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7 pages, 231 KiB

Open AccessEditorial

Quantum Field Theory

by Ralf Hofmann

Universe 2024, 10(1), 14; https://doi.org/10.3390/universe10010014 - 28 Dec 2023

Viewed by 2745

Abstract

This Special Issue on quantum field theory presents work covering a wide and topical range of subjects mainly within the area of interacting 4D quantum field theories subject to certain backgrounds [...] Full article

(This article belongs to the Special Issue Quantum Field Theory)

Research

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6 pages, 256 KiB

Open AccessCommunication

Yang–Mills Instantons in the Dual-Superconductor Vacuum Can Become Confining

by Dmitry Antonov

Universe 2023, 9(6), 257; https://doi.org/10.3390/universe9060257 - 29 May 2023

Cited by 1 | Viewed by 981

Abstract

As known, the realistic, exponential, fall-off of the rate of production of light mesons in the chromo-electric field of a quark–antiquark string, as a function of the meson mass, can be obtained from the Schwinger-formula Gaussian fall-off within a phenomenological approach which assumes [...] Read more.

As known, the realistic, exponential, fall-off of the rate of production of light mesons in the chromo-electric field of a quark–antiquark string, as a function of the meson mass, can be obtained from the Schwinger-formula Gaussian fall-off within a phenomenological approach which assumes a certain distribution of the string tension. This approach gets a clear meaning in the London limit of the dual superconductor, where the logarithmic increase of the chromo-electric field towards the core of the string leads precisely to the change of the Gaussian fall-off to the exponential one, thus allowing for an identification of the phenomenological distribution of the string tension. In this paper, we demonstrate that, for this distribution of the string tension, the distribution of large-size Yang–Mills instantons, which are interacting with the confining monopole background, becomes

O (1 / ρ^{3})

, where

ρ

is the size of an instanton. Since such a distribution of large-size instantons is known to yield confinement, we conclude that, in the London limit of the dual-superconductor vacuum, instantons can form a confining medium, and we evaluate their contribution to the total string tension. Full article

(This article belongs to the Special Issue Quantum Field Theory)

24 pages, 492 KiB

Open AccessArticle

Bosonic Casimir Effect in an Aether-like Lorentz-Violating Scenario with Higher Order Derivatives

by Robson A. Dantas, Herondy F. Santana Mota and Eugênio R. Bezerra de Mello

Universe 2023, 9(5), 241; https://doi.org/10.3390/universe9050241 - 20 May 2023

Cited by 7 | Viewed by 1057

Abstract

In this paper, we investigate the bosonic Casimir effect in a Lorentz-violating symmetry scenario. The theoretical model adopted consists of a real massive scalar quantum field confined in a region between two large parallel plates, having its dynamics governed by a modified Klein–Gordon [...] Read more.

In this paper, we investigate the bosonic Casimir effect in a Lorentz-violating symmetry scenario. The theoretical model adopted consists of a real massive scalar quantum field confined in a region between two large parallel plates, having its dynamics governed by a modified Klein–Gordon equation that presents a Lorentz symmetry-breaking term. In this context, we admit that the quantum field obeys specific boundary conditions on the plates. The Lorentz-violating symmetry is implemented by the presence of an arbitrary constant space-like vector in a CPT-even aether-like approach, considering a direct coupling between this vector with the derivative of the field in higher order. The modification of the Klein–Gordon equation produces important corrections on the Casimir energy and pressure. Thus, we show that these corrections strongly depend on the order of the higher derivative term and the specific direction of the constant vector, as well as the boundary conditions considered. Full article

(This article belongs to the Special Issue Quantum Field Theory)

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6 pages, 244 KiB

Open AccessCommunication

On the Temperature Dependence of the String-Breaking Distance in QCD

by Dmitry Antonov

Universe 2023, 9(2), 97; https://doi.org/10.3390/universe9020097 - 13 Feb 2023

Cited by 2 | Viewed by 1280

Abstract

The temperature dependence of the QCD string-breaking distance is evaluated in terms of the string tension and the rate of production of light mesons in the chromo-electric field of a flux tube. As a function of the meson mass, the mentioned rate can [...] Read more.

