9 research outputs found
Cosmic microwave anisotropies from BPS semilocal strings
We present the first ever calculation of cosmic microwave background CMB
anisotropy power spectra from semilocal cosmic strings, obtained via
simulations of a classical field theory. Semilocal strings are a type of
non-topological defect arising in some models of inflation motivated by
fundamental physics, and are thought to relax the constraints on the symmetry
breaking scale as compared to models with (topological) cosmic strings. We
derive constraints on the model parameters, including the string tension
parameter mu, from fits to cosmological data, and find that in this regard BPS
semilocal strings resemble global textures more than topological strings. The
observed microwave anisotropy at l = 10 is reproduced if Gmu = 5.3x10^{-6} (G
is Newton's constant). However as with other defects the spectral shape does
not match observations, and in models with inflationary perturbations plus
semilocal strings the 95% confidence level upper bound is Gmu<2.0x10^{-6} when
CMB data, Hubble Key Project and Big Bang Nucleosynthesis data are used (c.f.
Gmu<0.9x10^{-6} for cosmic strings). We additionally carry out a Bayesian model
comparison of several models with and without defects, showing models with
defects are neither conclusively favoured nor disfavoured at present.Comment: 15 pages, 13 figures. Minor correction of numerical results, matches
published versio
Constraints on Brane Inflation and Cosmic Strings
By considering simple, but representative, models of brane inflation from a
single brane-antibrane pair in the slow roll regime, we provide constraints on
the parameters of the theory imposed by measurements of the CMB anisotropies by
WMAP including a cosmic string component. We find that inclusion of the string
component is critical in constraining parameters. In the most general model
studied, which includes an inflaton mass term, as well as the brane-antibrane
attraction, values n_s < 1.02 are compatible with the data at 95 % confidence
level. We are also able to constrain the volume of internal manifold (modulo
factors dependent on the warp factor) and the value of the inflaton field to be
less than 0.66M_P at horizon exit. We also investigate models with a mass term.
These observational considerations suggest that such models have r < 2*10^-5,
which can only be circumvented in the fast roll regime, or by increasing the
number of antibranes. Such a value of r would not be detectable in CMB
polarization experiment likely in the near future, but the B-mode signal from
the cosmic strings could be detectable. We present forecasts of what a similar
analysis using PLANCK data would yield and find that it should be possible to
rule out G\mu > 6.5*10^-8 using just the TT, TE and EE power spectra.Comment: 11 pages, 3 figures, revtex4, typos corrected, references adde
D-term inflation in non-minimal supergravity
D-term inflation is one of the most interesting and versatile models of
inflation. It is possible to implement naturally D-term inflation within high
energy physics, as for example SUSY GUTs, SUGRA, or string theories. D-term
inflation avoids the -problem, while in its standard form it always ends
with the formation of cosmic strings. Given the recent three-year WMAP data on
the cosmic microwave background temperature anisotropies, we examine whether
D-term inflation can be successfully implemented in non-minimal supergravity
theories. We show that for all our choices of K\"ahler potential, there exists
a parameter space for which the predictions of D-term inflation are in
agreement with the measurements. The cosmic string contribution on the measured
temperature anisotropies is always dominant, unless the superpotential coupling
constant is fine tuned; a result already obtained for D-term inflation within
minimal supergravity. In conclusion, cosmic strings and their r\^ole in the
angular power spectrum cannot be easily hidden by just considering a non-flat
K\"ahler geometry.Comment: 29 pages, 9 figures; minor changes to match publihed versio
Textures and Semi-Local Strings in SUSY Hybrid Inflation
Global topological defects may account for the large cold spot observed in
the Cosmic Microwave Background. We explore possibilities of constructing
models of supersymmetric F-term hybrid inflation, where the waterfall fields
are globally SU(2)-symmetric. In contrast to the case where SU(2) is gauged,
there arise Goldstone bosons and additional moduli, which are lifted only by
masses of soft-supersymmetry breaking scale. The model predicts the existence
of global textures, which can become semi-local strings if the waterfall fields
are gauged under U(1)_X. Gravitino overproduction can be avoided if reheating
proceeds via the light SU(2)-modes or right-handed sneutrinos. For values of
the inflaton- waterfall coupling >=10^-4, the symmetry breaking scale imposed
by normalisation of the power spectrum generated from inflation coincides with
the energy scale required to explain the most prominent of the cold spots. In
this case, the spectrum of density fluctuations is close to scale-invariant
which can be reconciled with measurements of the power spectrum by the
inclusion of the sub-dominant component due to the topological defects.Comment: 29 page
Magnetogenesis from Cosmic String Loops
Large-scale coherent magnetic fields are observed in galaxies and clusters,
but their ultimate origin remains a mystery. We reconsider the prospects for
primordial magnetogenesis by a cosmic string network. We show that the magnetic
flux produced by long strings has been overestimated in the past, and give
improved estimates. We also compute the fields created by the loop population,
and find that it gives the dominant contribution to the total magnetic field
strength on present-day galactic scales. We present numerical results obtained
by evolving semi-analytic models of string networks (including both one-scale
and velocity-dependent one-scale models) in a Lambda-CDM cosmology, including
the forces and torques on loops from Hubble redshifting, dynamical friction,
and gravitational wave emission. Our predictions include the magnetic field
strength as a function of correlation length, as well as the volume covered by
magnetic fields. We conclude that string networks could account for magnetic
fields on galactic scales, but only if coupled with an efficient dynamo
amplification mechanism.Comment: 10 figures; v3: small typos corrected to match published version.
