8,346 research outputs found
mixing in the minimal flavor-violating two-Higgs-doublet models
The two-Higgs-doublet model (2HDM), as one of the simplest extensions of the
Standard Model (SM), is obtained by adding another scalar doublet to the SM,
and is featured by a pair of charged scalars, which could affect many
low-energy processes. In the "Higgs basis" for a generic 2HDM, only one scalar
doublet gets a nonzero vacuum expectation value and, under the criterion of
minimal flavor violation, the other one is fixed to be either color-singlet or
color-octet, which are named as the type-III and the type-C 2HDM, respectively.
In this paper, we study the charged-scalar effects of these two models on the
mixing, an ideal process to probe New Physics (NP) beyond the
SM. Firstly, we perform a complete one-loop computation of the box diagrams
relevant to the mixing, keeping the mass and momentum of the
external strange quark up to the second order. Together with the up-to-date
theoretical inputs, we then give a detailed phenomenological analysis, in the
cases of both real and complex Yukawa couplings of the charged scalars to
quarks. The parameter spaces allowed by the current experimental data on the
mass difference and the CP-violating parameter are
obtained and the differences between these two 2HDMs are investigated, which
are helpful to distinguish them from each other from a phenomenological point
of view.Comment: 30 pages,10 figures, 2 table
Stacking sequence determines Raman intensities of observed interlayer shear modes in 2D layered materials - A general bond polarizability model
2D layered materials have recently attracted tremendous interest due to their
fascinating properties and potential applications. The interlayer interactions
are much weaker than the intralayer bonds, allowing the as-synthesized
materials to exhibit different stacking sequences (e.g. ABAB, ABCABC), leading
to different physical properties. Here, we show that regardless of the space
group of the 2D material, the Raman frequencies of the interlayer shear modes
observed under the typical configuration blue shift for AB stacked materials,
and red shift for ABC stacked materials, as the number of layers increases. Our
predictions are made using an intuitive bond polarizability model which shows
that stacking sequence plays a key role in determining which interlayer shear
modes lead to the largest change in polarizability (Raman intensity); the modes
with the largest Raman intensity determining the frequency trends. We present
direct evidence for these conclusions by studying the Raman modes in few layer
graphene, MoS2, MoSe2, WSe2 and Bi2Se3, using both first principles
calculations and Raman spectroscopy. This study sheds light on the influence of
stacking sequence on the Raman intensities of intrinsic interlayer modes in 2D
layered materials in general, and leads to a practical way of identifying the
stacking sequence in these materials.Comment: 30 pages, 8 figure
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