Exclusive J/\psi Productions at e^+ e^- Colliders

Exclusive quarkonium pair production in electron-positron collisions is studied in non-relativistic QCD. The obtained cross section for J/\psi + \eta_c production in the leading order is confronted against the recent measurements by the Belle Collaboration at KEKB. It is shown that a large renormalization K-factor is necessary to explain the experimental data. We point out that the J^{PC}=0^{-+} nature of the hadronic systems that are assigned to be \eta_c should be tested by the triple angular distributions in terms of the scattering angle, and, polar and azimuthal angles of J/\psi into leptons. We further study J/\psi + J/\psi and \Upsilon + \Upsilon productions at LEP energies. Although the axial-vector couplings of the Z-boson to charm and bottom quarks allow production of such pairs when one of them is polarised transversally and the other longitudinally, we find that the integrated luminosity at Z pole accumulated by LEP is not large enough to observe the exclusive pair production of quarkonium.Comment: 11 pages, 2 eps figures, LaTe

A Model for Spectral States and Their Transition in Cyg X-1

A new accretion picture based on a small disk surrounding a black hole is developed for the wind-fed source Cyg X-1. The hard and soft spectral states of Cyg X-1 are interpreted in terms of co-spatial two component flows for the innermost region of an accretion disk. The state transitions result from the outward expansion and inward recession of this inner disk for the hard to soft and soft to hard transition respectively. The theoretical framework for state transitions in black hole X-ray binaries with high mass companions involving a change in the inner disk size, thus, differs from systems with low mass companions involving the change in the outer disk size. This fundamental difference stems from the fact that matter captured and supplied to the black hole in wind-fed systems has low specific angular momentum and is hot essentially heated in the bow and spiral shocks, whereas it has high specific angular momentum and is cool in Roche lobe overflow systems. The existence of a weak cool disk around the ISCO region in the hard state allows for the presence of a relativistically broadened Fe K line. The small disk fed by gas condensation forms without an extensive outer disk, precluding thermal instabilities and large outbursts, resulting in the lack of large amplitude outbursts and hysteresis effects in the light curve of high mass black hole X-ray binaries. Their relatively persistent X-ray emission is attributed to their wind-fed nature.Comment: 13 pages, 2 figures. Accepted for publication in Ap

The value premium puzzle, behavior versus risk: new evidence from China

This paper investigates the value premium puzzle in the Chinese stock market. After establishing that the value premium does exist in the Chinese stock market, it uses an innovative technique based on stochastic dominance theory to test the behavior based versus risk based explanations for the puzzle. We find no evidence of a systematic behavioral factor, such as over/under-reaction, that is driving this premium. This finding is robust with respect to negative and positive return regimes. We do, however, find strong evidence that the value premium reflects compensation for bearing more risk associated with financial inflexibility

Unbalanced edge modes and topological phase transition in gated trilayer graphene

Gapless edge modes hosted by chirally-stacked trilayer graphene display unique features when a bulk gap is opened by applying an interlayer potential difference. We show that trilayer graphene with half-integer valley Hall conductivity leads to unbalanced edge modes at opposite zigzag boundaries, resulting in a natural valley current polarizer. This unusual characteristic is preserved in the presence of Rashba spin-orbit coupling that turns a gated trilayer graphene into a ${Z}_2$ topological insulator with an odd number of helical edge mode pairs.Comment: 5 pages, 4 figure

Valley-Hall Kink and Edge States in Multilayer Graphene

We report on a theoretical study of one-dimensional (1D) states localized at few-layer graphene system ribbon edges, and at interfaces between few-layer graphene systems with different valley Hall conductivities. These 1D states are topologically protected when valley mixing is neglected. We address the influence on their properties of stacking arrangement, interface structure, and external electric field perpendicular to the layers. We find that 1D states are generally absent at multilayer ribbon armchair direction edges, but present irrespective of crystallographic orientation at any internal valley-Hall interface of an ABC stacked multilayer.Comment: 5 pages, 3 figure

Theories of risk: testing investor behaviour on the Taiwan stock and stock index futures markets

This paper considers four utility functions - concave, convex, S-shaped, and reverse S-shaped - to analyze the behavior of different types of investors on the Taiwan stock index and its corresponding index futures. Using stochastic dominance (SD) rules, we show that the existence of all four investor types is plausible. Risk averters prefer spot to futures, whereas risk seekers prefer futures to spot. Investors with S-shaped utility functions prefer spot (futures) to futures (spot) when markets move upward (downward). Investors with reverse S-shaped utility functions prefer futures (spot) to spot (futures) when markets move upward (downward). We show that both spot and futures markets can exist when only risk averters are present, but futures can dominate spot only if there is some risk seeking behavior. These results are robust with respect to sub-periods, spot returns including dividends and diversification