Model Independent Z′Z' Constraints at Future e+e−e^+e^- Colliders}

Model independent constraints on the mass of extra neutral gauge bosons and their couplings to charged leptons are given for LEP~II and a 500\,GeV $e^+e^-$ collider. Analytical exclusion limits are derived in the Born approximation. The $Z'$ limits obtained with radiative corrections are always worse than those calculated at the Born level. Polarized beams are only useful for degrees of polarization essentially larger than 50\%. Known discovery limits on extra $Z$ bosons predicted by popular $Z'$ models are reproduced as special cases. The $Z'$ constraints are compared to those predicted by four fermion contact interactions.Comment: 10 Latex pages, uses epsf.sty, 5 uuencoded figures obtainable via anonymous ftp from convex.ifh.de in /pub/preprint/ as file desy93-154.uu, DESY 93-15

Experimental Constraints on the Scale of New Physics in Top Condensate Models

We obtain mass limits on the extra neutral gauge boson which is predicted in a model with hidden gauge symmetry and dynamical breaking of the electroweak symmetry by a top quark condensate. For typical model assumptions, present LEP data exclude masses below 3\,TeV. With LEP200 or an electron-positron collider of a c.m. energy of 500 GeV masses below 15\,TeV or 50\,TeV could be excluded, respectively. Such high mass limits allow the calculation of the observables used in the analysis in the context of the Nambu-Jona-Lasinio model.Comment: 7 pages, 2 figures(appended as PS files), DESY 93-111, LMU-04/9

Production Mechanisms for BcB_c Mesons in Photon--Photon Collisions

Using photon-photon collisions as a particularly transparent study case we investigate the production mechanisms for $B_c$ mesons. In nonrelativistic approximation and to $O(\alpha^2\alpha_s^2)$ it is shown that recombination of $\bar{b}$- and $c$-quarks dominates by far over $\bar{b}$ and $c$ fragmentation. This dominance persists up to the highest accessible transverse momenta and leads to distributions in energy which differ completely from the spectra expected on the basis of the fragmentation functions. For processes in which a $b \bar{b}$-pair is radiated from a primary $c$-quark, the fragmentation description is found to be inadequate. We anticipate important implications of these results for hadronic production of heavy quark resonances. Using realistic photon spectra we predict two-photon production rates for $B_c$ and $B_c^*$ at present and future $e^+e^-$-machines.Comment: 10 pages Latex, 6 postscript figures (included by epsf

Universal Reinforcement Learning Algorithms: Survey and Experiments

Many state-of-the-art reinforcement learning (RL) algorithms typically assume that the environment is an ergodic Markov Decision Process (MDP). In contrast, the field of universal reinforcement learning (URL) is concerned with algorithms that make as few assumptions as possible about the environment. The universal Bayesian agent AIXI and a family of related URL algorithms have been developed in this setting. While numerous theoretical optimality results have been proven for these agents, there has been no empirical investigation of their behavior to date. We present a short and accessible survey of these URL algorithms under a unified notation and framework, along with results of some experiments that qualitatively illustrate some properties of the resulting policies, and their relative performance on partially-observable gridworld environments. We also present an open-source reference implementation of the algorithms which we hope will facilitate further understanding of, and experimentation with, these ideas.Comment: 8 pages, 6 figures, Twenty-sixth International Joint Conference on Artificial Intelligence (IJCAI-17

Towards information optimal simulation of partial differential equations

Most simulation schemes for partial differential equations (PDEs) focus on minimizing a simple error norm of a discretized version of a field. This paper takes a fundamentally different approach; the discretized field is interpreted as data providing information about a real physical field that is unknown. This information is sought to be conserved by the scheme as the field evolves in time. Such an information theoretic approach to simulation was pursued before by information field dynamics (IFD). In this paper we work out the theory of IFD for nonlinear PDEs in a noiseless Gaussian approximation. The result is an action that can be minimized to obtain an informationally optimal simulation scheme. It can be brought into a closed form using field operators to calculate the appearing Gaussian integrals. The resulting simulation schemes are tested numerically in two instances for the Burgers equation. Their accuracy surpasses finite-difference schemes on the same resolution. The IFD scheme, however, has to be correctly informed on the subgrid correlation structure. In certain limiting cases we recover well-known simulation schemes like spectral Fourier Galerkin methods. We discuss implications of the approximations made