 8 figures, submitted to MNRAS
Cosmic strings were postulated by Kibble in 1976 and, from a theoretical point of view, their existence finds support in modern superstring theories, both in compactification models and in theories with extended additional dimensions. Their eventual discovery would lead to significant advances in both cosmology and fundamental physics. One of the most effective ways to detect cosmic strings is through their lensing signatures which appear to be significantly different from those introduced by standard lenses (id est, compact clumps of matter). In 2003, the discovery of the peculiar object CSL-1 (Sazhin et al.2003) raised the interest of the physics community since its morphology and spectral features strongly argued in favour of it being the first case of gravitational lensing by a cosmic string. In this paper we provide a detailed description of the expected observational effects of a cosmic string and show, by means of simulations, the lensing signatures produced on background galaxies. While high angular resolution images obtained with HST, revealed that CSL-1 is a pair of interacting ellipticals at redshift 0.46, it represents a useful lesson to plan future surveys.

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An introduction to Gravitational Lensing in TeVeS gravity

Authors: HongSheng Zhao
Comments: 7p, Lecture notes for Sicily Gravitational Lensing School, Oct 29-Nov 3. Comments Welcome
Bekenstein's (2004) TeVeS theory has added an interesting twist to the search for dark matter and dark energy, modifying the landscape of gravity-related astronomy day by day. Built bottom-up rather than top-down as most gravity theories, TeVeS-like theories are healthily rooted on empirical facts, hence immediately passing sanity checks on galaxy rotation curves, solar system constraints, even bullet cluster of galaxies and cosmology with the help of 2eV neutrinos. Nonetheless, empirical checks are far from perfect and complete, and groups of different expertises are rapidly increasing the number of falsifiable properties of the theory. The theory has also been made much simpler and more general thanks to the work of Zlosnik, Ferreira, Starkman (gr-qc/0606039, astro-ph/0607411). Here I attempt a tutorial of how to compute lensing convergence, time delays etc in TeVeS-like theories for non-spherical lenses. I gave examples to illustrate a few common caveats of Dark-Matter-guided intuitions.

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High-resolution imaging of the cosmic mass distribution from gravitational lensing of pregalactic HI (suggested by Josh)

Authors: R. Benton Metcalf, S.D.M. White
Comments: 19 pages, 11 figures, submitted to MNRAS
Low-frequency radio observations of neutral hydrogen during and before the epoch of cosmic reionisation will provide ~ 1000 quasi-independent source planes, each of precisely known redshift, which can be used to reconstruct the projected mass distribution of foreground material. Structure in these source planes is linear and gaussian at high redshift (30 < z < 300) but is nonlinear and nongaussian during reionisation. At both epochs, significant power is expected down to sub-arcsecond scales. We demonstrate that this structure can, in principle, be used to make mass images with a formal signal-to-noise per pixel exceeding 10, even for pixels as small as an arc-second. With an ideal telescope, both resolution and signal-to-noise can exceed those of even the most optimistic idealised mass maps from galaxy lensing by more than an order of magnitude. Individual dark halos similar in mass to that of the Milky Way could be imaged with high signal-to-noise out to z ~ 10. Even with a much less ambitious telescope, a wide-area survey of 21 cm lensing would provide very sensitive constraints on cosmological parameters, in particular on dark energy. These are up to 20 times tighter than the constraints obtainable from comparably sized, very deep surveys of galaxy lensing, although the best constraints come from combining data of the two types. Any radio telescope capable of mapping the 21cm brightness temperature with good frequency resolution (~< 0.5 MHz) over a band of width ~> 10 MHz should be able to make mass maps of high quality.

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Cosmological Parameters from the SDSS DR5 Velocity Dispersion Function of Early-Type Galaxies through Radio-Selected Lens Statistics (suggested by Josh)

Authors: Kyu-Hyun Chae
Comments: ApJL, submitted
We improve strong lensing constraints on cosmological parameters in light of the new measurement of the velocity dispersion function of early-type galaxies based on the SDSS DR5 data and recent semi-analytical modeling of galaxy formation. Using both the number statistics of the CLASS statistical sample and the image separation distribution of the CLASS and the PANELS radio-selected lenses, we find the cosmological matter density $\Om = 0.25^{+0.13}_{-0.08}$ (68% CL) assuming evolutions of galaxies predicted by a semi-analytical model of galaxy formation and $\Om = 0.27^{+0.11}_{-0.09}$ assuming no evolution of galaxies for a flat cosmology with an Einstein cosmological constant. For a flat cosmology with a generalized dark energy, we find the non-evolving dark energy equation of state $w_x < -1.3$ ($w_x < -0.5$) at the 68% CL (95% CL).

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