arXiv subjects

Uwe Ritschel

Publications and source records attributed to Uwe Ritschel.

5 recordsLinked to original sources

arXiv1997

X-Ray Scattering at FeCo(001) Surfaces and the Crossover between Ordinary and Normal Transitions

In a recent experiment by Krimmel et al. [PRL 78, 3880 (1997)], the critical behavior of FeCo near a (001) surface was studied by x-ray scattering. Here the experimental data are reanalyzed, taking into account recent theoretical results on order-parameter profiles in the crossover regime between ordinary and normal transitions. Excellent agreement between theoretical expectations and the experimental results is found.

cond-mat.stat-mech↗

arXiv1997

Casimir Forces at Tricritical Points: Theory and Possible Experiments

Using field-theoretical methods and exploiting conformal invariance, we study Casimir forces at tricritical points exerted by long-range fluctuations of the order-parameter field. Special attention is paid to the situation where the symmetry is broken by the boundary conditions (extraordinary transition). Besides the parallel-plate configuration, we also discuss the geometries of two separate spheres and a single sphere near a planar wall, which may serve as a model for colloidal particles immersed in a fluid. In the concrete case of ternary mixtures a quantitative comparison with critical Casimir and van der Waals forces shows that, especially with symmetry-breaking boundaries, the tricritical Casimir force is considerably stronger than the critical one and dominates also the competing van der Waals force.

cond-mat.soft↗

arXiv1996

Near-Surface Long-Range Order at the Ordinary Transition

We study the spatial dependence of the order parameter near surfaces belonging to the universality class of the ordinary transition. Special attention is paid to the influence of a small surface magnetic field h_1 at and above the bulk critical temperature. A detailed scaling analysis (which is confirmed by a perturbative calculation) reveals that h_1 may give rise to an anomalous short-distance behavior of the order parameter. Close to the surface the magnetization increases with a power law m\sim z^{\,κ} with κ=1-η_{\perp}^{ord} \simeq 0.23 for the three-dimensional Ising model. These results are closely related to experimental findings where exponents of the ordinary transition were observed in Fe_3 Al, while superstructure reflections revealed the existence of long-range order near the surface [X. Mailänder et al., Phys. Rev. Lett. {\bf 64}, 2527 (1990)].

cond-mat↗

arXiv1993

Autonomous Renormalization of Phi^4 in Finite Geometry

The autonomous renormalization of the O(N)-symmetric scalar theory is based on an infinite re-scaling of constant fields, whereas finite-momentum modes remain finite. The natural framework for a detailed analysis of this method is a system of finite size, where all non-constant modes can be integrated out perturbatively and the constant mode is treated by a saddle-point approximation in the thermodynamic limit. The calculation provides a better understanding of the properties of of the effective action and corroborates earlier findings concerning a heavy Higgs particle at about 2 TeV.

hep-th↗

arXiv1992

Non-Gaussian Corrections to Higgs Mass in Autonomous lambda phi**4

Recent calculations in one-loop and Gaussian appro- ximation, using the so-called autonomous renormalization scheme, indicate a comparatively massive, narrow Higgs excitation at about 2 TeV. Here I show that this result qualitatively persists in the framework of a post-Gaussian variational approximation for the pure O(N)-symmetric phi**4-theory for N>1. The method is based on nonlinear transformations of path-integral variables, and the optimization amounts to a Schwinger-Dyson-type summation of diagrams. In the case of O(4), for example, I find M_Higgs = 2.3 TeV, compared to 1.9 TeV and 2.1 TeV in 1-loop and Gaussian approximation, respectively.

hep-ph↗