| FAQ: What is Munch? |
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arXiv:0709.3308 [ps, pdf, other] :
Title: Are There Enough Ionizing Photons to Reionize the Universe by z=6?
Author: Nickolay Y. Gnedin
Comments: submitted to ApJ. Comments and objections are welcome
An estimate for the number of ionizing photons per baryon as a function of redshift is computed based on the plausible extrapolation of the observed galaxy UV luminosity function and the latest results on the properties of the escape fraction of ionizing radiation. It is found that, if the escape fraction for low mass galaxies (Mtot< 10^{11} Msun) is assumed to be negligibly small, as indicated by numerical simulations, then there are not enough ionizing photons to reionize the universe by z=6 for the cosmology favored by the WMAP 3rd year results, while the WMAP 1st year cosmology is marginally consistent with the reionization requirement. The escape fraction as a function of galaxy mass would have to be constant to within a factor of two for the whole mass range of galaxies for reionization to be possible within the WMAP 3rd year cosmology. |
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arXiv:0709.3189 [ps, pdf, other] :
Title: The necessity of dark matter in MOND within galactic scales
Authors: Ignacio Ferreras, Mairi Sakellariadou, Muhammad Furqaan Yusaf
Comments: 5 pages, 2 figures, 1 table
To further test MOdified Newtonian Dynamics (MOND) on galactic scales -- originally proposed to explain the rotation curves of disk galaxies without dark matter -- we study a sample of six strong gravitational lensing early-type galaxies from the CASTLES database. To determine whether dark matter is present in these galaxies, we compare the total mass (from lensing) with the stellar mass content (from a comparison of photometry and stellar population synthesis). We find that strong gravitational lensing on galactic scales requires a significant amount of dark matter, even within MOND. On such scales a 2 eV neutrino cannot explain this excess matter -- in contrast with recent claims to explain the lensing data of the bullet cluster. This is a serious challenge to MOND unless the proper treatment of lensing is qualitatively different (possibly to be developed within a consistent theory such as TeVeS). |
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arXiv:0710.0364 [ps, pdf, other] :
Title: Modified Gravity: Cosmology without dark matter or a cosmological constant
Authors: J. W. Moffat, V. T. Toth
Comments: 10 pages, 3 figures
We explore the cosmological consequences of Modified Gravity (MOG), and find that it provides, using a minimal number of parameters, good fits to data, including CMB temperature anisotropy, galaxy mass power spectrum, and supernova luminosity-distance observations. The MOG cosmology is flat and predicts an age of the universe of ~34 billion years. |
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arXiv:0710.0373 [ps, pdf, other] :
Title: To Bin or Not To Bin: Decorrelating the Cosmic Equation of State
Authors: Roland de Putter, Eric V. Linder
Comments: 26 pages, 28 figures
The physics behind the acceleration of the cosmic expansion can be elucidated through comparison of the predictions of dark energy equations of state to observational data. In seeking to optimize this, we investigate the advantages and disadvantages of using principal component analysis, uncorrelated bandpowers, and the equation of state within redshift bins. We demonstrate that no one technique is a panacea, with tension between clear physical interpretation from localization and from decorrelated errors, as well as model dependence and form dependence. Specific lessons include the critical role of proper treatment of the high redshift expansion history and the lack of a unique, well defined signal-to-noise or figure of merit. |
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arXiv:0709.3672 [ps, pdf, other] :
Title: Baryon Acoustic Oscillation Intensity Mapping of Dark Energy
Authors: Tzu-Ching Chang, Ue-Li Pen, Jeffrey B. Peterson, Patrick McDonald
Comments: 4 pages, submitted to PRL
The expansion of the universe appears to be accelerating, and the mysterious anti-gravity agent of this acceleration has been called ``dark energy''. To measure the dynamics of dark energy, Baryon Acoustic Oscillations (BAO) can be used. Previous discussions of the BAO dark energy test have focused on direct measurements of redshifts of as many as 10^9 individual galaxies, by observing the 21cm line or by detecting optical emission. Here we show how the study of acoustic oscillation in the 21 cm brightness can be accomplished by economical three dimensional brightness mapping. If our estimates gain acceptance they may be the starting point for a new class of dark energy experiments dedicated to large angular scale mapping of the radio sky, shedding light on dark energy. |
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arXiv:0709.3985 [ps, pdf, other] :
Title: Measuring Supersymmetry
Authors: Remi Lafaye, Tilman Plehn, Michael Rauch, Dirk Zerwas
Comments: 43 pages, 55 figures, 13 tables
If new physics is found at the LHC (and the ILC) the reconstruction of the underlying theory should not be biased by assumptions about high-scale models. For the mapping of many measurements onto high-dimensional parameter spaces we introduce SFitter with its new weighted Markov chain technique. SFitter determines the best-fitting parameter point and produces a ranked list of the most likely parameter points. More generally, SFitter constructs a likelihood map, which can be reduced to lower-dimensional profile likelihoods or Bayesian probability maps. We show how it should be possible to analyze high-dimensional new-physics parameter spaces at the LHC. A combination of LHC and ILC measurements might well be able to completely cover highly complex TeV-scale parameter spaces. |
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arXiv:0709.4301 [ps, pdf, other] :
Title: A bright millisecond radio burst of extragalactic origin
Authors: D. R. Lorimer, M. Bailes, M. A. McLaughlin, D. J. Narkevic, F. Crawford
Comments: 18 pages, 4 figures. Accepted by Science. Published electronically via Science Express on September 27, 2007
Pulsar surveys offer one of the few opportunities to monitor even a small fraction (~0.00001) of the radio sky for impulsive burst-like events with millisecond durations. In analysis of archival survey data, we have discovered a 30-Jy dispersed burst of duration <5 ms located three degrees from the Small Magellanic Cloud. The burst properties argue against a physical association with our Galaxy or the Small Magellanic Cloud. Current models for the free electron content in the Universe imply a distance to the burst of <1 Gpc No further bursts are seen in 90-hr of additional observations, implying that it was a singular event such as a supernova or coalescence of relativistic objects. Hundreds of similar events could occur every day and act as insightful cosmological probes. |
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arXiv:0709.2871 [ps, pdf, other] :
Title: Photometric Redshift Requirements for Self-Calibration of Cluster Dark Energy Studies
Authors: Marcos Lima, Wayne Hu
Comments: 18 pages, 8 figures, submitted to PRD
The ability to constrain dark energy from the evolution of galaxy cluster counts is limited by the imperfect knowledge of cluster redshifts. Ongoing and upcoming surveys will mostly rely on redshifts estimated from broad-band photometry (photo-z's). For a Gaussian distribution for the cluster photo-z errors and a high cluster yield cosmology defined by the WMAP 1 year results, the photo-z bias and scatter needs to be known better than 0.003 and 0.03, respectively, in order not to degrade dark energy constrains by more than 10% for a survey with specifications similar to the South Pole Telescope. Smaller surveys and cosmologies with lower cluster yields produce weaker photo-z requirements, though relative to worse baseline constraints. Comparable photo-z requirements are necessary in order to employ self-calibration techniques when solving for dark energy and observable-mass parameters simultaneously. On the other hand, self-calibration in combination with external mass inferences helps reduce photo-z requirements and provides important consistency checks for future cluster surveys. In our fiducial model, training sets with spectroscopic redshifts for ~5%-15% of the detected clusters are required in order to keep degradations in the dark energy equation of state lower than 20%. |
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