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arXiv:0712.1643 [ps, pdf, other] :
Title: Passive Evolution of Galaxy Clustering
Authors: Hee-Jong Seo, Daniel J. Eisenstein, Idit Zehavi
Comments: Accepted for publication in ApJ. 22 emulated apj pages with 15 figures and 4 table
We present a numerical study of the evolution of galaxy clustering when galaxies flow passively from high redshift, respecting the continuity equation throughout. While passive flow is a special case of galaxy evolution, it allows a well-defined study of galaxy ancestry and serves as an interesting limit to be compared to non-passive cases. We use dissipationless N-body simulations, assign galaxies to massive halos at z=1 and z=2 using various HOD models, and trace these galaxy particles to lower redshift while conserving their number. We find that passive flow results in an asymptotic convergence at low redshift in the HOD and in galaxy clustering on scales above ~3Mpc/h for a wide range of initial HODs. As galaxies become less biased with respect to mass asymptotically with time, the HOD parameters evolve such that M1/Mm decreases while alpha converges toward unity, where Mm is the characteristic halo mass to host a central galaxy, M1 is the halo mass to host one satellite galaxy, and alpha is the power-law index in the halo-mass dependence of the average number of satellites per halo. The satellite populations converge toward the Poisson distribution at low redshift. The convergence is robust for different number densities and is enhanced when galaxies evolve from higher redshift. We compare our results with the observed LRG sample from Sloan Digital Sky Survey that has the same number density. We claim that if LRGs have experienced a strict passive flow, their should be close to a power law with an index of unity in halo mass. Discrepancies could be due to dry galaxy merging or new members arising between the initial and the final redshifts. The spatial distribution of passively flowing galaxies within halos appears on average more concentrated than the halo mass profile at low redshift. (abridged) |
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arXiv:0711.4518 [ps, pdf, other] :
Title: Energy Dependence of Air Fluorescence Yield measured by AIRFLY
Authors: M. Ave et al. (AIRFLY Collaboration)
Comments: presented at the 5th Fluorescence Workshop, El Escorial - Madrid, Spain, 16 - 20 September 2007, to appear in Nuclear Instruments and Methods A
In the fluorescence detection of ultra high energy (> 10**18 eV) cosmic rays, the number of emitted fluorescence photons is assumed to be proportional to the energy deposited in air by shower particles. We have performed measurements of the fluorescence yield in atmospheric gases excited by electrons over energies ranging from keV to hundreds of MeV in several accelerators. We found that within the measured energy ranges the proportionality holds at the level of few %. |
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arXiv:0712.1148 [ps, pdf, other] :
Title: Detection of primordial non-Gaussianity (fNL) in the WMAP 3-year data at above 99.5% confidence
Authors: Amit P. S. Yadav, Benjamin D. Wandelt
Comments: 4 pages, 2 figures, 2 tables, submitted to PRL, references added
We present evidence for the detection of primordial non-Gaussianity of the local type (fNL), using the temperature information of the Cosmic Microwave Background (CMB) from the WMAP 3-year data. We employ the bispectrum estimator of non-Gaussianity described in Yadav et al. 2007b which allows us to analyze the entirety of the WMAP data without an arbitrary cut-off in angular scale. Using the combined information from WMAP's two main science channels up to l_{max}=750 and the conservative Kp0 foreground mask we find 26.9 < fNL < 146.7 at 95% C.L., with a central value of fNL=86.8. This corresponds to a rejection of fNL=0 at more than 99.5% significance. We find that this detection is robust to variations in l_{max}, frequency and masks. We conclude that the WMAP 3-year data disfavors single field slow-roll inflation. |
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arXiv:0711.3854 [ps, pdf, other] :
Title: A Simultaneous Solution to the 6Li and 7Li Big Bang Nucleosynthesis Problems from a Long-Lived Negatively-Charged Leptonic Particle
Authors: Motohiko Kusakabe, Toshitaka Kajino, Richard N. Boyd, Takashi Yoshida, Grant J. Mathews
Comments: 6 pages, 2 figures, to be published in Physical Review D
The 6Li abundance observed in metal poor halo stars exhibits a plateau similar to that for 7Li suggesting a primordial origin. However, the observed abundance of 6Li is a factor of 10^3 larger and that of 7Li is a factor of 3 lower than the abundances predicted in the standard big bang when the baryon-to-photon ratio is fixed by WMAP. Here we show that both of these abundance anomalies can be explained by the existence of a long-lived massive, negatively-charged leptonic particle during nucleosynthesis. Such particles would capture onto the synthesized nuclei thereby reducing the reaction Coulomb barriers and opening new transfer reaction possibilities, and catalyzing a second round of big bang nucleosynthesis. This novel solution to both of the Li problems can be achieved with or without the additional effects of stellar destruction. |
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arXiv:0712.1250 [ps, pdf, other] :
