The anisotropic multichannel spin-SS Kondo model: Calculation of scales from a novel exact solution

A novel exact solution of the multichannel spin-$S$ Kondo model is presented, based on a lattice path integral approach of the single channel spin-1/2 case. The spin exchange between the localized moment and the host is of $XXZ$-type, including the isotropic $XXX$ limit. The free energy is given by a finite set of non-linear integral equations, which allow for an accurate determination of high- and low-temperature scales.Comment: 18 pages, 7 figure

Spin- and entanglement-dynamics in the central spin model with homogeneous couplings

We calculate exactly the time-dependent reduced density matrix for the central spin in the central-spin model with homogeneous Heisenberg couplings. Therefrom, the dynamics and the entanglement entropy of the central spin are obtained. A rich variety of behaviors is found, depending on the initial state of the bath spins. For an initially unpolarized unentangled bath, the polarization of the central spin decays to zero in the thermodynamic limit, while its entanglement entropy becomes maximal. On the other hand, if the unpolarized environment is initially in an eigenstate of the total bath spin, the central spin and the entanglement entropy exhibit persistent monochromatic large-amplitude oscillations. This raises the question to what extent entanglement of the bath spins prevents decoherence of the central spin.Comment: 8 pages, 2 figures, typos corrected, published versio

The open XXZ-chain: Bosonisation, Bethe ansatz and logarithmic corrections

We calculate the bulk and boundary parts of the free energy for an open spin-1/2 XXZ-chain in the critical regime by bosonisation. We identify the cutoff independent contributions and determine their amplitudes by comparing with Bethe ansatz calculations at zero temperature T. For the bulk part of the free energy we find agreement with Lukyanov's result [Nucl.Phys.B 522, 533 (1998)]. In the boundary part we obtain a cutoff independent term which is linear in T and determines the temperature dependence of the boundary susceptibility in the attractive regime for $T\ll 1$. We further show that at particular anisotropies where contributions from irrelevant operators with different scaling dimensions cross, logarithmic corrections appear. We give explicit formulas for these terms at those anisotropies where they are most important. We verify our results by comparing with extensive numerical calculations based on a numerical solution of the T=0 Bethe ansatz equations, the finite temperature Bethe ansatz equations in the quantum-transfer matrix formalism, and the density-matrix renormalisation group applied to transfer matrices.Comment: 35 pages, 8 figure

Global Diversification in Medicine Regulation: Insights from Regenerative Stem Cell Medicine

This is the final version. Available on open access from Taylor & Francis via the DOI in this record. Data Access Statement: The research data supporting this publication are provided within this paper.Medicine regulation worldwide has undergone a process of regulatory diversification. The evidence-based medicine (EBM) paradigm, centered on multi-phase randomized controlled trials, is increasingly contested and replaced by new models of clinical validation. To explain these changes, STS research has cited just a few factors, e.g. growing pressure form health consumers; the role of pharmaceutical companies to lobby for fast, affordable drug development; the influence of neoliberal ideas and libertarian advocacy of deregulation; and the agency of national governments to enable domestic innovation opportunities in the context of global competition and inequalities. Those factors individually cannot account for the increasing variation in medicine regulation at both national and global levels. Instead it is helpful to integrate elements of existing explanations into a framework with four pairs of conflicting regulatory choices, which play a central role in the formation of medicine regulation. We use this framework to compare regulatory changes in the USA, European Union, China, India, Argentina, and Japan. Across these jurisdictions, the case studies illustrate four dynamics of diversification. Key regulatory concepts such as evidence, risk, safety, efficacy, responsibility and accountability acquire different meanings, reshaping medicine innovation in far-reaching and often contradictory ways. The boundaries between medical research and healthcare provision, commerce and humanitarian service, as well as state control and medical self-regulation are re-defined.Economic and Social Research Council (ESRC)European Research CouncilUniversidad Nacional de Quilme

The one-dimensional Hubbard model with open ends: Universal divergent contributions to the magnetic susceptibility

The magnetic susceptibility of the one-dimensional Hubbard model with open boundary conditions at arbitrary filling is obtained from field theory at low temperatures and small magnetic fields, including leading and next-leading orders. Logarithmic contributions to the bulk part are identified as well as algebraic-logarithmic divergences in the boundary contribution. As a manifestation of spin-charge separation, the result for the boundary part at low energies turns out to be independent of filling and interaction strength and identical to the result for the Heisenberg model. For the bulk part at zero temperature, the scale in the logarithms is determined exactly from the Bethe ansatz. At finite temperature, the susceptibility profile as well as the Friedel oscillations in the magnetisation are obtained numerically from the density-matrix renormalisation group applied to transfer matrices. Agreement is found with an exact asymptotic expansion of the relevant correlation function.Comment: 30 pages, 8 figures, reference adde