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arXiv:0710.3783 [ps, pdf, other] :
Title: Search for axion-like particles using a variable baseline photon regeneration technique
Authors: A.S. Chou, W. Wester, A. Baumbaugh, H.R. Gustafson, Y. Irizarry-Valle, P.O. Mazur, J.H. Steffen, R. Tomlin, X. Yang, J. Yoo
Comments: 4 pages, 3 figures
We report the first results of the GammeV experiment, a search for milli-eV mass particles with axion-like couplings to two photons. The search is performed using a ``light shining through a wall'' technique where incident photons oscillate into new weakly interacting particles that are able to pass through the wall and subsequently regenerate back into detectable photons. The oscillation baseline of the apparatus is continuously variable, thus allowing probes of different values of particle mass. We find no excess of events above background and are able to constrain the two-photon couplings of possible new scalar (pseudoscalar) particles to be less than $3.2\times 10^{-7} {GeV}^{-1}$ ($3.2\times 10^{-7} {GeV}^{-1}$) in the limit of massless particles. |
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arXiv:0710.3616 [ps, pdf, other] :
Title: Coincidences of Dark Energy with Dark Matter -- Clues for a Simple Alternative?
Authors: HongSheng Zhao
Comments: to appear in ApJ Letters, 4 pages
A rare coincidence of scales in standard particle physics is needed to explain why $\Lambda$ or the negative pressure of cosmological dark energy (DE) coincides with the positive pressure $P_0$ of random motion of dark matter (DM) in bright galaxies. Recently Zlosnik et al. (2007) propose to modify the Einsteinian curvature by adding a non-linear pressure from a medium flowing with a four-velocity vector field $U^\mu$. We propose to check whether a smooth extension of GR with a simple kinetic Lagrangian of $U^\mu$ can be constructed, and whether the pressure can bend space-time sufficiently to replace the roles of a $w=-1$ DE, $w=0$ Cold DM and heavy neutrinos in explaining anomalous accelerations at all scales. As a specific proof of concept we find a Vector-for-$\Lambda$ model (${\mathbf V\Lambda}$-model) and its variants. With essentially {\it no free parameters}, these appear broadly consistent with the solar system, gravitational potentials in dwarf spiral galaxies and the bullet cluster of galaxies, early universe with inflation, structure formation and BBN, and late acceleration with a 1:3 ratio of DM:DE. |
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arXiv:0710.3755 [ps, pdf, other] :
Title: The Standard Model Higgs boson as the inflaton
Authors: F. Bezrukov, M. Shaposhnikov
Comments: 5 pages, 2 figures
We argue that the Higgs boson of the Standard Model can lead to inflation and produce cosmological perturbations in accordance with cosmological observations. An essential requirement is the non-minimal coupling of the Higgs scalar field to gravity; no new particle besides already present in the electroweak theory is required. |
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arXiv:0710.3169 [ps, pdf, other] :
Title: New Gamma-Ray Contributions to Supersymmetric Dark Matter Annihilation
Authors: Torsten Bringmann, Lars Bergstrom, Joakim Edsjo
Comments: 9 pages revtex4; 5 figures
We compute the electromagnetic radiative corrections to all leading annihilation processes which may occur in the Galactic dark matter halo, for dark matter in the framework of supersymmetric extensions of the Standard Model (MSSM and mSUGRA), and present the results of scans over the parameter space that is consistent with present observational bounds on the dark matter density of the Universe. Although these processes have previously been considered in some special cases by various authors, our new general analysis shows novel interesting results with large corrections that may be of importance, e.g., for searches at the soon to be launched GLAST gamma-ray space telescope. In particular, it is pointed out that regions of parameter space where there is a near degeneracy between the dark matter neutralino and the tau sleptons, radiative corrections may boost the gamma-ray yield by up to three or four orders of magnitude, even for neutralino masses considerably below the TeV scale, and will enhance the very characteristic signature of dark matter annihilations, namely a sharp step at the mass of the dark matter particle. Since this is a particularly interesting region for more constrained mSUGRA models of supersymmetry, we use an extensive scan over this parameter space to verify the significance of our findings. We also re-visit the direct annihilation of neutralinos into photons and point out that, for a considerable part of the parameter space, internal bremsstrahlung is more important for indirect dark matter searches than line signals. |
