Cosmic string induced CMB maps

We compute maps of CMB temperature fluctuations seeded by cosmic strings using high resolution simulations of cosmic strings in a Friedmann-Robertson-Walker universe. We create full-sky, 18-degree and 3-degree CMB maps, including the relevant string contribution at each resolution from before recombination to today. We extract the angular power spectrum from these maps, demonstrating the importance of recombination effects. We briefly discuss the probability density function of the pixel temperatures, their skewness and kurtosis.Comment: 5 pages, 4 figures, submitted to PRD; v2: 6 pages, 5 figures, matches published versio

Scattering of a Long Cosmic String by a Rotating Black Hole

The scattering of a straight, infinitely long string by a rotating black hole is considered. We assume that a string is moving with velocity v and that initially the string is parallel to the axis of rotation of the black hole. We demonstrate that as a result of scattering, the string is displaced in the direction perpendicular to the velocity by an amount kappa(v,b), where b is the impact parameter. The late-time solution is represented by a kink and anti-kink, propagating in opposite directions at the speed of light, and leaving behind them the string in a new ``phase''. We present the results of the numerical study of the string scattering and their comparison with the weak-field approximation, valid where the impact parameter is large, b/M >> 1, and also with the scattering by a non-rotating black hole which was studied in earlier works.Comment: 27 pages, 14 figures, to be published in Classical and Quantum Gravit

Large Angle CMB Fluctuations from Cosmic Strings with a Comological Constant

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 $\mu$. For a flat matter-dominated model ($\Omega_{M}=1$) we find $G\mu/c^2 \approx 0.7\times 10^{-6}$, 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 $G\mu/c^2$ less than 10% higher.Comment: 5 pages, 5 figures; replaced with version to appear in Physical Review

Cosmic string loop distribution on all length scales and at any redshift

We analytically derive the expected number density distribution of Nambu-Goto cosmic string loops at any redshift soon after the time of string formation to today. Our approach is based on the Polchinski-Rocha model of loop formation from long strings which we adjust to fit numerical simulations and complement by a phenomenological modelling of gravitational backreaction. Cosmological evolution drives the loop distribution towards scaling on all length scales in both the radiation and matter era. Memory of any reasonable initial loop distribution in the radiation era is shown to be erased well before Big Bang Nucleosynthesis. In the matter era, the loop distribution reaches full scaling, up to some residual loops from the radiation era which may be present for extremely low string tension. Finally, the number density of loops below the gravitational cutoff is shown to be scale independent, proportional to a negative power of the string tension and insensitive to the details of the backreaction modelling. As an application, we show that the energy density parameter of loops today cannot exceed 10^(-5) for currently allowed string tension values, while the loop number density cannot be less than 10^(-6) per Mpc^3. Our result should provide a more robust basis for studying the cosmological consequences of cosmic string loops.Comment: 24 pages, 4 figures, uses iopart. References added, matches published versio

The interplay between high energy physics and cosmology: an example

Cosmology and high energy physics are two closely connected areas. In this lecture I present an example of their rich interplay.Comment: Invited talk at the DPU workshop: The density fluctuations in the Universe: Beyond the inflationary paradigm (Dimokritos, Athens 2004) (see http://physics.ntua.gr/dpu/). 8 two column page

Production of topological defects at the end of inflation

Hybrid inflation within supersymmetric grand unified theories, as well as inflation through brane collisions within braneworld cosmological models, lead to the formation of one-dimensional defects. Observational data, mainly from the cosmic microwave background temperature anisotropies but also from the gravitational wave background, impose constraints on the free parameters of the models. I review these inflationary models and discuss the constraints from the currently available data.Comment: 9 pages, Invited talk in the Conference "Challenges in Particle Astrophysics" -- 6th Rencontres du Vietnam, Hanoi (Vietnam) 6-12 Aug. 200

Constraints on Supersymmetric Grand Unified Theories from Cosmology

Within the context of SUSY GUTs, cosmic strings are generically formed at the end of hybrid inflation. However, the WMAP CMB measurements strongly constrain the possible cosmic strings contribution to the angular power spectrum of anisotropies. We investigate the parameter space of SUSY hybrid (F- and D- term) inflation, to get the conditions under which theoretical predictions are in agreement with data. The predictions of F-term inflation are in agreement with data, only if the superpotential coupling $\kappa$ is small. In particular, for SUSY SO(10), the upper bound is \kappa\lsim 7\times 10^{-7}. This fine tuning problem can be lifted if we employ the curvaton mechanism, in which case \kappa\lsim 8\times 10^{-3}; higher values are not allowed by the gravitino constraint. The constraint on $\kappa$ is equivalent to a constraint on the SSB mass scale $M$, namely M \lsim 2\times 10^{15} GeV. The study of D-term inflation shows that the inflaton field is of the order of the Planck scale; one should therefore consider SUGRA. We find that the cosmic strings contribution to the CMB anisotropies is not constant, but it is strongly dependent on the gauge coupling $g$ and on the superpotential coupling $\lambda$. We obtain g\lsim 2\times 10^{-2} and \lambda \lsim 3\times 10^{-5}. SUGRA corrections induce also a lower limit for $\lambda$. Equivalently, the Fayet-Iliopoulos term $\xi$ must satisfy \sqrt\xi \lsim 2\times 10^{15} GeV. This constraint holds for all allowed values of $g$.Comment: 32 pages, 7 figures. To match published versio

Non-linear inflationary perturbations

We present a method by which cosmological perturbations can be quantitatively studied in single and multi-field inflationary models beyond linear perturbation theory. A non-linear generalization of the gauge-invariant Sasaki-Mukhanov variables is used in a long-wavelength approximation. These generalized variables remain invariant under time slicing changes on long wavelengths. The equations they obey are relatively simple and can be formulated for a number of time slicing choices. Initial conditions are set after horizon crossing and the subsequent evolution is fully non-linear. We briefly discuss how these methods can be implemented numerically in the study of non-Gaussian signatures from specific inflationary models.Comment: 10 pages, replaced to match JCAP versio

Formation and evolution of cosmic D-strings

We study the formation of D and F-cosmic strings in D-brane annihilation after brane inflation. We show that D-string formation by quantum de Sitter fluctuations is severely suppressed, due to suppression of RR field fluctuations in compact dimensions. We discuss the resonant mechanism of production of D and F-strings, which are formed as magnetic and electric flux tubes of the two orthogonal gauge fields living on the world-volume of the unstable brane. We outline the subsequent cosmological evolution of the D-F string network. We also compare the nature of these strings with the ordinary cosmic strings and point out some differences and similarities.Comment: Added discussion and reference