72 research outputs found
State-of-the-Art Calculation of the Decay Rate of Electroweak Vacuum in Standard Model
The decay rate of the electroweak (EW) vacuum is calculated in the framework
of the standard model (SM) of particle physics, using the recent progresses in
the understanding of the decay rate of metastable vacuum in gauge theories. We
give a manifestly gauge-invariant expression of the decay rate. We also perform
a detailed numerical calculation of the decay rate. With the best-fit values of
the SM parameters, we find that the decay rate of the EW vacuum per unit volume
is about ; with the uncertainty in the top
mass, the decay rate is estimated as .Comment: 5 pages, 1 figure, published versio
Higgs Mixing in the NMSSM and Light Higgsinos
We explore the effects of Higgs mixing in the general next-to-minimal
supersymmetric Standard Model (NMSSM). Extended to include a gauge singlet, the
Higgs sector can naturally explain the observed Higgs boson mass in TeV scale
supersymmetry without invoking large stop mixing. This is particularly the case
when the singlet scalar is light so that singlet-doublet mixing increases the
mass of the SM-like Higgs boson. In such a case the Higgs mixing has
interesting implications following from the fact that the higgsino mass
parameter and the singlet coupling to Higgs bilinear crucially depend on the
Higgs boson masses and mixing angles. For the mixing compatible with the
current LHC data on the Higgs signal rates, the higgsinos are required to be
relatively light, around or below a few hundred GeV, as long as the heavy
doublet Higgs boson has a mass smaller than about 250\sqrt{\tan\beta} GeV and
the singlet-like Higgs boson is consistent with the LEP constraint. In
addition, the Higgs coupling to photons can receive a sizable contribution of
either sign from the charged-higgsino loops combined with singlet-doublet
mixing.Comment: 26 pages, 5 figures, Higgs data updated, discussion extended, typos
fixed, to appear in JHE
Migdal Effect in Dark Matter Direct Detection Experiments
The elastic scattering of an atomic nucleus plays a central role in dark
matter direct detection experiments. In those experiments, it is usually
assumed that the atomic electrons around the nucleus of the target material
immediately follow the motion of the recoil nucleus. In reality, however, it
takes some time for the electrons to catch up, which results in ionization and
excitation of the atoms. In previous studies, those effects are taken into
account by using the so-called Migdal's approach, in which the final state
ionization/excitation are treated separately from the nuclear recoil. In this
paper, we reformulate the Migdal's approach so that the "atomic recoil" cross
section is obtained coherently, where we make transparent the energy-momentum
conservation and the probability conservation. We show that the final state
ionization/excitation can enhance the detectability of rather light dark matter
in the GeV mass range via the {\it nuclear} scattering. We also discuss the
coherent neutrino-nucleus scattering, where the same effects are expected.Comment: Integrated probability data fixed and Si.dat adde
On the Gauge Invariance of the Decay Rate of False Vacuum
We study the gauge invariance of the decay rate of the false vacuum for the
model in which the scalar field responsible for the false vacuum decay has
gauge quantum number. In order to calculate the decay rate, one should
integrate out the field fluctuations around the classical path connecting the
false and true vacua (i.e., so-called bounce). Concentrating on the case where
the gauge symmetry is broken in the false vacuum, we show a systematic way to
perform such an integration and present a manifestly gauge-invariant formula of
the decay rate of the false vacuum.Comment: 17 pages, published versio
Renormalization-Scale Uncertainty in the Decay Rate of False Vacuum
We study radiative corrections to the decay rate of false vacua, paying
particular attention to the renormalization-scale dependence of the decay rate.
The decay rate exponentially depends on the bounce action. The bounce action
itself is renormalization scale dependent. To make the decay rate
scale-independent, radiative corrections, which are due to the field
fluctuations around the bounce, have to be included. We show quantitatively
that the inclusion of the fluctuations suppresses the scale dependence, and
hence is important for the precise calculation of the decay rate. We also apply
our analysis to a supersymmetric model and show that the radiative corrections
are important for the Higgs-stau system with charge breaking minima.Comment: 15 pages, 2 figures; added reference
最小超対称標準模型のゲージ一重項拡張とヒッグス混合の現象論
Tohoku University山口昌弘課
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