Three-dimensional time dependent computation of turbulent flow

The three-dimensional, primitive equations of motion are solved numerically for the case of isotropic box turbulence and the distortion of homogeneous turbulence by irrotational plane strain at large Reynolds numbers. A Gaussian filter is applied to governing equations to define the large scale field. This gives rise to additional second order computed scale stresses (Leonard stresses). The residual stresses are simulated through an eddy viscosity. Uniform grids are used, with a fourth order differencing scheme in space and a second order Adams-Bashforth predictor for explicit time stepping. The results are compared to the experiments and statistical information extracted from the computer generated data

Invariances and Equations of Motion in Double Field Theory

We investigate the full set of equations of motion in double field theory and discuss their O(D,D) symmetry and gauge transformation properties. We obtain a Ricci-like tensor, its associated Bianchi identities, and relate our results to those with a generalized metric formulation.Comment: 24 page

Frame-like Geometry of Double Field Theory

We relate two formulations of the recently constructed double field theory to a frame-like geometrical formalism developed by Siegel. A self-contained presentation of this formalism is given, including a discussion of the constraints and its solutions, and of the resulting Riemann tensor, Ricci tensor and curvature scalar. This curvature scalar can be used to define an action, and it is shown that this action is equivalent to that of double field theory.Comment: 35 pages, v2: minor corrections, to appear in J. Phys.

Double Field Theory Formulation of Heterotic Strings

We extend the recently constructed double field theory formulation of the low-energy theory of the closed bosonic string to the heterotic string. The action can be written in terms of a generalized metric that is a covariant tensor under O(D,D+n), where n denotes the number of gauge vectors, and n additional coordinates are introduced together with a covariant constraint that locally removes these new coordinates. For the abelian subsector, the action takes the same structural form as for the bosonic string, but based on the enlarged generalized metric, thereby featuring a global O(D,D+n) symmetry. After turning on non-abelian gauge couplings, this global symmetry is broken, but the action can still be written in a fully O(D,D+n) covariant fashion, in analogy to similar constructions in gauged supergravities.Comment: 28 pages, v2: minor changes, version published in JHE

On factorizations in perturbative quantum gravity

Some features of Einstein gravity are most easily understood from string theory but are not manifest at the level of the usual Lagrangian formulation. One example is the factorization of gravity amplitudes into gauge theory amplitudes. Based on the recently constructed `double field theory' and a geometrical frame-like formalism developed by Siegel, we provide a framework of perturbative Einstein gravity coupled to a 2-form and a dilaton in which, as a consequence of T-duality, the Feynman rules factorize to all orders in perturbation theory. We thereby establish the precise relation between the field variables in different formulations and discuss the Lagrangian that, when written in terms of these variables, makes a left-right factorization manifest.Comment: 18 pages, v2: reference added, to appear in JHE

Unusual low-temperature thermopower in the one-dimensional Hubbard model

The low-temperature thermoelectric power of the repulsive-interaction one-dimensional Hubbard model is calculated using an asymptotic Bethe ansatz for holons and spinons. The competition between the entropy carried by the holons and that carried by the backflow of the spinons gives rise to an unusual temperature and doping dependence of the thermopower which is qualitatively similar to that observed in the normal state of high-$T_{c}$ superconductors.Comment: 11 pages, REVTEX 3.

Massive Type II in Double Field Theory

We provide an extension of the recently constructed double field theory formulation of the low-energy limits of type II strings, in which the RR fields can depend simultaneously on the 10-dimensional space-time coordinates and linearly on the dual winding coordinates. For the special case that only the RR one-form of type IIA carries such a dependence, we obtain the massive deformation of type IIA supergravity due to Romans. For T-dual configurations we obtain a `massive' but non-covariant formulation of type IIB, in which the 10-dimensional diffeomorphism symmetry is deformed by the mass parameter.Comment: 21 page

Strong spin-phonon coupling unveiled by coherent phonon oscillations in Ca2RuO4

© 2019 American Physical Society. We utilize near-infrared femtosecond pulses to investigate coherent phonon oscillations of Ca2RuO4. The coherent Ag phonon mode of the lowest frequency changes abruptly not only its amplitude but also the oscillation phase as the spin order develops. In addition, the phonon mode shows a redshift entering the magnetically ordered state, which indicates a spin-phonon coupling in the system. Density functional theory calculations reveal that the Ag oscillations result in octahedral tilting distortions, which are exactly in sync with the lattice deformation driven by the magnetic ordering. We suggest that the structural distortions by the spin-phonon coupling can induce the unusual oscillation phase shift between impulsive and displacive type oscillation