A Laplace Transform Method for Molecular Mass Distribution Calculation from Rheometric Data

Polydisperse linear polymer melts can be microscopically described by the tube model and fractal reptation dynamics, while on the macroscopic side the generalized Maxwell model is capable of correctly displaying most of the rheological behavior. In this paper, a Laplace transform method is derived and different macroscopic starting points for molecular mass distribution calculation are compared to a classical light scattering evaluation. The underlying assumptions comprise the modern understanding on polymer dynamics in entangled systems but can be stated in a mathematically generalized way. The resulting method is very easy to use due to its mathematical structure and it is capable of calculating multimodal molecular mass distributions of linear polymer melts

Structural and magnetic transition in CeFeAsO: separated or connected?

Using an adapted Sn-flux growth technique we obtained comparatively large CeFeAsO single crystals of better quality than previously reported polycrystals or single crystals, as evidenced by much sharper anomalies at the structural and magnetic phase transitions as well as a much higher residual resistivity ratio of 12. In the magnetically ordered phase we observe a very pronounced metallic behavior of the in-plane resistivity, which excludes a Mott insulator regime at low temperature. The separation Delta_T = T_0 - T_N between structural and magnetic ordering temperatures decreases with increasing sample quality, from 18 K in the initial reports to 6 K in the present single crystals, demonstrating that this separation is not an intrinsic property of the RFeAsO systems. Our results indicate that the coupling between magnetic ordering and structural distortion is very similar in AFe2As2 and RFeAsO type of compounds, much more similar than previously thought. The implications of our experimental results give arguments both in favor and against the nematic phase model.Comment: published in PRB with the title 'Coupling between the structural and magnetic transition in CeFeAsO

Effects of the low lying Dirac modes on excited hadrons in lattice QCD

Chiral symmetry breaking in Quantum Chromodynamics is associated with the low lying spectral modes of the Dirac operator according to the Banks-Casher relation. Here we study how removal of a variable number of low lying modes from the valence quark sector affects the masses of the ground states and first excited states of baryons and mesons in two flavor lattice QCD.Comment: 6 pages, 2 figures. Contribution to proceedings of "Excited QCD 2012", May 6-12, 2012, Peniche, Portuga

Symmetries of hadrons after unbreaking the chiral symmetry

We study hadron correlators upon artificial restoration of the spontaneously broken chiral symmetry. In a dynamical lattice simulation we remove the lowest lying eigenmodes of the Dirac operator from the valence quark propagators and study evolution of the hadron masses obtained. All mesons and baryons in our study, except for a pion, survive unbreaking the chiral symmetry and their exponential decay signals become essentially better. From the analysis of the observed spectroscopic patterns we conclude that confinement still persists while the chiral symmetry is restored. All hadrons fall into different chiral multiplets. The broken U(1)_A symmetry does not get restored upon unbreaking the chiral symmetry. We also observe signals of some higher symmetry that includes chiral symmetry as a subgroup. Finally, from comparison of the \Delta - N splitting before and after unbreaking of the chiral symmetry we conclude that both the color-magnetic and the flavor-spin quark-quark interactions are of equal importance.Comment: 12 pages, 14 figures; final versio

More effects of Dirac low-mode removal

In previous studies we have shown that hadrons, except for a pion, survive the removal of the lowest lying Dirac eigenmodes from the valence quark propagators. The low-modes are tied to the dynamical breaking of chiral symmetry and we found chiral symmetry to be restored by means of matching masses of chiral partners, like, e.g., the vector and axial vector currents. Here we investigate the influence of removing the lowest part of the Dirac spectrum on the locality of the Dirac operator. Moreover, we analyze the influence of low-mode truncation on the quark momenta and thereupon on the hadron spectrum and, finally, introduce a reweighting scheme to extend the truncation to the sea quark sector.Comment: 7pages, 4 figures. Proceedings of the 31st International Symposium on Lattice Field Theory, July 29 - August 3, 2013, Mainz, German