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arXiv:0804.0810 [ps, pdf, other] :
Title: Cosmic Strings as the Source of Small-Scale Microwave Background Anisotropy
Authors: Levon Pogosian, S.-H. Henry Tye, Ira Wasserman, Mark Wyman
Comments: 5 pages, 2 figures
Cosmic string networks generate cosmological perturbations actively throughout the history of the universe. Thus, the string sourced anisotropy of the cosmic microwave background is not affected by Silk damping as much as the anisotropy seeded by inflation. The spectrum of perturbations generated by strings does not match the observed CMB spectrum on large angular scales (l<1000) and is bounded to contribute no more than 10% of the total power on those scales. However, when this bound is marginally saturated, the anisotropy created by cosmic strings on small angular scales (l>2000) will dominate over that created by the primary inflationary perturbations. This range of angular scales in the CMB is presently being measured by a number of experiments; their results will test this prediction of cosmic string networks soon. |
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arXiv:0712.0778 [ps, pdf, other] :
Title: A Nearly Scale Invariant Spectrum of Gravitational Radiation from Global Phase Transitions
Authors: Katherine Jones-Smith, Lawrence M. Krauss, Harsh Mathur
Comments: 4 pages, submitted to PRL
Using a large N sigma model approximation we explicitly calculate the predicted power spectrum of gravitational waves arising from a global phase transition in the early universe and we confirm that it is in fact scale invariant, imply an observation of such a spectrum may not be a unique feature of inflation. Moreover, the predicted amplitude can be over 3 orders of magnitude larger than the initial prediction based on dimensional analysis, implying that even a transition that occurs after inflation may be measurable in Cosmic Microwave Background polarization studies. |
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arXiv:0804.1487 [ps, pdf, other] :
Title: The SDSS Discovery of a Strongly Lensed Post-Starburst Galaxy at z=0.766
Authors: Min-Su Shin et al.
Comments: Accepted for publication in AJ
We present the first result of a survey for strong galaxy-galaxy lenses in Sloan Digital Sky Survey (SDSS) images. SDSS J082728.70+223256.4 was selected as a lensing candidate using selection criteria based on the color and positions of objects in the SDSS photometric catalog. Follow-up imaging and spectroscopy showed this object to be a lensing system. The lensing galaxy is an elliptical at z = 0.349 in a galaxy cluster. The lensed galaxy has the spectrum of a post-starburst galaxy at z = 0.766. The lensing galaxy has an estimated mass of $\sim 1.2 \times 10^{12} M_{\odot}$ and the corresponding mass to light ratio in the B-band is $\sim 26 M_{\odot}/L_{\odot}$ inside 1.1 effective radii of the lensing galaxy. Our study shows how catalogs drawn from multi-band surveys can be used to find strong galaxy-galaxy lenses having multiple lens images. Our strong lensing candidate selection based on photometry-only catalogs will be useful in future multi-band imaging surveys such as SNAP and LSST. |
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arXiv:0804.0554 [ps, pdf, other] :
Title: Searching for Neutrinos from WIMP Annihilations in the Galactic Stellar Disk
Authors: Zacharia Myers, Adi Nusser
Comments: 8 pages, 3 figures, Submitted to MNRAS
Weakly interacting massive particles (WIMPs) are a viable candidate for the relic abundance of dark matter (DM) produced in the early universe. So far WIMPs have eluded direct detection through interactions with baryonic matter. Neutrino emission from accumulated WIMP annihilations in the solar core has been proposed as a signature of DM, but has not yet been detected. These null results may be due to small scale DM density fluctuations in the halo with the density of our local region being lower than the average (around 0.3 GeV/cm^3 ). However, the accumulated neutrino signal from WIMP annihilations in the Galactic stellar disk would be insensitive to local density variations. Inside the disk, dark matter can be captured by stars causing an enhanced annihilation rate and therefore a potentially higher neutrino flux than what would be observed from elsewhere in the halo. We estimate a neutrino flux from the WIMP annihilations in the stellar disk to be enhanced by more than an order of magnitude compared to the neutrino fluxes from the halo. We offer a conservative estimate for this enhanced flux, based on the WIMP-nucleon cross-sections obtained from direct-detection experiments by assuming a density of around 0.3 GeV/cm^3 for the local DM. We also compare the detectability of these fluxes with a signal of diffuse high energy neutrinos produced in the Milky Way by the interaction of cosmic rays (CRs) with the interstellar medium (ISM). These comparative signals should be observable by large neutrino detectors. |
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arXiv:0804.1088 [ps, pdf, other] :
Title: On the interpretation of the cosmic-ray anisotropy at ultra-high energies
Authors: D.S. Gorbunov, P.G. Tinyakov, I.I. Tkachev, S.V. Troitsky
Comments: 12 pages, 3 figures
A natural interpretation of the correlation between nearby Active Galactic Nuclei (AGN) and the highest-energy cosmic rays observed recently by the Pierre Auger Collaboration is that the sources of the cosmic rays are either AGN or other objects with a similar spatial distribution (the ``AGN hypothesis''). We question this interpretation. We calculate the expected distribution of the arrival directions of cosmic rays under the AGN hypothesis and argue that it is not supported by the data, one of manifestations of the discrepancy being the deficit of events from the direction of the Virgo supercluster. We briefly discuss possible alternative explanations including the origin of a significant part of the observed events from Cen A. |
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arXiv:0804.0799 [ps, pdf, other] :
Title: Constraining Anisotropic Baryon Oscillations
Authors: Nikhil Padmanabhan, Martin White
Comments: 4 pages, 2 figs
We present an analysis of anisotropic baryon acoustic oscillations and elucidate how a mis-estimation of the cosmology, which leads to incorrect values of the angular diameter distance, d_A, and Hubble parameter, H, manifest themselves in changes to the monopole and quadrupole power spectrum of biased tracers of the density field. Previous work has focused on the monopole power spectrum, and shown that the isotropic "dilation" combination d_A^2/H is robustly constrained by an overall shift in the scale of the baryon feature. We extend this by demonstrating that the quadrupole power spectrum is sensitive to an anisotropic "warping" mode d_A H, allowing one to break the degeneracy between d_A and H. We describe a method for measuring this warping, explicitly marginalizing over the form of redshift space distortions. We verify this method on N-body simulations and estimate that d_A H can be measured with a fractional accuracy of ~ 3/sqrt(V) % where the survey volume is estimated in (Gpc/h)^3. |
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arXiv:0802.4403 [ps, pdf, other] :
Title: The puzzling MILAGRO hot spots
Authors: Luke Drury, Felix Aharonian
Comments:-
We discuss the reported detection by the MILAGRO experiment of localised hot spots in the cosmic ray arrival distribution and the difficulty of interpreting these observations. A model based on secondary neutron production in the heliotail is shown to fail. An alternative model based on loss-cone leakage through a magnetic trap from a local source region is proposed. |
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