Field Theoretical Approach Research Articles

Using a field probe to study the mechanism of partial discharges in very small air gaps under direct voltage

Due to growing use of high-voltage direct current (HVDC) for power transmission, it is of interest whether diagnostic tools introduced in past for insulation condition assessment of high-voltage alternating current (HVAC) apparatus are also applicable for quality assurance tests of HVDC equipment. This refers in particular to measurement of partial (PD) in compliance with international standard IEC 60270 [1], [2]. As PD events in gaseous cavities embedded in bulk dielectric of HV equipment are most harmful ones, mechanism of such internal should be well known to judge PD severity as well as to specify appropriate procedures and quantities for PD tests under direct voltage. According to Devins cavity can be classified as Townsendlike discharges and streamer-like discharges [3]. Even if this classification seems to be reasonable for cavity under both alternating and direct voltage [4]-[6], this has been rejected by Bartnikas. So, he argued in [7] that the term 'streamer' by itself, when applied to PD in relatively short gaps or small cavity diameters, introduces unnecessarily a misleading term in PD lexicon. PD, when occurring in short gaps, may assume different forms: rapid and slow rise time spark-type pulses. This is also consistent with worldwide established PD model according to Kreuger [8], which is based on hypothesis that virtual cavity capacitance is discharged via a conductive spark channel. Despite simplicity, this concept was rejected by Pedersen and his coworkers [9], [10]. As an alternative, they promoted a more sophisticated field-theoretical approach based on a dipole model. As their concept is not easily understandable, this was presented in a more simplified manner in this Magazine [11], [12] as well as in [13].

Formula omitted] as a companion pole of [formula omitted

We study the light scalar sector up to 1.8 GeV by using a quantum field theoretical approach which includes a single kaonic state in a Lagrangian with both derivative and non-derivative interactions. By performing a fit to πK phase shift data in the I=1/2, J=0 channel, we show that K0⁎(800) (or κ) emerges as a dynamically generated companion pole of K0⁎(1430). This is a result of investigating quantum fluctuations with one kaon and one pion circulating in the loops dressing K0⁎(1430). We determine the position of the poles on the complex plane in the context of our approach: for K0⁎(1430) we get (1.413±0.002)−i(0.127±0.003) (in GeV), while for κ we get (0.746±0.019)−i(0.262±0.014) (in GeV). The model-dependence of these results and related uncertainties are discussed in the paper. A large-Nc study confirms that K0⁎(1430) is predominantly a quarkonium and that K0⁎(800) is a molecular-like dynamically generated state.

Hot and dense matter beyond relativistic mean field theory

Properties of hot and dense matter are calculated in the framework of quantum hadro-dynamics by including contributions from two-loop (TL) diagrams arising from the exchange of iso-scalar and iso-vector mesons between nucleons. Our extension of mean-field theory (MFT) employs the same five density-independent coupling strengths which are calibrated using the empirical properties at the equilibrium density of iso-spin symmetric matter. Results of calculations from the MFT and TL approximations are compared for conditions of density, temperature, and proton fraction encountered in astrophysics applications involving compact objects. The TL results for the equation of state (EOS) of cold pure neutron matter at sub- and near-nuclear densities agree well with those of modern quantum Monte Carlo and effective field-theoretical approaches. Although the high-density EOS in the TL approximation for neutron-star matter is substantially softer than its MFT counterpart, it is able to support a $2M_\odot$ neutron star required by recent precise determinations. In addition, radii of $1.4M_\odot$ stars are smaller by $\sim 1$ km than obtained in MFT. In contrast to MFT, the TL results also give a better account of the single-particle or optical potentials extracted from analyses of medium-energy proton-nucleus and heavy-ion experiments. In degenerate conditions, the thermal variables are well reproduced by results of Landau's Fermi-Liquid theory in which density-dependent effective masses feature prominently. The ratio of the thermal components of pressure and energy density expressed as $\Gamma_{th}=1+(P_{th}/\epsilon_{th})$, often used in astrophysical simulations, exhibits a stronger dependence on density than on proton fraction and temperature in both MFT and TL calculations. The prominent peak of $\Gamma_{th}$ at supra-nuclear density found in MFT is, however, suppressed in TL calculations.

Tactical Innovation in Social Movements

Social movement researchers argue that tactical innovation occurs as a response to changes external to movements, such as police repression and shifts in political authority, or is due to internal movement processes, such as the characteristics of movement organizations and actors. In this study, we locate the roots of tactical innovation in the multiplicity of movement claims articulated at protest events. With data on more than 23,000 protest events that took place in the United States between 1960 and 1995, we develop novel measures of two forms of tactical innovation and the relationships between protest event claims. Our results show that multi-issue protest events are more likely to use novel recombinations of tactics, and protest events with more peripheral movement claims tend to introduce new protest tactics. Our approach brings together work on social movement dynamics, innovation, and field theoretic approaches to theorize about the relationship between the tools and content of activism.

