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ont style="color:red;background-color:#FFFF9F;">Constraintsont> on anisotropic cosmic expansion from supernovae


We test the isotropy of the expansion of the Universe by estimating the hemispherical anisotropy of supernova type Ia (SN Ia) Hubble diagrams at low redshifts (z < 0.2) We compare the best fit Hubble diagrams in pairs of hemispheres and search for the maximal asymmetric orientation. For an isotropic Universe, we expect only a small asymmetry due to noise and the presence of nearby structures. This test does not depend on the assumed content of the Universe, the assumed model of gravity, or the spatial curvature of the Universe. The expectation for possible fluctuations due to large scale structure is evaluated for the cold dark matter (CDM) model and is compared to the supernova data from the Constitution

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Probing the anisotropic expansion history of the universe with cosmic microwave background


We propose a simple technique to detect any anisotropic expansion stage in the history of theuniverse starting from the inflationary stage to the surface of last scattering from the CMBR data.We use the property that any anisotropic expansion in the universe would deform the shapes ofthe primordial density perturbations and this deformation can be detected in a shape analysis ofsuperhorizon fluctuations in CMBR. Using this analysis we obtain the constraint on any previousanisotropic expansion of the universe to be less than about 35 %.

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Probing the anisotropic expansion from supernovae and GRBs in a model-independent way


 ABSTRACT In this paper, we study the anisotropic expansion of the universe using type Iasupernovae Union 2.1 sample and 116 long gamma-ray bursts. The luminositydistance is expanded with model-independent cosmographic parameters as afunction of z/(1 + z) directly. Thus the results are independent of cosmologymodel. We find a dipolar anisotropy in the direction (l = 309.2◦ ± 15.8◦,b = −8.6◦ ± 10.5◦) in galactic coordinates with a significant evidence 97.29%(more than 2 σ). The magnitude is (1.37 ± 0.57) × 10−3 for the dipole, and(2.6 ± 2.1) × 10−4 for the monopole, respectively. This dipolar anisotropy ismore si

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Measuring cosmic bulk flows with Type Ia Supernovae from the Nearby Supernova Factory


  ABSTRACT Context. Our Local Group of galaxies appears to be moving relative to the Cosmic Microwave Background with the source of thepeculiar motion still uncertain. While in the past this has been studied mostly using galaxies as distance indicators, the weight oftype Ia supernovae (SNe Ia) has increased recently with the continuously improving statistics of available low-redshift supernovae.Aims. We measured the bulk flow in the nearby universe (0:015 < z < 0:1) using 117 SNe Ia observed by the Nearby SupernovaFactory, as well as the Union2 compilation of SN Ia data already in the literature.Methods. The bulk flow velocity was determined from SN data binned in

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Supernovae as seen by off-center observers in a local void


Abstract. Inhomogeneous universe models have been proposed as an alternativeexplanation for the apparent acceleration of the cosmic expansion that does not requiredark energy. In the simplest class of inhomogeneous models, we live within a large,spherically symmetric void. Several studies have shown that such a model can bemade consistent with many observations, in particular the redshift–luminosity distancerelation for type Ia supernovae, provided that the void is of Gpc size and that we liveclose to the center. Such a scenario challenges the Copernican principle that we donot occupy a special place in the universe. We use the first-year Sloan Digital SkySurvey-II supernova search data set as well as the

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Cosmological ont style="color:red;background-color:#FFFF9F;">Constraintsont> from Type Ia Supernovae Peculiar Velocity Measurements


The first compelling evidence that the Universe is undergoinga period of accelerated expansion was providedby observations of Type Ia supernovae (SNe) [1, 2].The data from many current [3, 4, 5] and near future[6, 7, 8, 9] surveys should eventually constrain the effectivedark energy equation of state to better than 10%.Density inhomogeneities cause the SNe to deviate fromthe Hubble flow, as gravitational instability leads to matterflowing out of under-densities and into over-densities.These “peculiar velocities” (PVs) lead to an increasedscatter in the Hubble diagram, of which several studieshave been made [10, 11, 12, 13, 14, 15, 16, 17, 18, 19, 20,21, 22]. When combining low a

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Using measurements of the cosmic bulk f(R) Gravity


As an alternative explanation for the cosmic acceleration, f(R) theories of gravitycan predict an almost identical expansion history to standard CDM, yet make verydierent predictions for the growth of cosmological structures. Measurements of thecosmic bulk ow provides a method for determining the strength of gravity over thehistory of structure formation. We use the modied gravity N-body code ECOSMOGto simulate dark matter particles and make predictions for the bulk ow magnitudein both CDM and f(R) gravity. With the peculiar velocities output by ECOSMOGwe determine the bulk ow at depths ranging from 20h????1Mpc to 50h????1Mpc, follow-ing the redshift and sky distribution of the 2MASS Tully-Fisher survey (2MTF). Ateach

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On the Evidence for Cosmic Variation of the Fine Structure Constant


We review the evidence behind recent claims of spatial variation in the ne structureconstant deriving from observations of ionic absorption lines in the light from distantquasars. To this end we expand upon previous non-Bayesian analyses limited by the as-sumptions of an unbiased and strictly Normal distribution for the \unexplained errors"of the benchmark quasar dataset. Through the technique of reverse logistic regressionwe estimate and compare marginal likelihoods for three competing hypotheses|(i)the null hypothesis (no cosmic variation), (ii) the monopole hypothesis (a constantEarth-to-quasar oset), and (iii) the monopole+dipole hypothesis (a cosmic variationmanifest to the Earth-bound observer as

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Cosmic Bulk Flow and the Local Motion from Cosmicflows-2


Full sky surveys of peculiar velocity are arguably the best way to map the large scalestructure (LSS) out to distances of a few100 h????1Mpc. Using the largest and most accurateever catalog of galaxy peculiar velocities Cosmicflows-2, the LSS has been reconstructed bymeans of the Wiener filter (WF) and constrained realizations (CRs) assuming as a Bayesianprior model the CDM model with the WMAP inferred cosmological parameters. The presentpaper focuses on studying the bulk flow of the local flow field, defined as the mean velocityof top-hat spheres with radii ranging out to R = 500 h????1Mpc. The estimated LSS, in general,and the bulk flow, in particular, are determined by the tension between the observational dat

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دانلود The Cosmic Microwave Background


توضیحات : The series of texts composing this book is based on the lectures presented during the II José Plínio Baptista School of Cosmology, held in Pedra Azul (Espírito Santo, Brazil) between 9 and 14 March 2014. This II JBPCosmo has been entirely devoted to the problem of understanding theoretical and observational aspects of Cosmic Background Radiation (CMB).The CMB is one of the most important phenomena in Physics and a fundamental probe of our Universe when it was only 400,000 years old. It is an extraordinary laboratory where we can learn from particle physics to cosmology; its discovery in 1965 has been a landmark event in the history of physics.The observations of the anisotropy of the cosmic micr

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