arXiv subjects

Chuan Liu

Publications and source records attributed to Chuan Liu.

At least 109 records · Page 6Linked to original sources

arXiv2014

Low-energy Scattering of $(D\bar{D}^{*})^\pm$ System And the Resonance-like Structure $Z_c(3900)$

In this exploratory lattice study, low-energy scattering of the $(D\bar{D}^{*})^\pm$ meson system is analyzed using lattice QCD with $N_f=2$ twisted mass fermion configurations with three pion mass values. The calculation is performed within single-channel Lüscher's finite-size formalism. The threshold scattering parameters, namely the scattering length $a_0$ and the effective range $r_0$, for the $s$-wave scattering in $J^P=1^+$ channel are extracted. For the cases in our study, the interaction between the two charmed mesons is weakly repulsive. Our lattice results therefore do not support the possibility of a shallow bound state for the two mesons for the pion mass values we studied. This calculation provides some useful information on the nature of the newly discovered resonance-like structure $Z_c(3900)$ by various experimental groups.

hep-lat↗

arXiv2014

Recent results from Lattice QCD

Recent Lattice QCD results are reviewed with an emphasis on spectroscopic results concerning the charm quark. It is demonstrated that, with accurate computations from lattice QCD in recent years that can be compared with the existing or upcoming experiments, stringent test of the Standard Model can be performed which will greatly sharpen our knowledge on the strong interaction.

hep-lat↗

arXiv2014

Glueballs in charmonia radiative decays

Scalar \cite{scalar_paper} and tensor \cite{tensor_paper} glueballs created in $J/ψ$ radiative decays are studied in quenched lattice QCD. Using two anisotropic lattices to approach the continuum limit, we compute the relevant form factors responsible for the decay rates for $J/ψ\rightarrowγG_{0^{++}}$ and $J/ψ\rightarrowγG_{2^{++}}$. Comparing with the existing experimental data, it is argued that $f_0(1710)$ is a favorable candidate for scalar glueball. The decay rate for $J/ψ\rightarrowγG_{2^{++}}$ is found to be quite substantial. A comprehensive search in the tensor channel on BESIII is therefore suggested.

hep-lat↗

arXiv2014

Generalized Lüscher's Formula in Multichannel Baryon-Baryon Scattering

In this paper, Lüscher's formula is generalized to the case of two spin-$\frac{1}{2}$ particles in two-channel scattering based on Ref. \cite{Li:2012bi}. This is first done in a non-relativistic quantum mechanics model and then generalized to quantum field theory. We show that Lüscher's formula obtained from these two different methods are equivalent up to terms that are exponentially suppressed in the box size. This formalism can be readily applied to future lattice QCD calculations.

hep-lat↗

arXiv2013

Lattice Study of Radiative $J/ψ$ Decay to a Tensor Glueball

The radiative decay of $J/ψ$ into a pure gauge tensor glueball is studied in the quenched lattice QCD formalism. With two anisotropic lattices, the mutlipole amplitudes E_1(0), M_2(0) and E_3(0) are obtained to be 0.114(12)(6)GeV, -0.011(5)(1)GeV, and 0.023(8)(1)GeV, respectively. The first error comes from the statistics, the Q^2 interpolation, and the continuum extrapolation, while the second is due to the uncertainty of the scale parameter r_0^{-1}=410(20) MeV. Thus the partial decay width $Γ(J/ψ\rightarrow γG_{2^{++}})$ is estimated to be 1.01(22)(10) keV which corresponds to a large branch ratio 1.1(2)(1)x10^{-2}. The phenomenological implication of this result is also discussed.

hep-lat↗

arXiv2013

On paratopological groups

In this paper, we firstly construct a Hausdorff non-submetrizable paratopological group $G$ in which every point is a $G_δ$-set, which gives a negative answer to Arhangel'ski\vı\ and Tkachenko's question [Topological Groups and Related Structures, Atlantis Press and World Sci., 2008]. We prove that each first-countable Abelian paratopological group is submetrizable. Moreover, we discuss developable paratopological groups and construct a non-metrizable, Moore paratopological group. Further, we prove that a regular, countable, locally $k_ω$-paratopological group is a discrete topological group or contains a closed copy of $S_ω$. Finally, we discuss some properties on non-H-closed paratopological groups, and show that Sorgenfrey line is not H-closed, which gives a negative answer to Arhangel'ski\vı\ and Tkachenko's question [Topological Groups and Related Structures, Atlantis Press and World Sci., 2008]. Some questions are posed.

math.GN↗

arXiv2013

Scalar Glueball in Radiative $J/ψ$ Decay on Lattice

The form factors in the radiative decay of $J/ψ$ to a scalar glueball are studied within quenched lattice QCD on anisotropic lattices. The continuum extrapolation is carried out by using two different lattice spacings. With the results of these form factors, the partial width of $J/ψ$ radiatively decaying into the pure gauge scalar glueball is predicted to be 0.35(8) keV, which corresponds to a branching ratio of 3.8(9)x10^{-3}. By comparing with the experiments, out results indicate that f_0(1710) has a larger overlap with the pure gauge glueball than other related scalar mesons.