MagnetiCS, the code described in paper, is available at
http://markcwyman.com/ and
http://www.damtp.cam.ac.uk/user/dhw22/code/index.htm
WMAP constraints on inflationary models with global defects
We use the cosmic microwave background angular power spectra to place upper
limits on the degree to which global defects may have aided cosmic structure
formation. We explore this under the inflationary paradigm, but with the
addition of textures resulting from the breaking of a global O(4) symmetry
during the early stages of the Universe. As a measure of their contribution, we
use the fraction of the temperature power spectrum that is attributed to the
defects at a multipole of 10. However, we find a parameter degeneracy enabling
a fit to the first-year WMAP data to be made even with a significant defect
fraction. This degeneracy involves the baryon fraction and the Hubble constant,
plus the normalization and tilt of the primordial power spectrum. Hence,
constraints on these cosmological parameters are weakened. Combining the WMAP
data with a constraint on the physical baryon fraction from big bang
nucleosynthesis calculations and high-redshift deuterium abundance, limits the
extent of the degeneracy and gives an upper bound on the defect fraction of
0.13 (95% confidence).Comment: 10pp LaTeX/RevTeX, 6 eps figs; matches accepted versio
Observational constraints on cosmic strings: Bayesian analysis in a three dimensional parameter space
Current data exclude cosmic strings as the primary source of primordial
density fluctuations. However, in a wide class of inflationary models, strings
can form at later stages of inflation and have potentially detectable
observational signatures. We study the constraints from WMAP and SDSS data on
the fraction of primordial fluctuations sourced by local cosmic strings. The
Bayesian analysis presented in this brief report is restricted to the minimal
number of parameters. Yet it is useful for two reasons. It confirms the results
of Pogosian et al (2003) using an alternative statistical method. Secondly, it
justifies the more costly multi-parameter analysis. Already, varying only three
parameters -- the spectral index and the amplitudes of the adiabatic and string
contributions -- we find that the upper bound on the cosmic string contribution
is of order 10%. We expect that the full multi-parameter study, currently
underway, will likely loosen this bound.Comment: v3: 4 pages, 5 figures, slight modifications to match published
versio
Seeking String Theory in the Cosmos
We review the existence, formation and properties of cosmic strings in string
theory, the wide variety of observational techniques that are being employed to
detect them, and the constraints that current observations impose on string
theory models.Comment: 25 pages; contribution for String Cosmology issue of Classical and
Quantum Gravity. References added and other improvements. Matches journal
versio
Planck 2015 results. XIII. Cosmological parameters
We present results based on full-mission Planck observations of temperature and polarization anisotropies of the CMB. These data are consistent with the six-parameter inflationary LCDM cosmology. From the Planck temperature and lensing data, for this cosmology we find a Hubble constant, H0= (67.8 +/- 0.9) km/s/Mpc, a matter density parameter Omega_m = 0.308 +/- 0.012 and a scalar spectral index with n_s = 0.968 +/- 0.006. (We quote 68% errors on measured parameters and 95% limits on other parameters.) Combined with Planck temperature and lensing data, Planck LFI polarization measurements lead to a reionization optical depth of tau = 0.066 +/- 0.016. Combining Planck with other astrophysical data we find N_ eff = 3.15 +/- 0.23 for the effective number of relativistic degrees of freedom and the sum of neutrino masses is constrained to < 0.23 eV. Spatial curvature is found to be |Omega_K| < 0.005. For LCDM we find a limit on the tensor-to-scalar ratio of r <0.11 consistent with the B-mode constraints from an analysis of BICEP2, Keck Array, and Planck (BKP) data. Adding the BKP data leads to a tighter constraint of r < 0.09. We find no evidence for isocurvature perturbations or cosmic defects. The equation of state of dark energy is constrained to w = -1.006 +/- 0.045. Standard big bang nucleosynthesis predictions for the Planck LCDM cosmology are in excellent agreement with observations. We investigate annihilating dark matter and deviations from standard recombination, finding no evidence for new physics. The Planck results for base LCDM are in agreement with BAO data and with the JLA SNe sample. However the amplitude of the fluctuations is found to be higher than inferred from rich cluster counts and weak gravitational lensing. Apart from these tensions, the base LCDM cosmology provides an excellent description of the Planck CMB observations and many other astrophysical data sets