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Large Angle CMB Fluctuations from Cosmic Strings with a Comological Constant
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Large Angle CMB Fluctuations from Cosmic Strings with a Comological Constant
M. Landriau?
Laboratoire de l’Acce?le?rateur Line?aire,
IN2P3-CNRS et Universite? Paris-Sud,
B.P. 34, 91898 Orsay Cedex, France
E.P.S. Shellard?
Department of Applied Mathematics and Theoretical Physics,
Centre for Mathematical Sciences,
University of Cambridge
Wilberforce Road, Cambridge CB3 0WA, U.K.
(Dated: August 1, 2003)
In this paper, we present results for large-angle CMB anisotropies generated from high resolution
simulations of cosmic string networks in a range of flat FRW universes with a cosmological constant.
Using an ensemble of all-sky maps, we compare with the COBE data to infer a normalization (or
upper bound) on the string linear energy density μ. For a flat matter-dominated model (?M = 1)
we find Gμ/c2 ≈ 0.7 × 10?6, which is lower than previous constraints probably because of the
more accurate inclusion of string small-scale structure. For a cosmological constant within an
observationally acceptable range, we find a relatively weak dependence with Gμ/c2 less than 10%
higher.
PACS numbers: 98.80.-k, 98.80.Cq
I. INTRODUCTION
Given the growing evidence for a cosmological constant
or dark energy component in the Universe, it is impor-
tant to determine whether this significantly impacts the
evolution of cosmic strings and their observational signa-
tures. The strongest constraints limiting the energy scale
of cosmic strings is currently the COBE normalisation of
large-angle CMB anisotropy. In this paper, we will infer
this normalisation from maps computed using the meth-
ods presented in [1] and determine how this is influenced
by late-time domination by a cosmological constant.
II. METHOD
A. Geometry of Simulations
To compute all-sky maps, the “observers” are located
inside the simulation box. Following [2], we place eight
such observers at each corner of a cube of side L/2 where
L is the size of the box i
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