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R. J. Rivers

Publications and source records attributed to R. J. Rivers.

At least 37 records · Page 2Linked to original sources
arXiv2003

Decoherence in Field Theory: General Couplings and Slow Quenches

We study the onset of a classical order parameter after a second-order phase transition in quantum field theory. We consider a quantum scalar field theory in which the system-field (long-wavelength modes), interacts with its environment, represented both by a set of scalar fields and by its own short-wavelength modes. We compute the decoherence times for the system-field modes and compare them with the other time scales of the model. We analyze different couplings between the system and the environment for slow quenches. Within our approximations decoherence is in general a short time event.

hep-ph↗
arXiv2003

Scaling Laws for Fluxon Formation in Annular Josephson Tunnel Junctions

It has been argued by Zurek and Kibble that the likelihood of producing defects in a continuous phase transition depends in a characteristic way on the quench rate. In this paper we discuss our experiment for measuring the Zurek-Kibble scaling exponent $σ$ for the production of fluxons in annular symmetric Josephson Tunnel Junctions. The predicted exponent is $% σ=0.25$, and we find $σ=0.27\pm 0.05$. Further, there is agreement with the ZK prediction for the overall normalisation.

cond-mat.supr-con↗
arXiv2002

The Formation of Classical Defects After a Slow Quantum Phase Transition

Classical defects (monopoles, vortices, etc.) are a characteristic consequence of many phase transitions of quantum fields. We show a model in which the onset of classical probability distributions, for the long-wavelength modes at early times, allows the identification of line-zeroes of the field with vortex separation. We obtain a refined version of Kibble's causal results for defect separation, but from a completely different approach. It is apparent that vortices are not created from thermal fluctuations in the Ginzburg regime.

hep-ph↗
arXiv2002

Transport Coefficients and Analytic Continuation in Dual 1+1 Dimensional Models at Finite Temperature

The conductivity of a finite temperature 1+1 dimensional fermion gas described by the massive Thirring model is shown to be related to the retarded propagator of the dual boson sine-Gordon model. Duality provides a natural resummation which resolves infra-red problems, and the boson propagator can be related to the fermion gas at non-zero temperature and chemical potential or density. In addition, at high temperatures, we can apply a dimensional reduction technique to find resummed closed expressions for the boson self-energy and relate them to the fermion conductivity. Particular attention is paid to the discussion of analytic continuation. The resummation implicit in duality provides a powerful alternative to the standard diagrammatic evaluation of transport coefficients at finite temperature.

hep-th↗
arXiv2002

Classical Behaviour After a Phase Transition: II. The Formation of Classical Defects

Classical defects (monopoles, vortices, etc.) are a characteristic consequence of many phase transitions of quantum fields. Most likely these include transitions in the early universe and such defects would be expected to be present in the universe today. We continue our analysis of the onset of classical behaviour after a second-order phase transition in quantum field theory and show how defects appear after such transitions

hep-ph↗
arXiv2002

Classical Behaviour After a Phase Transition: I. Classical Order Parameters

We analyze the onset of classical field configurations after a phase transition. Firstly, we motivate the problem by means of a toy model in quantum mechanics. Subsequently, we consider a scalar field theory in which the system-field interacts with its environment, represented both by further scalar fields and by its own short-wavelength modes. We show that, for very rapid quenches, the order parameter can be treated classically by the time that it has achieved its ground state values (spinodal time).

hep-ph↗
arXiv2001

Classical behaviour after a phase transition

We analyze the onset of classical behaviour after a second-order phase transition by considering a scalar field theory in which the system-field interacts with its environment, represented both by further fields and by its own short-wavelength modes. Within our approximations we see that the long-wavelength modes have become classical by the time that the transition has been first implemented (the spinodal time).

hep-ph↗
arXiv2000

Non-Equilibrium Duality

The dual 'worldline', or 'string', description of adiabatic Ginzburg-Landau field theory near a phase transition in terms of quasi-Brownian strings and loops is well understood. In reality, the implementation of a transition is intrinsically non-equilibrium. We sketch how time-dependent Ginzburg-Landau theory leads to a modified dual string picture in which a causal bound on the growth of unstable string prevents the uncontrolled proliferation of string (the Shockley-Hagedorn transition) suggested by the adiabatic approximation.

cond-mat↗
arXiv2000

Exploiting duality in a toy model of QCD at non-zero temperature and chemical potential: the massive Thirring model, sine-Gordon model and Coulomb gases

We focus on the massive Thirring model in 1+1 dimensions at finite temperature and non-zero chemical potential, and comment on some parallels between this model and QCD. In QCD, calculations of physical quantities such as transport coefficients are extremely difficult. In the massive Thirring model, similar calculations are greatly simplified by exploiting the duality which exists with the sine-Gordon model and its relation, at high temperature, to the exactly solvable classical Coulomb gas on the line.

