arXiv subjects

Louise M Griffiths

Publications and source records attributed to Louise M Griffiths.

4 recordsLinked to original sources

arXiv2002

Large extra dimensions, the galaxy power spectrum and the end of inflation

We consider the production of gravitational KK modes via cosmological photon-photon and electron-positron annihilation in models with large factorisable extra dimensions. We place constraints on this production using recent results from a joint analysis of the power spectra of the 2dF Galaxy Redshift Survey (2dFGS) and the cosmic microwave background (CMB) anisotropies. We obtain a more accurate upper limit for the temperature corresponding to matter-radiation equality and show that, even for the case of 6 extra dimensions and a fundamental scale of 1 TeV, a period of inflation is required that ends at a temperature much lower than that of the QCD phase transition.

hep-ph↗

arXiv2001

CMB Constraints on a Baryonic Dark Matter-Dominated Universe

In recent years, upper limits on the cosmic microwave background (CMB) anisotropies combined with predictions made by theories of galaxy formation, have been extremely powerful in ruling out purely baryonic dark matter (BDM) universes. However, it has recently been argued that the absence of a prominent second peak in the anisotropy spectrum measured by the BOOMERanG-98 and MAXIMA-1 experiments seems to favour a $Λ$BDM model when combined with standard Big Bang Nucleosynthesis (BBN) constraints. In this {\it Letter}, we further investigate this result showing that, using the CMB data {\it alone}, a purely baryonic adiabatic model of structure formation seems unlikely if the universe is flat ($Ω=1$). Combining the CMB data with supernova type Ia (SNIa) data renders purely baryonic models inconsistent with flatness at high significance and more than $3 σ$ away from both the BBN constraints and the HST key project result $h=0.72 \pm 0.08$. These results indicate that only a radical revision of cosmology with {\it ad hoc} properties could bring baryonic models such as those advocated by MOND enthusiasts back into agreement with current observations.

astro-ph↗

arXiv2001

Cosmic microwave background constraints on the epoch of reionization

We use a compilation of cosmic microwave anisotropy data to constrain the epoch of reionization in the Universe, as a function of cosmological parameters. We consider spatially-flat cosmologies, varying the matter density $Ω_0$ (the flatness being restored by a cosmological constant), the Hubble parameter $h$ and the spectral index $n$ of the primordial power spectrum. Our results are quoted both in terms of the maximum permitted optical depth to the last-scattering surface, and in terms of the highest allowed reionization redshift assuming instantaneous reionization. For critical-density models, significantly-tilted power spectra are excluded as they cannot fit the current data for any amount of reionization, and even scale-invariant models must have an optical depth to last scattering of below 0.3. For the currently-favoured low-density model with $Ω_0 = 0.3$ and a cosmological constant, the earliest reionization permitted to occur is at around redshift 35, which roughly coincides with the highest estimate in the literature. We provide general fitting functions for the maximum permitted optical depth, as a function of cosmological parameters. We do not consider the inclusion of tensor perturbations, but if present they would strengthen the upper limits we quote.

astro-ph↗

arXiv2001

The effect of reionization on the COBE normalization

We point out that the effect of reionization on the microwave anisotropy power spectrum is not necessarily negligible on the scales probed by COBE. It can lead to an upward shift of the COBE normalization by more than the one-sigma error quoted ignoring reionization. We provide a fitting function to incorporate reionization into the normalization of the matter power spectrum.

astro-ph↗