arXiv subjects

T. W. B. Kibble

Publications and source records attributed to T. W. B. Kibble.

48 records · Page 3Linked to original sources

arXiv1995

Big bang simulation in superfluid 3He-B -- Vortex nucleation in neutron-irradiated superflow

We report the observation of vortex formation upon the absorption of a thermal neutron in a rotating container of superfluid $^3$He-B. The nuclear reaction n + $^3$He = p + $^3$H + 0.76MeV heats a cigar shaped region of the superfluid into the normal phase. The subsequent cooling of this region back through the superfluid transition results in the nucleation of quantized vortices. Depending on the superflow velocity, sufficiently large vortex rings grow under the influence of the Magnus force and escape into the container volume where they are detected individually with nuclear magnetic resonance. The larger the superflow velocity the smaller the rings which can expand. Thus it is possible to obtain information about the morphology of the initial defect network. We suggest that the nucleation of vortices during the rapid cool-down into the superfluid phase is similar to the formation of defects during cosmological phase transitions in the early universe.

cond-mat↗

arXiv1995

An Extension to Models for Cosmic String Formation

The canonical Monte-Carlo algorithm for simulating the production of string-like topological defects at a phase transition is extended by introducing a distribution of domain sizes. A strong correlation is found between the fraction in the form of `infinite' string and the variance of the volume of the regions of constant phase.

hep-ph↗

arXiv1995

Defect Production in Slow First Order Phase Transitions

We study the formation of vortices in a U(1) gauge theory following a first-order transition proceeding by bubble nucleation, in particular the effect of a low velocity of expansion of the bubble walls. To do this, we use a two-dimensional model in which bubbles are nucleated at random points in a plane and at random times and then expand at some velocity $v_{\rm b}<c$. Within each bubble, the phase angle is assigned one of three discrete values. When bubbles collide, magnetic `fluxons' appear: if the phases are different, a fluxon--anti-fluxon pair is formed. These fluxons are eventually trapped in three-bubble collisions when they may annihilate or form quantized vortices. We study in particular the effect of changing the bubble expansion speed on the vortex density and the extent of vortex--anti-vortex correlation.

hep-ph↗

arXiv1995

Phase equilibration in bubble collisions

In the context of an Abelian gauge symmetry, spontaneously broken at a first-order transition, we discuss the evolution of the phase difference between the Higgs fields in colliding bubbles. We show that the effect of dissipation, represented by a finite plasma conductivity, is to cause the phases to equlibrate on a time-scale, determined by the conductivity, which can be much smaller than the bubble radii at the time of collision. Currents induced during the phase equilibration generate a magnetic flux, which is determined by the initial phase difference. In a three-bubble collision, the fluxes produced by each pair of bubbles combine, and a vortex can be formed. We find that, under most conditions, the probability of trapping magnetic flux to form a vortex is correctly given by the ``geodesic rule''.

hep-ph↗

arXiv1995

Density of strings formed at a second-order cosmological phase transition

We discuss the problem of estimating the characteristic length scale $ξ_{\rm s}$, and hence the initial density, of a system of cosmic strings formed at a continuous, second-order phase transition in the early universe. In particular, we examine the roles of the correlation length (or string width) $ξ_{\rm c}$ and the Ginzburg length $ξ_{\rm G}$ which defines the ``fuzziness'' of long strings. We argue that strings acquire a clear identity only once $ξ_{\rm s}$ exceeds both $ξ_{\rm c}$ and $ξ_{\rm G}$, and estimate its magnitude at that time.

hep-ph↗

arXiv1994

High Harmonic Configurations of Cosmic Strings: An Analysis of Self-Intersections

A general formulation for describing odd-harmonic cosmic strings is developed and used to determine the self-intersection properties of high-harmonic loops. This is important because loop formation mechanisms produce high-harmonic components (kinks) which can only be eliminated very slowly by gravitational radiation, damping by the dense surrounding plasma in the era of string formation, or by the expansion of the Universe. For the class of loops examined it has been found that in the high-harmonic limit, essentially all cosmic loops self-intersect.

