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Li Zhao

Publications and source records attributed to Li Zhao.

216 records · Page 12Linked to original sources

First dark matter search results from the PandaX-I experiment

We report on the first dark-matter (DM) search results from PandaX-I, a low threshold dual-phase xenon experiment operating at the China Jinping Underground Laboratory. In the 37-kg liquid xenon target with 17.4 live-days of exposure, no DM particle candidate event was found. This result sets a stringent limit for low-mass DM particles and disfavors the interpretation of previously-reported positive experimental results. The minimum upper limit, $3.7\times10^{-44}$\,cm$^2$, for the spin-independent isoscalar DM-particle-nucleon scattering cross section is obtained at a DM-particle mass of 49\,GeV/c$^2$ at 90\% confidence level.

hep-ex↗

Resonance Mass Spectra of Gravity and Fermion on Bloch Branes

In this paper, by presenting the potentials of Kaluza-Klein (KK) modes in the corresponding Schrödinger equations, we investigate the localization and resonances of gravity and fermion on the symmetric and asymmetric Bloch {branes}. We find that the localization properties of zero modes for gravity and fermion in the symmetric brane case are the same, whereas, for the asymmetric brane case, the fermion zero mode is localized on one of the sub-branes, while the gravity zero mode is localized on another sub-brane. The spectra of the gravity and the left- or right-handed fermion are composed of a bound zero mode and a series of gapless continuous massive KK modes. Among the continuous massive KK modes, we obtain some discrete gravity and fermion resonant (quasilocalized) KK states on the brane, which have a finite probability of escaping into the bulk. The KK states with lower resonant masses have a longer lifetime on the brane. And the number of the resonant KK states increases linearly with the width of the brane and the scalar-fermion coupling constant, {but it decreases with the asymmetric factor $β$}. The structure of the resonance spectrum is investigated in detail.

hep-th↗

Resonances of Kalb-Ramond field on symmetric and asymmetric thick branes

In this paper, we investigate the localization of the Kalb-Ramond field on symmetric and asymmetric thick branes, which are generated by a background scalar field. In order to localize the Kalb-Ramond field, we introduce a coupling with the background scalar field, and find that there exist some Kaluza-Klein resonant modes. For the case of symmetric brane, we seek the resonances by using the relative probability method and transfer matrix method, and obtain the same result for the two methods. For the asymmetric case, we use the transfer matrix method. We find that the number of resonances will decrease with the increase of the asymmetry.

hep-th↗

Anisotropic dielectric and ferroelectric response of multiferroic LiCu2O2 in magnetic field

LiCu2O2 is the first multiferroic cuprate to be reported and its ferroelectricity is induced by complex magnetic ordering in ground state, which is still in controversy today. Herein, we have grown nearly untwinned LiCu2O2 single crystals of high quality and systematically investigated their dielectric and ferroelectric behaviours in external magnetic fields. The highly anisotropic response observed in different magnetic fields apparently contradicts the prevalent bc- or ab- plane cycloidal spin model. Our observations give strong evidence supporting a new helimagnetic picture in which the normal of the spin helix plane is along the diagonal of CuO4 squares which form the quasi-1D spin chains by edge-sharing. Further analysis suggests that the spin helix in the ground state is elliptical and in the intermediate state the present c-axis collinear SDW model is applicable with some appropriate modifications. In addition, our studies show that the dielectric and ferroelectric measurements could be used as probes for the characterization of the complex spin structures in multiferroic materials due to the close tie between their magnetic and electric orderings.

cond-mat.str-el↗

Localization and Mass Spectra of Fermions on Symmetric and Asymmetric Thick Branes

A three-parameter (positive odd integer $s$, thickness factor $λ$, and asymmetry factor $a$) family of asymmetric thick brane solutions in five dimensions were constructed from a two-parameter ($s$ and $λ$) family of symmetric ones in [R. Guerrero, R.O. Rodriguez, and R. Torrealba, Phys. Rev. D \textbf{72}, 124012 (2005).]. The values $s=1$ and $s\geq3$ correspond to single branes and double branes, respectively. These branes have very rich inner structure. In this paper, by presenting the mass-independent potentials of Kaluza--Klein (KK) modes in the corresponding Schrödinger equations, we investigate the localization and mass spectra of fermions on the symmetric and asymmetric thick branes in an AdS background. In order to analyze the effect of gravity-fermion interaction (i.e., the effect of the inner structure of the branes) and scalar-fermion interaction to the spectrum of fermion KK modes, we consider three kinds of typical kink-fermion couplings. The spectra of left chiral fermions for these couplings are consisted of a bound zero mode and a series of gapless continuous massive KK modes, some discrete bound KK modes including zero mode (exist mass gaps) and a series of continuous massive KK modes, infinite discrete bound KK modes, respectively. The structures of the spectra are investigated in detail.

