29,127 research outputs found
Covariant Light-Front Approach for transition form factors
In the covariant light-front quark model, we investigate the form factors of
decays into
mesons. The form factors in the spacelike region are directly
evaluated. To extrapolate the form factors to the full kinematic region, we fit
the form factors by adopting a three-parameter form from the spacelike region.
transition form factors at maximally recoiling point () are
smaller than and transition form factors, while the form factors at zero recoiling point are close to each other. In the
fitting procedure, we find the parameters for the form factors and strongly depend on the decay constants of
and mesons. Fortunately, the semileptonic and nonleptonic decays
are not sensitive to these form factors. With the form factors, we also
investigate the branching fractions, polarizations of the semileptonic decays. Semileptonic and decays have much larger branching fractions than . In the three kinds of decays, contributions
from the longitudinal polarized vector is comparable with those from the
transversely polarized vector. These predictions will be tested at the ongoing
and forthcoming hadron colliders.Comment: 15 pages, 1 figure, uncertainties reanalyzed, several parts
reorganized, conclusions unchange
Holographic model for antiferromagnetic quantum phase transition induced by magnetic field
We propose a gravity dual of antiferromagnetic quantum phase transition (QPT)
induced by magnetic field and study the critical behavior around the quantum
critical point (QCP). It turns out that the boundary critical theory is a
strong coupling theory with dynamic exponent and that the hyperscaling
law is violated and logarithmic corrections appear near the QCP. Some novel
scaling relations are predicated, which can be tested by experiment data in
future. We also make some comparison with experimental data on low-dimensional
magnets BiCoPO and pyrochlores ErYTiO.Comment: published versions in PR
Vibrational modes and lattice distortion of a nitrogen-vacancy center in diamond from first-principles calculations
We investigate vibrational properties and lattice distortion of negatively
charged nitrogen-vacancy (NV) center in diamond. Using the first-principles
electronic structure calculations, we show that the presence of NV center leads
to appearance of a large number of quasilocalized vibrational modes (qLVMs)
with different degree of localization. The vibration patterns and the
symmetries of the qLVMs are presented and analyzed in detail for both ground
and excited orbital states of the NV center. We find that in the high-symmetry
() excited orbital state a pair of degenerate qLVMs becomes unstable,
and the stable excited state has lower () symmetry. This is a direct
indication of the Jahn-Teller effect, and our studies suggest that dynamical
Jahn-Teller effect in the weak coupling regime takes place. We have also
performed a detailed comparison of our results with the available experimental
data on the vibrations involved in optical emission/absorption of the NV
centers. We have directly demonstrated that, among other modes, the qLVMs
crucially impact the optical properties of the NV centers in diamond, and
identified the most important groups of qLVMs. Our results are important for
deeper understanding of the optical properties and the orbital relaxation
associated with lattice vibrations of the NV centers.Comment: 10 RevTeX pages, 10 EPS figure
Hawking Radiation as a Mechanism for Inflation
The Friedman-Robertson-Walker (FRW) space-time exhibits particle creation
similar to Hawking radiation of a black hole. In this essay we show that this
FRW Hawking radiation leads to an effective negative pressure fluid which can
drive an inflationary period of exponential expansion in the early Universe.
Since the Hawking temperature of the FRW space-time decreases as the Universe
expands this mechanism naturally turns off and the inflationary stage
transitions to a power law expansion associated with an ordinary radiation
dominated Universe.Comment: 6 pages. Published version -- Awarded "Honorable Mention" for the
2012 Gravity Research Foundation Essay Contes
Transition form factors of B decays into p-wave axial-vector mesons in the perturbative QCD approach
The form factors are studied in perturbative QCD approach
( denote a vector meson and two kinds of p-wave axial-vector mesons:
and states, respectively.). The form factors are directly
studied in the large recoiling region and extrapolated to the whole kinematic
region within the dipole parametrization. Adopting decay constants with
different signs for the two kinds of axial-vectors, we find that the two kinds
of form factors have the same sign. The two strange mesons
and mix with each other via the SU(3) symmetry breaking effect. In
order to reduce the ambiguities in the mixing angle between and
, we propose a model-independent way that utilizes the B decay data.
Most of the branching fractions of the semilteptonic decays
are of the order , which still need experimental tests in the on-going
and forthcoming experiments.Comment: 22 pages, 7 figure
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