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C. Liu

Publications and source records attributed to C. Liu.

228 records · Page 13Linked to original sources
arXiv2007

Study of Hadron Scattering Using an Asymmetric Box

We propose to study hadron-hadron scattering using lattice QCD in an asymmetric box which allows one to access more non-degenerate low-momentum modes for a given volume. The conventional Lüscher's formula applicable in a symmetric box is modified accordingly. To illustrate the feasibility of this approach, pion-pion elastic scattering phase shifts in the I=2, J=0 channel are calculated within quenched approximation using improved gauge and Wilson fermion actions on anisotropic lattices in an asymmetric box. After the chiral and continuum extrapolation, we find that our quenched results for the scattering phase shifts in this channel are consistent with the experimental data when the three-momentum of the pion is below 300MeV. Agreement is also found when compared with previous theoretical results from lattice and other means. Moreover, with the usage of asymmetric volume, we are able to compute the scattering phases in the low-momentum range (pion three momentum less than about 350MeV in the center of mass frame) for over a dozen values of the pion three-momenta, much more than using the conventional symmetric box with comparable volume.

hep-lat↗
arXiv2007

Kernel Regression For Determining Photometric Redshifts From Sloan Broadband Photometry

We present a new approach, kernel regression, to determine photometric redshifts for 399,929 galaxies in the Fifth Data Release of the Sloan Digital Sky Survey (SDSS). In our case, kernel regression is a weighted average of spectral redshifts of the neighbors for a query point, where higher weights are associated with points that are closer to the query point. One important design decision when using kernel regression is the choice of the bandwidth. We apply 10-fold cross-validation to choose the optimal bandwidth, which is obtained as the cross-validation error approaches the minimum. The experiments show that the optimal bandwidth is different for diverse input patterns, the least rms error of photometric redshift estimation arrives at 0.019 using color+eClass as the inputs, the less rms error amounts to 0.020 using ugriz+eClass as the inputs. Here eClass is a galaxy spectra type. Then the little rms scatter is 0.021 with color+r as the inputs.

astro-ph↗
arXiv2006

Initial growth behavior and resulting microstructural properties of heteroepitaxial ZnO thin films on sapphire (0001) substrates

We have investigated the initial growth behavior and resulting microstructural properties of heteroepitaxial ZnO thin films prepared by pulsed laser deposition on sapphire (0001) substrates. High-resolution x-ray diffraction and transmission electron microscopy studies revealed that the initial growth behavior and the microstructure of the films significantly depend on the growth parameters. ZnO films grown at 700 oC with 20 mTorr O2 partial pressure initiated with a columnar growth mode and contained two kinds of domains. These domains were in-plane orientated either ZnO[112-0]//Al2O3[101-0] or ZnO[101-0]//Al2O3[101-0], and were surrounded by highly defective domain boundaries with threading dislocations. The films grown at 800 oC with 1 mTorr O2 showed 2-dimensional layered growth with only one in-plane epitaxial relationship, ZnO[112-0]//Al2O3[101-0]. Most of the defects in the layered grown films were basal plane stacking faults near the interface between ZnO and the substrate. The formation mechanism of the 30o-twisted domains with the in-plane orientation of ZnO[101-0]//Al2O3[101-0] is discussed.

cond-mat.mtrl-sci↗
arXiv2006

Self-organization behavior in a constrained minority game

In the standard minority game, every agent switches to his best strategy in hand at each time step. If only a small number of agents are allowed to switch their strategies at each time step, the population variance of the system plunges. The variance reaches a low value and remains steady for a period of time. Then without any sign it starts to rise abruptly to a high value and then decreases smoothly to the previous low value again. The process of an abrupt rise followed by a gentle decrease repeats again and again but without obvious characteristic length as time goes on. The phenomenon is similar to the collapse of a sand pile with sands being added continuously from the top. We define the scale of collapse of the population variance by the difference of the variance before and after an abrupt rise. We then find that the logarithmic plot of the frequency versus scale of the collapses follows a power law.

physics.data-an↗
arXiv2005

The Multiwavelength Survey by Yale-Chile (MUSYC): Survey Design and Deep Public UBVRIz' Images and Catalogs of the Extended Hubble Deep Field South

We present UBVRIz' optical images of the 0.32 square degree Extended Hubble Deep Field South. This is one of four fields comprising the MUSYC survey, which is optimized for the study of galaxies at z=3, AGN demographics, and Galactic structure. We calculate corrected aperture photometry and its uncertainties and find through tests that these provide a significant improvement upon standard techniques. Our photometric catalog of 62968 objects is complete to a total magnitude of R_AB=25. We select z=3 Lyman break galaxy (LBG) candidates from their UVR colors and find a sky surface density of 1.4/sq. arcmin and an angular correlation function w(theta) = 2.3+-1.0 theta^{-0.8}. (Abridged)

astro-ph↗
arXiv2004

$D_{sJ}^+(2632)$: 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 $D_s η$ 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.

hep-ph↗
arXiv2000

Scalar and Tensor Glueballs on Asymmetric Coarse Lattices

Scalar and tensor glueball spectrum is studied using an improved gluonic action on asymmetric lattices in the pure SU(3) gauge theory. The smallest spatial lattice spacing is about 0.08fm which makes the extrapolation to the continuum limit more reliable. In particular, attention is paid to the scalar glueball mass which is known to have problems in the extrapolation. Converting our lattice results to physical units using the scale set by the static quark potential, we obtain the following results for the glueball masses: $M_G(0^{++})=1730(90)MeV$ for the scalar glueball mass and $M_G(2^{++})=2400(95)MeV$ for the tensor glueball.

hep-lat↗
arXiv1997

Efficiency of Molecular Hydrogen Formation on Silicates

We report on laboratory measurements of molecular hydrogen formation and recombination on an olivine slab as a function of surface temperature under conditions relevant to those encountered in the interstellar medium. On the basis of our experimental evidence, we recognize that there are two main regimes of H coverage that are of astrophysical importance; for each of them we provide an expression giving the production rate of molecular hydrogen in interstellar clouds.

astro-ph↗
arXiv1996

Thermodynamics of lattice QCD with two light quark flavours on a 16^3 x 8 lattice II

We have extended our earlier simulations of the high temperature behaviour of lattice QCD with two light flavours of staggered quarks on a $16^3 \times 8$ lattice to lower quark mass (m_q=0.00625). The transition from hadronic matter to a quark-gluon plasma is observed at $6/g^2=5.49(2)$ corresponding to a temperature of $T_c \approx 140$MeV. We present measurements of observables which probe the nature of the quark-gluon plasma and serve to distinguish it from hadronic matter. Although the transition is quite abrupt, we have seen no indications that it is first order.

hep-lat↗
arXiv1996

Low-Lying Eigenvalues of the Wilson-Dirac Operator

An exploratory study of the low-lying eigenvalues of the Wilson-Dirac operator and their corresonding eigenvectors is presented. Results for the eigenvalues from quenched and unquenched simulations are discussed. The eigenvectors are studied with respect to their localization properties in the quenched approximation for the cases of SU(2) and SU(3).

hep-lat↗
arXiv1994

Strongly Interacting Higgs Sector without Technicolor

Simulation results are presented on Higgs mass calculations in the spontaneously broken phase of the Higgs sector in the minimal Standard Model with a higher derivative regulator. A heavy Higgs particle is found in the TeV mass range in the presence of a complex conjugate ghost pair at higher energies. The ghost pair evades easy experimental detection. As a finite and unitary theory in the continuum, this model serves as an explicit and simple example of a strongly interacting Higgs sector without technicolor.

hep-lat↗