hep-th↗

Mining Compressed Repetitive Gapped Sequential Patterns Efficiently

Mining frequent sequential patterns from sequence databases has been a central research topic in data mining and various efficient mining sequential patterns algorithms have been proposed and studied. Recently, in many problem domains (e.g, program execution traces), a novel sequential pattern mining research, called mining repetitive gapped sequential patterns, has attracted the attention of many researchers, considering not only the repetition of sequential pattern in different sequences but also the repetition within a sequence is more meaningful than the general sequential pattern mining which only captures occurrences in different sequences. However, the number of repetitive gapped sequential patterns generated by even these closed mining algorithms may be too large to understand for users, especially when support threshold is low. In this paper, we propose and study the problem of compressing repetitive gapped sequential patterns. Inspired by the ideas of summarizing frequent itemsets, RPglobal, we develop an algorithm, CRGSgrow (Compressing Repetitive Gapped Sequential pattern grow), including an efficient pruning strategy, SyncScan, and an efficient representative pattern checking scheme, -dominate sequential pattern checking. The CRGSgrow is a two-step approach: in the first step, we obtain all closed repetitive sequential patterns as the candidate set of representative repetitive sequential patterns, and at the same time get the most of representative repetitive sequential patterns; in the second step, we only spend a little time in finding the remaining the representative patterns from the candidate set. An empirical study with both real and synthetic data sets clearly shows that the CRGSgrow has good performance.

cs.DB↗

Direct Observation of Photonic Jets and Corresponding Backscattering Enhancement at Microwave frequencies

We experimentally verified the phenomena of photonic jets generated by plane-electromagnetic-wave-illuminated dielectric micro-cylinders with diameter comparable to the corresponding wavelength at microwave frequencies. Using a home-made 2D spatial field mapping system, we carried out a point-by-point measurement of both phase and intensity of spatial electric field distribution inside and around scattering cylinders, providing a clear complete electromagnetic field picture for these phenomena. Correspondingly, the theoretically predicted super-enhancement of the backscattering induced by small particles of deeply-subwavelength size located within the photonic jets was also confirmed. Our measurements agreed well with the numerical simulations, indicating that the photonic jets indeed can provide a promising powerful way for deeply subwavelength detection and imaging.

physics.optics↗

Fermions in gravity and gauge backgrounds on a brane world

We solve the fermionic zero modes in gravity and gauge backgrounds on a brane involving a warped geometry, and study the localization of spin 1/2 fermionic field on the brane world. The result is that there exist massless spin 1/2 fermions which can be localized on the bulk with the exponentially decreasing warp factor if including U(1) gauge background. Two special cases of gauge backgrounds on the extra dimensional manifold are discussed.

hep-th↗

Self-Dual Vortices in the Fractional Quantum Hall System

Based on the $ϕ$-mapping theory, we obtain an exact Bogomol'nyi self-dual equation with a topological term, which is ignored in traditional self-dual equation, in the fractional quantum Hall system. It is revealed that there exist self-dual vortices in the system. We investigate the inner topological structure of the self-dual vortices and show that the topological charges of the vortices are quantized by Hopf indices and Brouwer degrees. Furthermore, we study the branch processes in detail. The vortices are found generating or annihilating at the limit points and encountering, splitting or merging at the bifurcation points of the vector field $\vecϕ$.

hep-th↗

Fermions in Self-dual Vortex Background on a String-like Defect

By using the self-dual vortex background on extra two-dimensional Riemann surfaces in 5+1 dimensions, the localization mechanism of bulk fermions on a string-like defect with the exponentially decreasing warp-factor is obtained. We give the conditions under which localized spin 1/2 and 3/2 fermions can be obtained.

hep-th↗

Localization of Fermions on a String-like Defect

We study localization of bulk fermions on a string-like defect with the exponentially decreasing warp factor in six dimensions with inclusion of U(1) gauge background from the viewpoint of field theory, and give the conditions under which localized spin 1/2 and 3/2 fermions can be obtained.

hep-th↗

Fermion Absorption Cross Section and Topology of Spherically Symmetric Black Holes