hep-lat↗

arXiv2013

Lattice study on $η_{c2}$ and X(3872)

Properties of $2^{-+}$ charmonium $η_{c2}$ are investigated in quenched lattice QCD. The mass of $η_{c2}$ is determined to be 3.80(3) GeV, which is close to the mass of $D$-wave charmonium $ψ(3770)$ and in agreement with quark model predictions. The transition width of $η_{c2}\to γJ/ψ$ is also obtained with a value $Γ=3.8(9)$ keV. Since the possible $2^{-+}$ assignment to X(3872) has not been ruled out by experiments, our results help to clarify the nature of X(3872).

hep-lat↗

arXiv2012

Generalized Lüscher Formula in Multi-channel Baryon-Meson Scattering

Lüscher's formula relates the elastic scattering phase shifts to the two-particle energy levels in a finite cubic box. The original formula was obtained for elastic scattering of two massive spinless particles in the center of mass frame. In this paper, we consider the case for the scattering of a spin 1/2 particle with a spinless particle in multi-channel scattering. A generalized relation between the energy of two particle system and the scattering matrix elements is established. We first obtain this relation using quantum-mechanics in both center-of-mass frame and in a general moving frame. The result is then generalized to quantum field theory using methods outlined in Ref. \cite{Hansen:2012tf}. We verify that the results obtained using both methods are equivalent up to terms that are exponentially suppressed in the box size.

hep-lat↗

arXiv2011

A note on rectifiable spaces

In this paper, we firstly discuss the question: Is $l_{2}^{\infty}$ homeomorphic to a rectifiable space or a paratopological group? And then, we mainly discuss locally compact rectifiable spaces, and show that a locally compact and separable rectifiable space is $σ$-compact, which gives an affirmative answer to A.V. Arhangel'skiǐ and M.M. Choban's question [On remainders of rectifiable spaces, Topology Appl., 157(2010), 789-799]. Next, we show that a rectifiable space $X$ is strongly Fr$\acute{e}$chet-Urysohn if and only if $X$ is an $α_{4}$-sequential space. Moreover, we discuss the metrizabilities of rectifiable spaces, which gives a partial answer for a question posed in \cite{LFC2009}. Finally, we consider the remainders of rectifiable spaces, which improve some results in \cite{A2005, A2007, A2009, Liu2009}.

math.GN↗

arXiv2011

Complementary-like Graphene Logic Gates Controlled by Electrostatic Doping

Realization of logic circuits from graphene is very attractive for high-speed nanoelectronics. However, the intrinsic ambipolar nature hinders the formation of graphene logic devices with the conventional complementary architecture. Using electrostatic doping modulation, we show here a facile method to control the charge neutrality points and form a complementary-like structure, in which the ambipolar conduction is used as a benefit rather than a drawback to construct logic devices. A band gap is also introduced in the channels to improve the switching ratio of the graphene transistors. For the first time, complementary-like NOR and NAND logic gates were demonstrated. This method provides a possible route for logic circuits from ambipolar graphene and, in principle, can be also extended to other ambipolar semiconductors, such as organic compounds and carbon nanotube thin films.

cond-mat.mes-hall↗

arXiv2011

Radiative transitions in charmonium from $N_f=2$ twisted mass lattice QCD

We present a study for charmonium radiative transitions: $J/ψ\rightarrowη_cγ$, $χ_{c0}\rightarrow J/Ψγ$ and $h_c\rightarrowη_cγ$ using $N_f=2$ twisted mass lattice QCD gauge configurations. The single-quark vector form factors for $η_c$ and $χ_{c0}$ are also determined. The simulation is performed at a lattice spacing of $a= 0.06666$ fm and the lattice size is $32^3\times 64$. After extrapolation of lattice data at nonzero $Q^2$ to 0, we compare our results with previous quenched lattice results and the available experimental values.

hep-lat↗

arXiv2010

Enhanced Logic Performance with Semiconducting Bilayer Graphene Channels

Realization of logic circuits in graphene with an energy gap (EG) remains one of the main challenges for graphene electronics. We found that large transport EGs (>100 meV) can be fulfilled in dual-gated bilayer graphene underneath a simple alumina passivation top gate stack, which directly contacts the graphene channels without an inserted buffer layer. With the presence of EGs, the electrical properties of the graphene transistors are significantly enhanced, as manifested by enhanced on/off current ratio, subthreshold slope and current saturation. For the first time, complementary-like semiconducting logic graphene inverters are demonstrated that show a large improvement over their metallic counterparts. This result may open the way for logic applications of gap-engineered graphene.