Oscillating Yukawa fluid at a hard wall: field theory description

ABSTRACTA field-theoretical approach is applied to study the structure of an oscillating Yukawa fluid in contact with a hard wall. The system is described beyond the mean field approximation with the Gaussian fluctuations taken into account. Analytical expressions for the pair correlation function, the density profiles, and the adsorption coefficient are derived. These results are analysed for different values of the temperature and the bulk density as well as the parameters of the pair potential. In order to estimate the validity of the applied approximations, the theoretical results are compared with the original computer simulations data. We show that the Gaussian approximation provides a much better description of the fluid density profile as compared to the mean field approximation.

Mayer expansion of the Nekrasov prepotential: The subleading ε2-order

The Mayer cluster expansion technique is applied to the Nekrasov instanton partition function of N=2SU(Nc) super Yang–Mills. The subleading small ε2-correction to the Nekrasov–Shatashvili limiting value of the prepotential is determined by a detailed analysis of all the one-loop diagrams. Indeed, several types of contributions can be distinguished according to their origin: long range interaction or potential expansion, clusters self-energy, internal structure, one-loop cyclic diagrams, etc. The field theory result derived more efficiently in [1], under some minor technical assumptions, receives here definite confirmation thanks to several remarkable cancellations: in this way, we may infer the validity of these assumptions for further computations in the field theoretical approach.

Causality and quantum criticality in long-range lattice models.

Long-range quantum lattice systems often exhibit drastically different behavior than their short-range counterparts. In particular, because they do not satisfy the conditions for the Lieb-Robinson theorem, they need not have an emergent relativistic structure in the form of a light cone. Adopting a field-theoretic approach, we study the one-dimensional transverse-field Ising model with long-range interactions, and a fermionic model with long-range hopping and pairing terms, explore their critical and near-critical behavior, and characterize their response to local perturbations. We deduce the dynamic critical exponent, up to the two-loop order within the renormalization group theory, which we then use to characterize the emergent causal behavior. We show that beyond a critical value of the power-law exponent of the long-range couplings, the dynamics effectively becomes relativistic. Various other critical exponents describing correlations in the ground state, as well as deviations from a linear causal cone, are deduced for a wide range of the power-law exponent.

A Field-Theoretic Approach to the Wiener Sausage

The Wiener Sausage, the volume traced out by a sphere attached to a Brownian particle, is a classical problem in statistics and mathematical physics. Initially motivated by a range of field-theoretic, technical questions, we present a single loop renormalised perturbation theory of a stochastic process closely related to the Wiener Sausage, which, however, proves to be exact for the exponents and some amplitudes. The field-theoretic approach is particularly elegant and very enjoyable to see at work on such a classic problem. While we recover a number of known, classical results, the field-theoretic techniques deployed provide a particularly versatile framework, which allows easy calculation with different boundary conditions even of higher momenta and more complicated correlation functions. At the same time, we provide a highly instructive, non-trivial example for some of the technical particularities of the field-theoretic description of stochastic processes, such as excluded volume, lack of translational invariance and immobile particles. The aim of the present work is not to improve upon the well-established results for the Wiener Sausage, but to provide a field-theoretic approach to it, in order to gain a better understanding of the field-theoretic obstacles to overcome.

Phase diagram of Model C in the parametric space of order parameter and space dimensions

The scaling behavior of Model C describing the dynamical behavior of the $n$-component nonconserved order parameter coupled statically to a scalar conserved density is considered in $d$-dimensional space. Conditions for the realization of different types of scaling regimes in the $(n,d)$ plane are studied within the field-theoretical renormalization group approach. Borders separating these regions are calculated on the base of high-order RG functions using $\ensuremath{\epsilon}$ expansions as well as by fixed dimension $d$ approach with resummation.

Nonequilibrium many-body steady states via Keldysh formalism.

Many-body systems with both coherent dynamics and dissipation constitute a rich class of models which are nevertheless much less explored than their dissipationless counterparts. The advent of numerous experimental platforms that simulate such dynamics poses an immediate challenge to systematically understand and classify these models. In particular, nontrivial many-body states emerge as steady states under nonequilibrium dynamics. While these states and their phase transitions have been studied extensively with mean-field theory, the validity of the mean-field approximation has not been systematically investigated. In this paper, we employ a field-theoretic approach based on the Keldysh formalism to study nonequilibrium phases and phase transitions in a variety of models. In all cases, a complete description via the Keldysh formalism indicates a partial or complete failure of the mean-field analysis. Furthermore, we find that an effective temperature emerges as a result of dissipation, and the universal behavior including the dynamics near the steady state is generically described by a thermodynamic universality class.