In 1997, Liberati and Pollifrone in Phys. Rev. D56 (1997) 6458 (hep-th/9708014) achieved a new formulation of the Bekenstein-Hawking formula, where the entropy and the Euler characteristic are related by $S=χA/8$. In this work we present a relation between the low-energy absorption cross section for minimally coupled fermions and the Euler characteristic of (3+1)-dimensional spherically symmetric black holes, i.e. $σ=χg_h^{-1}A$. Based on the relation, using the Gauss--Bonnet--Chern theorem and the $ϕ$-mapping method, an absorption cross section density is introduced to describe the topology of the absorption cross section. It is shown that the absorption cross section and its density are determined by the singularities of the timelike Killing vector field of the spacetime and these singularities carry the topological numbers, Hopf indices and Brouwer degrees, naturally.

hep-th↗

Topological Vortex Lines in Two-Gap Superconductor

Based on the U(1) gauge potential decomposition theory and the $ϕ$-mapping method, we study the vortex lines in two-gap superconductor and obtain the condition, under which the vortices can carry an arbitrary fraction of magnetic flux. It has been pointed out that the Chern-Simon action is a topological invariant, which is just the total sum of all the self-linking numbers and all the linking numbers of the knot family.

cond-mat.supr-con↗

Knotted Solitons in a Charged Two-Condensate Bose System

By making use of the decomposition of U(1) gauge potential theory and the ϕmapping method, we propose that a charged two-condensate Bose system possesses vortex lines and two classes of knotted solitons. The topological charges of the vortex lines are characterized by the Hopf indices and the Brower degrees of ϕ-mapping, and the knotted solitons are described by the nontrivial Hopf invariant and the BF action, respectively.

cond-mat.supr-con↗

Novel Topological Invariant in the U(1) Gauge Field Theory

Based on the decomposition of U(1) gauge potential theory and the $ϕ$-mapping topological current theory, the three-dimensional knot invariant and a four-dimensional new topological invariant are discussed in the U(1) gauge field.

hep-th↗

Topological aspect of black hole with Skyrme hair

Based on the $ϕ$-mapping topological current theory, we show that the presence of the black hole leaves fractional baryon charge outside the horizon in the Einstein-Skyrme theory. A topological current is derived from the Einstein-Skyrme system, which corresponds to the monopoles around the black hole. The branch process (splitting, merging and intersection) is simply discussed during the evolution of the monopoles.

hep-th↗

The U(1) Topological Gauge Field Theory for Topological Defects in Liquid Crystals

A novel U(1) topological gauge field theory for topological defects in liquid crystals is constructed by considering the U(1) gauge field is invariant under the director inversion. Via the U(1) gauge potential decomposition theory and the $ϕ$-mapping topological current theory, the decomposition expression of U(1) gauge field and the unified topological current for monopoles and strings in liquid crystals are obtained. It is revealed that monopoles and strings are located in different spatial dimensions and their topological charges are just the winding numbers of $ϕ$-mapping.

hep-th↗

Faster Algorithm of String Comparison

In many applications, it is necessary to determine the string similarity. Edit distance[WF74] approach is a classic method to determine Field Similarity. A well known dynamic programming algorithm [GUS97] is used to calculate edit distance with the time complexity O(nm). (for worst case, average case and even best case) Instead of continuing with improving the edit distance approach, [LL+99] adopted a brand new approach-token-based approach. Its new concept of token-base-retain the original semantic information, good time complex-O(nm) (for worst, average and best case) and good experimental performance make it a milestone paper in this area. Further study indicates that there is still room for improvement of its Field Similarity algorithm. Our paper is to introduce a package of substring-based new algorithms to determine Field Similarity. Combined together, our new algorithms not only achieve higher accuracy but also gain the time complexity O(knm) (k<0.75) for worst case, O(*n) where <6 for average case and O(1) for best case. Throughout the paper, we use the approach of comparative examples to show higher accuracy of our algorithms compared to the one proposed in [LL+99]. Theoretical analysis, concrete examples and experimental result show that our algorithms can significantly improve the accuracy and time complexity of the calculation of Field Similarity. [US97] D. Guseld. Algorithms on Strings, Trees and Sequences, in Computer Science and Computational Biology. [LL+99] Mong Li Lee, Cleansing data for mining and warehousing, In Proceedings of the 10th International Conference on Database and Expert Systems Applications (DEXA99), pages 751-760,August 1999. [WF74] R. Wagner and M. Fisher, The String to String Correction Problem, JACM 21 pages 168-173, 1974.

cs.DS↗