The temperature dependence of the QCD string-breaking distance is evaluated in terms of the string tension and the rate of production of light mesons in the chromo-electric field of a flux tube. As a function of the meson mass, the mentioned rate can be falling off either as a Gaussian, as suggested by the Schwinger formula, or as an exponential, which is the case in the London limit of the dual superconductor. We find an excellent agreement of the so-evaluated temperature dependence of the string-breaking distance with the respective lattice data, for the case of the meson-production rate corresponding to the London limit. Full article

(This article belongs to the Special Issue Quantum Field Theory)

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11 pages, 352 KiB

Open AccessArticle

From Soft Dirac Monopoles to the Dirac Equation

by Manfried Faber

Universe 2022, 8(8), 387; https://doi.org/10.3390/universe8080387 - 22 Jul 2022

Cited by 3 | Viewed by 1465

Abstract

In the model of topological particles we have four types of topologically stable dual Dirac monopoles with soft cores and finite mass. We discuss the steps for getting a Dirac equation for these particles. We show for the free and the interacting case [...] Read more.

In the model of topological particles we have four types of topologically stable dual Dirac monopoles with soft cores and finite mass. We discuss the steps for getting a Dirac equation for these particles. We show for the free and the interacting case that we arrive at the Dirac equation in the limit, where the soft solitons approach singular dual Dirac monopoles. Full article

(This article belongs to the Special Issue Quantum Field Theory)

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9 pages, 280 KiB

Open AccessArticle

On Emergent Particles and Stable Neutral Plasma Balls in SU(2) Yang-Mills Thermodynamics

by Ralf Hofmann and Thierry Grandou

Universe 2022, 8(2), 117; https://doi.org/10.3390/universe8020117 - 12 Feb 2022

Cited by 5 | Viewed by 4649

Abstract

For a pure SU(2) Yang–Mills theory in 4D, we revisit the spatial (3D), ball-like region of radius

r_{0}

in its bulk subject to the pressureless, deconfining phase at

T_{0} = 1.32 T_{c}

, where

T_{c}

denotes the critical temperature [...] Read more.

For a pure SU(2) Yang–Mills theory in 4D, we revisit the spatial (3D), ball-like region of radius

r_{0}

in its bulk subject to the pressureless, deconfining phase at

T_{0} = 1.32 T_{c}

, where

T_{c}

denotes the critical temperature for the onset of the deconfining–preconfining phase transition. Such a region possesses finite energy density and represents the self-intersection of a figure-eight shaped center-vortex loop if a BPS monopole of core radius ∼

\frac{r_{0}}{52.4}

, isolated from its antimonopole by repulsion externally invoked through a transient shift of (anti)caloron holonomy (pair creation), is trapped therein. The entire soliton (vortex line plus region of self-intersection of mass

m_{0}

containing the monopole) can be considered an excitation of the pressureless and energyless ground state of the confining phase. Correcting an earlier estimate of

r_{0}

, we show that the vortex-loop self-intersection region associates to the central part of a(n) (anti)caloron and that this region carries one unit of electric U(1) charge via the (electric-magnetic dually interpreted) charge of the monopole. The monopole core quantum vibrates at a thermodynamically determined frequency

ω_{0}

and is unresolved. For a deconfining-phase plasma oscillation about the zero-pressure background at

T = T_{0}

, we compute the lowest frequency

Ω_{0}

within a neutral and homogeneous spatial ball (no trapped monopole) in dependence of its radius

R_{0}

. For

R_{0} = r_{0}

a comparison of

Ω_{0}

with

ω_{0}

reveals that the neutral plasma oscillates much slower than the same plasma driven by the oscillation of a monopole core. Full article

