Search results for "Age of the universe"
showing 7 items of 7 documents
Heavy Elements and Age Determinations
2002
The age of the universe, measured from the Big Bang to the present, is at the focus of cosmology. Its determination relies, however, on the use of stellar objects or their products. Stellar explosions, like type Ia supernovae serve as standard(izable) candles to measure the expansion of the universe. Hertzsprung—Russell diagrams of globular clusters can determine the age of such clusters and thus are lower limits of the age of the galaxy and therefore also the universe. Some nuclear isotopes with half-lives comparable to the age of galaxies (and the universe) can serve as clocks (chronometers) for the duration of nucleosynthesis. The isotopes 238U and 232Th with half-lives of 4.5 × l09 and …
Gamma-ray detection from gravitino dark matter decay in the μνSSM
2009
16 pages, 3 figures.
Constraints on neutrino masses from Planck and Galaxy clustering data
2013
We present here bounds on neutrino masses from the combination of recent Planck cosmic microwave background (CMB) measurements and galaxy clustering information from the Baryon Oscillation Spectroscopic Survey, part of the Sloan Digital Sky Survey-III. We use the full shape of either the photometric angular clustering (Data Release 8) or the 3D spectroscopic clustering (Data Release 9) power spectrum in different cosmological scenarios. In the Lambda CDM scenario, spectroscopic galaxy clustering measurements improve significantly the existing neutrino mass bounds from Planck data. We find Sigma m(v) < 0.39 eV at 95% confidence level for the combination of the 3D power spectrum with Planck C…
Cosmic Dark Radiation and Neutrinos
2013
New measurements of the cosmic microwave background (CMB) by the Planck mission have greatly increased our knowledge about the universe. Dark radiation, a weakly interacting component of radiation, is one of the important ingredients in our cosmological model which is testable by Planck and other observational probes. At the moment, the possible existence of dark radiation is an unsolved question. For instance, the discrepancy between the value of the Hubble constant, H-0, inferred from the Planck data and local measurements of H-0 can to some extent be alleviated by enlarging the minimal ACDM model to include additional relativistic degrees of freedom. From a fundamental physics point of v…
Observational constraints on the LLTB model
2010
We directly compare the concordance LCDM model to the inhomogeneous matter-only alternative represented by LTB void models. To achieve a "democratic" confrontation we explore LLTB models with non-vanishing cosmological constant and perform a global likelihood analysis in the parameter space of cosmological constant and void radius. In our analysis we carefully consider SNe, Hubble constant, CMB and BAO measurements, marginalizing over spectral index, age of the universe and background curvature. We find that the LCDM model is not the only possibility compatible with the observations, and that a matter-only void model is a viable alternative to the concordance model only if the BAO constrain…
Relaxing cosmological neutrino mass bounds with unstable neutrinos
2020
At present, cosmological observations set the most stringent bound on the neutrino mass scale. Within the standard cosmological model ($\Lambda$CDM), the Planck collaboration reports $\sum m_\nu < 0.12\,\text{eV}$ at 95% CL. This bound, taken at face value, excludes many neutrino mass models. However, unstable neutrinos, with lifetimes shorter than the age of the universe $\tau_\nu \lesssim t_U$, represent a particle physics avenue to relax this constraint. Motivated by this fact, we present a taxonomy of neutrino decay modes, categorizing them in terms of particle content and final decay products. Taking into account the relevant phenomenological bounds, our analysis shows that 2-body deca…
Gravitational violation of R parity and its cosmological signatures
1996
The discrete R-parity ($R_P$) usually imposed on the Supersymmetric (SUSY) models is expected to be broken at least gravitationally. If the neutralino is a dark matter particle its decay channels into positrons, antiprotons and neutrinos are severely constrained from astrophysical observations. These constraints are shown to be violated even for Planck-mass-suppressed dimension-five interactions arising from gravitational effects. We perform a general analysis of gravitationally induced $R_P$ violation and identify two plausible and astrophysically consistent scenarios for achieving the required suppression.