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T. W. B. Kibble

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

At least 37 records · Page 2Linked to original sources
arXiv2004

Spontaneous vortex formation on a superconductor film

We carry out numerical simulations to investigate spontaneous vortex formation during a temperature quench of a superconductor film from the normal to the superconducting phase in the absence of an external magnetic field. Our results agree roughly with quantitative predictions of the flux trapping scenario: In fast quenches the agreement is almost perfect, but there appears to be some discrepancy in slower ones. In particular, our simulations demonstrate the crucial role the electromagnetic field plays in this phenomenon, making it very different from vortex formation in superfluids. Besides superconductor experiments, our findings also shed more light on the possible formation of cosmic defects in the early universe.

cond-mat.supr-con↗
arXiv2003

Estimation of vortex density after superconducting film quench

This paper addresses the problem of vortex formation during a rapid quench in a superconducting film. It builds on previous work showing that in a local gauge theory there are two distinct mechanisms of defect formation, based on fluctuations of the scalar and gauge fields, respectively. We show how vortex formation in a thin film differs from the fully two-dimensional case, on which most theoretical studies have focused. We discuss ways of testing theoretical predictions in superconductor experiments and analyse the results of recent experiments in this light.

cond-mat↗
arXiv2002

The monopole mass in the three-dimensional Georgi-Glashow model

We study the three-dimensional Georgi-Glashow model to demonstrate how magnetic monopoles can be studied fully non-perturbatively in lattice Monte Carlo simulations, without any assumptions about the smoothness of the field configurations. We examine the apparent contradiction between the conjectured analytic connection of the `broken' and `symmetric' phases, and the interpretation of the mass (i.e., the free energy) of the fully quantised 't Hooft-Polyakov monopole as an order parameter to distinguish the phases. We use Monte Carlo simulations to measure the monopole free energy and its first derivative with respect to the scalar mass. On small volumes we compare this to semi-classical predictions for the monopole. On large volumes we show that the free energy is screened to zero, signalling the formation of a confining monopole condensate. This screening does not allow the monopole mass to be interpreted as an order parameter, resolving the paradox.

hep-lat↗
arXiv2002

Symmetry breaking and defects

Symmetry-breaking phase transitions are ubiquitous in condensed matter systems and in quantum field theories. There is also good reason to believe that they feature in the very early history of the Universe. At many such transitions topological defects of one kind or another are formed. Because of their inherent stability, they can have important effects on the subsequent behaviour of the system. In the first of these lectures I shall review a number of examples of spontaneous symmetry breaking, many of which will be discussed in more detail by other lecturers, and discuss their general features. The second lecture will be mainly devoted to the conditions under which topological defects can appear and their classification in terms of homotopy groups of the underlying vacuum manifold. In my final lecture, I will discuss the `cosmology in the laboratory' experiments which have been done to try to test some of the ideas thrown up by discussions of defect formation in the early Universe by looking at analogous processes in condensed-matter systems.

cond-mat↗
arXiv2001

Testing cosmological defect formation in the laboratory

Topological defects such as cosmic strings may have been formed at early-universe phase transitions. Direct tests of this idea are impossible, but the mechanism can be elucidated by studying analogous processes in low-temperature condensed-matter systems. Experiments on vortex formation in superfluid helium and in superconductors have so far yielded somewhat confusing results. I shall discuss their possible interpretation.

cond-mat.soft↗
arXiv2001

Nielsen-Olesen vortex in varying-alpha theories

We consider soliton solutions to Bekenstein's theory, for which the fine structure constant $α=e^2/(4π\hbar c)$ is allowed to vary due to the presence of a dielectric field pervading the vacuum. More specifically we investigate the effects of a varying $α$ upon a complex scalar field with a U(1) electromagnetic gauge symmetry subject to spontaneous symmetry breaking. We find vortex solutions to this theory, similar to the Nielsen-Olesen vortex. Near the vortex core the electric charge is typically much larger than far away from the string, lending these strings a superconducting flavour. In general the dielectric field coats the usual local string with a global string envelope. We discuss the cosmological implications of networks of such strings, with particular emphasis on their ability to generate inhomogeneous recombination scenarios. We also consider the possibility of the dielectric being a charged free field. Even though the vacuum of such a field is trivial, we find that the dielectric arranges itself in the shape of a local string, with a quantized magnetic flux at the core -- presumably borrowing these topological features from the underlying Nielsen-Olesen vortex.

