Constituent quark model for nuclear stopping in high energy nuclear collisions

We study the nuclear stopping in high energy nuclear collisions using the constituent quark model. It is assumed that wounded nucleons with different number of interacted quarks hadronize in different ways. The probabilities of having such wounded nucleons are evaluated for proton-proton, proton-nucleus and nucleus-nucleus collisions. After examining our model in proton-proton and proton-nucleus collisions and fixing the hadronization functions, it is extended to nucleus-nucleus collisions. It is used to calculate the rapidity distribution and the rapidity shift of final state protons in nucleus-nucleus collisions. The computed results are in good agreement with the experimental data on ^{32}\mbox{S} +\ ^{32}\mbox{S} at $E_{lab} = 200$ AGeV and ^{208}\mbox{Pb} +\ ^{208}\mbox{Pb} at $E_{lab} = 160$ AGeV. Theoretical predictions are also given for proton rapidity distribution in ^{197}\mbox{Au} +\ ^{197}\mbox{Au} at $\sqrt{s} = 200$ AGeV (BNL-RHIC). We predict that the nearly baryon free region will appear in the midrapidity region and the rapidity shift is $\langle \Delta y \rangle = 2.22$.Comment: 40 pages, 16 Postscript figures, submitted to Phys. Rev.

Affine maps of density matrices

For quantum systems described by finite matrices, linear and affine maps of matrices are shown to provide equivalent descriptions of evolution of density matrices for a subsystem caused by unitary Hamiltonian evolution in a larger system; an affine map can be replaced by a linear map, and a linear map can be replaced by an affine map. There may be significant advantage in using an affine map. The linear map is generally not completely positive, but the linear part of an equivalent affine map can be chosen to be completely positive and related in the simplest possible way to the unitary Hamiltonian evolution in the larger system.Comment: 4 pages, title changed, sentence added, reference update

Charmonium levels near threshold and the narrow state X(3872) \to \pi^{+}\pi^{-}\jpsi

We explore the influence of open-charm channels on charmonium properties, and profile the 1:3D2, 1:3D3 and 2:1P1 charmonium candidates for X(3872). The favored candidates, the 1:3D2 and 1:3D3 levels, both have prominent radiative decays. The 1:3D2 might be visible in the $D^{0}\bar{D}^{*0}$ channel, while the dominant decay of the 1:3D3 state should be into $D\bar{D}$. We propose that additional discrete charmonium levels can be discovered as narrow resonances of charmed and anticharmed mesons.Comment: 8 pages, 6 figures, uses RevTeX and boxedeps; few transcription errors corrected in Tables IV and VI, three entries added in Table V, updated references. Version to appear in Phys. Rev.

Dynamic model for failures in biological systems

A dynamic model for failures in biological organisms is proposed and studied both analytically and numerically. Each cell in the organism becomes dead under sufficiently strong stress, and is then allowed to be healed with some probability. It is found that unlike the case of no healing, the organism in general does not completely break down even in the presence of noise. Revealed is the characteristic time evolution that the system tends to resist the stress longer than the system without healing, followed by sudden breakdown with some fraction of cells surviving. When the noise is weak, the critical stress beyond which the system breaks down increases rapidly as the healing parameter is raised from zero, indicative of the importance of healing in biological systems.Comment: To appear in Europhys. Let

Dynamics of Vortex Core Switching in Ferromagnetic Nanodisks

Dynamics of magnetic vortex core switching in nanometer-scale permalloy disk, having a single vortex ground state, was investigated by micromagnetic modeling. When an in-plane magnetic field pulse with an appropriate strength and duration is applied to the vortex structure, additional two vortices, i.e., a circular- and an anti-vortex, are created near the original vortex core. Sequentially, the vortex-antivortex pair annihilates. A spin wave is created at the annihilation point and propagated through the entire element; the relaxed state for the system is the single vortex state with a switched vortex core.Comment: to appear in Appl. Phys. Let

Electronic and phonon excitations in {\alpha}-RuCl3_3

We report on THz, infrared reflectivity and transmission experiments for wave numbers from 10 to 8000 cm$^{-1}$ ($\sim$ 1 meV - 1 eV) and for temperatures from 5 to 295 K on the Kitaev candidate material {\alpha}-RuCl$_3$. As reported earlier, the compound under investigation passes through a first-order structural phase transition, from a monoclinic high-temperature to a rhombohedral low-temperature phase. The phase transition shows an extreme and unusual hysteretic behavior, which extends from 60 to 166 K. In passing this phase transition, in the complete frequency range investigated we found a significant reflectance change, which amounts almost a factor of two. We provide a broadband spectrum of dielectric constant, dielectric loss and optical conductivity from the THz to the mid infrared regime and study in detail the phonon response and the low-lying electronic density of states. We provide evidence for the onset of an optical energy gap, which is of order 200 meV, in good agreement with the gap derived from measurements of the DC electrical resistivity. Remarkably, the onset of the gap exhibits a strong blue shift on increasing temperatures.Comment: 18 pages, 7 figure

CP Violation in the Top-Quark Pair Production at a Next Linear Collider

We provide a detailed, model-independent, study for CP violation effects due to the T-odd top-quark electric dipole moment (EDM) and weak dipole moment (WDM) in the top-quark pair production via $e^+e^-$ and two-photon annihilation at a next $e^+e^-$ linear collider (NLC). There are two methods in detecting CP violation effects in these processes. One method makes use of measurements of various spin correlations in the final decay products of the produced top-quark pair, while the other is to measure various CP-odd polarization asymmetry effects of the initial states. In the $e^+e^-$ case only the first method can be used, and in the $\gamma\gamma$ case both methods can be employed. We provide a complete classification of angular correlations of the $t$ and $\bar{t}$ decay products under CP and CP\tilde{T} which greatly faciliate CP tests in the $e^+e^-$ mode. Concentrating on the second method with the Compton back-scattered high-energetic laser light off the electron or positron beam in the two-photon mode, we construct two CP-odd and CP\tilde{T}-even initial polarization configurations and apply them to investigating CP-violating effects due to the top-quark EDM. With a typical set of experimental parameters at the NLC, we compare the 1-\sigma sensitivities to the top-quark EDM and WDM in the $e^+e^-$ mode and the two-photon mode. Some model expectation values of the T-odd parameters are compared with the results.Comment: 45 pages(LaTeX), 10 eps figures, uses epsfig.st

Intersecting Brane World from Type I Compactification

We elaborate that general intersecting brane models on orbifolds are obtained from type I string compactifications and their T-duals. Symmetry breaking and restoration occur via recombination and parallel separation of branes, preserving supersymmetry. The Ramond-Ramond tadpole cancelation and the toron quantization constrain the spectrum as a branching of the adjoints of SO(32), up to orbifold projections. Since the recombination changes the gauge coupling, the single gauge coupling of type I could give rise to different coupling below the unification scale. This is due to the nonlocal properties of the Dirac-Born-Infeld action. The weak mixing angle sin^2 theta_W = 3/8 is naturally explained by embedding the quantum numbers to those of SO(10).Comment: 31 pages, 5 figure