arXiv subjects
Publications and source records attributed to James O. Dunn.
We discuss a degeneracy between the geometry of the universe and the dark energy equation of state $w_{\rm X}$ which exists in the power spectrum of the cosmic microwave background. In particular, for the case with $w_{\rm X} < -1$, this degeneracy has interesting implications to a lower bound on $w_{\rm X}$ from observations. It is also discussed how this degeneracy can be removed using current observations of type Ia supernovae.
A particular kind of quintessence is considered, with equation of motion $p_Q/ρ_Q = -1$, corresponding to a cosmological term with time-dependence $Λ(t) = Λ(t_0) (R(t_0)/R(t))^{P}$ which we examine initially for $0 \leq P < 3$. Energy conservation is imposed, as is consistency with big-bang nucleosynthesis, and the range of allowed $P$ is thereby much restricted to $0 \leq P < 0.2$. The position of the first Doppler peak is computed analytically and the result combined with analysis of high-Z supernovae to find how values of $Ω_m$ and $Ω_Λ$ depend on $P$. Some comparison is made to the CMBFAST public code.
A particular kind of quintessence is considered, with equation of motion $p_Q/ρ_Q = -1$, corresponding to a cosmological term with time-dependence $Λ(t) = Λ(t_0) (R(t_0)/R(t))^{P}$ which we examine initially for $0 \leq P < 3$. Energy conservation is imposed, as is consistency with big-bang nucleosynthesis, and the range of allowed $P$ is thereby much restricted to $0 \leq P < 0.2$. The position of the first Doppler peak is computed analytically and the result combined with analysis of high-Z supernovae to find how values of $Ω_m$ and $Ω_Λ$ depend on $P$.
The origin of the highest-energy cosmic rays remains elusive. The decay of a superheavy particle (X) into an ultra-energetic neutrino which scatters from a relic (anti-)neutrino at the Z-resonance has attractive features. Given the necessary X mass of $10^{14\sim15}$ GeV, the required lifetime, $10^{15\sim16}$ y, renders model-building a serious challenge but three logical possibilities are considered: (i) X is a Higgs scalar in SU(15) belonging to high-rank representation, leading to {\it power}-enhanced lifetime; (ii) a global X quantum number has {\it exponentially}-suppressed symmetry-breaking by instantons; and (iii) with additional space dimension(s) localisation of X within the real-world brane leads to {\it gaussian} decay suppression, the most efficient of the suppression mechanisms considered.