Subscribe to the gold package and get unlimited access to Shamra Academy
Register a new userThe power spectra of CMB and density fluctuations seeded by local cosmic strings
84
0
0.0
(
0
)
Ask ChatGPT about the research
No Arabic abstract
We compute the power spectra in the cosmic microwave background and cold dark matter (CDM) fluctuations seeded by strings, using the largest string simulations performed so far to evaluate the two-point functions of their stress energy tensor. We find that local strings differ from global defects in that the scalar components of the stress-energy tensor dominate over vector and tensor components. This result has far reaching consequences. We find that cosmic strings exhibit a single Doppler peak of acceptable height at high $ell$. They also seem to have a less severe bias problem than global defects, although the CDM power spectrum in the ``standard cosmology (flat geometry, zero cosmological constant, 5% baryonic component) is the wrong shape to fit large scale structure data.
rate research
Read More
In cosmological models where local cosmic strings are formed at the end of a period of inflation, the perturbations are seeded both by the defects and by the quantum fluctuations. In a subset of these models, for example those based on $D$-term inflation, the amplitudes are similar. Using our recent calculations of structure formation with cosmic strings, we point out that in a flat cosmology with zero cosmological constant and 5% baryonic component, strings plus inflation fits the observational data much better than each component individually. The large-angle CMB spectrum is mildly tilted, for Harrison-Zeldovich inflationary fluctuations. It then rises to a thick Doppler bump, covering $ell=200-600$, modulated by soft secondary undulations. The standard CDM anti-biasing problem is cured, giving place to a slightly biased scenario of galaxy formation.
We study the effect of weak lensing by cosmic (super-)strings on the anisotropies of cosmic microwave background (CMB). In developing a method to calculate the lensing convergence field due to strings, and thereby temperature and polarization angular power spectra of CMB, we clarify how the nature of strings, characterized by the intercommuting probability, can influence these CMB anisotropies. Assuming that the power spectrum is dominated by Poisson-distributed string segments, we find that the convergence spectrum peaks at low multipoles and is mostly contributed from strings located at relatively low redshifts. As the intercommuting probability decreases, the spectra of the convergence and hence the lensed temperature and polarizations are gained because the number density of string segments becomes larger. An observationally important feature of the string-induced CMB polarizations is that the string-lensed spectra decay more slowly on small scales compared with primordial scalar perturbations from standard inflation.
We simulate the anisotropy in the cosmic microwave background (CMB) induced by cosmic strings. By numerically evolving a network of cosmic strings we generate full-sky CMB temperature anisotropy maps. Based on $192$ maps, we compute the anisotropy power spectrum for multipole moments $ell le 20$. By comparing with the observed temperature anisotropy, we set the normalization for the cosmic string mass-per-unit-length $mu$, obtaining $Gmu/c^2=1.05 {}^{+0.35}_{-0.20} times10^{-6}$, which is consistent with all other observational constraints on cosmic strings. We demonstrate that the anisotropy pattern is consistent with a Gaussian random field on large angular scales.
We present a new analytical method to calculate the small angle CMB temperature angular power spectrum due to cosmic (super-)string segments. In particular, using our method, we clarify the dependence on the intercommuting probability $P$. We find that the power spectrum is dominated by Poisson-distributed string segments. The power spectrum for a general value of $P$ has a plateau on large angular scales and shows a power-law decrease on small angular scales. The resulting spectrum in the case of conventional cosmic strings is in very good agreement with the numerical result obtained by Fraisse et al.. Then we estimate the upper bound on the dimensionless tension of the string for various values of $P$ by assuming that the fraction of the CMB power spectrum due to cosmic (super-)strings is less than ten percents at various angular scales up to $ell=2000$. We find that the amplitude of the spectrum increases as the intercommuting probability. As a consequence, strings with smaller intercommuting probabilities are found to be more tightly constrained.
We study diffusion damping of acoustic waves in the photon-baryon fluid due to cosmic strings, and calculate the induced $mu$- and $y$-type spectral distortions of the cosmic microwave background. For cosmic strings with tension within current bounds, their contribution to the spectral distortions is subdominant compared to the distortions from primordial density perturbations.
Log in to be able to interact and post comments
comments
Fetching comments
Sign in to be able to follow your search criteria
