11,848 research outputs found
Field theory on --Minkowski space revisited: Noether charges and breaking of Lorentz symmetry
This paper is devoted to detailed investigations of free scalar field theory
on -Minkowski space. After reviewing necessary mathematical tools we
discuss in depth the Lagrangian and solutions of field equations. We analyze
the spacetime symmetries of the model and construct the conserved charges
associated with translational and Lorentz symmetry. We show that the version of
the theory usually studied breaks Lorentz invariance in a subtle way: There is
an additional trans-Planckian mode present, and an associated conserved charge
(the number of such modes) is not a Lorentz scalar.Comment: 22 pages, 1 figure, formulas in sect. III correcte
Reconstructing Neogene surface uplift of the Alps: Integrating stable isotope paleoaltimetry and paleoclimate modelling
Paleoaltimetry - the reconstruction of the elevation of mountain ranges in the geological past - is key to understanding the geodynamic drivers of surface uplift. Simultaneously, surface uplift of Earth’s major mountain ranges redirected atmospheric flow and impacted climate globally. At a smaller scale, mountain building affects regional climate and biodiversity.
Stable isotope paleoaltimetry is a powerful tool to quantify the past elevation of mountain ranges. It is based on the inverse relationship between the stable isotopic composition of meteoric waters and elevation, which is represented by the so-called isotopic lapse rate. However, variations in climatic parameters modify isotopic lapse rates and impact moisture transport over the continents and consequently affect paleoelevation reconstructions.
Here, we show the results of a combined stable isotope paleoaltimetry and paleoclimate modeling approach in the European Alps. This approach allows for an improved and more realistic estimation of isotopic lapse rates, large-scale isotope-in-precipitation patterns over Europe and hence Alpine paleoaltimetry calculations. The European Alps are an ideal target for a combined paleoaltimetry - climate modeling approach, given that they are (a) one of the most-studied mountain ranges for which many geoscientific data are available, and (b) sufficiently small and oriented near-parallel to dominant atmospheric circulation patterns. The latter implies that no major global climatic changes are expected in response to Alpine surface uplift, as opposed to e.g. the Andes or the Tibet-Himalaya mountain ranges.
Results from 4D-MB SPP phase 1 and 2 show that: (1) Changing the surface elevation of even a small orogen can complicate stable isotope paleoaltimetry by mixing the elevation and climate signal in a more complex way than commonly assumed. Climate models can help separate these signals and constrain surface uplift histories. (2) The Central Alps were already high during the Early and Middle Miocene, whereas the Eastern Alps were still at significantly lower elevations, thereby confirming that surface uplift propagated from west to east, as would be expected from oblique continent-continent collision. Together, the results highlight the importance and viability of this combined, interdisciplinary approach.
Based on the results from 4D-MB SPP phase 1 and 2, we propose that future efforts to reconstruct surface uplift of mountain ranges follow this state-of-the-art approach, while keeping local limitations to proxy material availability and access to facilities in mind
Universality of ac-conduction in anisotropic disordered systems: An effective medium approximation study
Anisotropic disordered system are studied in this work within the random
barrier model. In such systems the transition probabilities in different
directions have different probability density functions. The
frequency-dependent conductivity at low temperatures is obtained using an
effective medium approximation. It is shown that the isotropic universal
ac-conduction law, , is recovered if properly scaled
conductivity () and frequency () variables are used.Comment: 5 pages, no figures, final form (with corrected equations
Periodic-Orbit Theory of Level Correlations
We present a semiclassical explanation of the so-called
Bohigas-Giannoni-Schmit conjecture which asserts universality of spectral
fluctuations in chaotic dynamics. We work with a generating function whose
semiclassical limit is determined by quadruplets of sets of periodic orbits.
The asymptotic expansions of both the non-oscillatory and the oscillatory part
of the universal spectral correlator are obtained. Borel summation of the
series reproduces the exact correlator of random-matrix theory.Comment: 4 pages, 1 figure (+ web-only appendix with 2 pages, 1 figure
Dynamical regimes and hydrodynamic lift of viscous vesicles under shear
The dynamics of two-dimensional viscous vesicles in shear flow, with
different fluid viscosities and inside and
outside, respectively, is studied using mesoscale simulation techniques.
Besides the well-known tank-treading and tumbling motions, an oscillatory
swinging motion is observed in the simulations for large shear rate. The
existence of this swinging motion requires the excitation of higher-order
undulation modes (beyond elliptical deformations) in two dimensions.
Keller-Skalak theory is extended to deformable two-dimensional vesicles, such
that a dynamical phase diagram can be predicted for the reduced shear rate and
the viscosity contrast . The simulation results
are found to be in good agreement with the theoretical predictions, when
thermal fluctuations are incorporated in the theory. Moreover, the hydrodynamic
lift force, acting on vesicles under shear close to a wall, is determined from
simulations for various viscosity contrasts. For comparison, the lift force is
calculated numerically in the absence of thermal fluctuations using the
boundary-integral method for equal inside and outside viscosities. Both methods
show that the dependence of the lift force on the distance of
the vesicle center of mass from the wall is well described by an effective
power law for intermediate distances with vesicle radius .
The boundary-integral calculation indicates that the lift force decays
asymptotically as far from the wall.Comment: 13 pages, 13 figure
New bases for a general definition for the moving preferred basis
One of the challenges of the Environment-Induced Decoherence (EID) approach
is to provide a simple general definition of the moving pointer basis or moving
preferred basis. In this letter we prove that the study of the poles that
produce the decaying modes in non-unitary evolution, could yield a general
definition of the relaxation, the decoherence times, and the moving preferred
basis. These probably are the most important concepts in the theory of
decoherence, one of the most relevant chapters of theoretical (and also
practical) quantum mechanics. As an example we solved the Omnes (or
Lee-Friedrich) model using our theory.Comment: 6 page
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