Title: Gravitational Wave Detection with Atom Interferometry
Authors: Savas Dimopoulos, Peter W. Graham, Jason M. Hogan, Mark A. Kasevich, Surjeet Rajendran
Comments: 5 pages, 5 figures
We propose two distinct atom interferometer gravitational wave detectors, one terrestrial and another satellite-based, utilizing the core technology of the Stanford 10 m atom interferometer presently under construction. The terrestrial experiment can operate with strain sensitivity ~10^{-19}/sqrt{Hz} in the 1 Hz - 10 Hz band, inaccessible to LIGO, and can detect gravitational waves from solar mass binaries out to megaparsec distances. The satellite experiment probes the same frequency spectrum as LISA with better strain sensitivity ~10^{-20}/sqrt{Hz}. Each configuration compares two widely separated atom interferometers run using common lasers. The effect of the gravitational waves on the propagating laser field produces the main effect in this configuration and enables a large enhancement in the gravitational wave signal while significantly suppressing many backgrounds. The use of ballistic atoms (instead of mirrors) as inertial test masses improves systematics coming from vibrations and acceleration noise, and reduces spacecraft control requirements. |
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arXiv:0712.0618 [ps, pdf, other] :
Title: Precision of Hubble constant derived using black hole binary absolute distances and statistical redshift information
Authors: Chelsea L. MacLeod, Craig J. Hogan
Comments: 9 pages, 4 figures, submitted to Phys. Rev. D
Measured gravitational waveforms from black hole binary inspiral events directly determine absolute luminosity distances. To use these data for cosmology, it is necessary to independently obtain redshifts for the events, which may be difficult for those without electromagnetic counterparts. Here it is demonstrated that certainly in principle, and possibly in practice, clustering of galaxies allows extraction of the redshift information from a sample statistically for the purpose of estimating mean cosmological parameters, without identification of host galaxies for individual events. We extract mock galaxy samples from the 6th Data Release of the Sloan Digital Sky Survey resembling those that would be associated with inspiral events of stellar mass black holes falling into massive black holes at redshift z ~ 0.1 to 0.5. A simple statistical procedure is described to estimate a likelihood function for the Hubble constant H_0: each galaxy in a LISA error volume contributes linearly to the log likelihood for the source redshift, and the log likelihood for each source contributes linearly to that of H_0. This procedure is shown to provide an accurate and unbiased estimator of H_0. It is estimated that a precision better than one percent in H_0 may be possible if the rate of such events is sufficiently high, on the order of 20 to z = 0.5. |
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arXiv:0712.1147 [ps, pdf, other] :
Title: Upper limit on the cosmic-ray photon flux above 10^19 eV using the surface detector of the Pierre Auger Observatory
Authors: Pierre Auger Collaboration
Comments: 28 pages, 9 figures
A method is developed to search for air showers initiated by photons using data recorded by the surface detector of the Auger Observatory. The approach is based on observables sensitive to the longitudinal shower development, the signal risetime and the curvature of the shower front. Applying this method to the data, upper limits on the flux of photons of 3.8*10^-3, 2.5*10^-3, and 2.2*10^-3 km^-2 sr^-1 yr^-1 above 10^19 eV, 2*10^19 eV, and 4*10^19 eV are derived, with corresponding limits on the fraction of photons being 2.0%, 5.1%, and 31% (all limits at 95% c.l.). These photon limits disfavor certain exotic models of sources of cosmic rays. The results also show that the approach adopted by the Auger Observatory to calibrate the shower energy is not strongly biased by a contamination from photons. |
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arXiv:0712.1036 [ps, pdf, other] :
Title: The lowest-mass stellar black holes: catastrophic death of neutron stars in gamma-ray bursts
Authors: K. Belczynski, R. O'Shaughnessy, V. Kalogera, F. Rasio, R. Taam, T. Bulik
Comments: 4 pages, submitted to Science
Mergers of double neutron stars are considered the most likely progenitors for short gamma-ray bursts. Indeed such a merger can produce a black hole with a transient accreting torus of nuclear matter and the conversion of the torus mass-energy to radiation can power a gamma-ray burst. Using available binary pulsar observations supported by our extensive evolutionary calculations of double neutron star formation, we demonstrate that the fraction of mergers that can form a black hole -- torus system depends very sensitively on the (largely unknown) maximum neutron star mass. We show that the available observations and models put a very stringent constraint on this maximum mass under the assumption that a majority of short gamma-ray bursts originate in double neutron star mergers. Specifically, we find that the maximum neutron star mass must be within 2--2.5 Msun. Moreover, a single unambiguous measurement of a neutron star mass above 2.5 Msun would exclude double neutron star mergers as short gamma-ray burst progenitors. |
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