65,893 research outputs found
Interband impact ionization and nonlinear absorption of terahertz radiations in semiconductor heterostructures
We have theoretically investigated nonlinear free-carrier absorption of
terahertz radiation in InAs/AlSb heterojunctions. By considering multiple
photon process and conduction-valence interband impact ionization (II), we have
determined the field and frequency dependent absorption rate. It is shown that
(i) electron-disorder scatterings are important at low to intermediate field,
and (ii) most importantly, the high field absorption is dominated by II
processes. Our theory can satisfactorily explain a long standing experimental
result on the nonlinear absorption in THz regime.Comment: 4 pages including 3 EPS fig
Phase Transition in Evolutionary Games
The evolution of cooperative behaviour is studied in the deterministic
version of the Prisoners' Dilemma on a two-dimensional lattice. The payoff
parameter is set at the critical region , where clusters of
cooperators are formed in all spatial sizes. Using the factorial moments
developed in particle and nuclear physics for the study of phase transition,
the distribution of cooperators is studied as a function of the bin size
covering varying numbers of lattice cells. From the scaling behaviour of the
moments a scaling exponent is determined and is found to lie in the range where
phase transitions are known to take place in physical systems. It is therefore
inferred that when the payoff parameter is increased through the critical
region the biological system of cooperators undergoes a phase transition to
defectors. The universality of the critical behaviour is thus extended to
include also this particular model of evolution dynamics.Comment: 12 pages + 3 figures, latex, submitted to Natur
Combined Effect of QCD Resummation and QED Radiative Correction to W boson Observables at the Tevatron
A precise determination of the W boson mass at the Fermilab Tevatron requires
a theoretical calculation in which the effects of the initial-state multiple
soft-gluon emission and the final-state photonic correction are simultaneously
included . Here, we present such a calculation and discuss its prediction on
the transverse mass distribution of the W boson and the transverse momentum
distribution of its decay charged lepton, which are the most relevant
observables for measuring the W boson mass at hadron colliders.Comment: 10 pages, 3 Postscript figures, uses revtex4.st
Erraticity of Rapidity Gaps
The use of rapidity gaps is proposed as a measure of the spatial pattern of
an event. When the event multiplicity is low, the gaps between neighboring
particles carry far more information about an event than multiplicity spikes,
which may occur very rarely. Two moments of the gap distrubiton are suggested
for characterizing an event. The fluctuations of those moments from event to
event are then quantified by an entropy-like measure, which serves to describe
erraticity. We use ECOMB to simulate the exclusive rapidity distribution of
each event, from which the erraticity measures are calculated. The dependences
of those measures on the order of of the moments provide single-parameter
characterizations of erraticity.Comment: 10 pages LaTeX + 5 figures p
Critical Behavior of Hadronic Fluctuations and the Effect of Final-State Randomization
The critical behaviors of quark-hadron phase transition are explored by use
of the Ising model adapted for hadron production. Various measures involving
the fluctuations of the produced hadrons in bins of various sizes are examined
with the aim of quantifying the clustering properties that are universal
features of all critical phenomena. Some of the measures involve wavelet
analysis. Two of the measures are found to exhibit the canonical power-law
behavior near the critical temperature. The effect of final-state randomization
is studied by requiring the produced particles to take random walks in the
transverse plane. It is demonstrated that for the measures considered the
dependence on the randomization process is weak. Since temperature is not a
directly measurable variable, the average hadronic density of a portion of each
event is used as the control variable that is measurable. The event-to-event
fluctuations are taken into account in the study of the dependence of the
chosen measures on that control variable. Phenomenologically verifiable
critical behaviors are found and are proposed for use as a signature of
quark-hadron phase transition in relativistic heavy-ion collisions.Comment: 17 pages (Latex) + 24 figures (ps file), submitted to Phys. Rev.
Next-to-Leading Order Corrections to Single Top Quark Production and Decay at the Tevatron: 1. s-channel Process
We present a study of s-channel single top quark production at the upgraded
Tevatron collider, including the next-to-leading order (NLO) QCD
corrections to the production and the decay of the top quark. The "modified"
narrow width approximation was adopted to preserve the spin of the top quark in
its production and decay. We discuss the effect of the different
contributions on the inclusive cross section as well as various kinematic
distributions after imposing the relevant cuts to select s-channel single top
signal events. In particular the decay contribution, while small
in size, has a significant impact on several distributions. With the help of
the best-jet algorithm to reconstruct the top quark we demonstrate that it is
possible to study kinematical and spin correlations in s-channel single top
events. We furthermore compare top quark spin measurements in two different
basis and show how NLO corrections have to be taken into consideration in
searches for the Higgs boson through associated production at the
Tevatron.Comment: 39 pages, 37 figure
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