arXiv subjects

Matts Roos

Publications and source records attributed to Matts Roos.

24 records · Page 2Linked to original sources

arXiv2000

How flat is the Universe?

In order to answer this question, we combine ten independent astrophysical constraints in the space of the density parameters $Ω_m$ of gravitating matter and $Ω_Λ$ of vacuum energy. We find that $Ω_m=0.31\pm 0.07$, $Ω_Λ=0.63\pm 0.21$, and thus $Ω_m + Ω_Λ=0.94\pm 0.22$. The total $χ^2$ is 4.1 for 8 degrees of freedom, testifying that the various systematic errors included are generous. We also determine $Ω_m$ in the exactly flat case. Five supplementary flat-case constraints can then be included in our fit, with the result $Ω_m=1-Ω_Λ= 0.337\pm0.031$. It follows that the age of the Universe is $t_0 = 13.5\pm 1.3$ (0.68/h) Gyr.

astro-ph↗

arXiv1999

Determination of the dynamical parameters of the Universe and its age

We determine the density parameters $Ω_m$ of gravitating matter and $Ω_Λ$ of vacuum energy, by making a $χ^2$ fit to nine independent astrophysical constraints. Paying rigorous attention to statistical detail, we find that the present best values are $Ω_m=0.31\pm 0.07, Ω_Λ=0.70\pm 0.13$, where these $1σ$ errors are approximately Gaussian (thus trivially convertible to whatever percentage confidence range desired). The total $χ^2$ is 2.5 for 7 degrees of freedom, testifying that the various systematic errors included are generous. Since $Ω_m + Ω_Λ= 1.01\pm 0.15$, it follows that the Einstein-de Sitter model is very strongly ruled out, that also any low-density model with $Ω_Λ=0$ is ruled out, and that a flat cosmology is not only possible, but clearly preferred. In the flat case we find $Ω_m=0.31\pm 0.04$, from which it follows that the age of the Universe is $t_0 = 13.7^{+1.2}_{-1.1}(0.68/h)$ Gyr.

astro-ph↗

arXiv1997

The case for a cosmological constant

Taking the Hubble constant to be in the range 60 - 75 km/s Mpc we show that three independent conditions strongly rule out the standard model of flat space with vanishing cosmological constant.

astro-ph↗

arXiv1996

Reply to the Comment by Harada, Sannino and Schechter on "Confirmation of the Sigma Meson"

We reply to the comment of Harada, Sannino and Schechter (hep-ph/9609428) on our recent paper in the Phys. Rev. Letters on the sigma meson. This concerns the question, raised by Isgur and Speth in another comment, of whether a detailed crossing symmetric form is necessary to understand the data. The discussion gives further support on the existence of the broad sigma near 500 MeV.

hep-ph↗

arXiv1996

Dangers of Unphysical Regions

We discuss the appearance of negative numbers of events in radiochemical experiments and negative squared antineutrino mass $m^2_{\barν_e}$ in tritium beta decay. Going beyond the standard discussion about how to extract upper limits in those cases, we show that the problem is much more profound. We explain the circumstances which are the likely cause of the persistently negative values of $m^2_{\barν_e}$ in all modern tritium beta decay experiments.

hep-ex↗

arXiv1995

Resurrection of the Sigma Meson

It is shown from a very general model and an analysis of data on the lightest 0++ meson nonet that the f0(980) and f0(1200) resonance poles are two manifestations of the same ss state. Similarily the a0(980) and the a0(1450) are likely to be two manifestations of the same qq state. On the other hand, the uu+dd state, when unitarized and strongly distorted by hadronic mass shifts, becomes an extremely broad Breit-Wigner-like background, m=860 MeV, Gamma=880 MeV, with its pole at s=(0.158-i0.235) GeV^2. This we identify with the sigma meson required by models for spontaneous breaking of chiral symmetry.

hep-ph↗