arXiv subjects

Klaus Sibold

Publications and source records attributed to Klaus Sibold.

At least 19 recordsLinked to original sources

arXiv2024

EMT,Pseudo-EMT and all that Improvement and Superpotentials

Within Einstein-Hilbert gravity, higher derivatives and a scalar field as representative of matter different versions of tensorlike quantities are discussed.The concepts of improvement and superpotential help to understand the details of their construction and meaning. On this basis it is claimed that the higher derivatives which are necessary for defining higher orders in perturbation theory donot ruin the physical content of the model.

hep-th↗

arXiv2024

Einstein-Hilbert gravity, higher derivatives and a scalar matter field

The present paper extends two previous one's on pure gravity dealing with Einstein-Hilbert and higher derivatives by including a massless scalar field as representative of matter. We study the renormalization to all orders of perturbation theory, provide the Slavnov-Taylor identity, symmetric partial differential equations and derive finiteness properties in the Landau gauge. It is shown that beginning with one-loop negative norm states originating from higher derivatives disappear.

hep-th↗

arXiv2024

On the Perturbative Quantization of Einstein-Hilbert Gravity Embedded in a Higher Derivative Model II

In a previous paper we presented the renormalization of Einstein-Hilbert gravity under inclusion of higher derivative terms and proposed a projection down to the physical state space of Einstein-Hilbert. In the present paper we describe this procedure in more detail via decomposing the original double-pole field $h^{μν}$ in the bilinear field sector into a massless and a massive spin two field. Those are associated with the poles at zero mass resp. at non-zero mass of $h$ in the tree approximation. We show that the massive fields have no poles in higher orders hence do not correspond to particles. $S$-matrix unitarity is violated only in tree approximation. On the way to these results we derive finiteness properties which are valid in the Landau gauge. Those simplify the renormalization group analysis of the model considerably. We also establish a rigid Weyl identity which represents a proper substitute for a Callan-Symanzik equation in flat spacetime.

hep-th↗

arXiv2021

On the Perturbative Quantization of Einstein-Hilbert Gravity Embedded in a Higher Derivative Model

In a perturbative approach Einstein-Hilbert gravity is quantized about a flat background. In order to render the model power counting renormalizable, higher order curvature terms are added to the action. They serve as Pauli-Villars type regulators and require an expansion in the number of fields in addition to the standard expansion in the number of loops. Renormalization is then performed within the BPHZL scheme, which provides the action principle to construct the Slavnov-Taylor identity and invariant differential operators. The final physical state space of the Einstein-Hilbert theory is realized via the quartet mechanism of Kugo and Ojima. Renormalization group and Callan-Symanzik equation are derived for the Green functions and, formally, also for the $S$-matrix.

hep-th↗

arXiv2016

Conjugate variables in quantum field theory and a refinement of Paulis theorem

For the case of spin zero we construct conjugate pairs of operators on Fock space. On states multiplied by polarization vectors coordinate operators Q conjugate to the momentum operator P exist. The massive case is derived from a geometrical quantity, the massless case is realized by taking the limit mass going to zero on the one hand, on the other from conformal transformations. Crucial is the norm problem of the states on which the Q's act: they determine eventually how many independent conjugate pairs exist. It is intriguing that light wedge variables and hence the wedge-local case seems to be preferred.

hep-th↗

arXiv2016

Learning a Deep Model for Human Action Recognition from Novel Viewpoints

Recognizing human actions from unknown and unseen (novel) views is a challenging problem. We propose a Robust Non-Linear Knowledge Transfer Model (R-NKTM) for human action recognition from novel views. The proposed R-NKTM is a deep fully-connected neural network that transfers knowledge of human actions from any unknown view to a shared high-level virtual view by finding a non-linear virtual path that connects the views. The R-NKTM is learned from dense trajectories of synthetic 3D human models fitted to real motion capture data and generalizes to real videos of human actions. The strength of our technique is that we learn a single R-NKTM for all actions and all viewpoints for knowledge transfer of any real human action video without the need for re-training or fine-tuning the model. Thus, R-NKTM can efficiently scale to incorporate new action classes. R-NKTM is learned with dummy labels and does not require knowledge of the camera viewpoint at any stage. Experiments on three benchmark cross-view human action datasets show that our method outperforms existing state-of-the-art.