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arXiv:0710.3586 [ps, pdf, other] :
Title: Baryon oscillations in galaxy and matter power-spectrum covariance matrices
Author: Mark C. Neyrinck, Istvan Szapudi
Comments: 12 pages, 11 figures, submitted to MNRAS
We investigate large-amplitude baryon acoustic oscillations (BAO's) in off-diagonal entries of cosmological power-spectrum covariance matrices. These covariance-matrix BAO's describe the increased attenuation of power-spectrum BAO's caused by upward fluctuations in large-scale power. We derive an analytic approximation to covariance-matrix entries in the BAO regime, and check the analytical predictions using N-body simulations. These BAO's look much stronger than the BAO's in the power spectrum, but seem detectable only at about a one-sigma level in gigaparsec-scale galaxy surveys. In estimating cosmological parameters using matter or galaxy power spectra, including the covariance-matrix BAO's can have a several-percent effect on error-bar widths for some parameters directly related to the BAO's, such as the baryon fraction. Also, we find that including the numerous galaxies in small haloes in a survey can reduce error bars in these cosmological parameters more than the simple reduction in shot noise might suggest. |
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arXiv:0710.3896 [ps, pdf, other] :
Title: Verifying the Cosmological Utility of Type Ia Supernovae: Implications of a Dispersion in the Ultraviolet Spectra
Authors: R. Ellis, et al.
Comments: Accepted for publication in ApJ
We analyze the mean rest-frame ultraviolet (UV) spectrum of Type Ia Supernovae (SNe Ia) and its dispersion using high signal-to-noise Keck-I/LRIS-B spectroscopy for a sample of 36 events at intermediate redshift (z=0.5) discovered by the Canada-France-Hawaii Telescope Supernova Legacy Survey (SNLS). We introduce a new method for removing host galaxy contamination in our spectra, exploiting the comprehensive photometric coverage of the SNLS SNe and their host galaxies, thereby providing the first quantitative view of the UV spectral properties of a large sample of distant SNe Ia. Although the mean SN Ia spectrum has not evolved significantly over the past 40% of cosmic history, precise evolutionary constraints are limited by the absence of a comparable sample of high quality local spectra. Within the high-redshift sample, we discover significant UV spectral variations and exclude dust extinction as the primary cause by examining trends with the optical SN color. Although progenitor metallicity may drive some of these trends, the variations we see are much larger than predicted in recent models and do not follow expected patterns. An interesting new result is a variation seen in the wavelength of selected UV features with phase. We also demonstrate systematic differences in the SN Ia spectral features with SN light curve width in both the UV and the optical. We show that these intrinsic variations could represent a statistical limitation in the future use of high-redshift SNe Ia for precision cosmology. We conclude that further detailed studies are needed, both locally and at moderate redshift where the rest-frame UV can be studied precisely, in order that future missions can confidently be planned to fully exploit SNe Ia as cosmological probes [ABRIDGED]. |
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arXiv:0710.4162 [ps, pdf, other] :
Title: Impact of reionization on CMB polarization tests of slow-roll inflation
Authors: Michael J. Mortonson, Wayne Hu
Comments: 9 pages, 6 figures; submitted to Phys. Rev. D
Estimates of inflationary parameters from the CMB B-mode polarization spectrum on the largest scales depend on knowledge of the reionization history, especially at low tensor-to-scalar ratio. Assuming an incorrect reionization history in the analysis of such polarization data can strongly bias the inflationary parameters. One consequence is that the single-field slow-roll consistency relation between the tensor-to-scalar ratio and tensor tilt might be excluded with high significance even if this relation holds in reality. We explain the origin of the bias and present case studies with various tensor amplitudes and noise characteristics. A more model-independent approach can account for uncertainties about reionization, and we show that parametrizing the reionization history by a set of its principal components with respect to E-mode polarization removes the bias in inflationary parameter measurement with little degradation in precision. |
