Better Higgs-CP Tests Through Information Geometry

Measuring the CP symmetry in the Higgs sector is one of the key tasks of the LHC and a crucial ingredient for precision studies, for example in the language of effective Lagrangians. We systematically analyze which LHC signatures offer dedicated CP measurements in the Higgs-gauge sector, and discuss the nature of the information they provide. Based on the Fisher information measure, we compare the maximal reach for CP-violating effects in weak boson fusion, associated ZH production, and Higgs decays into four leptons. We find a subtle balance between more theory-independent approaches and more powerful analysis channels, indicating that rigorous evidence for CP violation in the Higgs-gauge sector will likely require a multi-step process.Comment: 27 pages, 8 figure

Phase diagram of an exactly solvable t-J ladder model

We study a system of one-dimensional t-J models coupled to a ladder system. A special choice of the interaction between neighbouring rungs leads to an integrable model with supersymmetry, which is broken by the presence of rung interactions. We analyze the spectrum of low-lying excitations and ground state phase diagram at zero temperature.Comment: LaTeX, 8 pp. incl. 1 figur

On the dynamics of coupled S=1/2 antiferromagnetic zig-zag chains

We investigate the elementary excitations of quasi one-dimensional S=1/2 systems built up from zig-zag chains with general isotropic exchange constants, using exact (Lanczos) diagonalization for 24 spins and series expansions starting from the decoupled dimer limit. For the ideal one-dimensional zig-zag chain we discuss the systematic variation of the basic (magnon) triplet excitation with general exchange parameters and in particular the presence of practically flat dispersions in certain regions of phase space. We extend the dimer expansion in order to include the effects of 3D interactions on the spectra of weakly interacting zig-zag chains. In an application to KCuCl_3 we show that this approach allows to determine the exchange interactions between individual pairs of spins from the spectra as determined in recent neutron scattering experiments.Comment: 8 pages, 9 figures; some changes, figure added; final versio

Weakly supervised causal representation learning

Learning high-level causal representations together with a causal model from unstructured low-level data such as pixels is impossible from observational data alone. We prove under mild assumptions that this representation is however identifiable in a weakly supervised setting. This involves a dataset with paired samples before and after random, unknown interventions, but no further labels. We then introduce implicit latent causal models, variational autoencoders that represent causal variables and causal structure without having to optimize an explicit discrete graph structure. On simple image data, including a novel dataset of simulated robotic manipulation, we demonstrate that such models can reliably identify the causal structure and disentangle causal variables

Efficient multibeam sonar calibration and performance evaluation

Quantitative applications of mobile multibeam sonar in aquatic ecology and fisheries require accurate and efficient in-tank calibration methodologies. Calibration factors for a Simrad SM20 multibeam sonar are experimentally extracted thereby enabling sonar estimation of target strength and volume backscattering strength. Measured and modeled sonar characteristics are systematically compared and show good overall correlation. Due to the limited angular span of the sonar head array, well quantified sonar operation is restricted to an equatorial angular sector of only 80° (vs. rated 120°) in 'imaging' mode. In 'echo-sounder' mode, the 'high' power transmit setting appears to introduce artifacts. A routine in-tank measurement procedure is described which for given multibeam sonar minimizes the time required for quality multibeam calibration

Modification of the twist angle in chiral nematic polymer films by photoisomerization of the chiral dopant

A method for the production of polarization sensitive recordings in liquid crystalline polymers is presented. The system is based on local modification of the twist angle of chiral nematic polymer films. The twist angle of the polymer film is varied by modifying the chemical structure of the chiral dopant. Here a photoisomerizable menthone derivative is used that has a fivefold difference in helical twisting power between the E and the Z isomer. The twist angle of the film can be varied between –90° and 0° by introducing a nonphotosensitive chiral dopant with opposite twisting sense. Complex pictures with gray scales can be recorded in the films with black and white contrasts higher than 20

Quenched growth of nanostructured lead thin films on insulating substrates

Lead island films were obtained via vacuum vapor deposition on glass and ceramic substrates at 80 K. Electrical conductance was measured during vapor condensation and further annealing of the film up to room temperature. The resistance behavior during film formation and atomic force microscopy of annealed films were used as information sources about their structure. A model for the quenched growth, based on ballistic aggregation theory, was proposed. The nanostructure, responsible for chemiresistive properties of thin lead films and the mechanism of sensor response are discussed.Comment: 2 figures; accepted to Thin Solid Film

Dynamical Structure Factors for Dimerized Spin Systems

We discuss the transition strength between the disordered ground state and the basic low-lying triplet excitation for interacting dimer materials by presenting theoretical calculations and series expansions as well as inelastic neutron scattering results for the material KCuCl_3. We describe in detail the features resulting from the presence of two differently oriented dimers per unit cell and show how energies and spectral weights of the resulting two modes are related to each other. We present results from the perturbation expansion in the interdimer interaction strength and thus demonstrate that the wave vector dependence of the simple dimer approximation is modified in higher orders. Explicit results are given in 10th order for dimers coupled in 1D, and in 2nd order for dimers coupled in 3D with application to KCuCl_3 and TlCuCl_3.Comment: 17 pages, 6 figures, part 2 is based on cond-mat/021133

Models of impurities in valence bond spin chains and ladders

We present the class of models of a nonmagnetic impurity in S=1/2 generalized ladder with an AKLT-type valence bond ground state, and of a S=1/2 impurity in the S=1 AKLT chain. The ground state in presence of impurity can be found exactly. Recently studied phenomenon of local enhancement of antiferromagnetic correlations around the impurity is absent for this family of models.Comment: 4 pages revtex, 3 figures embedde