A new family of matrix product states with Dzyaloshinski-Moriya interactions

We define a new family of matrix product states which are exact ground states of spin 1/2 Hamiltonians on one dimensional lattices. This class of Hamiltonians contain both Heisenberg and Dzyaloshinskii-Moriya interactions but at specified and not arbitrary couplings. We also compute in closed forms the one and two-point functions and the explicit form of the ground state. The degeneracy structure of the ground state is also discussed.Comment: 15 pages, 1 figur

ADE functional dilogarithm identities and integrable models

We describe a new infinite family of multi-parameter functional equations for the Rogers dilogarithm, generalizing Abel's and Euler's formulas. They are suggested by the Thermodynamic Bethe Ansatz approach to the Renormalization Group flow of 2D integrable, ADE-related quantum field theories. The known sum rules for the central charge of critical fixed points can be obtained as special cases of these. We conjecture that similar functional identities can be constructed for any rational integrable quantum field theory with factorized S-matrix and support it with extensive numerical checks.Comment: LaTeX, 9 pages, no figure

Implementation of Spin Hamiltonians in Optical Lattices

We propose an optical lattice setup to investigate spin chains and ladders. Electric and magnetic fields allow us to vary at will the coupling constants, producing a variety of quantum phases including the Haldane phase, critical phases, quantum dimers etc. Numerical simulations are presented showing how ground states can be prepared adiabatically. We also propose ways to measure a number of observables, like energy gap, staggered magnetization, end-chain spins effects, spin correlations and the string order parameter

Nonlinear integral equations for finite volume excited state energies of the O(3) and O(4) nonlinear sigma-models

We propose nonlinear integral equations for the finite volume one-particle energies in the O(3) and O(4) nonlinear sigma-models. The equations are written in terms of a finite number of components and are therefore easier to solve numerically than the infinite component excited state TBA equations proposed earlier. Results of numerical calculations based on the nonlinear integral equations and the excited state TBA equations agree within numerical precision.Comment: numerical results adde

Excitation spectrum and critical exponents of a one-dimensional integrable model of fermions with correlated hopping

We investigate the excitation spectrum of a model of $N$ colour fermions with correlated hopping which can be solved by a nested Bethe ansatz. The gapless excitations of particle-hole type are calculated as well as the spin-wave like excitations which have a gap. Using general predictions of conformal field theory the long distance behaviour of some groundstate correlation functions are derived from a finite-size analysis of the gapless excitations. From the algebraic decay we show that for increasing particle density the correlation of so-called $N$-multiplets of particles dominates over the density-density correlation. This indicates the presence of bound complexes of these $N$-multiplets. This picture is also supported by the calculation of the effective mass of charge carriers.Comment: 15 pages, 3 PostScript figures appende

Association between COVID-19 lockdown measures and the incidence of iatrogenic versus spontaneous very preterm births in the Netherlands:a retrospective study

Background: The COVID-19 pandemic led to regional or nationwide lockdowns as part of risk mitigation measurements in many countries worldwide. Recent studies suggest an unexpected and unprecedented decrease in preterm births during the initial COVID-19 lockdowns in the first half of 2020. The objective of the current study was to assess the effects of the two months of the initial national COVID-19 lockdown period on the incidence of very and extremely preterm birth in the Netherlands, stratified by either spontaneous or iatrogenic onset of delivery, in both singleton and multiple pregnancies. Methods: Retrospective cohort study using data from all 10 perinatal centers in the Netherlands on very and extremely preterm births during the initial COVID-19 lockdown from March 15 to May 15, 2020. Incidences of very and extremely preterm birth were calculated using an estimate of the total number of births in the Netherlands in this period. As reference, we used data from the corresponding calendar period in 2015–2018 from the national perinatal registry (Perined). We differentiated between spontaneous versus iatrogenic onset of delivery and between singleton versus multiple pregnancies. Results: The incidence of total preterm birth < 32 weeks in singleton pregnancies was 6.1‰ in the study period in 2020 versus 6.5‰ in the corresponding period in 2015–2018. The decrease in preterm births in singletons was solely due to a significant decrease in iatrogenic preterm births, both < 32 weeks (OR 0.71; 95%CI 0.53 to 0.95) and < 28 weeks (OR 0.53; 95%CI 0.29 to 0.97). For multiple pregnancies, an increase in preterm births < 28 weeks was observed (OR 2.43; 95%CI 1.35 to 4.39). Conclusion: This study shows a decrease in iatrogenic preterm births during the initial COVID-19-related lockdown in the Netherlands in singletons. Future studies should focus on the mechanism of action of lockdown measures and reduction of preterm birth and the effects of perinatal outcome

