SearcharxivSearch

arXiv subjects

Jobst Ziebell

Publications and source records attributed to Jobst Ziebell.

12 recordsLinked to original sources

Countability Properties of Weakly Compact Sets in Asymmetric Locally Convex Spaces

A dual pair formulation for asymmetric locally convex spaces is developed that strictly generalises the ordinary vector space setting. The concept of a polar topology carries over to the asymmetric case and some familiar results are reproduced or generalised such as the bipolar theorem and a Mackey-Arens type theorem. The implications of weak compactness and countability properties are studied and appear intimately connected to separation properties. An asymmetric analogue $C_a(K)$ of the well-known space $C_p(K)$ is introduced and the properties of (relatively) (countably respectively sequentially) compact subspaces are investigated. In particular, it is shown that $C_a([0,1])$ is not angelic. However, for Hausdorff subspaces satisfying a simple closure condition, the different compactness conditions are equivalent and imply the Fr\'echet-Urysohn property. Moreover, an analogue of the Eberlein-\v{S}mulian theorem holds in asymmetrically normed spaces.

math.GN

Wetterich's Equation and its Boundary Conditions for Radon Measures on Locally Convex Spaces

Wetterich's equation and corresponding flows of effective average actions are used frequently in theoretical physics to study the properties of quantum field theories. Under appropriate conditions, Wetterich's equation also holds for Radon measures on locally convex spaces and the domain of the effective average action is the Lusin affine kernel of the measure. The resulting flow interpolates between the convex conjugate of the cumulant-generating function of the measure in question and its (generalised) Onsager-Machlup function. The underlying metric of the latter is induced by a family of measurable bilinear functionals that can be understood as bilinear versions of Lusin measurable linear functionals.

math.FA

Tikhonov Well-Posedness and Differentiability on Asymmetrically Normed Spaces

On normed vector spaces there is a well-known connection between the Tikhonov well-posedness of a minimisation problem and the differentiability of an associated convex conjugate function. We show how this duality naturally generalises to the setting of asymmetrically normed spaces and prove a universal differentiability property of the convex conjugate of the cumulant-generating function of a mean-zero measure on a locally convex space.

math.FA

Existence theorem on the UV limit of Wilsonian RG flows of Feynman measures

In nonperturbative formulation of Euclidean signature quantum field theory (QFT), the vacuum state is characterized by the Wilsonian renormalization group (RG) flow of Feynman measures. Such an RG flow is a family of Feynman measures on the space of ultraviolet (UV) regularized fields, linked by the Wilsonian renormalization group equation. In this paper we show that under mild conditions, a Wilsonian RG flow of Feynman measures extending to arbitrary regularization strengths has a factorization property: there exists an ultimate Feynman measure (UV limit) on the distribution sense fields, such that the regularized instances in the flow are obtained from this UV limit via taking the marginal measure against the regulator. Existence theorems on the flow and UV limit of the corresponding action functional are also discussed.

hep-th

A Rigorous Derivation of the Functional Renormalisation Group Equation

The functional renormalisation group equation is derived in a mathematically rigorous fashion in a framework suitable for the Osterwalder-Schrader formulation of quantum field theory. To this end, we devise a very general regularisation scheme which retains reflection positivity as well as the infinite degrees of freedom including smoothness. Furthermore, it is shown how the classical limit is altered by the regularisation process leading to an inevitable breaking of translation invariance. We also give precise conditions for the convergence of the obtained theories upon removal of the regularisation.

math-ph

$\theta$-splitting Densities and Reflection Positivity

A simple condition is given that is sufficient to determine whether a measure that is absolutely continuous with respect to a Gau{\ss}ian measure on the space of distributions is reflection positive. It readily generalises conventional lattice results to an abstract setting, enabling the construction of many reflection positive measures that are not supported on lattices.

math-ph

Pauli-Term-Induced Fixed Points in $d$-dimensional QED

We explore the fixed-point structure of QED-like theories upon the inclusion of a Pauli spin-field coupling. We concentrate on the fate of UV-stable fixed points recently discovered in $d=4$ spacetime dimensions upon generalizations to lower as well as higher dimensions for an arbitrary number of fermion flavors $N_\mathrm{f}$. As an overall trend, we observe that going away from $d=4$ dimensions and increasing the flavor number tends to destabilize the non-Gaussian fixed points discovered in four spacetime dimensions. A notable exception is a non-Gaussian fixed point at finite Pauli spin-field coupling but vanishing gauge coupling, which also remains stable down to $d=3$ dimensions and for small flavor numbers. This includes also the range of degrees of freedom used in effective theories of layered condensed-matter systems. As an application, we construct renormalization group trajectories that emanate from the non-Gaussian fixed point and approach a long-range regime in the conventional QED${}_3$ universality class that is governed by the interacting (quasi) fixed point in the gauge coupling.