hep-ph↗
arXiv2000

Topological defects in lattice gauge theories

We present a non-perturbative formalism for measuring defect free energies (monopole mass or vortex tension) in three-dimensional SU(2)+adjoint Higgs models. Starting from twisted, translation invariant boundary conditions, we perform a change of variables that allows us to express the defect free energies in terms of 't Hooft loops. We propose that the defect free energies can be used to distinguish between phases in this model, and also more generally in other gauge field theories where no local order parameters exist. In the case of monopoles, our construction can also be used in four-dimensional pure-gauge SU(2) theory, where it gives the monopole mass in the maximally Abelian gauge without the need of actually fixing the gauge in the simulation. Moreover, the expression is manifestly independent of the choice of the Abelian projection as long as it is compatible with the classical 't Hooft-Polyakov solution.

hep-lat↗
arXiv2000

Composite defect extends cosmology - 3He analogy

Spin-mass vortices have been observed to form in rotating superfluid 3He-B following the absorption of a thermal neutron and a rapid transition from the normal to superfluid state. The spin-mass vortex is a composite defect which consists of a planar soliton (wall) which terminates on a linear core (string). This observation fits well within the framework of a cosmological scenario for defect formation, known as the Kibble-Zurek mechanism. It suggests that in the early Universe analogous cosmological defects might have formed.

cond-mat↗
arXiv2000

Dynamics and properties of chiral cosmic strings in Minkowski space

Chiral cosmic strings are produced naturally at the end of inflation in supersymmetric models where the symmetry is broken via a D-term. Consequently in such theories, where both inflation and cosmic strings contribute to the density and CMBR (microwave background) perturbations, it is necessary to understand the evolution of chiral cosmic string networks. We study the dynamics of chiral cosmic strings in Minkowski space and comment on a number of differences with those of Nambu-Goto strings. To do this we follow the work of Carter and Peter who showed that the equations of motion for chiral cosmic strings reduce to a wave equation and two constraints, only one of which is different from the familiar Nambu-Goto constraints. We study chiral string loop solutions consisting of many harmonics and determine their self-intersection probabilities, and comment on the possible cosmological significance of these results.

astro-ph↗
arXiv1999

Electroweak Vacuum Geometry

We analyse symmetry breaking in the Weinberg-Salam model paying particular attention to the underlying geometry of the theory. In this context we find two natural metrics upon the vacuum manifold: an isotropic metric associated with the scalar sector, and a squashed metric associated with the gauge sector. Physically, the interplay between these metrics gives rise to many of the non-perturbative features of Weinberg-Salam theory.

hep-th↗
arXiv1999

Surface Quantum Effects in a Fireball Model of Gamma Ray Bursts

Recent rapid advances in the observations of Gamma Ray Bursts (GRBs) lend much confidence to the cosmological fireball (FB) model: there is now compelling evidence that the radiation is emitted by a relativistic shock where a high speed upstream flow terminates. The question concerning what generates such an outflow is central to our search for the ultimate trigger mechanism. A key requirement, not well explained by current theories, is that the flow must have high entropy-to-baryon ratio. In this Letter we point out that a quantum discharge induced by the radiation of the initial FB may be the explanation. The effect is likely to be relevant, because the FB energy density inferred from GRB data is large enough that the radiation pressure leads to the formation of a surface electric field which is unstable to pair creation. Under suitable conditions, such as those of a supernova core, the discharge can convert a substantial fraction of the FB energy into surface pairs. This pair plasma is not contaminated by FB baryons because it is formed outside the FB. We demonstrate that the pairs can then develop relativistic bulk expansion, reaching a maximum speed that meets the constraints required to form a GRB.

