24,340 research outputs found

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

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

### Semileptonic B decays into excited charmed mesons from QCD sum rules

Exclusive semileptonic $B$ 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 $D$ mesons ($D_1$, $D_2^*$, $D'_0$, and $D'_1$) 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

(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

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

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 $B$ Meson Decays Into A Highly Excited Charmed Meson Doublet

We study the heavy quark effective theory prediction for semileptonic $B$
decays into an orbital excited $F$-wave charmed doublet, the ($2^{+}$, $3^{+}$)
states ($D^{*'}_{2}$, $D_{3}$), 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 $\Gamma_{B\to
D^{*'}_{2}\ell\overline{\nu}}=1.85\times10^{-19} {GeV}$ and $\Gamma_{B\to
D_{3}\ell\overline{\nu}}=1.78\times10^{-19} {GeV}$. The branching ratios are
$\mathcal {B}(B\to D_{2}^{*'}\ell\overline{\nu})=4.6\times10^{-7}$ and
$\mathcal {B}(B\to D_{3}\ell\overline{\nu})=4.4\times10^{-7}$, respectively.Comment: 6 pages,2 figure

### Symmetry-preserving Loop Regularization and Renormalization of QFTs

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 $M_c$ and sliding energy scale $\mu_s$ 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 $D^+_{sJ}(2317)$ and $D^+_{sJ}(2460)$ with Sum Rules in HQET

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

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