(This article belongs to the Special Issue Quantum Field Theory)

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7 pages, 494 KiB

Open AccessArticle

Implications of Quantum Gravity for Dark Matter Searches with Atom Interferometers

by Xavier Calmet and Nathaniel Sherrill

Universe 2022, 8(2), 103; https://doi.org/10.3390/universe8020103 - 5 Feb 2022

Cited by 4 | Viewed by 1690

Abstract

In this brief paper, we show that atom interferometer experiments such as MAGIS, AION and AEDGE do not only have the potential to probe very light dark matter models, but will also probe quantum gravity. We show that the linear coupling of a [...] Read more.

In this brief paper, we show that atom interferometer experiments such as MAGIS, AION and AEDGE do not only have the potential to probe very light dark matter models, but will also probe quantum gravity. We show that the linear coupling of a singlet scalar dark matter particle to electrons or photons is already ruled out by our current understanding of quantum gravity coupled to data from torsion pendulum experiments. On the other hand, the quadratic coupling of scalar dark matter to electrons and photons has a large viable parameter space which will be probed by these atom interferometers. Implications for searches of quantum gravity are discussed. Full article

(This article belongs to the Special Issue Quantum Field Theory)

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10 pages, 291 KiB

Open AccessArticle

Dual Superconductor Model of Confinement: Quantum-String Representation of the 4D Yang–Mills Theory on a Torus and the Correlation Length away from the London Limit

by Dmitry Antonov

Universe 2022, 8(1), 7; https://doi.org/10.3390/universe8010007 - 24 Dec 2021

Cited by 2 | Viewed by 2258

Abstract

This paper is devoted to the dual superconductor model of confinement in the 4D Yang–Mills theory. In the first part, we consider the latter theory compactified on a torus, and use the dual superconductor model in order to obtain the Polchinski–Strominger term in [...] Read more.

This paper is devoted to the dual superconductor model of confinement in the 4D Yang–Mills theory. In the first part, we consider the latter theory compactified on a torus, and use the dual superconductor model in order to obtain the Polchinski–Strominger term in the string representation of a Wilson loop. For a certain realistic critical value of the product of circumferences of the compactification circles, which is expressed in terms of the gluon condensate and the vacuum correlation length, the coupling of the Polchinski–Strominger term turns out to be such that the string conformal anomaly cancels out, making the string representation fully quantum. In the second part, we use the analogy between the London limit of the dual superconductor and the low-energy limit of the 4D compact QED, to obtain the partition function of the dual superconductor model away from the London limit. There, we find a decrease of the vacuum correlation length, and derive the corresponding potential of monopole currents. Full article

(This article belongs to the Special Issue Quantum Field Theory)

16 pages, 322 KiB

Open AccessFeature PaperEditor’s ChoiceArticle

The Black Hole Firewall Transformation and Realism in Quantum Mechanics

by Gerard ’t Hooft

Universe 2021, 7(8), 298; https://doi.org/10.3390/universe7080298 - 13 Aug 2021

Cited by 12 | Viewed by 9917

Abstract

A procedure to derive a unitary evolution law for a quantised black hole has been proposed by the author. The proposal requires that one starts off with the entire Penrose diagram for the eternal black hole as the background metric, after which one [...] Read more.

A procedure to derive a unitary evolution law for a quantised black hole has been proposed by the author. The proposal requires that one starts off with the entire Penrose diagram for the eternal black hole as the background metric, after which one has to invoke the antipodal identification in order to see how the two asymptotic domains of this metric both refer to the same outside world. In this paper, we focus on the need to include time reversal in applying this identification. This forces us to postulate the existence of an ‘anti-vacuum’ state in our world, which is the state where energy density reaches a maximal value. We find that this squares well with the deterministic interpretation of quantum mechanics, according to which quantum Hilbert space is to be regarded as the ‘vector representation’ of a real world. One has to understand how to deal with gravity in such considerations. The non-perturbative component of the gravitational force seems to involve cut-and-paste procedures as dynamical features of space and time, of which the re-arrangement of space-time into two connected domains in the Penrose diagram is a primary example. Thus, we attempt to obtain new insights in the nature of particle interactions at the Planck scale, as well as quantum mechanics itself. Full article

