24,340 research outputs found

    DsJ+(2632)D_{sJ}^+(2632): An Excellent Candidate of Tetraquarks

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    We analyze various possible interpretations of the narrow state DsJ(2632)D_{sJ}(2632) which lies 100 MeV above threshold. This interesting state decays mainly into DsηD_s \eta instead of D0K+D^0 K^+. If this relative branching ratio is further confirmed by other experimental groups, we point out that the identification of DsJ(2632)D_{sJ}(2632) either as a csˉc\bar s state or more generally as a 3ˉ{\bf {\bar 3}} state in the SU(3)FSU(3)_F representation is probably problematic. Instead, such an anomalous decay pattern strongly indicates DsJ(2632)D_{sJ}(2632) is a four quark state in the SU(3)FSU(3)_F 15{\bf 15} representation with the quark content 122(dsdˉ+sddˉ+suuˉ+usuˉ2sssˉ)cˉ{1\over 2\sqrt{2}} (ds\bar{d}+sd\bar{d}+su\bar{u}+us\bar{u}-2ss\bar{s})\bar{c}. We discuss its partners in the same multiplet, and the similar four-quark states composed of a bottom quark BsJ0(5832)B_{sJ}^0(5832). Experimental searches of other members especially those exotic ones are strongly called for

    Semileptonic B decays into excited charmed mesons from QCD sum rules

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    Exclusive semileptonic BB decays into excited charmed mesons are studied with QCD sum rules in the leading order of heavy quark effective theory. Two universal Isgur-Wise functions \tau and \zeta for semileptonic B decays into four lowest lying excited DD mesons (D1D_1, D2D_2^*, D0D'_0, and D1D'_1) are determined. The decay rates and branching ratios for these processes are calculated.Comment: RevTeX, 17 pages including 2 figure

    Hyperaccretion Disks around Neutron Stars

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    (Abridged) We here study the structure of a hyperaccretion disk around a neutron star. We consider a steady-state hyperaccretion disk around a neutron star, and as a reasonable approximation, divide the disk into two regions, which are called inner and outer disks. The outer disk is similar to that of a black hole and the inner disk has a self-similar structure. In order to study physical properties of the entire disk clearly, we first adopt a simple model, in which some microphysical processes in the disk are simplified, following Popham et al. and Narayan et al. Based on these simplifications, we analytically and numerically investigate the size of the inner disk, the efficiency of neutrino cooling, and the radial distributions of the disk density, temperature and pressure. We see that, compared with the black-hole disk, the neutron star disk can cool more efficiently and produce a much higher neutrino luminosity. Finally, we consider an elaborate model with more physical considerations about the thermodynamics and microphysics in the neutron star disk (as recently developed in studying the neutrino-cooled disk of a black hole), and compare this elaborate model with our simple model. We find that most of the results from these two models are basically consistent with each other.Comment: 44 pages, 10 figures, improved version following the referees' comments, main conclusions unchanged, accepted for publication in Ap

    Two-Dimensional Inversion Asymmetric Topological Insulators in Functionalized III-Bi Bilayers

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    The search for inversion asymmetric topological insulators (IATIs) persists as an effect for realizing new topological phenomena. However, so for only a few IATIs have been discovered and there is no IATI exhibiting a large band gap exceeding 0.6 eV. Using first-principles calculations, we predict a series of new IATIs in saturated Group III-Bi bilayers. We show that all these IATIs preserve extraordinary large bulk band gaps which are well above room-temperature, allowing for viable applications in room-temperature spintronic devices. More importantly, most of these systems display large bulk band gaps that far exceed 0.6 eV and, part of them even are up to ~1 eV, which are larger than any IATIs ever reported. The nontrivial topological situation in these systems is confirmed by the identified band inversion of the band structures and an explicit demonstration of the topological edge states. Interestingly, the nontrivial band order characteristics are intrinsic to most of these materials and are not subject to spin-orbit coupling. Owning to their asymmetric structures, remarkable Rashba spin splitting is produced in both the valence and conduction bands of these systems. These predictions strongly revive these new systems as excellent candidates for IATI-based novel applications.Comment: 17 pages,5figure

    X-Ray Flares from Postmerger Millisecond Pulsars

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    Recent observations support the suggestion that short-duration gamma-ray bursts are produced by compact star mergers. The X-ray flares discovered in two short gamma-ray bursts last much longer than the previously proposed postmerger energy release time scales. Here we show that they can be produced by differentially rotating, millisecond pulsars after the mergers of binary neutron stars. The differential rotation leads to windup of interior poloidal magnetic fields and the resulting toroidal fields are strong enough to float up and break through the stellar surface. Magnetic reconnection--driven explosive events then occur, leading to multiple X-ray flares minutes after the original gamma-ray burst.Comment: 10 pages, published in Scienc

    Semileptonic BB Meson Decays Into A Highly Excited Charmed Meson Doublet

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    We study the heavy quark effective theory prediction for semileptonic BB decays into an orbital excited FF-wave charmed doublet, the (2+2^{+}, 3+3^{+}) states (D2D^{*'}_{2}, D3D_{3}), at the leading order of heavy quark expansion. The corresponding universal form factor is estimated by using the QCD sum rule method. The decay rates we predict are ΓBD2ν=1.85×1019GeV\Gamma_{B\to D^{*'}_{2}\ell\overline{\nu}}=1.85\times10^{-19} {GeV} and ΓBD3ν=1.78×1019GeV\Gamma_{B\to D_{3}\ell\overline{\nu}}=1.78\times10^{-19} {GeV}. The branching ratios are B(BD2ν)=4.6×107\mathcal {B}(B\to D_{2}^{*'}\ell\overline{\nu})=4.6\times10^{-7} and B(BD3ν)=4.4×107\mathcal {B}(B\to D_{3}\ell\overline{\nu})=4.4\times10^{-7}, respectively.Comment: 6 pages,2 figure

    Symmetry-preserving Loop Regularization and Renormalization of QFTs

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    A new symmetry-preserving loop regularization method proposed in \cite{ylw} is further investigated. It is found that its prescription can be understood by introducing a regulating distribution function to the proper-time formalism of irreducible loop integrals. The method simulates in many interesting features to the momentum cutoff, Pauli-Villars and dimensional regularization. The loop regularization method is also simple and general for the practical calculations to higher loop graphs and can be applied to both underlying and effective quantum field theories including gauge, chiral, supersymmetric and gravitational ones as the new method does not modify either the lagrangian formalism or the space-time dimension of original theory. The appearance of characteristic energy scale McM_c and sliding energy scale μs\mu_s offers a systematic way for studying the renormalization-group evolution of gauge theories in the spirit of Wilson-Kadanoff and for exploring important effects of higher dimensional interaction terms in the infrared regime.Comment: 13 pages, Revtex, extended modified version, more references adde

    Understanding the DsJ+(2317)D^+_{sJ}(2317) and DsJ+(2460)D^+_{sJ}(2460) with Sum Rules in HQET

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    In the framework of heavy quark effective theory we use QCD sum rules to calculate the masses of the cˉs\bar c s (0+,1+)(0^+, 1^+) and (1+,2+)(1^+, 2^+) excited states. The results are consistent with that the states DsJ(2317)D_{sJ}(2317) and DsJ(2460)D_{sJ}(2460) observed by BABAR and CLEO are the 0+0^+ and 1+1^+ states in the jl=12+j_l={1\over 2}^+ doublet