hep-ph↗

arXiv1994

Characteristics of Cosmic String Scaling Configurations

Using the formalism developed in a previous paper we analyze the cosmological implications of our conclusions concerning the scaling behaviour of a network of cosmic strings, in particular the idea that once gravitational back-reaction becomes important the transient scaling regime so far explored by numerical simulations will be replaced by a new `full scaling' regime, with slightly different parameters. This has consequences for the normalization of the string tension on all scales. We show how the new scaling solutions affect the gravitational wave bound from nucleosynthesis and the milli-second pulsar, and also describe the consequences from large scale structure up to COBE scales.

hep-ph↗

arXiv1994

Cosmic strings

The topic of cosmic strings provides a bridge between the physics of the very small and the very large. They are predicted by some unified theories of particle interactions. If they exist, they may help to explain some of the largest-scale structures seen in the Universe today. They are `topological defects' that may have been formed at phase transitions in the very early history of the Universe, analogous to those found in some condensed-matter systems --- vortex lines in liquid helium, flux tubes in type-II superconductors, or disclination lines in liquid crystals. In this review, we describe what they are, why they have been hypothesized and what their cosmological implications would be. The relevant background from the standard models of particle physics and cosmology is described in section 1. In section 2, we review the idea of symmetry breaking in field theories, and show how the defects formed are constrained by the topology of the manifold of degenerate vacuum states. We also discuss the different types of cosmic strings that can appear in different field theories. Section 3 is devoted to the dynamics of cosmic strings, and section 4 to their interaction with other fields. The formation and evolution of cosmic strings in the early Universe is the subject of section 5, while section 6 deals with their observational implications. Finally, the present status of the theory is reviewed in section 7.

hep-ph↗

arXiv1994

Non Intercommuting Configurations in the Collisions of Type-I $U(1)$ Cosmic Strings

It is shown that for small relative angle and kinetic energy two type I $U(1)$ strings can form bound states upon collision instead of the more familiar intercommuting configuration. The velocity below which this may happen is estimated as function of the ratio of the coupling constants in the theory, crossing angle and initial kinetic energy.

hep-ph↗

arXiv1994

Cosmic Rays From Cosmic Strings

It has been speculated that cosmic string networks could produce ultra-high energy cosmic rays as a by-product of their evolution. By making use of recent work on the evolution of such networks, it will be shown that the flux of cosmic rays from cosmologically useful, that is GUT scale strings, is too small to be used as a test for strings with any foreseeable technology.

hep-ph↗

arXiv1993

Evolution of cosmic string configurations

We extend and develop our previous work on the evolution of a network of cosmic strings. The new treatment is based on an analysis of the probability distribution of the end-to-end distance of a randomly chosen segment of left-moving string of given length. The description involves three distinct length scales: $ξ$, related to the overall string density, $\barξ$, the persistence length along the string, and $ζ$, describing the small-scale structure, which is an important feature of the numerical simulations that have been done of this problem. An evolution equation is derived describing how the distribution develops in time due to the combined effects of the universal expansion, of intercommuting and loop formation, and of gravitational radiation. With plausible assumptions about the unknown parameters in the model, we confirm the conclusions of our previous study, that if gravitational radiation and small-scale structure effects are neglected, the two dominant length scales both scale in proportion to the horizon size. When the extra effects are included, we find that while $ξ$ and $\barξ$ grow, $ζ$ initially does not. Eventually, however, it does appear to scale, at a much lower level, due to the effects of gravitational back-reaction.

hep-ph↗

arXiv1992

How Efficient Is The Langacker-Pi Mechanism of Monopole Annihilation?

We investigate the dynamics of monopole annihilation by the Langacker-Pi mechanism. We find taht considerations of causality, flux-tube energetics and the friction from Aharonov-Bohm scatteering suggest that the monopole annihilation is most efficient if electromagnetism is spontaneously broken at the lowest temperature ($T_{em} \approx 10^6 GeV$) consistent with not having the monopoles dominate the energy density of the universe.

hep-ph↗