Cosmic Strings and Superstrings (0911.1345v3)

Abstract: Cosmic strings are predicted by many field-theory models, and may have been formed at a symmetry-breaking transition early in the history of the universe, such as that associated with grand unification. They could have important cosmological effects. Scenarios suggested by fundamental string theory or M-theory, in particular the popular idea of brane inflation, also strongly suggest the appearance of similar structures. Here we review the reasons for postulating the existence of cosmic strings or superstrings, the various possible ways in which they might be detected observationally, and the special features that might discriminate between ordinary cosmic strings and superstrings.

• The paper presents a comprehensive framework for understanding cosmic strings and superstrings, emphasizing their formation during symmetry-breaking transitions and their subsequent cosmological evolution.
• It employs theoretical models, including the U(1) gauge theory and Nambu-Goto action, to analyze string dynamics and the scaling behavior of cosmic networks.
• The study identifies observational signatures such as gravitational radiation and lensing effects that could distinguish cosmic superstrings from conventional cosmic strings.

Analysis of "Cosmic Strings and Superstrings"

The research paper titled "Cosmic Strings and Superstrings" by Edmund J. Copeland and T.W.B. Kibble provides a comprehensive examination of cosmic strings as linear topological defects predicted by various field-theory models and their analogues, superstrings, which arise from fundamental string theory or M-theory. The paper explores cosmic strings' formation at symmetry-breaking transitions during the early universe and their potential cosmological implications, alongside the scenarios in string theory that suggest the existence of similar structures. The paper explores theoretical postulations, detection methodologies, differentiation between cosmic strings and superstrings, and their implications for cosmic evolution.

Cosmic Strings Formation and Dynamics

Cosmic strings are produced during symmetry-breaking phase transitions, analogous to defects in condensed matter systems. The formation is associated with simple models like the U(1) gauge theory, yielding stable cosmic strings if the fundamental group $\pi_1(M)$ of the manifold $M$ is non-trivial. Strings are characterized by their tension $\mu$, dependent on the energy scale, which is related to the unified theory's transition temperatures. The dynamics of strings involve a complex interplay between their intrinsic tension-mediated evolution and cosmological expansion, driven initially by friction and later by relativistic motion described by the Nambu-Goto action.

Evolution of String Networks

The paper investigates the evolution of cosmic string networks undergoing initial friction-dominated growth, scaling dynamics, and energy loss. A key point in the paper is the transition to a scaling regime, where the characteristic scale $\xi$ remains proportional to the Hubble radius, maintaining energy density proportionate to the universe's ambient density. The formation of closed loops is identified as a crucial mechanism for stabilization, even as simulations offer varying predictions on loop sizes and implications of small-scale string structures.

Transition to Cosmic Superstrings

Cosmic superstrings differ significantly due to their origins in string theory, constrained by ten-dimensional spacetime requirements. They can form due to warping or large compact dimension scenarios, facilitating lower tension values compatible with cosmological observations. The paper analyzes various models, such as the Kachru-Kallosh-Linde-Trivedi (K) model, that propose inflation from brane collisions in the throat of a warped Calabi-Yau manifold facilitates F- and D-string formations. Such transitions exemplify robust mechanisms that bring together superstrings with cosmic cosmology.

Distinguishing Features and Detection

A distinguishing feature of cosmic superstrings is their reduced intercommutation probability and junction-forming capabilities upon crossing with other types, manifesting as (p, q)-string networks. This is recognized as a potential signature differentiating cosmic superstrings from standard cosmic strings. Notably, the paper addresses observational constraints such as lensing effects, cosmic microwave background perturbations, gravitational radiation, and the potential implications of superconducting mechanisms imbibed in superstring structures. The resonance of cosmic superstrings in enhanced gravitational radiation detection pathways, as advocated by numerical models, underscores their unique observability.

Theoretical and Practical Implications

The existence and paper of cosmic strings and superstring networks bear significant implications for the understanding of the cosmological structure and unified field theories. Cosmic superstrings particularly propose a viable avenue for empirically testing string theory and the broader cosmic evolution models. Their potential gravitational wave signatures, lensing capabilities, and CMB effects align with current experimental probes that may offer insights into the elusive properties of high-energy physics and universal topology.

Conclusion

The investigation into cosmic strings and superstrings as depicted in the paper offers a robust synthesis of theoretical predictions and observational parameters. While cosmic strings remain hypothetical, the evolving models and potential detection techniques underline their relevance in bridging quantum field theories and cosmological observations. The paper thus contributes significant depth to the paper of string theory effects in cosmological contexts and presents opportunities for continued advancements in theoretical and experimental physics, aligned with the progression towards understanding the universe's topological constructs.