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Atomic defects and dopants in ternary Z-phase transition-metal nitrides CrMN with M=V, Nb, Ta investigated with density functional theory
A density functional theory study of atomic defects and dopants in ternary
Z-phase transition-metal nitrides CrMN with M=V, Nb, or Ta is presented.
Various defect formation energies of native point defects and of substitutional
atoms of other metal elements which are abundant in the steel as well, are
evaluated. The dependence thereof on the thermodynamic environment, i.e. the
chemical conditions of a growing Z-phase precipitate, is studied and different
growth scenarios are compared. The results obtained may help to relate results
of experimental atomic-scale analysis, by atom probe tomography or transmission
electron microscopy, to the theoretical modeling of the formation process of
the Z phase from binary transition metal nitrides
Scalaron-Higgs inflation
In scalaron-Higgs inflation the Standard Model Higgs boson is non-minimally
coupled to gravity and the Einstein-Hilbert action is supplemented by the
quadratic scalar curvature invariant. For the quartic Higgs self-coupling
fixed at the electroweak scale, we find that the resulting
inflationary two-field model effectively reduces to a single field model with
the same predictions as in Higgs inflation or Starobinsky inflation, including
the limit of a vanishing non-minimal coupling. For the same model, but with the
scalar field a priori not identified with the Standard Model Higgs boson, we
study the inflationary consequences of an extremely small . Depending
on the initial conditions for the inflationary background trajectories, we find
that the two-field dynamics either again reduces to an effective single-field
model with a larger tensor-to-scalar ratio than predicted in Higgs inflation
and Starobinsky inflation, or involves the full two-field dynamics and leads to
oscillatory features in the inflationary power spectrum. Finally, we
investigate under which conditions the inflationary scenario with extremely
small can be realized dynamically by the Standard Model
renormalization group flow and discuss how the scalaron-Higgs model can provide
a natural way to stabilize the electroweak vacuum.Comment: References added, abstract changed, overall discussion improved, 31
pages (two-column layout), 18 figures; new subsection (VI C) added with
precise conditions for a SM RG driven realization of the extremely small
Higgs self-coupling scenari
The Theory of Scanning Quantum Dot Microscopy
Electrostatic forces are among the most common interactions in nature and
omnipresent at the nanoscale. Scanning probe methods represent a formidable
approach to study these interactions locally. The lateral resolution of such
images is, however, often limited as they are based on measuring the force
(gradient) due to the entire tip interacting with the entire surface. Recently,
we developed scanning quantum dot microscopy (SQDM), a new technique for the
imaging and quantification of surface potentials which is based on the gating
of a nanometer-size tip-attached quantum dot by the local surface potential and
the detection of charge state changes via non-contact atomic force microscopy.
Here, we present a rigorous formalism in the framework of which SQDM can be
understood and interpreted quantitatively. In particular, we present a general
theory of SQDM based on the classical boundary value problem of electrostatics,
which is applicable to the full range of sample properties (conductive vs
insulating, nanostructured vs homogeneously covered). We elaborate the general
theory into a formalism suited for the quantitative analysis of images of
nanostructured but predominantly flat and conductive samples
Question of quantum equivalence between Jordan frame and Einstein frame
In the framework of a general scalar-tensor theory, we investigate the
equivalence between two different parametrizations of fields that are commonly
used in cosmology - the so-called Jordan frame and Einstein frame. While it is
clear that both parametrizations are mathematically equivalent at the level of
the classical action, the question about their mathematical equivalence at the
quantum level as well as their physical equivalence is still a matter of debate
in cosmology. We analyze whether the mathematical equivalence still holds when
the first quantum corrections are taken into account. We explicitly calculate
the one-loop divergences in both parametrizations by using the generalized
Schwinger-DeWitt algorithm and compare both results. We find that the quantum
corrections do not coincide off shell and hence induce an off shell dependence
on the parametrization. According to the equivalence theorem, the one-loop
divergences should however coincide on shell. For a cosmological background, we
show explicitly that the on shell equivalence is indeed realized by a
nontrivial cancellation.Comment: 18 pages, 1 figure, revised version accepted for publication in
Physical Review D, new title, section V, VI and VIII of previous arXiv
version removed, references update
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