9,116 research outputs found

### Constraints from Type IA Supernovae on {\lambda}-CDM Model in Randers-Finsler Space

Gravitational field equations in Randers-Finsler space of approximate Berwald
type are investigated. A modified Friedmann equation and a new luminosity
distance-redshift relation is proposed. A best-fit to the Type Ia supernovae
(SNe) observations yields that the $\Omega_{\Lambda}$ in the $\Lambda$-CDM
model is suppressed to almost zero. This fact indicates that the astronomical
observations on the Type Ia SNe can be described well without invoking any form
of dark energy. The best-fit age of the universe is given. It is in agreement
with the age of our galaxy.Comment: 14 pages, 3 figure

### 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

### Cosmological model with local symmetry of very special relativity and constraints on it from supernovae

Based on Cohen \& Glashow's very special relativity [A. G. Cohen and S. L.
Glashow, Phys. Rev. Lett. {\bf 97} (2006) 021601], we propose an anisotropic
modification to the Friedmann-Robertson-Walker (FRW) line element. An
arbitrarily oriented 1-form is introduced and the FRW spacetime becomes of the
Randers-Finsler type. The 1-form picks out a privileged axis in the universe.
Thus, the cosmological redshift as well as the Hubble diagram of the type Ia
supernovae (SNe Ia) becomes anisotropic. By directly analyzing the Union2
compilation, we obtain the privileged axis pointing to
$(l,b)=({304^\circ}\pm{43^\circ},{-27^\circ}\pm{13^\circ})$
($68\%~\rm{C.L.}$). This privileged axis is close to those obtained by
comparing the best-fit Hubble diagrams in pairs of hemispheres. It should be
noticed that the result is consistent with isotropy at the $1\sigma$ level
since the anisotropic magnitude is $D=0.03\pm 0.03$.Comment: 13 pages, 2 figures. Published at EPJC(2013

### Prey capture and meat-eating by the wild colobus monkey _Rhinopithecus bieti_ in Yunnan, China

If it is true that extant primates evolved from an insectivorous ancestor, then primate entomophagy would be a primitive trait. Many taxa, however, have undergone a dietary shift from entomophagy to phytophagy, evolving a specialised gut and dentition and becoming exclusive herbivores. The exclusively herbivorous taxa are the Malagasy families Indriidae and Lepilemuridae, and the Old World Monkey subfamily Colobinae, and among these meat-eating has not been observed except as an anomaly, with the sole exception of the Hanuman langur (_Semnopithecus entellus_), which feeds on insects seasonally, and a single observation of a nestling bird predated by wild Sichuan snub-nosed monkeys (_Rhinopithecus roxellana_). Here, we describe the regular capture of warm-blooded animals and the eating of meat by a colobine, the critically endangered Yunnan snub-nosed monkey (_Rhinopithecus bieti_). This monkey engages in scavenge hunting as a male-biased activity that may, in fact, be related to group structure and spatial spread. In this context, meat-eating can be regarded as an energy/nutrient maximization feeding strategy rather than as a consequence of any special characteristic of meat itself. The finding of meat-eating in forest-dwelling primates might provide new insights into the evolution of dietary habits in early humans

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