Improved lattice QCD with quarks: the 2 dimensional case

QCD in two dimensions is investigated using the improved fermionic lattice Hamiltonian proposed by Luo, Chen, Xu, and Jiang. We show that the improved theory leads to a significant reduction of the finite lattice spacing errors. The quark condensate and the mass of lightest quark and anti-quark bound state in the strong coupling phase (different from t'Hooft phase) are computed. We find agreement between our results and the analytical ones in the continuum.Comment: LaTeX file (including text + 10 figures

Comment on "Time-Dependent Density-Matrix Renormalization Group: A Systematic Method for the Study of Quantum Many-Body Out-of- Equilibrium Systems"

In a recent Letter [Phys. Rev. Lett. 88, 256403(2002), cond-mat/0109158] Cazalilla and Marston proposed a time-dependent density- matrix renormalization group (TdDMRG) algorithm for the accurate evaluation of out-of-equilibrium properties of quantum many-body systems. For a point contact junction between two Luttinger liquids, a current oscillation develops after initial transient in the insulating regime. Here we would like to point out that (a) the observed oscillation is an artifact of the method; (b) the TdDMRG can be significantly improved by incorporating the non-equilibrium evolution of the goundstate into the density matrix.Comment: 1 page, 2 figure

Bound States and Critical Behavior of the Yukawa Potential

We investigate the bound states of the Yukawa potential $V(r)=-\lambda \exp(-\alpha r)/ r$, using different algorithms: solving the Schr\"odinger equation numerically and our Monte Carlo Hamiltonian approach. There is a critical $\alpha=\alpha_C$, above which no bound state exists. We study the relation between $\alpha_C$ and $\lambda$ for various angular momentum quantum number $l$, and find in atomic units, $\alpha_{C}(l)= \lambda [A_{1} \exp(-l/ B_{1})+ A_{2} \exp(-l/ B_{2})]$, with $A_1=1.020(18)$, $B_1=0.443(14)$, $A_2=0.170(17)$, and $B_2=2.490(180)$.Comment: 15 pages, 12 figures, 5 tables. Version to appear in Sciences in China

On defining partition entropy by inequalities

Partition entropy is the numerical metric of uncertainty within a partition of a finite set, while conditional entropy measures the degree of difficulty in predicting a decision partition when a condition partition is provided. Since two direct methods exist for defining conditional entropy based on its partition entropy, the inequality postulates of monotonicity, which conditional entropy satisfies, are actually additional constraints on its entropy. Thus, in this paper partition entropy is defined as a function of probability distribution, satisfying all the inequalities of not only partition entropy itself but also its conditional counterpart. These inequality postulates formalize the intuitive understandings of uncertainty contained in partitions of finite sets.We study the relationships between these inequalities, and reduce the redundancies among them. According to two different definitions of conditional entropy from its partition entropy, the convenient and unified checking conditions for any partition entropy are presented, respectively. These properties generalize and illuminate the common nature of all partition entropies

Nature of eclipsing pulsars

We present a model for pulsar radio eclipses in some binary systems, and test this model for PSRs B1957+20 and J2051-0827. We suggest that in these binaries the companion stars are degenerate dwarfs with strong surface magnetic fields. The magnetospheres of these stars are permanently infused by the relativistic particles of the pulsar wind. We argue that the radio waves emitted by the pulsar split into the eigenmodes of the electron-positron plasma as they enter the companion's magnetosphere and are then strongly damped due to cyclotron resonance with the ambient plasma particles. Our model explains in a natural way the anomalous duration and behavior of radio eclipses observed in such systems. In particular, it provides stable, continuous, and frequency-dependent eclipses, in agreement with the observations. We predict a significant variation of linear polarization both at eclipse ingress and egress. In this paper we also suggest several possible mechanisms of generation of the optical and $X$-ray emission observed from these binary systems.Comment: 12 pages, 5 figures, submitted to Ap

Political connections with corrupt government bureaucrats and corporate M&A decisions: A natural experiment from the anti-corruption cases in China

Using 29 recent high level anti-corruption cases in China as a natural experiment, we examine the patterns in merger and acquisition (M&A) decisions and performance in Chinese non-state owned enterprises (non-SOEs) before and after the exogenous severing of political connections. We identify a set of listed related non-SOEs whose managers bribed or had connections, through past working and educational experience, with corrupt bureaucrats from 2005 to 2011. We document that, after the arrest of corrupt bureaucrats, corruption related non-SOEs lose their competitive advantages in the M&A market. We observe a significant reduction in the likelihood of conducting M&As and the ability to access local and state-owned targets for these firms. They pay a higher takeover premium and consequently have worse post-M&A performance. Our results are robust when we exclude bribing firms, and firms whose related corrupt bureaucrats are arrested within a year before the announcement of the M&A. Furthermore, the influence of anti-corruption events varies across regions that have different levels of corruption index and industries with different levels of government support and competition. Overall, our study provides direct evidence to the question of why firms seek to establish connections with government officials through bribery or personal connections, and we reveal the benefits and costs of such connections

Family control and corporate cash holdings: Evidence from China

This study examines the effect of family control on the cash holding policy in China. We find that family firms with excess control rights tend to have high cash holdings that are tunneled rather than being invested or paid to shareholders. We further show that the incentive for controlling families to hold cash and for tunneling is exacerbated by the agency conflict between controlling and minority shareholders, i.e., it is weakened after the Chinese Non-tradable share (NTS) reform and strengthened by the presence of multiple large shareholders who probably play no monitoring role in Chinese family firms. Furthermore, family firms' incentive to hold cash for tunneling is influenced by the unique characteristics of Chinese firms in the following ways: the incentive is stronger when the family founder has one child and face family succession problem, and when the founder has political connections and directly involves in firm's management; while it is weakened by family founder's social interpersonal trust with other entrepreneurs through their membership of Chambers of Commerce. Overall, we argue that family firms in China tend to hold high levels of cash for tunneling, which harms firm value, while the severe controlling-minority shareholder agency conflicts and unique Chinese family characteristics only make this situation worse