(This article belongs to the Special Issue Quantum Field Theory)

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31 pages, 527 KiB

Open AccessArticle

Firewall from Effective Field Theory

by Pei-Ming Ho and Yuki Yokokura

Universe 2021, 7(7), 241; https://doi.org/10.3390/universe7070241 - 13 Jul 2021

Cited by 17 | Viewed by 2481

Abstract

For an effective field theory in the background of an evaporating black hole with spherical symmetry, we consider non-renormalizable interactions and their relevance to physical effects. The background geometry is determined by the semi-classical Einstein equation for an uneventful horizon where the vacuum [...] Read more.

For an effective field theory in the background of an evaporating black hole with spherical symmetry, we consider non-renormalizable interactions and their relevance to physical effects. The background geometry is determined by the semi-classical Einstein equation for an uneventful horizon where the vacuum energy–momentum tensor is small for freely falling observers. Surprisingly, after Hawking radiation appears, the transition amplitude from the Unruh vacuum to certain multi-particle states grows exponentially with time for a class of higher-derivative operators after the collapsing matter enters the near-horizon region, despite the absence of large curvature invariants. Within the scrambling time, the uneventful horizon transitions towards a firewall, and eventually the effective field theory breaks down. Full article

(This article belongs to the Special Issue Quantum Field Theory)

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Review

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24 pages, 449 KiB

Open AccessReview

QCD Effective Locality: A Theoretical and Phenomenological Review

by Herbert M. Fried, Yves Gabellini, Thierry Grandou and Peter H. Tsang

Universe 2021, 7(12), 481; https://doi.org/10.3390/universe7120481 - 7 Dec 2021

Cited by 2 | Viewed by 2188

Abstract

About ten years ago, the use of standard functional manipulations was demonstrated to imply an unexpected property satisfied by the fermionic Green’s functions of QCD and dubbed Effective Locality. This feature of QCD is non-perturbative, as it results from a full gauge [...] Read more.

About ten years ago, the use of standard functional manipulations was demonstrated to imply an unexpected property satisfied by the fermionic Green’s functions of QCD and dubbed Effective Locality. This feature of QCD is non-perturbative, as it results from a full gauge invariant integration of the gluonic degrees of freedom. In this review article, a few salient theoretical aspects and phenomenological applications of this property are summarized. Full article

(This article belongs to the Special Issue Quantum Field Theory)

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34 pages, 457 KiB

Open AccessReview

Real Clifford Algebras and Their Spinors for Relativistic Fermions

by Stefan Floerchinger

Universe 2021, 7(6), 168; https://doi.org/10.3390/universe7060168 - 28 May 2021

Cited by 6 | Viewed by 2516

Abstract

Real Clifford algebras for arbitrary numbers of space and time dimensions as well as their representations in terms of spinors are reviewed and discussed. The Clifford algebras are classified in terms of isomorphic matrix algebras of real, complex or quaternionic type. Spinors are [...] Read more.

Real Clifford algebras for arbitrary numbers of space and time dimensions as well as their representations in terms of spinors are reviewed and discussed. The Clifford algebras are classified in terms of isomorphic matrix algebras of real, complex or quaternionic type. Spinors are defined as elements of minimal or quasi-minimal left ideals within the Clifford algebra and as representations of the pin and spin groups. Two types of Dirac adjoint spinors are introduced carefully. The relationship between mathematical structures and applications to describe relativistic fermions is emphasized throughout. Full article

(This article belongs to the Special Issue Quantum Field Theory)

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