14,885 research outputs found
Determining at Electron-Positron Colliders
Verifying is critical to test the three generation
assumption of the Standard Model. So far our best knowledge of is
inferred either from the unitarity of CKM matrix or from single
top-quark productions upon the assumption of universal weak couplings. The
unitarity could be relaxed in new physics models with extra heavy quarks and
the universality of weak couplings could also be broken if the coupling
is modified in new physics models. In this work we propose to measure
in the process of without prior knowledge of the number
of fermion generations or the strength of the coupling. Using an
effective Lagrangian approach, we perform a model-independent analysis of the
interactions among electroweak gauge bosons and the third generation quarks,
i.e. the , and couplings. The electroweak symmetry
of the Standard Model specifies a pattern of deviations of the --
and -- couplings after one imposes the known experimental
constraint on the -- coupling. We demonstrate that, making use of
the predicted pattern and the accurate measurements of top-quark mass and width
from the energy threshold scan experiments, one can determine from the
cross section and the forward-backward asymmetry of top-quark pair production
at an {\it unpolarized} electron-positron collider.Comment: publish versio
On black hole spectroscopy via adiabatic invariance
In this paper, we obtain the black hole spectroscopy by combining the black
hole property of adiabaticity and the oscillating velocity of the black hole
horizon. This velocity is obtained in the tunneling framework. In particular,
we declare, if requiring canonical invariance, the adiabatic invariant quantity
should be of the covariant form . Using it,
the horizon area of a Schwarzschild black hole is quantized independent of the
choice of coordinates, with an equally spaced spectroscopy always given by
in the Schwarzschild and Painlev\'{e}
coordinates.Comment: 13 pages, some references added, to be published in Phys. Lett.
Quarkonium Production in an Improved Color Evaporation Model
We propose an improved version of the color evaporation model to describe
heavy quarkonium production. In contrast to the traditional color evaporation
model, we impose the constraint that the invariant mass of the intermediate
heavy quark-antiquark pair to be larger than the mass of produced quarkonium.
We also introduce a momentum shift between heavy quark-antiquark pair and the
quarkonium. Numerical calculations show that our model can describe the
charmonium yields as well as ratio of over better than
the traditional color evaporation model.Comment: 6 pages, 4 figure
Three-dimensional structures of the spatiotemporal nonlinear Schrödinger equation with power-law nonlinearity in PT-symmetric potentials
The spatiotemporal nonlinear Schrödinger equation with power-law nonlinearity in PT-symmetric potentials is investigated, and two families of analytical three-dimensional spatiotemporal structure solutions are obtained. The stability of these solutions is tested by the linear stability analysis and the direct numerical simulation. Results indicate that solutions are stable below some thresholds for the imaginary part of PT-symmetric potentials in the self-focusing medium, while they are always unstable for all parameters in the self-defocusing medium. Moreover, some dynamical properties of these solutions are discussed, such as the phase switch, power and transverse power-flow density. The span of phase switch gradually enlarges with the decrease of the competing parameter k in PT-symmetric potentials. The power and power-flow density are all positive, which implies that the power flow and exchange from the gain toward the loss domains in the PT cell.Funded by the National Natural Science Foundation of China (Grant No. 11375007), the Zhejiang Provincial Natural Science Foundation of China (Grant
No. LY13F050006)
Crystalline and Electronic Structures of Molecular Solid CCl: First-Principles Calculation
A molecular solid CCl with possible crystalline structures,
including the hexagonal-close-packed (hcp) phase, the face-centered cubic (fcc)
phase, and a hexagonal monolayer, is predicted in terms of first-principles
calculation within the density functional theory. The stable structures are
determined from the total-energy calculations, where the hcp phase is uncovered
more stable than the fcc phase and the hexagonal monolayer in energy per
molecule. The energy bands and density of states for hcp and fcc
CCl are presented. The results show that CCl%
molecules can form either a hcp or fcc indirect-gap band insulator or an
insulating hexagonal monolayer.Comment: 5 pages, 6 figure
Half-Metallic Silicon Nanowires: Multiple Surface Dangling Bonds and Nonmagnetic Doping
By means of first-principles density functional theory calculations, we find
that hydrogen-passivated ultrathin silicon nanowires (SiNWs) along [100]
direction with symmetrical multiple surface dangling bonds (SDBs) and boron
doping can have a half-metallic ground state with 100% spin polarization, where
the half-metallicity is shown quite robust against external electric fields.
Under the circumstances with various SDBs, the H-passivated SiNWs can also be
ferromagnetic or antiferromagnetic semiconductors. The present study not only
offers a possible route to engineer half-metallic SiNWs without containing
magnetic atoms but also sheds light on manipulating spin-dependent properties
of nanowires through surface passivation.Comment: 4 pages, 5 figure
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