120 research outputs found
Chaotic Electron Motion in Superlattices. Quantum-Classical Correspondence of the Structure of Eigenstates and LDOS
We investigate the classical-quantum correspondence for particle motion in a
superlattice in the form of a 2D channel with periodic modulated boundaries.
Its classical dynamics undergoes the generic transition to chaos of Hamiltonian
systems as the amplitude of the modulation is increased. We show that for
strong chaotic motion, the classical counterpart of the structure of
eigenstates (SES) in energy space reveals an excellent agreement with the
quantum one. This correspondence allows us to understand important features of
the SES in terms of classical trajectories. We also show that for typical 2D
modulated waveguides there exist, at any energy range, extremely localized
eigenstates (in energy) which are practically unperturbed by the modulation.
These states contribute to the strong fluctuations around the classical SES.
The approach to the classical limit is discussed.Comment: 4 pages, 4 figure
Ballistic Localization in Quasi-1D Waveguides with Rough Surfaces
Structure of eigenstates in a periodic quasi-1D waveguide with a rough
surface is studied both analytically and numerically. We have found a large
number of "regular" eigenstates for any high energy. They result in a very slow
convergence to the classical limit in which the eigenstates are expected to be
completely ergodic. As a consequence, localization properties of eigenstates
originated from unperturbed transverse channels with low indexes, are strongly
localized (delocalized) in the momentum (coordinate) representation. These
eigenstates were found to have a quite unexpeted form that manifests a kind of
"repulsion" from the rough surface. Our results indicate that standard
statistical approaches for ballistic localization in such waveguides seem to be
unappropriate.Comment: 5 pages, 4 figure
Quantum-classical correspondence for local density of states and eigenfunctions of a chaotic periodic billiard
Classical-quantum correspondence for conservative chaotic Hamiltonians is
investigated in terms of the structure of the eigenfunctions and the local
density of states, using as a model a 2D rippled billiard in the regime of
global chaos. The influence of the observed localized and sparsed states in the
quantum-classical correspondence is discussed.Comment: 8 pages, 4 figure
A Green's function approach to transmission of massless Dirac fermions in graphene through an array of random scatterers
We consider the transmission of massless Dirac fermions through an array of
short range scatterers which are modeled as randomly positioned -
function like potentials along the x-axis. We particularly discuss the
interplay between disorder-induced localization that is the hallmark of a
non-relativistic system and two important properties of such massless Dirac
fermions, namely, complete transmission at normal incidence and periodic
dependence of transmission coefficient on the strength of the barrier that
leads to a periodic resonant transmission. This leads to two different types of
conductance behavior as a function of the system size at the resonant and the
off-resonance strengths of the delta function potential. We explain this
behavior of the conductance in terms of the transmission through a pair of such
barriers using a Green's function based approach. The method helps to
understand such disordered transport in terms of well known optical phenomena
such as Fabry Perot resonances.Comment: 22 double spaced single column pages. 15 .eps figure
Search for Higgs bosons decaying to tautau pairs in ppbar collisions at sqrt(s) = 1.96 TeV
We present a search for the production of neutral Higgs bosons decaying into
tautau pairs in ppbar collisions at a center-of-mass energy of 1.96 TeV. The
data, corresponding to an integrated luminosity of 5.4 fb-1, were collected by
the D0 experiment at the Fermilab Tevatron Collider. We set upper limits at the
95% C.L. on the product of production cross section and branching ratio for a
scalar resonance decaying into tautau pairs, and we then interpret these limits
as limits on the production of Higgs bosons in the minimal supersymmetric
standard model (MSSM) and as constraints in the MSSM parameter space.Comment: 7 pages, 5 figures, submitted to PL
Search for scalar bottom quarks and third-generation leptoquarks in ppbar collisions at sqrt(s) = 1.96 TeV
We report the results of a search for pair production of scalar bottom quarks
(sbottom) and scalar third-generation leptoquarks in 5.2 fb-1 of ppbar
collisions at the D0 experiment of the Fermilab Tevatron Collider. Scalar
bottom quarks are assumed to decay to a neutralino and a quark, and we set
95% C.L. lower limits on their production in the (m_sbottom, m_neutralino) mass
plane such as m_sbottom>247 GeV for m_neutralino=0 and m_neutralino>110 GeV for
160<m_sbottom<200 GeV. The leptoquarks are assumed to decay to a tau neutrino
and a quark, and we set a 95% C.L. lower limit of 247 GeV on the mass of a
charge-1/3 third-generation scalar leptoquark.Comment: Published by Phys. Lett.
High mass exclusive diffractive dijet production in collisions at = 1.96 TeV
We present evidence for diffractive exclusive dijet production with an
invariant dijet mass greater than 100 GeV in data collected with the D0
experiment at the Fermilab Tevatron Collider. A discriminant based on
calorimeter information is used to measure a significant number of events with
little energy (typically less than 10 GeV) outside the dijet system, consistent
with the diffractive exclusive dijet production topology. The probability for
these events to be explained by other dijet production processes is , corresponding to a 4.1 standard deviation significance.Comment: submitted to Phys. Lett.
Measurement of the differential cross section for the production of an isolated photon with associated jet in ppbar collisions at sqrt(s)=1.96 TeV
The process ppbar -> photon + jet + X is studied using 1.0 fb^-1 of data
collected by the D0 detector at the Fermilab Tevatron ppbar collider at a
center-of-mass energy sqrt(s)=1.96 TeV. Photons are reconstructed in the
central rapidity region |y_gamma|<1.0 with transverse momenta in the range
30<Pt_gamma<400 GeV while jets are reconstructed in either the central
|y_jet|15 GeV.
The differential cross section d^3sigma/dPt_gamma dy_gamma dy_jet is measured
as a function of Pt_gamma in four regions, differing by the relative
orientations of the photon and the jet in rapidity. Ratios between the
differential cross sections in each region are also presented. Next-to-leading
order QCD predictions using different parameterizations of parton distribution
functions and theoretical scale choices are compared to the data. The
predictions do not simultaneously describe the measured normalization and
Pt_gamma dependence of the cross section in any of the four measured regions.Comment: 13 pages, 10 figure
Measurement of the ttbar production cross section and top quark mass extraction using dilepton events in ppbar collisions
We present a measurement of the top quark pair production cross section in
ppbar collisions at \sqrt{s}=1.96 TeV using approximately 1 fb^{-1} of data
collected with the D0 detector. We consider decay channels containing two high
pt charged leptons where one lepton is identified as an electron or a muon
while the other lepton can be an electron, a muon or a hadronically decaying
tau lepton. For a mass of the top quark of 170 GeV, the measured cross section
is 7.5 +1.0-1.0 (stat) +0.7-0.6 (syst) +0.6-0.5 (lumi) pb. Using lepton+tau
events only, we measure: \sigma_ttbar \times B(ttbar to ltau bbbar) = 0.13
+0.09-0.08 (stat) +0.06-0.06 (syst) +0.02-0.02 (lumi) pb. Comparing the
measured cross section as a function of the mass of the top quark with a
partial next-to-next-to leading order Quantum Chromodynamics theoretical
prediction, we extract a mass of the top quark of 171.5 +9.9-8.8 GeV, in
agreement with direct measurements.Comment: published in Phys. Lett. B, 10 pages, 7 figure
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