* Astronomy

Blobrana · L

RE: Cosmic Strings

Blobrana · L

Title: Cosmic Strings and Cosmic Superstrings
Authors: Mairi Sakellariadou
(Version v2)

In these lectures, I review the current status of cosmic strings and cosmic superstrings. I first discuss topological defects in the context of Grand Unified Theories, focusing in particular in cosmic strings arising as gauge theory solitons. I discuss the reconciliation between cosmic strings and cosmological inflation, I review cosmic string dynamics, cosmic string thermodynamics and cosmic string gravity, which leads to a number of interesting observational signatures. I then proceed with the notion of cosmic superstrings arising at the end of brane inflation, within the context of brane-world cosmological models inspired from string theory. I discuss the differences between cosmic superstrings and their solitonic analogues, I review our current understanding about the evolution of cosmic superstring networks, and I then briefly describe the variety of observational consequences, which may help us to get an insight into the stringy description of our Universe.

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Blobrana · L

For astronomers, understanding what happened in the early moments of the universe could answer many questions in physics and astronomy. One possible player in the early universe is cosmic strings, which arise naturally in particle physics models. However, cosmic strings are quite strange hypothetical entities: theyre thinner than a proton, but can be as long as the universe. Cosmic strings might have formed as imperfections when the early universe was undergoing drastic phase changes.

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Blobrana · L

Title: Cosmic Sparks from Superconducting Strings
Authors: Tanmay Vachaspati
(Version v3)

We investigate cosmic sparks from cusps on superconducting cosmic strings in light of the recently discovered millisecond radio burst by Lorimer et al [1]. We find that the observed duration, fluence, spectrum, and event rate can be reasonably explained by Grand Unification scale superconducting cosmic strings that carry currents ~ 10^5 GeV. The superconducting string model predicts an event rate that falls off only as S^{-1/2}, where S is the energy flux, and hence predicts a population of very bright bursts. Other surveys, with different observational parameters, are shown to impose tight constraints on the superconducting string model.

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Blobrana · L

Physicists in the US and Singapore are the first to use light from distant galaxies to perform a systematic search for cosmic strings massive structures that may have been created just after the Big Bang. Although the team has found no evidence of cosmic strings in the small patch of sky they surveyed, they have been able to set an upper limit on the mass per unit length of the strings. The team is now working to improve their results by looking at larger patches of the sky.

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Blobrana · L

Title: Cosmic (super)string constraints from 21 cm radiation
Authors: Rishi Khatri, Benjamin D. Wandelt

We calculate the contribution of cosmic strings arising from a phase transition in the early universe, or cosmic superstrings arising from brane inflation, to the cosmic 21 cm power spectrum at redshifts z > 30. Future experiments can exploit this effect to constrain the cosmic string tension Gu and probe virtually the entire brane inflation model space allowed by current observations. Although current experiments with a collecting area of ~ 1 km² will not provide any useful constraints, future experiments with a collecting area of 10^4-10^6 km² covering the cleanest 10% of the sky can in principle constrain cosmic strings with tension Gu > 10^(-10) to 10^(-12) (superstring/phase transition mass scale >10^13 GeV).

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Blobrana · L

A team of physicists and astronomers from the University of Sussex and Imperial College London have uncovered hints that there may be cosmic strings - lines of pure mass-energy - stretching across the entire Universe.
Cosmic strings are predicted by high energy physics theories, including superstring theory. This is based on the idea that particles are not just little points, but tiny vibrating bits of string Cosmic strings are predicted to have extraordinary amounts of mass - perhaps as much as the mass of the Sun - packed into each metre of a tube whose width is less a billion billionth of the size of an atom.

This is an exciting result for physicists. Cosmic strings are relics of the very early Universe and signposts that would help construct a theory of all forces and particles - Lead researcher Dr Mark Hindmarsh, Reader in Physics at the University of Sussex.

His team took data from NASA's Wilkinson Microwave Anisotropy Probe (WMAP), which is a satellite currently mapping the intensity of cosmic microwaves from all directions, and carefully compared the predictions of what should be seen with and without strings.

We cannot yet see these strings directly. They are many billion light years away. We can only look for indirect evidence of their existence through precision measurements of the cosmic microwave background, of cosmic rays, gravitational radiation, and looking for double images of distant quasars - Dr Mark Hindmarsh.

The four-person team are members of COSMOS, the UK's world-leading cosmology supercomputing consortium fronted by Stephen Hawking. Using a Silicon Graphics supercomputer they made predictions of how the strings would affect the Cosmic Microwave Background, relic radio waves from the Big Bang which fill the universe. It turned out that the best explanation for the pattern of this radiation was a theory which included strings.
Dr Hindmarsh said that better data is required before the existence of cosmic strings can be confirmed. He hopes this will be produced by the European Space Agency's Planck Satellite mission (due for launch this year).
The results are published in Physical Review Letters on 18 January, 2008.

Source : University of Sussex

-- Edited by Blobrana at 02:04, 2008-01-21

Blobrana · L

Title: Cosmic Strings and Weak Gravitational Lensing
Authors: Sergei Dyda, Robert H. Brandenberger (McGill University)

We study the deflection of light in the background of a "wiggly" cosmic string, and investigate whether it is possible to detect cosmic strings by means of weak gravitational lensing. For straight strings without small-scale structure there are no signals. In the case of strings with small-scale structure leading to a local gravitational attractive force towards the string, there is a small signal, namely a preferential elliptical distortion of the shape of background galaxies in the direction corresponding to the projection of the string onto the sky. The signal can be statistically distinguished from the signal produced by a linear distribution of black holes by employing an ellipticity axis distribution statistic.

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