cond-mat.mes-hall↗

arXiv2010

More on volume dependence of spectral weight function

Spectral weight functions are easily obtained from two-point correlation functions and they might be used to distinguish single-particle from multi-particle states in a finite-volume lattice calculation, a problem crucial for many lattice QCD simulations. In previous studies, it is shown that the spectral weight function for a broad resonance shares the typical volume dependence of a two-particle scattering state i.e. proportional to $1/L^3$ in a large cubic box of size $L$ while the narrow resonance case requires further investigation. In this paper, a generalized formula is found for the spectral weight function which incorporates both narrow and broad resonance cases. Within Lüscher's formalism, it is shown that the volume dependence of the spectral weight function exhibits a single-particle behavior for a extremely narrow resonance and a two-particle behavior for a broad resonance. The corresponding formulas for both $A^+_1$ and $T^-_1$ channels are derived. The potential application of these formulas in the extraction of resonance parameters are also discussed.

hep-lat↗

arXiv2010

A Quenched Study of SU(3) Glueballs at Finite Temperature

Thermal properties of glueballs in SU(3) Yang-Mills theory are investigated in a large temperature range from $0.3T_c$ to $1.9T_c$ on anisotropic lattices. The glueball operators are optimized for the projection of the ground states by the variational method with a smearing scheme. Their thermal correlators are calculated in all 20 symmetry channels. It is found in all channels that the pole masses $M_G$ of glueballs remain almost constant when the temperature is approaching the critical temperature $T_c$ from below, and start to reduce gradually with the temperature going above $T_c$. The correlators in the $0^{++}$, $0^{-+}$, and $2^{++}$ channels are also analyzed based on the Breit-Wigner $\emph{Ansatz}$ by assuming a thermal width $Γ$ to the pole mass $ω_0$ of each thermal glueball ground state. While the values of $ω_0$ are insensitive to $T$ in the whole temperature range, the thermal widths $Γ$ exhibit distinct behaviors at temperatures below and above $T_c$. The widths are very small (approximately few percent of $ω_0$ or even smaller) when $T T_c$ and reach values of roughly $Γ\sim ω_0/2$ at $T\approx 1.9T_c$.

hep-lat↗

arXiv2009

A general study on the volume dependence of spectral weights in lattice field theory

It has been suggested that the volume dependence of the spectral weight could be utilized to distinguish single and multi-particle states in Monte Carlo simulations. In a recent study using a solvable model, the Lee model, we found that this criteria is applicable only for stable particles and narrow resonances, not for the broad resonances. In this paper, the same question is addressed within the finite size formalism outlined by Lüscher. Using a quantum mechanical scattering model, the conclusion that was found in previous Lee model study is recovered. Then, following similar arguments as in Lüscher's, it is argued that the result is valid for a general massive quantum field theory under the same conditions as the Lüscher's formulae. Using the spectral weight function, a possibility of extracting resonance parameters is also pointed out.

hep-lat↗

arXiv2009

Low-energy $D^{*+}D^0_1$ Scattering and the Resonance-like Structure $Z^+(4430)$

Low-energy scattering of $D^*$ and $D_1$ meson are studied using quenched lattice QCD with improved lattice actions on anisotropic lattices. The calculation is performed within Lüscher's finite-size formalism which establishes the relation between the scattering phase in the infinite volume and the exact energy level in the finite volume. The threshold scattering parameters, namely the scattering length $a_0$ and the effective range $r_0$, for the s-wave scattering in $J^P=0^-$ channel are extracted. After the chiral and continuum extrapolations, we obtain: $a_0=2.52(47)$fm and $r_0=0.7(1)$fm where the errors are purely statistical. Based on these results, we discuss the possibility of a shallow bound state for the two charmed mesons within the non-relativistic potential scattering model. It is argued that, albeit the interaction between the two charmed mesons being attractive, it is unlikely that they can form a shallow bound state in this channel. This calculation provides some useful information on the nature of the newly discovered resonance-like structure $Z^+(4430)$ by the Belle Collaboration.

hep-lat↗

arXiv2008

Volume Dependence of Spectral Weights for Unstable Particles in a Solvable Model

Volume dependence of the spectral weight is usually used as a simple criteria to distinguish single-particle states from multi-particle states in lattice QCD calculations. Within a solvable model, the Lee model, we show that this criteria is in principle only valid for a stable particle or a narrow resonance. If the resonance being studied is broad, then the volume dependence of the corresponding spectral weight resembles that of a multi-particle state instead of a single-particle one. For an unstable $V$-particle in the Lee model, the transition from single-particle to multi-particle volume dependence is governed by the ratio of its physical width to the typical level spacing in the finite volume. We estimate this ratio for practical lattice QCD simulations and find that, for most cases, the resonance studied in lattice QCD simulations still resembles the single particle behavior.

hep-lat↗