cs.CV↗

arXiv2014

Reduction of couplings and its application in particle physics, Finite theories, Higgs and top mass predictions

In this report we tell the story of the notion "reduction of couplings" as we witnessed it in the course of time. Born as an innocent child of renormalization theory it first served the study of asymptotic behavior of several couplings in a given model. Reduced couplings appeared as functions of a primary one, compatible with the renormalization group equation and thus solutions of a specific set of ordinary differential equations. If these functions have the form of power series the respective theories resemble standard renormalizable ones and thus widen considerably the area covered until then by symmetries as a tool for constraining the number of couplings consistently. Still on the more abstract level reducing couplings enabled one to construct theories with beta-functions vanishing to all orders of perturbation theory. Reduction of couplings became physicswise truely interesting and phenomenologically important when applied to the standard model and its possible extensions. In particular in the context of supersymmetric theories it became the most powerful tool known today once it was learned how to apply it also to couplings having dimension of mass and to mass parameters. Technically this all relies on the basic property that reducing couplings is a renormalization scheme independent procedure. Predictions of top and Higgs mass prior to their experimental finding highlight the fundamental physical significance of this notion. Twenty-two original articles and one set of lectures are being commented, put into historical perspective and interrelated with each other.

hep-ph↗

arXiv2010

Conjugate variables in quantum field theory: the basic case

Within standard quantum field theory of one scalar field we define operators conjugate to the energy-momentum operators of the theory. They are singled out by calculational simplicity in Fock space. In terms of the underlying scalar field they are non-local. We establish their algebra where it turns out that time and space operators do not commute. Their transformation properties with respect to the conformal group are derived. Solving their eigenvalue problem permits to reconstruct the Fock space in terms of the eigenstates. It is indicated how Paulis theorem may be circumvented. As an application we form the analogue of S-matrices which yields information on the structure of the underlying spacetime. Similarly we define fields and look at their equations of motion.

hep-th↗

arXiv2005

Quantized equations of motion in non-commutative theories

Quantum field theories based on interactions which contain the Moyal star product suffer, in the general case when time does not commute with space, from several diseases: quantum equation of motions contain unusual terms, conserved currents can not be defined and the residual spacetime symmetry is not maintained. All these problems have the same origin: time ordering does not commute with taking the star product. Here we show that these difficulties can be circumvented by a new definition of time ordering: namely with respect to a light-cone variable. In particular the original spacetime symmetries SO(1,1) x SO(2) and translation invariance turn out to be respected. Unitarity is guaranteed as well.

hep-th↗

arXiv2004

On Double Gauging of U(1) Symmetry on Noncommutative Space

We point out that a field ϕcharged under a global U(1) symmetry generally allows for a starred localized extension with the transformation rule, ϕ\to U_L\starϕ\star U_R^{-1}. This results in a double gauging of the global U(1) symmetry on noncommutative space. We interpret the gauge theory so obtained in terms of the gauge fields that in the commutative limit appear naturally and are respectively the gauge field responsible for the charge and a decoupled vector field. The interactions are shown to be very different from those obtained by assigning a transformation rule of ϕ\to U\starϕor ϕ\star U^{-1}.

hep-th↗

arXiv2002

Renormalization of the Minimal Supersymmetric Standard Model

The renormalization of the Minimal Supersymmetric Standard Model (MSSM) is presented. We describe symmetry identities that constitute a framework in which the MSSM is completely characterized and renormalizability can be proven. Furthermore, we discuss applications of this framework for the determination of symmetry-restoring counterterms, the gauge dependence of tan(beta) and the derivation of non-renormalization theorems.

hep-ph↗

arXiv2002

Spectral Representation and Dispersion Relations in Field Theory on Noncommutative Space