astro-ph↗
arXiv1998

The evolution of a network of cosmic string loops

We set up and analyse a model for the non-equilibrium evolution of a network of cosmic strings initially containing only loops and no infinite strings. Due to this particular initial condition, our analytical approach differs significantly from existing ones. We describe the average properties of the network in terms of the distribution function n(l,t) dl, the average number of loops per unit volume with physical length between l and l + dl at time t. The dynamical processes which change the length of loops are then estimated and an equation, which we call the `rate equation', is derived for (dn/dt). In a non-expanding universe, the loops should reach the equilibrium distribution predicted by string statistical mechanics. Analysis of the rate equation gives results consistent with this. We then study the rate equation in an expanding universe and suggest that three different final states are possible for the evolving loop network, each of which may well be realised for some initial conditions. If the initial energy density in loops in the radiation era is low, then the loops rapidly disappear. For large initial energy densities, we expect that either infinite strings are formed or that the loops tend towards a scaling solution in the radiation era and then rapidly disappear in the matter era. Such a scenario may be relevant given recent work highlighting the problems with structure formation from the standard cosmic string scenario.

hep-ph↗
arXiv1998

Gamma Ray Burst as Vacuum Discharge of Super-Schwinger Electric Fields

A theory is proposed to explain with simplicity the basic observed properties of a Gamma Ray Burst (GRB). It employs a well-known result of Schwinger, that static electric fields in excess of a critical value are unstable to pair creation, and catastrophically produces a thermal plasma at temperatures <= 0.5 MeV. By using observational values for the energy and volume of the source, it is shown that the radiation pressure of an expanding GRB `fireball' leads to the formation of a Schwinger critical field at the ambient medium immediately outside the `fireball'. This naturally provides a runaway solution which is inevitable, and which must involve a burst of gamma radiation in the core of the observed energy range and in an optically thin environment. The observed burst duration of 1 -- 10 seconds is also a straightforward consequence of the theory.

astro-ph↗
arXiv1998

Wick's Theorem for non-symmetric normal ordered products and contractions

We consider arbitrary splits of field operators into two parts, and use the corresponding definition of normal ordering introduced by Evans and Steer. In this case the normal ordered products and contractions have none of the special symmetry properties assumed in existing proofs of Wick's theorem. Despite this, we prove that Wick's theorem still holds in its usual form as long as the contraction is a c-number. Wick's theorem is thus shown to be much more general than existing derivations suggest, and we discuss possible simplifying applications of this result.

hep-ph↗
arXiv1997

Non-Abelian String Conductivity

We examine current-carrying configurations of cosmic strings in non-Abelian gauge theories. We study the solutions numerically and point out that the currents will be at best dynamically stable and not subject to any topological quantisation or conservation, as in conventional models of string superconduction. We suggest that non-Abelian string loops may be unable to support persistent currents in the absence of external fields. This will have relevance to vorton stability.

hep-ph↗
arXiv1996

On Phase Ordering Behind the Propagating Front of a Second-Order Transition

In a real system the heating is nonuniform and a second-order phase transition into a broken symmetry phase occurs by propagation of the temperature front. Two parameters, the cooling rate $τ_Q$ and the velocity $v_T$ of the transition front, determine the nucleation of topological defects. Depending on the relation of these parameters two regimes are found: in the regime of fast propagation defects are created according to the Zurek scenario for the homogeneous case, while in the slow propagation regime vortex formation is suppressed.

cond-mat↗
arXiv1996

Quench Induced Vortices in the Symmetry Broken Phase of Liquid $^4$He

Motivated by the study of cosmological phase transitions, our understanding of the formation of topological defects during spontaneous symmetry-breaking and the associated non-equilibrium field theory has recently changed. Experiments have been performed in superfluid $^4$He to test the new ideas involved. In particular, it has been observed that a vortex density is seen immediately after pressure quenches from just below the $λ$ transition. We discuss possible interpretations of these vortices, conclude they are consistent with our ideas of vortex formation and propose a modification of the original experiments.

cond-mat↗