Cardiac time intervals and myocardial performance index for prediction of twin-twin transfusion syndrome

Objectives To explore whether intertwin discordance in myocardial performance index (MPI) or cardiac time intervals enables the prediction of twin-twin transfusion syndrome (TTTS) in monochorionic diamniotic (MCDA) pregnancies with amniotic fluid discordance.Methods Prospective cohort study of MCDA pregnancies with amniotic fluid discordance >= 4 cm. Serial ultrasound examinations consisted of evaluation of amniotic fluid, fetal Dopplers and fetal cardiac function.Results We included 21 "future-TTTS" (group I), 18 selective fetal growth restriction (sFGR; group II) and 20 uncomplicated MCDA twin pairs (group III). Group I had a higher intertwin difference in left ventricle (LV) MPI and right ventricle (RV) MPI compared to group II and III. The intertwin difference in global heart relaxation time was significantly higher in group I compared to group III. Future recipient twins had significantly higher relaxation times of the global heart and RV and lower contraction times of the global heart and RV compared to the "expected recipients" in group II and III.Conclusion Intertwin discordance in LV-MPI and RV-MPI differentiate between TTTS and MCDA pregnancies with transient discordant amniotic fluid volume. Cardiac time intervals identify future recipient twins. The clinical utility of cardiac time intervals and MPI should be investigated in large prospective studies.Research into fetal development and medicin

Exactly solvable two-dimensional quantum spin models

A method is proposed for constructing an exact ground-state wave function of a two-dimensional model with spin 1/2. The basis of the method is to represent the wave function by a product of fourth-rank spinors associated with the sites of a lattice and the metric spinors corresponding to bonds between nearest neighbor sites. The function so constructed is an exact wave function of a 14-parameter model. The special case of this model depending on one parameter is analyzed in detail. The ground state is always a nondegenerate singlet, and the spin correlation functions decay exponentially with distance. The method can be generalized for models with spin 1/2 to other types of lattices.Comment: 15 pages, 9 figures, Revte

Nonlinear Integral Equation and Finite Volume Spectrum of Sine-Gordon Theory

We examine the connection between the nonlinear integral equation (NLIE) derived from light-cone lattice and sine-Gordon quantum field theory, considered as a perturbed c=1 conformal field theory. After clarifying some delicate points of the NLIE deduction from the lattice, we compare both analytic and numerical predictions of the NLIE to previously known results in sine-Gordon theory. To provide the basis for the numerical comparison we use data from Truncated Conformal Space method. Together with results from analysis of infrared and ultraviolet asymptotics, we find evidence that it is necessary to change the rule of quantization proposed by Destri and de Vega to a new one which includes as a special case that of Fioravanti et al. This way we find strong evidence for the validity of the NLIE as a description of the finite size effects of sine-Gordon theory.Comment: LaTeX2e, 49 pages, 14 eps figures. Presentation shortened and improved, some typos correcte

Thermal Conductivity of Spin-1/2 Chains

We study the low-temperature transport properties of clean one-dimensional spin-1/2 chains coupled to phonons. Due to the presence of approximate conservation laws, the heat current decays very slowly giving rise to an exponentially large heat conductivity, $\kappa ~ e^{T^*/T}$. As a result of an interplay of Umklapp scattering and spinon-phonon coupling, the characteristic energy scale $T^*$ turns out to be of order $\Theta_D/2$, where $\Theta_D$ is the Debye energy, rather than the magnetic exchange interaction $J$ -- in agreement with recent measurements in SrCuO compounds. A large magnetic field strongly affects the heat transport by two distinct mechanisms. First, it induces a LINEAR spinon--phonon coupling, which alters the nature of the $T -> 0$ fixed point: the elementary excitations of the system are COMPOSITE SPINON-PHONON objects. Second, the change of the magnetization and the corresponding change of the wave vector of the spinons strongly affects the way in which various Umklapp processes can relax the heat current, leading to a characteristic fractal--like spiky behavior of $\kappa$ when plotted as a function of magnetization at fixed T.Comment: 16 pages, RevTex4, 2 figures included; revised refs. and some useful comments on experimental relevance. On July 12 2005, added an appendix correcting an error in the form of the phonon propagator. The main result is unchange