We study the spectral representation and dispersion relations that follow from some basic assumptions and the reduced spacetime symmetries on noncommutative (NC) space. Kinematic variables involving the NC parameter appear naturally as parametric variables in this analysis. When subtractions are necessary to remove ultraviolet divergences, they are always made at the fixed values of these NC variables. This point is also illustrated by a perturbative analysis of self-energies. Our analysis of the reduced spacetime symmetries suggests a weaker microcausality requirement. Starting from it, we make a first attempt at dispersion relations for forward scattering. It turns out that the attempt is hampered by a new unphysical region specified by a given motion in the NC plane which does not seem to be surmountable using the usual tricks. Implications for a possible subtraction and renormalization scheme for NC field theory in which the ultraviolet-infrared (UV/IR) mixing is removed are also briefly commented on.

hep-th↗

arXiv2002

Renormalization of the Minimal Supersymmetric Standard Model

The renormalization of the Minimal Supersymmetric Standard Model of electroweak interactions is presented to all orders of perturbation theory using the algebraic method. Special attention is directed to the issues of soft supersymmetry breaking, gauge fixing, and infrared finiteness. We discuss the implications of $\hbar$-dependent field parametrizations on the counterterm structure and provide a complete set of on-shell normalization conditions.

hep-ph↗

arXiv2002

Time-ordered Perturbation Theory on Noncommutative Spacetime: Basic Rules

Assuming the S-matrix on noncommutative (NC) spacetime can still be developped perturbatively in terms of the time-ordered exponential of the interaction Lagrangian, we investigate the perturbation theory of NC field theory. We first work out with care some typical Green functions starting from the usual concepts of time-ordering and commutation relations for free fields. The results are found to be very different from those in the naive approach pursued in the literature. A simple framework then appears naturally which can incorporate the new features of our results and which turns out to be the usual time-ordered perturbation theory extended to the NC context. We provide the prescriptions for computing S-matrix elements and Green functions in this framework. We also emphasize that the naive seemingly covariant approach cannot be reproduced from the current one, in contrast to the field theory on ordinary spacetime. We attribute this to the phase-like nonlocal interaction intrinsic in NC field theory which modifies the analytic properties of Green functions significantly.

hep-th↗

arXiv2002

Time-ordered Perturbation Theory on Noncommutative Spacetime II: Unitarity

We examine the unitarity issue in the recently proposed time-ordered perturbation theory on noncommutative (NC) spacetime. We show that unitarity is preserved as long as the interaction Lagrangian is explicitly Hermitian. We explain why it makes sense to distinguish the Hermiticity of the Lagrangian from that of the action in perturbative NC field theory and how this requirement fits in the framework.

hep-th↗

arXiv2002

Supercurrent and Local Coupling in the Wess-Zumino Model

We study the Wess-Zumino model with the coupling extended to a chiral superfield. In order to incorporate the renormalization effects a further external real field has to be introduced. It is then possible to derive a Callan-Symanzik equation and to prove renormalizability. By constructing the supercurrent in this context the whole machinery for describing the superconformal symmetries becomes available. The presence of the external fields allows also to define multiple insertions of all relevant composite operators. Interesting relations to the curved superspace treatment show up.

hep-th↗

arXiv2001

Supersymmetry Transformation of Quantum Fields

In the Wess-Zumino gauge, supersymmetry transformations become non-linear and are usually incorporated together with BRS transformations in the form of Slavnov-Taylor identities, such that they appear at first sight to be even non-local. Furthermore, the gauge fixing term breaks supersymmetry. In the present paper, we clarify in which sense supersymmetry is still a symmetry of the system and how it is realized on the level of quantum fields.

hep-th↗

arXiv1998

Conformal Transformation Properties of the Supercurrent in Four Dimensional Supersymmetric Theories

We investigate the superconformal transformation properties of Green functions with one or more insertions of the supercurrent in N=1 supersymmetric quantum field theories. These Green functions are conveniently obtained by coupling the supercurrent and its trace to a classical supergravity background. We derive flat space superconformal Ward identities from diffeomorphisms and Weyl transformations on curved superspace. For the classification of potential quantum superconformal anomalies in the massless Wess-Zumino model on curved superspace a perturbative approach is pursued, using the BPHZ scheme for renormalisation. By deriving a local Callan-Symanzik equation the usual dilatational anomalies are identified and it is shown that no further superconformal anomalies involving the dynamical fields are present.

hep-th↗