499 research outputs found

### Finslerian dipolar modulation of the CMB power spectra at scales $2<l<600$

A common explanation for the CMB power asymmetry is to introduce a dipolar
modulation at the stage of inflation, where the primordial power spectrum is
spatially varying. If the universe in the stage of inflation is Finslerian, and
if the Finsler spacetime is non-reversible under parity flip, $x\rightarrow-x$,
then a three dimensional spectrum which is the function of wave vector and
direction is valid. In this paper, a three dimensional primordial power
spectrum with preferred direction is derived in the framework of Finsler
spacetime. It is found that the amplitude of dipolar modulation is related to
the Finslerian parameter, which in turn is a function of wave vector. The
angular correlation coefficients are presented, and the numerical results for
the anisotropic correlation coefficients over the multipole range $2<l<600$ are
given.Comment: 13 pages, 1 figure, accepted by EPJ

### Testing the homogeneity of the Universe using gamma-ray bursts

In this paper, we study the homogeneity of the GRB distribution using a
subsample of the Greiner GRB catalogue, which contains 314 objects with
redshift $0<z<2.5$ (244 of them discovered by the Swift GRB Mission). We try to
reconcile the dilemma between the new observations and the current theory of
structure formation and growth. To test the results against the possible biases
in redshift determination and the incompleteness of the Greiner sample, we also
apply our analysis to the 244 GRBs discovered by Swift and the subsample
presented by the Swift Gamma-Ray Burst Host Galaxy Legacy Survey (SHOALS). The
real space two-point correlation function (2PCF) of GRBs, $\xi(r),$ is
calculated using a Landy-Szalay estimator. We perform a standard least-$\chi^2$
fit to the measured 2PCFs of GRBs. We use the best-fit 2PCF to deduce a
recently defined homogeneity scale. The homogeneity scale, $R_H$, is defined as
the comoving radius of the sphere inside which the number of GRBs $N(<r)$ is
proportional to $r^3$ within $1\%$, or equivalently above which the correlation
dimension of the sample $D_2$ is within $1\%$ of $D_2=3$. For the Swift
subsample of 244 GRBs, the correlation length and slope are $r_0= 387.51 \pm
132.75~h^{-1}$Mpc and $\gamma = 1.57\pm 0.65$ (at $1\sigma$ confidence level).
The corresponding scale for a homogeneous distribution of GRBs is $r\geq
7,700~h^{-1}$Mpc. The results help to alleviate the tension between the new
discovery of the excess clustering of GRBs and the cosmological principle of
large-scale homogeneity. It implies that very massive structures in the
relatively local Universe do not necessarily violate the cosmological principle
and could conceivably be present.Comment: 7 pages, 5 figures, accepted by Astronomy & Astrophysics. The data
used in this work (e.g. Tables 1 and 2) are publicly available online in
electronic form at the CDS via anonymous ftp to cdsarc.u-strasbg.fr
(130.79.128.5) or via http://cdsweb.u-strasbg.fr/cgi-bin/qcat?J/A+A

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