1,909 research outputs found
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 and velocity as
dynamical variables. In non-relativistic systems, we obtain a well-known
law, showing that loop production is important. For
electroweak cosmic strings, we show transient damped epoch scaling with
(or, in the matter era, ). A low initial
density implies an earlier period with . For GUT strings, the
approach to linear scaling is faster than previously estimated.Comment: 8 pages, uuencoded gziped .ps file. Paper submitted to Phys. Rev.
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