22,570 research outputs found
Density Functional Theory of the Hubbard-Holstein Model
We present a density functional theory (DFT) for lattice models with local
electron-electron (e-e) and electron-phonon (e-ph) interactions.
Exchange-correlation potentials are derived via dynamical mean field theory for
the infinite-dimensional Bethe lattice, and analytically for an isolated
Hubbard-Holstein site. These potentials exhibit discontinuities as a function
of the density, which depend on the relative strength of the e-e and e-ph
interactions. By comparing to exact benchmarks, we show that the DFT formalism
gives a good description of the linear conductance and real-time dynamics.Comment: 5 pages, 3 figures, supplemental material provided as pd
Taylor-Lagrange renormalization scheme. Application to light-front dynamics
The recently proposed renormalization scheme based on the definition of field
operators as operator valued distributions acting on specific test functions is
shown to be very convenient in explicit calculations of physical observables
within the framework of light-front dynamics. We first recall the main
properties of this procedure based on identities relating the test functions to
their Taylor remainder of any order expressed in terms of Lagrange's formulae,
hence the name given to this scheme. We thus show how it naturally applies to
the calculation of state vectors of physical systems in the covariant
formulation of light-front dynamics. As an example, we consider the case of the
Yukawa model in the simple two-body Fock state truncation.Comment: 18 pages, 6 figures, introduction changed, corrected typos, to be
published in Physical Review
The fine-tuning problem revisited in the light of the Taylor-Lagrange renormalization scheme
We re-analyse the perturbative radiative corrections to the Higgs mass within
the Standard Model in the light of the Taylor-Lagrange renormalization scheme.
This scheme naturally leads to completely finite corrections, depending on an
arbitrary dimensionless scale. This formulation avoids very large individual
corrections to the Higgs mass. In other words, it is a confirmation that the
so-called fine-tuning problem in the Standard Model is just an artefact of the
regularization scheme and should not lead to any physical interpretation in
terms of the energy scale at which new physics should show up, nor to the
appearance of a new symmetry. We analyse the characteristic physical scales
relevant for the description of these radiative corrections.Comment: 8 pages, 2 figure
The Relation between Solar Eruption Topologies and Observed Flare Features I: Flare Ribbons
In this paper we present a topological magnetic field investigation of seven
two-ribbon flares in sigmoidal active regions observed with Hinode, STEREO, and
SDO. We first derive the 3D coronal magnetic field structure of all regions
using marginally unstable 3D coronal magnetic field models created with the
flux rope insertion method. The unstable models have been shown to be a good
model of the flaring magnetic field configurations. Regions are selected based
on their pre-flare configurations along with the appearance and observational
coverage of flare ribbons, and the model is constrained using pre-flare
features observed in extreme ultraviolet and X-ray passbands. We perform a
topology analysis of the models by computing the squashing factor, Q, in order
to determine the locations of prominent quasi-separatrix layers (QSLs). QSLs
from these maps are compared to flare ribbons at their full extents. We show
that in all cases the straight segments of the two J-shaped ribbons are matched
very well by the flux-rope-related QSLs, and the matches to the hooked segments
are less consistent but still good for most cases. In addition, we show that
these QSLs overlay ridges in the electric current density maps. This study is
the largest sample of regions with QSLs derived from 3D coronal magnetic field
models, and it shows that the magnetofrictional modeling technique that we
employ gives a very good representation of flaring regions, with the power to
predict flare ribbon locations in the event of a flare following the time of
the model
Stellar laboratories: new Ge V and Ge VI oscillator strengths and their validation in the hot white dwarf RE 0503-289
State-of-the-art spectral analysis of hot stars by means of non-LTE
model-atmosphere techniques has arrived at a high level of sophistication. The
analysis of high-resolution and high-S/N spectra, however, is strongly
restricted by the lack of reliable atomic data for highly ionized species from
intermediate-mass metals to trans-iron elements. Especially data for the latter
has only been sparsely calculated. Many of their lines are identified in
spectra of extremely hot, hydrogen-deficient post-AGB stars. A reliable
determination of their abundances establishes crucial constraints for AGB
nucleosynthesis simulations and, thus, for stellar evolutionary theory.
In a previous analysis of the UV spectrum of RE 0503-289, spectral lines of
highly ionized Ga, Ge, As, Se, Kr, Mo, Sn, Te, I, and Xe were identified.
Individual abundance determinations are hampered by the lack of reliable
oscillator strengths. Most of these identified lines stem from Ge V. In
addition, we identified Ge VI lines for the first time. We calculated Ge V and
Ge VI oscillator strengths to consider their radiative and collisional
bound-bound transitions in detail in our non-LTE stellar-atmosphere models for
the analysis of the Ge IV - VI spectrum exhibited in high-resolution and
high-S/N UV spectra of RE 0503-289. We identify four Ge IV, 37 Ge V, and seven
Ge VI lines. Most of these are identified for the first time in any star. We
reproduce almost all Ge IV, Ge VI, and Ge VI lines in the observed spectrum of
RE 0503-289 (Teff = 70 kK, log g = 7.5) at log Ge = -3.8 +/- 0.3 (mass
fraction, about 650 times solar).
Reliable measurements and calculations of atomic data are a prerequisite for
stellar-atmosphere modeling. Our oscillator-strength calculations have allowed,
for the first time, Ge V and Ge VI lines to be successfully reproduced in a
white dwarf's spectrum and to determine its photospheric Ge abundance.Comment: 54 pages, 8 figure
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Palaeolimnology of Lake Sapanca and identification of historic earthquake signals, Northern Anatolian Fault Zone (Turkey)
Lake Sapanca is located on a strand of the Northern Anatolian Fault Zone (NAFZ, Turkey), where a series of strong earthquakes (Ms >6.0) have occurred over the past hundred years. Identifying prehistoric
earthquakes in and around Lake Sapanca is key to a better understanding of plate movements along the
NAFZ. This study contributes to the development of palaeolimnological tools to identify past earthquakes
in Lake Sapanca. To this end several promising proxies were investigated, specifically lithology, magnetic
susceptibility, grain size (thin-section and laser analysis), geochemistry, pollen concentration, diatom
assemblages, 137Cs and 210Pb. Sedimentological indicators provided evidence for reworked, turbidite-like
or homogeneous facies (event layers) in several short cores (<45 cm). Other indicators of sediment input
and the historical chronicles available for the area suggest that three of these event layers likely originated
from the AD 1957, 1967 and 1999 earthquakes. Recent changes in sediment deposition and nutrient
levels have also been identified, but are probably not related to earthquakes. This study demonstrates
that a combination of indicators can be used to recognize earthquake-related event layers in cores that encompass a longer period of time
Universal scaling behavior of the single electron box in the strong tunneling limit
We perform a numerical analysis of recently proposed scaling functions for
the single electron box. Specifically, we study the ``magnetic'' susceptibility
as a function of tunneling conductance and gate charge, and the effective
charging energy at zero gate charge as a function of tunneling conductance in
the strong tunneling limit. Our Monte Carlo results confirm the accuracy of the
theoretical predictions.Comment: Published versio
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