On the origin of dark matter axions

We discuss the possible sources of dark matter axions in the early universe. In the standard thermal scenario, an axion string network forms at the Peccei-Quinn phase transition T\sim \fa and then radiatively decays into a cosmological background of axions; to be the dark matter, these axions must have a mass \ma \sim 100 \mu eV with specified large uncertainties. An inflationary phase with a reheat temperature below the PQ-scale T_{reh} \lapp \fa can also produce axion strings through quantum fluctuations, provided that the Hubble parameter during inflation is large H_1 \gapp \fa; this case again implies a dark matter axion mass \ma \sim 100 \mu eV. For a smaller Hubble parameter during inflation H_1 \lapp \fa, `anthropic tuning' allows dark matter axions to have any mass in a huge range below \ma\lapp 1 meV.Comment: to be published in the proceedings of the 5th IFT Workshop on Axion

Cosmic string induced CMB maps

We compute maps of CMB temperature fluctuations seeded by cosmic strings using high resolution simulations of cosmic strings in a Friedmann-Robertson-Walker universe. We create full-sky, 18-degree and 3-degree CMB maps, including the relevant string contribution at each resolution from before recombination to today. We extract the angular power spectrum from these maps, demonstrating the importance of recombination effects. We briefly discuss the probability density function of the pixel temperatures, their skewness and kurtosis.Comment: 5 pages, 4 figures, submitted to PRD; v2: 6 pages, 5 figures, matches published versio

String Evolution with Friction

We study the effects of friction on the scaling evolution of string networks in condensed matter and cosmological contexts. We derive a generalized `one-scale' model with the string correlation length $L$ and velocity $v$ as dynamical variables. In non-relativistic systems, we obtain a well-known $L\propto t^{1/2}$ law, showing that loop production is important. For electroweak cosmic strings, we show transient damped epoch scaling with $L\propto t^{5/4}$ (or, in the matter era, $L\propto t^{3/2}$). A low initial density implies an earlier period with $L\propto t^{1/2}$. For GUT strings, the approach to linear scaling $L\propto t$ is faster than previously estimated.Comment: 8 pages, uuencoded gziped .ps file. Paper submitted to Phys. Rev. Let