MG12 - Talk detail
 

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Abstract

Some Alternative Unifying Models for Dark Energy and Dark Matter

The simple fact that the present closure contributions in dark matter and dark energy are nearly equal begs the question as to whether they could be different aspects of the same physical phenomenon. Here, we review constraints several postulates as to how this coincidence could be achieved. These include: 1) The possibility that the dark matter decays producing a bulk viscosity in the cosmic fluid; 2) cosmic acceleration produced by the inflow of dark matter from a bulk dimension in brane-world cosmology; and 3) The possibility of relativistic corrections to the Friedmann equation from the presence of local inhomogeneities. Constraints and observational tests of each of these cosmologies are proposed

Evidence for a Primordial Magnetic Field from the CMB Polarization and Power Spectra

Magnetic fields play an important role in many astronomical phenomena on various cosmological scales. In particular, a primordial magnetic field (PMF) could manifest itself in the cosmic microwave background (CMB) temperature and polarization anisotropies, and also in the formation of large- scale structure. We have developed a new high-precision theoretical framework in which to calculate the CMB temperature and polarization anisotropies, along with the matter power spectrum generated when a power-law PMF is present at the epoch of photon last-scattering. We discuss prelimminary evidence that the existing accumulated data on both the matter and CMB power spectra on small angular scales fixes both the upper and lower limits to the magnetic field strength and power spectral index. We find parameter values for the amplitude of the PMF of 2.248 nG < B < 3.055 nG and a spectral index in the range -2.387 < n < -1.367 at the present scale of 1 Mpc. This may be the first direct evidence that a primordial magnetic field was indeed present during the big bang. We also show that a the existence of a primordial magnetic field can lead to a new independent constraint on the neutrino mass.

Ultra High-Energy Neutrinos via Heavy-Meson Synchrotron Emission

We propose that the acceleration of ultra-relativistic protons and nuclei in the presence of strong magnetic fields (H ~10^15 G) in such environments as AGNs, Magnetars, or GRB central engines could be a viable site for strong meson synchrotron emission. We show that charged scalar mesons like pi+_, vector mesons like the rho, and even heavier mesons like D_S, J/Psi and Upsilon, could be emitted with high intensity (~10^3 times the photon intensity) through strong couplings to ultra-relativistic nucleons. These processes for meson synchrotron emission would eventually produce a burst of three flavors of ultra high-energy cosmic neutrinos with $ E_nu >10^12 eV. We evaluate the spectra of the mu- and tau-neutrinos, which might be produced by the decay of massive mesons like the Upsilon. We also estimate the event rate in energetic neutrino detectors and show that a nearby event might be detectable.

Effects of structure formation on the apparent expansion rate of the universe: a realistic estimate based on N-body simulations

Backreaction terms arise when the effective Friedmann equation is averaged over a spatial volume in a locally inhomogeneous cosmology. It has been suggested that these terms may contribute to the observed cosmic acceleration. Many perturbative methods for this averaging procedure have been proposed and investigated. In this paper, we first propose a new scheme that enables us to use N-body simulations to make realistic estimates of the magnitude of backreaction terms of general three dimensional inhomogeneities in space. We then quantitatively calculate the volume averaged expansion rate using an N-body simulation code and compare it with the expansion rate in a standard FRW cosmology. We also discuss the physical interpretation of the new expansion rate and its impact on other cosmological observables.

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