hep-th↗
arXiv2000

Testing the Kibble-Zurek Scenario with Annular Josephson Tunnel Junctions

In parallel with Kibble's description of the onset of phase transitions in the early universe, Zurek has provided a simple picture for the onset of phase transitions in condensed matter systems, strongly supported by agreement with experiments in He3. In this letter we show how experiments with annular Josephson tunnel Junctions can and do provide further support for this scenario.

cond-mat.supr-con↗
arXiv2000

The Onset of Phase Transitions in Condensed Matter and Relativistic QFT

Kibble and Zurek have provided a unifying causal picture for the appearance of topological defects like cosmic strings or vortices at the onset of phase transitions in relativistic QFT and condensed matter systems respectively. There is no direct experimental evidence in QFT, but in condensed matter the predictions are largely, but not wholly, supported in superfluid experiments on liquid helium. We provide an alternative picture for the initial appearance of strings/vortices that is commensurate with all the experimental evidence from condensed matter and consider some of its implications for QFT.

cond-mat↗
arXiv2000

Fluctuations and Phase Transition Dynamics

Kibble and Zurek have provided a unifying causal picture for the appearance of classical defects like cosmic strings or vortices at the onset of phase transitions in relativistic QFT and condensed matter systems respectively. In condensed matter the predictions are partially supported by agreement with experiments in superfluid helium. We provide an alternative picture for the initial appearance of defects that supports the experimental evidence. When the original predictions fail, this is understood, in part, as a consequence of thermal fluctuations (noise), which play a comparable role in both condensed matter and QFT.

hep-ph↗
arXiv1999

Slow $^{4}He$ Quenches Produce Fuzzy, Transient Vortices

We examine the Zurek scenario for the production of vortices in quenches of liquid $^{4}He$ in the light of recent experiments. Extending our previous results to later times, we argue that short wavelength thermal fluctuations make vortices poorly defined until after the transition has occurred. Further, if and when vortices appear, it is plausible that that they will decay faster than anticipated from turbulence experiments, irrespective of quench rates.

cond-mat↗
arXiv1999

Chiral Symmetry restoration in the massive Thirring model at finite T and $μ$: Dimensional reduction and the Coulomb gas

We show that in certain limits the (1+1)-dimensional massive Thirring model at finite temperature $T$ is equivalent to a one-dimensional Coulomb gas of charged particles at the same $T$. This equivalence is then used to explore the phase structure of the massive Thirring model. For strong coupling and $T>>m$ (the fermion mass) the system is shown to behave as a free gas of "molecules" (charge pairs in the Coulomb gas terminology) made of pairs of chiral condensates. This binding of chiral condensates is responsible for the restoration of chiral symmetry as $T\to\infty$. In addition, when a fermion chemical potential $μ\neq 0$ is included, the analogy with a Coulomb gas still holds with $μ$ playing the role of a purely imaginary external electric field. For small $T$ and $μ$ we find a typical massive Fermi gas behaviour for the fermion density, whereas for large $μ$ it shows chiral restoration by means of a vanishing effective fermion mass. Some similarities with the chiral properties of low-energy QCD at finite $T$ and baryon chemical potential are discussed.

hep-th↗
arXiv1999

Can we Measure Superflow on Quenching He4?

Zurek has provided a simple picture for the onset of the lamda-transition in He4, not currently supported by vortex density experiments. However, we argue that the seemingly similar argument by Zurek that superflow in an annulus of He4 at the quench will be measurable is still valid.

cond-mat↗
arXiv1998

Kinks versus fermions or the 2D sine-Gordon versus massive Thirring models, at nonzero temperature and chemical potential

We study bosonisation in the massive Thirring and sine-Gordon models at finite temperature and nonzero fermion chemical potential. Both canonical operator and path integral approaches are used to prove the equality of the partition functions of the two models at finite $T$ and zero chemical potential, as it has been recently shown. This enables the relationship between thermal normal ordering and path-integral renormalisation to be specified. Furthermore, we prove that thermal averages of zero-charge operators can also be identified. At nonzero chemical potential and temperature we show, in perturbation theory around the massless case, that the bosonised theory is the sine-Gordon model plus an additional topological term, accounting for the existence of zero charge excitations (the fermions or the kinks) in the thermal bath. This result is the 2D version of the low-energy lagrangian at finite baryon density.

hep-th↗
arXiv1998

Phase Transitions in Condensed Matter and Relativistic QFT

Kibble and Zurek have provided a unifying picture for the onset of phase transitions in relativistic QFT and condensed matter systems respectively, strongly supported by agreement with condensed matter experiments in He3. The failure of a recent experiment on He4 to agree with the predictions has prompted a reappraisal of this picture. We provide an alternative picture that explains the experimental evidence.

cond-mat↗