1,584 research outputs found
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 for gluons with fractional energy arises from the
Landau-Pomeranchuck-Migdal (LPM) interference. In a medium where the gluon's
dielectric constant is , the LPM interference pattern is shown to
become Cherenkov-like with an increased opening angle determined by the
dielectric constant . For a large dielectric
constant , 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 - 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 wave
final state interaction (FSI) for measuring the chromo-polarizabilities are
given. It is shown that the effect of the wave 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 -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 decay at
BES-III and CLEO-c and in the decay at B
factories.Comment: 5 pages, 3 figures, ReVTeX4. Version accepted for publication in
Phys. Rev.
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