7,367 research outputs found
Quantum phase transition in a three-level atom-molecule system
We adopt a three-level bosonic model to investigate the quantum phase
transition in an ultracold atom-molecule conversion system which includes one
atomic mode and two molecular modes. Through thoroughly exploring the
properties of energy level structure, fidelity, and adiabatical geometric
phase, we confirm that the system exists a second-order phase transition from
an atommolecule mixture phase to a pure molecule phase. We give the explicit
expression of the critical point and obtain two scaling laws to characterize
this transition. In particular we find that both the critical exponents and the
behaviors of ground-state geometric phase change obviously in contrast to a
similar two-level model. Our analytical calculations show that the ground-state
geometric phase jumps from zero to ?pi/3 at the critical point. This
discontinuous behavior has been checked by numerical simulations and it can be
used to identify the phase transition in the system.Comment: 8 pages,8 figure
violation in charmed hadron decays into neutral kaons
We find a new violating effect in charmed hadron decays into neutral
kaons, which is induced by the interference between the Cabibbo-favored and
doubly Cabibbo-suppressed amplitudes with the mixing.
It is estimated to be of order of , much larger than the
direct asymmetry, but missed in the literature. To reveal this new
violation effect, we propose a new observable, the difference of the
asymmetries in the and
modes. Once the new effect is determined by experiments, the direct
asymmetry then can be extracted and used to search for new physics.Comment: 6 pages, 3 figures. Contribution to the proceeding of The 15th
International Conference on Flavor Physics & CP Violation, 5-9 June 2017,
Prague, Czech Republi
Electron-cyclotron maser and solar microwave millisecond spike emission
An intense solar microwave millisecond spike emission (SMMSE) event was observed on May 16, 1981 by Zhao and Jin at Beijing Observatory. The peak flux density of the spikes is high to 5 x 100,000 s.f.u. and the corresponding brightness temperature (BT) reaches approx. 10 to the 15th K. In order to explain the observed properties of SMMSE, it is proposed that a beam of electrons with energy of tens KeV injected from the acceleration region downwards into an emerging magnetic arch forms so-called hollow beam distribution and causes electron-cyclotron maser (ECM) instability. The growth rate of second harmonic X-mode is calculated and its change with time is deduced. It is shown that the saturation time of ECM is t sub s approx. equals 0.42 ms and only at last short stage (delta t less than 0.2 t sub s) the growth rate decreases to zero rather rapidly. So a SMMSE with very high BT will be produced if the ratio of number density of nonthermal electrons to that of background electrons, n sub s/n sub e, is larger than 4 x .00001
Implications on the first observation of charm CPV at LHCb
Very recently, the LHCb Collaboration observed the violation (CPV) in
the charm sector for the first time, with .
This result is consistent with our prediction of obtained in the factorization-assisted
topological-amplitude (FAT) approach in [PRD86,036012(2012)]. It implies that
the current understanding of the penguin dynamics in charm decays in the
Standard Model is reasonable. Motivated by the success of the FAT approach, we
further suggest to measure the decay, which is the next
potential mode to reveal the CPV of the same order as .Comment: 10 page
Learning Robust and Discriminative Subspace With Low-Rank Constraints
IEEE Transactions on Neural Networks and Learning SystemsThe article of record as published may be found at http://dx.doi.org/10.1109/tnnls.2015.2464090In this paper, we aim at learning robust and discriminative subspaces from noisy data. Subspace learning is widely used in extracting discriminative features for classifica- tion. However, when data are contaminated with severe noise, the performance of most existing subspace learning methods would be limited. Recent advances in low-rank modeling provide effective solutions for removing noise or outliers contained in sample sets, which motivates us to take advantage of low-rank constraints in order to exploit robust and discriminative subspace for classification. In particular, we present a discriminative subspace learning method called the supervised regularization- based robust subspace (SRRS) approach, by incorporating the low-rank constraint. SRRS seeks low-rank representations from the noisy data, and learns a discriminative subspace from the recovered clean data jointly. A supervised regularization function is designed to make use of the class label information, and therefore to enhance the discriminability of subspace. Our approach is formulated as a constrained rank-minimization problem. We design an inexact augmented Lagrange multiplier optimization algorithm to solve it. Unlike the existing sparse representation and low-rank learning methods, our approach learns a low-dimensional subspace from recovered data, and explicitly incorporates the supervised information. Our approach and some baselines are evaluated on the COIL-100, ALOI, Extended YaleB, FERET, AR, and KinFace databases. The exper- imental results demonstrate the effectiveness of our approach, especially when the data contain considerable noise or variations.Funded by Naval Postgraduate SchoolNational Science Foundation Computer and Network SystemsONR Young InvestigatorOffice of Naval ResearchU.S. Army Research Office Young Investigato
Branching ratios and direct CP asymmetries in decays
We propose a theoretical framework for analyzing two-body nonleptonic
meson decays, based on the factorization of short-distance (long-distance)
dynamics into Wilson coefficients (hadronic matrix elements of four-fermion
operators). The parametrization of hadronic matrix elements in terms of several
nonperturbative quantities is demonstrated for the decays,
denoting a pseudoscalar meson. We consider the evolution of Wilson coefficients
with energy release in individual decay modes, and the Glauber strong phase
associated with the pion in nonfactorizable annihilation amplitudes, that is
attributed to the unique role of the pion as a Nambu-Goldstone boson and a
quark-anti-quark bound state simultaneously. The above inputs improve the
global fit to the branching ratios involving the meson, and resolves
the long-standing puzzle from the and
branching ratios, respectively. Combining short-distance dynamics associated
with penguin operators and the hadronic parameters determined from the global
fit to branching ratios, we predict direct CP asymmetries, to which the quark
loops and the scalar penguin annihilation give dominant contributions. In
particular, we predict , lower than the LHCb and CDF data.Comment: 17 pages, 3 figures, matches published versio
- …