arXiv subjects

Max Dohse

Publications and source records attributed to Max Dohse.

8 recordsLinked to original sources

arXiv2018

TikZ-FeynHand: Basic User Guide

This is a userguide for the LaTex package Tikz-FeynHand at https://ctan.org/pkg/tikz-feynhand which let's you draw Feynman diagrams using TikZ. It contains many examples and a 5-minute introduction to TikZ. The package is a low-end modification of the package TikZ-Feynman at https://ctan.org/pkg/tikz-feynman, one of whose principal advantages is the automatic generation of diagrams, for which it needs LuaTex. FeynHand only provides the manual mode and hence runs in LaTex without any reference to LuaTex. In addition it provides some NEW STYLES for vertices and propagators, alternative SHORTER KEYWORDS in addition to TikZ-Feynman's longer ones, some shortcut commands for QUICKLY CUSTOMIZING the diagrams' look, and the new feature to put one propagator "ON TOP" of another.

cs.OH↗

arXiv2017

Complex structures and quantum representations for scalar QFT in curved spacetimes

We confirm the equivalence of the Schr\"odinger representation and the holomorphic one, based on previous results of the General Boundary Formulation (GBF) of quantum field theory. On a wide class of curved spacetimes, we consider real Klein-Gordon theory in two types of regions: interval regions (consisting e.g. of a time interval times all of space), and rod regions (a solid ball of space extended over all of time). Using mode expansions, we provide explicit expressions for the Schr\"odinger vacuum (which determines this representation) and for the corresponding complex structure on the space of classical solutions (which determines the holomorphic representation). For both representations we give the corresponding coherent states and calculate the generalized free transition amplitudes of the GBF, which coincide and hence confirm the equivalence of the two representations. We also transcribe the complex structure to phase space and show that it agrees with earlier results.

math-ph↗

arXiv2016

General Boundary Quantum Field Theory in Anti de Sitter Spacetimes

We mainly study real Klein-Gordon theory on Anti de Sitter spacetimes, and apply the General Boundary Formulation (GBF) of Quantum Theory in order to compute a radial S-matrix. We consider first the classical theory, giving a complete list of Klein-Gordon solutions and the actions of the isometries of AdS on them. We study two symplectic structures on spaces of such solutions, and show that they are invariant under all isometries' actions. We also calculate the flat limits of the involved quantities, and find that it reproduces the respective counterparts of the theory on Minkowski spacetime. We proceed applying Holomorphic Quantization, whose amplitudes are determined by an inner product which is induced by the symplectic structure together with a complex structure on the space of classical solutions. We construct this complex structure such that the inner product becomes positive-definite, and its induced amplitudes are invariant under time-translations and spatial rotations. Further, our complex structure makes these radial amplitudes agree with the amplitudes of states on equal-time hypersurfaces, and also reproduce the amplitudes of the theory on Minkowski spacetime in the flat limit. (There is also a more detailed summary at the beginning of the document.)

math-ph↗

arXiv2015

Complex structures for an S-matrix of Klein-Gordon theory on AdS spacetimes

While the standard construction of the S-matrix fails on Anti-de Sitter (AdS) spacetime, a generalized S-matrix makes sense, based on the hypercylinder geometry induced by the boundary of AdS. In contrast to quantum field theory in Minkowski spacetime, there is not yet a standard way to resolve the quantization ambiguities arising in its construction. These ambiguities are conveniently encoded in the choice of a complex structure. We explore in this paper the space of complex structures for real scalar Klein-Gordon theory based on a number of criteria. These are: invariance under AdS isometries, induction of a positive definite inner product, compatibility with the standard S-matrix picture and recovery of standard structures in Minkowski spacetime under a limit of vanishing curvature. While there is no complex structure that satisfies all demands, we emphasize two interesting candidates that satisfy most: In one case we have to give up part of the isometry invariance, in the other case the induced inner product is indefinite.

hep-th↗

arXiv2012

Classical Klein-Gordon solutions, symplectic structures and isometry actions on AdS spacetimes

We study classical, real Klein-Gordon theory on Lorentzian Anti de Sitter (AdS_{1,d}) spacetimes with spatial dimension d. We give a complete list of well defined and bounded Klein-Gordon solutions for three types of regions on AdS: slice (time interval times all of space), rod hypercylinder (all of time times solid ball in space), and tube hypercylinder (all of time times solid shell in space). Hypercylinder regions are of natural interest for AdS since the neighborhood of the AdS-boundary is a tube. For the solution spaces of our regions we find the actions induced by the AdS isometry group SO(2,d). For all three regions we find one-to-one correspondences between initial data and solutions on the regions. For rod and tube regions this initial data can also be given on the AdS boundary. We calculate symplectic structures associated to the solution spaces, and show their invariance under the isometry actions. We compare our results to the corresponding expressions for (3+1)-dimensional Minkowski spacetime, arising from AdS_{1,3} in the limit of large curvature radius.

math-ph↗

arXiv2011

S-Matrix for AdS from General Boundary QFT

The General Boundary Formulation (GBF) is a new framework for studying quantum theories. After concise overviews of the GBF and Schrödinger-Feynman quantization we apply the GBF to resolve a well known problem on Anti-deSitter spacetime where due to the lack of temporally asymptotic free states the usual S-matrix cannot be defined. We construct a different type of S-matrix plus propagators for free and interacting real Klein-Gordon theory.

hep-th↗

arXiv2010

The S-matrix in Schr\"odinger Representation for Curved Spacetimes in General Boundary Quantum Field Theory

We use the General Boundary Formulation (GBF) of Quantum Field Theory to compute the S-matrix for a general interacting scalar field in a wide class of curved spacetimes. As a by-product we obtain the general expression of the Feynman propagator for the scalar field, defined in the following three types of spacetime regions. First, there are the familiar interval regions (e.g.~a time interval times all of space). Second, we consider the rod hypercylinder regions (all of time times a solid ball in space). Third, the tube hypercylinders (all of time times a solid shell in space) are related to interval regions, and result from removing a smaller rod from a concentric larger one. Using the Schr\"odinger representation for the quantum states combined with Feynman's path integral quantization, we obtain the S-matrix as the asymptotic limit of the GBF amplitude associated with finite interval and rod regions. For interval regions, whose boundary consists of two Cauchy surfaces, the asymptotic GBF-amplitude becomes the standard S-matrix. Our work generalizes previous results (obtained in Minkowski, Rindler, de Sitter, and Anti de Sitter spacetimes) to a wide class of curved spacetimes.

hep-th↗

arXiv2007

Configuration Space Methods and Time Ordering for Scalar Propagators in (Anti and) de Sitter Spacetimes

In this master thesis a configuration space method presented by C. Dullemond and E. van Beveren for computing all propagators of a scalar field (Wightman, Hadamard and Schwinger functions,retarded, advanced and Feynman propagator) is reviewed for four-dimensional Minkowski and Anti de Sitter spacetime AdS_4. This method is then applied for AdS_d as well as de Sitter spacetime dS_d of arbitrary dimension d, obtaining results in agreement with the literature. The advantages of the method are that it needs neither mode summation nor analytic continuation from euclidean time, while delivering the propagators above including (i-epsilon)-prescription, plus as a nice bonus the conformal dimension of a corresponding CFT field. General properties of the considered spacetimes (namely various coordinate systems and their metrics, chordal distances, relations between conformal dimensions Δand the mass m of the scalar field, geodesics and the invariance of time ordering) are also examined and compiled from various sources, providing an overview of geometrical properties of AdS and dS spacetimes.

hep-th↗