Relativistic and Nuclear Medium Effects on the Coulomb Sum Rule.

In light of the forthcoming high precision quasielastic electron scattering data from Jefferson Lab, it is timely for the various approaches to nuclear structure to make robust predictions for the associated response functions. With this in mind, we focus here on the longitudinal response function and the corresponding Coulomb sum rule for isospin-symmetric nuclear matter at various baryon densities. Using a quantum field-theoretic quark-level approach which preserves the symmetries of quantum chromodynamics, as well as exhibiting dynamical chiral symmetry breaking and quark confinement, we find a dramatic quenching of the Coulomb sum rule for momentum transfers |q|≳0.5 GeV. The main driver of this effect lies in changes to the proton Dirac form factor induced by the nuclear medium. Such a dramatic quenching of the Coulomb sum rule was not seen in a recent quantum MonteCarlo calculation for carbon, suggesting that the Jefferson Lab data may well shed new light on the explicit role of QCD in nuclei.

The Harari--Shupe Observation Without Preons --- a Glimpse of Physics to Come?

We argue that one has to distinguish between the Harari-Shupe model (HSM) and the Harari-Shupe observation (HSO). The former - in which quarks and leptons are viewed as composite objects built from confined fermionic subparticles (`rishons') - is known to be beset with many difficulties. The latter may be roughly defined as this part of the HSM that really works. We recall that the phase-space Clifford-algebra approach leads to the HSO without any of the HSM problems and discuss in some detail how this is achieved. The light which the phase-space-based view sheds on the HSO sets then a new direction along which the connection between space and particle properties could be studied and offers a glimpse into weird physics that probably lurks much deeper than the field-theoretical approach of the Standard Model.

Exclusive diffractive production ofπ+π−continuum and resonances within tensor pomeron approach

We discuss exclusive central diffractive dipion production in proton-(anti)proton collisions at high energies. The calculation is based on a tensor pomeron model and the amplitudes for the processes are formulated in an effective field-theoretic approach. We include the purely diffractive dipion continuum, and the scalar and tensor resonances decaying into the π + π − pairs as well as the photoproduction contributions ( ρ 0 , Drell-Soding). We discuss how two pomerons couple to tensor meson f 2 (1270) and the interference effects of resonance and dipion continuum. The theoretical results are compared with CDF and CMS experimental data. We show the influence of the experimental cuts on the integrated cross section and on various differential distributions for outgoing particles. We find that the relative contribution of resonant f 2 (1270) and dipion continuum strongly depends on the cut on proton transverse momenta (or four-momentum transfer squared t 1,2 ) which may explain some controversial observations made by different ISR experiments in the past. The cuts may play then the role of a ππ resonance filter. We suggest some experimental analyses to fix model parameters related to the pomeron-pomeron-meson coupling.

Quantum Detectors in Generic Non Flat FLRW Space-Times

A quantum field theoretical approach, in which a quantum probe is used to investigate the properties generic non-flat FLRW space-times is discussed. The probe is identified with a conformally coupled massless scalar field defined on a space-time with horizon and the procedure to investigate the local properties is realized by the use of Unruh-DeWitt detector and by the evaluation of the regularized quantum fluctuations. In the case of de Sitter space, the coordinate independence of our results is checked, and the Gibbons-Hawking temperature is recovered. A possible generalization to the electromagnetic probe is also briefly indicated.

A field theoretic approach to the electric interfacial layer — Mixture of trivalent rod-like and monovalent point-like ions between charged walls

In this paper, we study the interaction between charged macroions (surfaces) immersed in a solution of oppositely charged, rod-like counterions and point-like co-ions. The system is modeled by a field theoretic approach, which was extended to treat mixtures of rod- and point-like ions. The theory is applicable from the weak to the intermediate through to the strong coupling regimes. In the weak coupling limit, the force between the charged surfaces are only repulsive. In the intermediate coupling regime, the rod-like ions can induce attractive force between the charged surfaces. In the strong coupling limit, the inter-ionic charge correlations dominate the attractive forces at short separations between the charged surfaces.