hep-th

Super-Gaussian Decay of Exponentials: A Sufficient Condition

In this article, we present a sufficient condition for the exponential $\exp({-f})$ to have a tail decay stronger than any Gaussian, where $f$ is defined on a locally convex space $X$ and grows faster than a squared seminorm on $X$. In particular, our result proves that $\exp({-p(x)^{2+\varepsilon}+\alpha q(x)^2})$ is integrable for all $\alpha,\varepsilon>0$ w.r.t. a Radon Gaussian measure on a nuclear space $X$, if $p$ and $q$ are continuous seminorms on $X$ with compatible kernels. This can be viewed as an adaptation of Fernique's theorem and, for example, has applications in quantum field theory.

math.FA

Asymptotically Safe QED

High-energy completeness of quantum electrodynamics (QED) can be induced by an interacting ultraviolet fixed point of the renormalization flow. We provide evidence for the existence of two of such fixed points in the subspace spanned by the gauge coupling, the electron mass and the Pauli spin-field coupling. Renormalization group trajectories emanating from these fixed points correspond to asymptotically safe theories that are free from the Landau pole problem. We analyze the resulting universality classes defined by the fixed points, determine the corresponding critical exponents, study the resulting phase diagram, and quantify the stability of our results with respect to a systematic expansion scheme. We also compute high-energy complete flows towards the long-range physics. We observe the existence of a renormalization group trajectory that interconnects one of the interacting fixed points with the physical low-energy behavior of QED as measured in experiment. Within pure QED, we estimate the crossover from perturbative QED to the asymptotically safe fixed point regime to occur somewhat above the Planck scale but far below the scale of the Landau pole.

hep-th

Existence and Construction of Exact FRG Flows of a UV-Interacting Scalar Field Theory

We prove the existence and give a construction procedure of Euclidean-invariant exact solutions to the Wetterich equation in $d > 2$ dimensions satisfying the naive boundary condition of a massive and interacting real scalar $ϕ^4$ theory in the ultraviolet limit as well as a generalised free theory in the infrared limit. The construction produces the momentum-dependent correlation functions to all orders through an iterative scheme, based on a self-consistent ansatz for the four-point function. The resulting correlators are bounded at all regulator scales and we determine explicit bounds capturing the asymptotics in the UV and IR limits. Furthermore, the given construction principle may be extended to other systems and might become useful in the study of general properties of exact solutions.

hep-th

FlexibleSUSY: Precise automated calculations in any BSM theory

FlexibleSUSY is a software package for various calculations in any model of physics beyond the standard model (not just any supersymmetric model). FlexibleSUSY can solve boundary value problems and uses this to find $\overline{DR}/\overline{MS}$ parameters and calculate the Higgs and BSM particle masses, as well as other observables. FlexibleSUSY is designed to be adaptable, fast, precise and reliable. We describe FlexibleSUSY with particular emphasis on recent developments and the state of the art Higgs mass calculations it can perform. We also show some applications to illustrate how it can be used to obtain interesting physics results with the highest precision possible and with remarkable speed.

hep-ph

FlexibleSUSY 2.0: Extensions to investigate the phenomenology of SUSY and non-SUSY models

We document major new features and improvements of FlexibleSUSY, a Mathematica and C++ package with a dependency on the external package SARAH, that generates fast and precise spectrum generators. The extensions presented here significantly increase the generality and capabilities of the FlexibleSUSY package, which already works with a wide class of models, while maintaining an elegant structure and easy to use interfaces. The FlexibleBSM extension makes it possible to also create spectrum generators for non-supersymmetric extensions of the Standard Model. The FlexibleCPV extension adds the option of complex parameters to the spectrum generators, allowing the study of many interesting models with new sources of $CP$ violation. FlexibleMW computes the decay of the muon for the generated model and thereby allows FlexibleSUSY to predict the mass of the $W$ boson from the input parameters by using the more precise electroweak input of $\{ G_F, M_Z, α_{\text{em}} \}$ instead of $\{ M_W, M_Z, α_{\text{em}} \}$. The FlexibleAMU extension provides a calculator of the anomalous magnetic moment of the muon in any model FlexibleSUSY can generate a spectrum for. FlexibleSAS introduces a new solver for the boundary value problem which makes use of semi-analytic expressions for dimensionful parameters to find solutions in models where the classic two-scale solver will not work such as the constrained E$_6$SSM. FlexibleEFTHiggs is a hybrid calculation of the Higgs mass which combines the virtues of both effective field theory calculations and fixed-order calculations. All of these extensions are included in FlexibleSUSY 2.0, which is released simultaneously with this manual.

hep-ph