LPM Interference and Cherenkov-like Gluon Bremsstrahlung in Dense Matter

Gluon bremsstrahlung induced by multiple parton scattering in a finite dense medium has a unique angular distribution with respect to the initial parton direction. A dead-cone structure with an opening angle $\theta^2_0 \approx 2(1-z)/(zLE)$ for gluons with fractional energy $z$ arises from the Landau-Pomeranchuck-Migdal (LPM) interference. In a medium where the gluon's dielectric constant is $\epsilon >1$, the LPM interference pattern is shown to become Cherenkov-like with an increased opening angle determined by the dielectric constant $\cos^2\theta_c=z+(1-z)/\epsilon$. For a large dielectric constant $\epsilon \gg 1+2/z^2LE$, the corresponding total radiative parton energy loss is about twice that from normal gluon bremsstrahlung. Implications of this Cherenkov-like gluon bremsstrahlung to the jet correlation pattern in high-energy heavy-ion collisions is discussed.Comment: 4 pages in RevTEx with 1 postscript figur

Comparison of gold- and graphene-based resonant nano-structures for terahertz metamaterials and an ultra-thin graphene-based modulator

Graphene exhibits unique material properties and in electromagnetic wave technology, it raises the prospect of devices miniaturized down to the atomic length scale. Here we study split-ring resonator metamaterials made from graphene and we compare them to gold-based metamaterials. We find that graphene's huge reactive response derived from its large kinetic inductance allows for deeply subwavelength resonances, although its resonance strength is reduced due to higher dissipative loss damping and smaller dipole coupling. Nevertheless, tightly stacked graphene rings may provide for negative permeability and the electric dipole resonance of graphene meta-atoms turns out to be surprisingly strong. Based on these findings, we present a terahertz modulator based on a metamaterial with a multi-layer stack of alternating patterned graphene sheets separated by dielectric spacers. Neighbouring graphene flakes are biased against each other, resulting in modulation depths of over 75% at a transmission level of around 90%.Comment: 16 pages, 5 figure

Periodicities in the occurrence of aurora as indicators of solar variability

A compilation of records of the aurora observed in China from the Time of the Legends (2000 - 3000 B.C.) to the mid-18th century has been used to infer the frequencies and strengths of solar activity prior to modern times. A merging of this analysis with auroral and solar activity patterns during the last 200 years provides basically continuous information about solar activity during the last 2000 years. The results show periodicities in solar activity that contain average components with a long period (approx. 412 years), three middle periods (approx. 38 years, approx. 77 years, and approx. 130 years), and the well known short period (approx. 11 years)

Cherenkov Radiation from Jets in Heavy-ion Collisions

The possibility of Cherenkov-like gluon bremsstrahlung in dense matter is studied. We point out that the occurrence of Cherenkov radiation in dense matter is sensitive to the presence of partonic bound states. This is illustrated by a calculation of the dispersion relation of a massless particle in a simple model in which it couples to two different massive resonance states. We further argue that detailed spectroscopy of jet correlations can directly probe the index of refraction of this matter, which in turn will provide information about the mass scale of these partonic bound states.Comment: 4 pages, 5 figures, revte

Energy average formula of photon gas rederived by using the generalized Hermann-Feynman theorem

By virtue of the generalized Hermann-Feynmam theorem and the method of characteristics we rederive energy average formula of photon gas, this is another useful application of the theorem.Comment: 2 page

Evidance for an Oxygen Diffusion Model for the Electric Pulse Induced Resistance Change Effect in Oxides

Electric pulse induced resistance (EPIR) switching hysteresis loops for Pr0.7Ca0.7MnO3 (PCMO) perovskite oxide films were found to exhibit an additional sharp "shuttle peak" around the negative pulse maximum for films deposited in an oxygen deficient ambient. The device resistance hysteresis loop consists of stable high resistance and low resistance states, and transition regions between them. The resistance relaxation of the "shuttle peak" and its temperature behavior as well as the resistance relaxation in the transition regions were studied, and indicate that the resistance switching relates to oxygen diffusion with activation energy about 0.4eV. An oxygen diffusion model with the oxygen ions (vacancies) as the active agent is proposed for the non-volatile resistance switching effect in PCMO.Comment: 7 pages, 5 figure

Chromo-polarizability and pipi final state interaction

The chromo-polarizability of a quarkonium state is a measure of the amplitude of the $E1$-$E1$ chromo-electric interaction of the quarkonium with soft gluon fields and can be measured in the heavy quarkonium decays. Based on the chiral unitary approach, formulas with modification caused by the $S$ wave $\pi\pi$ final state interaction (FSI) for measuring the chromo-polarizabilities are given. It is shown that the effect of the $S$ wave $\pi\pi$ FSI is very important in extracting chromo-polarizabilities from the experimental data. The resultant values with the FSI are reduced to about 1/3 of those determined without the FSI. The consequences of the FSI correction in the $J/\psi$-nucleon scattering near the threshold are also discussed. The estimated lower bound of the total cross section is reduced from about 17 mb to 2.9 mb, which agrees with the experimental data point and is compatible with the previously estimated values in the literature. In order to understand the interaction of heavy quarkonia with light hadrons at low energies better and to obtain the chromo-polarizabilities of quarkonia accurately, more data should be accumulated. This can be done in the $J/\psi \to \pi^+\pi^-l^+l^-$ decay at BES-III and CLEO-c and in the $\Upsilon \to \pi^+\pi^-l^+l^-$ decay at B factories.Comment: 5 pages, 3 figures, ReVTeX4. Version accepted for publication in Phys. Rev.