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Abstract:

We have shown earlier that, contrary to popular belief, Einstein--de Sitter (E--deS) models can still fit the {\sl WMAP} data on the cosmic microwave background provided one adopts a low Hubble constant and relaxes the usual assumption that the primordial density perturbation is scale-free. The recent {\sl SDSS} measurement of the large-scale correlation function of luminous red galaxies at $z \sim 0.35$ has however provided a new constraint by detecting a `baryon acoustic peak'. Our best-fit E--deS models do possess a baryonic feature at a similar physical scale as the best-fit $\Lambda$CDM concordance model, but do not fit the new observations as well as the latter. In particular the shape of the correlation function in the range $\sim 10-100 h^{-1}$ Mpc cannot be reproduced properly without violating the CMB angular power spectrum in the multipole range $l \sim 100-1000$. Thus, the combination of the CMB fluctuations and the shape of the correlation function up to $\sim 100 h^{-1}$Mpc, if confirmed, does seem to require dark energy for a homogeneous cosmological model based on (adiabatic) inflationary perturbations.

Abstract:

Precision measurements of anisotropies in the cosmic microwave background and of the clustering of largescale structure have supposedly confirmed that the primordial density perturbation has a (nearly) scale-invariant spectrum. However this conclusion is based on assumptions about the world model and the nature of the dark matter. Physical models of inflation suggest that the spectrum may not in fact be scale-free, which would imply rather different cosmological parameters on the basis of the same observational data.

Abstract:

The Pierre Auger Observatory for cosmic rays provides a laboratory for studying fundamental interactions at energies well beyond those available at colliders. In addition to hadrons or photons, Auger is sensitive to ultra-high energy neutrinos in the cosmic radiation and models for new physics can be explored by observing neutrino interactions at center-of-mass energies beyond the TeV scale. By comparing the rate for quasi-horizontal, deeply penetrating air showers triggered by all types of neutrinos with the rate for slightly upgoing showers generated by Earth-skimming tau neutrinos, any deviation of the neutrino-nucleon cross-section from the Standard Model expectation can be constrained. We show that this can test models of low-scale quantum gravity (including processes such as Kaluza-Klein graviton exchange, microscopic black hole production and string resonances), as well as non-perturbative electroweak instanton mediated processes. Moreover, the observed ratios of neutrino flavors would severely constrain the possibility of neutrino decay.