Related papers: Quasar variability limits on cosmological density …
We consider a local cosmic string described by the Abelian-Higgs model in the framework of scalar-tensor gravities. We find the metric of the cosmic string in the weak-field approximation. The propagation of particles and light is analysed…
We argue that cosmic strings with high winding numbers generally form in first-order gauge symmetry breaking phase transitions, and we demonstrate this using computer simulations. These strings are heavier than single-winding strings and…
Strong lensing has developed into an important astrophysical tool for probing both cosmology and galaxies (their structure, formation, and evolution). Using the gravitational lensing theory and cluster mass distribution model, we try to…
We consider the femto-lensing due to a cosmic string. If a cosmic string with the deficit angle $\Delta\sim 100$ [femto-arcsec] $\sim10^{-18}$ [rad] exists around the line of sight to a gamma-ray burst, we may observe characteristic…
The variability of quasars across multiple wavelengths is a useful probe of physical conditions in active galactic nuclei. In particular, variable accretion rates, instabilities, and reverberation effects in the accretion disk of a…
The existence of cosmic superstrings may be probed by astronomical time domain surveys. When crossing the line of sight to point-like sources, strings produce a distinctive microlensing signature. We consider two avenues to hunt for a relic…
The interplay between cosmology and strongly coupled dynamics can yield transient spectral features that vanish at late times, but which may leave behind phenomenological signatures in the spectrum of primordial fluctuations. Of particular…
In this article we update constraints on superconducting cosmic strings (SCSs) in light of the recent observational developments of fast radio bursts (FRBs) astronomy. Assuming strings follow an exponential distribution characterized by…
We model the time variability of ~9,000 spectroscopically confirmed quasars in SDSS Stripe 82 as a damped random walk. Using 2.7 million photometric measurements collected over 10 years, we confirm the results of Kelly et al. (2009) and…
We summarize the attempts by our group and others to derive constraints on variations of fundamental constants over cosmic time using quasar absorption lines. Most upper limits reside in the range 0.5-1.5x10-5 at the 3sigma level over a…
Gravitational lensing predicts an enhancement of the density of bright, distant QSOs around foreground galaxies. We measure this QSO-galaxy correlation w_qg for two complete samples of radio-loud quasars, the southern 1Jy and Half-Jansky…
Ultra-light axions (ULAs) with masses in the range 10^{-33} eV <m <10^{-20} eV are motivated by string theory and might contribute to either the dark-matter or dark-energy density of the Universe. ULAs could suppress the growth of structure…
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…
We present a cosmic string on a warped five dimensional space time in Einstein-Yang-Mills theory. Four-dimensional cosmic strings show some serious problems concerning the mechanism of string smoothing related to the string mass per unit…
We investigate our knowledge of early universe cosmology by exploring how much additional energy density can be placed in different components beyond those in the $\Lambda$CDM model. To do this we use a method to separate early- and…
We develop a theoretical framework to describe the cosmological observables on the past light cone such as the luminosity distance, weak lensing, galaxy clustering, and the cosmic microwave background anisotropies. We consider that all the…
How much can we know about our Universe? All of our observations are restricted to a finite volume, and therefore our estimates of presumably global cosmological parameters are necessarily based on incomplete information. Even assuming that…
A network of cosmic strings would lead to gravitational waves which may be detected by pulsar timing or future interferometers. The details of the gravitational wave signal depend on the distribution of cosmic string loops, which are…
We place limits on the mean density of the universe and the slope of the linear power spectrum around a megaparsec scale by comparing the universal mass function to the observed luminosity function. Numerical simulations suggest that the…
The dynamics of cosmic strings is considered in anisotropic backgrounds. In particular, the behaviour of infinitely long straight cosmic strings and of cosmic string loops is determined. Small perturbations of a straight cosmic string are…