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arXiv:0710.4191 [ps, pdf, other] :
Title: Anisotropic Magnification Distortion of the 3D Galaxy Correlation: II. Fourier and Redshift Space
Authors: Lam Hui, Enrique Gaztanaga, Marilena LoVerde
Comments: 14 pages, paper I arXiv:0706.1071 treats the real space and addresses baryon acoustic oscillation measurements
In paper I of this series we discuss how magnification bias distorts the 3D correlation function by enhancing the observed correlation in the line-of-sight (LOS) orientation, especially on large scales. This lensing anisotropy is distinctive, making it possible to separately measure the galaxy-galaxy, galaxy-magnification and magnification-magnification correlations. Here we extend the discussion to the power spectrum, which has one key qualitative difference from the correlation function. In real space, pairs oriented close to the LOS direction are not protected against nonlinearity even if the pair separation is large; this is because nonlinear fluctuations can enter through gravitational lensing at a small transverse separation (i.e. impact parameter). The situation in Fourier space is different: by focusing on a small wavenumber k, as is usually done, linearity is guaranteed because both the LOS and transverse wavenumbers must be small. This is why magnification distortion of the galaxy correlation appears less severe in Fourier space. Nonetheless, the effect is non-negligible, especially for the transverse Fourier modes, and should be taken into account in interpreting precision measurements of the galaxy power spectrum, for instance those that focus on the baryon oscillations. The lensing induced anisotropy of the power spectrum has a shape that is distinct from the more well known anisotropies due to peculiar motions and the Alcock-Paczynski effect. The lensing anisotropy is highly localized in Fourier space while the latter two anisotropies are more spread out. The implied ability to isolate the magnification bias component means one can perform a gravitational lensing measurement without measuring galaxy shapes. |
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arXiv:0710.2433 [ps, pdf, other] :
Title: Astrophysical Condition on the attolensing as a possible probe for a modified gravity theory
Authors: Takahiro Sato, Bobby E. Gunara, Kazuhiro Yamamoto, Freddy P. Zen
Comments: Accepted for publication in IJMPA
We investigate the wave effect in the gravitational lensing by a black hole with very tiny mass less than 10^-19 solar mass, which is called attolensing, motivated by a recent report that the lensing signature might be a possible probe of a modified gravity theory in the braneworld scenario. We focus on the finite source size effect and the effect of the relative motion of the source to the lens, which are influential to the wave effect in the attolensing. Astrophysical condition that the lensed interference signature can be a probe of the modified gravity theory is demonstrated. The interference signature in the microlensing system is also discussed. |
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arXiv:0707.1296
arXiv:0707.1296
Title: No light shining through a wall : new results from a photoregeneration experiment
Authors: Cecile Robilliard, Remy Battesti, Mathilde Fouche, Julien Mauchain, Anne-Marie Sautivet, Francois Amiranoff, Carlo Rizzo
Abstract: Recently, axion-like particle search has received renewed interest. In particular, several groups have started ``light shining through a wall'' experiments based on magnetic field and laser both continuous, which is very demanding in terms of detector background. We present here the 2$\sigma$ limits obtained so far with our novel set-up consisting of a pulsed magnetic field and a pulsed laser. In particular, we have found that the axion-like particle two photons inverse coupling constant $M$ is $> 8\times 10^5$ GeV provided that the particle mass $m_\mathrm{a} \sim$ 1 meV. Our results definitively invalidate the axion interpretation of the original PVLAS optical measurements with a confidence level greater than 99.9%.
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