The particle production at the event horizon of a black hole as gravitational Fowler-Nordheim emission in uniformly accelerated frame, in the non-relativistic scenario

In the conventional scenario, the Hawking radiation is believed to be a tunneling process at the event horizon of the black hole. In the quantum field theoretic approach the Schwinger’s mechanism is generally used to give an explanation of this tunneling process. It is the decay of quantum vacuum into particle anti-particle pairs near the black hole surface. However, in a reference frame undergoing a uniform accelerated motion in an otherwise flat Minkowski space-time geometry, in the non-relativistic approximation, the particle production near the event horizon of a black hole may be treated as a kind of Fowler-Nordheim field emission, which is the typical electron emission process from a metal surface under the action of an external electrostatic field. This type of emission from metal surface is allowed even at extremely low temperature. It has been noticed that in one-dimensional scenario, the Schrödinger equation satisfied by the created particle (anti-particle) near the event horizon, can be reduced to a differential form which is exactly identical with that obeyed by an electron immediately after the emission from the metal surface under the action of a strong electrostatic field. The mechanism of particle production near the event horizon of a black hole is therefore identified with Schwinger process in relativistic quantum field theory, whereas in the non-relativistic scenario it may be interpreted as Fowler-Nordheim emission process, when observed from a uniformly accelerated frame.

Universal terms of entanglement entropy for 6d CFTs

We derive the universal terms of entanglement entropy for 6d CFTs by applying the holographic and the field theoretical approaches, respectively. Our formulas are conformal invariant and agree with the results of [34,35]. Remarkably, we find that the holographic and the field theoretical results match exactly for the $C^2$ and $Ck^2$ terms. Here $C$ and $k$ denote the Weyl tensor and the extrinsic curvature, respectively. As for the $k^4$ terms, we meet the splitting problem of the conical metrics. The splitting problem in the bulk can be fixed by equations of motion. As for the splitting on the boundary, we assume the general forms and find that there indeed exists suitable splitting which can make the holographic and the field theoretical $k^4$ terms match. Since we have much more equations than the free parameters, the match for $k^4$ terms is non-trivial.

Community as a mechanism for transcending wellbeing at the individual, social, and ecological levels

Community wellbeing, from a field theoretical perspective, derives from the interaction of three core elements reflecting different levels and units of analysis – individual, social, and ecological. These facets of community, and their related concepts, come together in a powerful way to shape relationships, opportunities for agency, and local adaptive capacities that lead to wellbeing. Unfortunately, much of the extant community literature moves across and among these three dimensions without regard to how efforts at one level impact another. The literature lacks a theoretical framework that links the individual, social, and ecological levels of wellbeing and community into a coherent whole. Here, we conducted a meta-study of data drawn from within the field theoretical approach to community literature and included a series of theoretical papers, books, journal articles, and community studies spanning from 1959 to 2013. We found that community, from a field theoretical view, contributes to and impacts wellbeing at the individual, social, and ecological levels. Further, we provide a framework, based within the field theoretical approach to community, which can be applied to the study of community and wellbeing at all levels. Practical applications and areas of further research are discussed.

Elucidating the Morphological Complexities of Linear Symmetric Triblock Polymers Confined Between Two Parallel Plates: A Self‐Consistent Field Theoretic Approach

Three dimensional self‐consistent field theoretic simulations have been performed to determine the equilibrium morphologies formed by linear ABC triblock polymer melts confined between two parallel plates that favor the middle block. Our primary goal is to elucidate the conditions under which the perpendicular lamella is stabilized, since this morphology plays a central role in many nanotechnology applications. Key factors, namely, the chain architecture, surface energy and the mismatch between the film thickness d and the bulk lamella period, L0, determine the final morphologies, e.g., perpendicular and parallel lamella, perforated lamella and wet substrate with parallel cylinders in the core, have been identified. Overall, our findings are fully consistent with the results of limited experimental studies focused on morphology development in thin films of triblock polymer melts. Finally, we have clearly demonstrated that ABC triblocks hold technological advantages over diblocks for nano‐lithographic fabrications.

A modified Poisson-Boltzmann theory: Effects of co-solvent polarizability

In this paper within a field-theoretical approach taking into account explicitly a co-solvent with a nonzero dipole and a polarizability tensor, we derive a modified Poisson-Boltzmann equation. Applying the modified Poisson-Boltzmann equation, we formulate a generalized Gouy-Chapman theory for the case when an electrolyte solution is mixed with a polar co-solvent having a large polarizability. We show that an increase of the co-solvent concentration as well as the co-solvent polarizability lead to a significant increase of differential capacitance at sufficiently high surface potentials of the electrode, whereas the profile of the electrostatic potential becomes considerably more long-ranged. On the contrary, an increase in the permanent dipole of the co-solvent only weakly affects the differential capacitance.