2,186 research outputs found
From Hubble diagrams to scale factors
We present a lower bound on the radius of the universe today and a
monotonicity constraint on the Hubble diagram. Our theoretical input is
Einstein's kinematics and maximally symmetric universes. Present supernova data
yield m. A first attempt to quantify the monotonicity
constraint is described. We do not see any indication of non-monotonicity.Comment: 13 pages, 6 figure
Maximal symmetry at the speed of light
We propose a relativistic version of the cosmological principle and confront
it to the Hubble diagram of supernovae and other probes.Comment: 11 pages, 1 figur
Einstein-Cartan, Bianchi I and the Hubble Diagram
We try to solve the dark matter problem in the fit between theory and the
Hubble diagram of supernovae by allowing for torsion via Einstein-Cartan's
gravity and for anisotropy via the axial Bianchi I metric. Otherwise we are
conservative and admit only the cosmological constant and dust. The failure of
our model is quantified by the relative amount of dust in our best fit:
Omega_{m0}= 27 % +/- 5 % at 1 sigma level.Comment: 11 pages, 1 figur
Negative Energies and a Constantly Accelerating Flat Universe
It has been shown that in the context of General Relativity (GR) enriched
with a new set of discrete symmetry reversal conjugate metrics, negative energy
states can be rehabilitated while avoiding the well-known instability issues.
We review here some cosmological implications of the model and confront them
with the supernovae and CMB data. The predicted flat universe constantly
accelerated expansion phase is found to be in rather good agreement with the
most recent cosmological data
Search for exotic Higgs outside the MSSM
Recent preliminary results of searches for Higgs bosons outside the minimal supersymmetric standard model (MSSM) are summarised. These results are based on data from the four LEP experiments: ALEPH, DELPHI, L3 and OPAL, at a centre-of-mass energies up to 189 GeV. Some new results from the two Tevatron experiments: CDF and D0, are also presented. Finally, the potential mass reach for exotic Higgs at future accelerators are discussed
Torsion, an alternative to the cosmological constant?
We confront Einstein-Cartan's theory with the Hubble diagram and obtain a
negative answer to the question in the title. Contrary findings in the
literature seem to stem from an error in the field equations.Comment: 10 pages, 1 figure. Version 2 corrects a factor 3 in Cartan's
equations to become
Modelling the relative velocities of isolated pairs of galaxies
We study the comoving relative velocities, v12, of model isolated galaxy
pairs at z=0.5. For this purpose, we use the predictions from the GALFORM
semi-analytical model of galaxy formation and evolution based on a Lambda cold
dark matter cosmology consistent with the results from WMAP7. In real space, we
find that isolated pairs of galaxies are predicted to form an angle t with the
line-of-sight that is uniformily distributed as expected if the Universe is
homogeneous and isotropic. We also find that isolated pairs of galaxies
separated by a comoving distance between 1 and 3 Mpc/h are predicted to have
=0. For galaxies in this regime, the distribution of the angle t is
predicted to change minimally from real to redshift space, with a change
smaller than 5% in . However, the distances defining the comoving
regime strongly depends on the applied isolation criteria.Comment: 4 pages, 4 figures, SF2A 2013 Proceedin
Catastrophic Photo-z Errors and the Dark Energy Parameter Estimates with Cosmic Shear
We study the impact of catastrophic errors occurring in the photometric
redshifts of galaxies on cosmological parameter estimates with cosmic shear
tomography. We consider a fiducial survey with 9-filter set and perform photo-z
measurement simulations. It is found that a fraction of 1% galaxies at
z_{spec}~0.4 is misidentified to be at z_{phot}~3.5. We then employ both chi^2
fitting method and the extension of Fisher matrix formalism to evaluate the
bias on the equation of state parameters of dark energy, w_0 and w_a, induced
by those catastrophic outliers. By comparing the results from both methods, we
verify that the estimation of w_0 and w_a from the fiducial 5-bin tomographic
analyses can be significantly biased. To minimize the impact of this bias, two
strategies can be followed: (A) the cosmic shear analysis is restricted to
0.5<z<2.5 where catastrophic redshift errors are expected to be insignificant;
(B) a spectroscopic survey is conducted for galaxies with 3<z_{phot}<4. We find
that the number of spectroscopic redshifts needed scales as N_{spec} \propto
f_{cata}\times A where f_{cata}=1% is the fraction of catastrophic redshift
errors (assuming a 9-filter photometric survey) and A is the survey area. For
A=1000 {deg}^2, we find that N_{spec}>320 and 860 respectively in order to
reduce the joint bias in (w_0,w_a) to be smaller than 2\sigma and 1\sigma. This
spectroscopic survey (option B) will improve the Figure of Merit of option A by
a factor \times 1.5 thus making such a survey strongly desirable.Comment: 25 pages, 9 figures. Revised version, as accepted for publication in
Ap
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