105 research outputs found
Structural fluctuations and quantum transport through DNA molecular wires: a combined molecular dynamics and model Hamiltonian approach
Charge transport through a short DNA oligomer (Dickerson dodecamer) in
presence of structural fluctuations is investigated using a hybrid
computational methodology based on a combination of quantum mechanical
electronic structure calculations and classical molecular dynamics simulations
with a model Hamiltonian approach. Based on a fragment orbital description, the
DNA electronic structure can be coarse-grained in a very efficient way. The
influence of dynamical fluctuations arising either from the solvent
fluctuations or from base-pair vibrational modes can be taken into account in a
straightforward way through time series of the effective DNA electronic
parameters, evaluated at snapshots along the MD trajectory. We show that charge
transport can be promoted through the coupling to solvent fluctuations, which
gate the onsite energies along the DNA wire
Charge transport through bio-molecular wires in a solvent: Bridging molecular dynamics and model Hamiltonian approaches
We present a hybrid method based on a combination of quantum/classical
molecular dynamics (MD) simulations and a mod el Hamiltonian approach to
describe charge transport through bio-molecular wires with variable lengths in
presence o f a solvent. The core of our approach consists in a mapping of the
bio-molecular electronic structure, as obtained f rom density-functional based
tight-binding calculations of molecular structures along MD trajectories, onto
a low di mensional model Hamiltonian including the coupling to a dissipative
bosonic environment. The latter encodes fluctuat ion effects arising from the
solvent and from the molecular conformational dynamics. We apply this approach
to the c ase of pG-pC and pA-pT DNA oligomers as paradigmatic cases and show
that the DNA conformational fluctuations are essential in determining and
supporting charge transport
The Effects of a New Vector Boson on the Top Quark Cross Section at the Tevatron
It has recently been shown that a new neutral vector boson , with a mass
of order 1~TeV and weak couplings to quarks only, could explain both the
anomalous values of and and the apparent excess of large jet
events measured by the CDF collaboration. We calculate the effects of
exchange on the production cross section at Tevatron
collider energies, including next-to-leading-order QCD corrections. We find a
significant enhancement of the cross section and study the resulting
invariant mass distribution, which could provide a decisive test of the
model.Comment: 7 pages, LATEX, 4 figures include
Power corrections and renormalons in Drell-Yan production
The resummed Drell-Yan cross section in the double-logarithmic approximation
suffers from infrared renormalons. Their presence was interpreted as an
indication for non-perturbative corrections of order \lqcd/(Q(1-z)). We find
that, once soft gluon emission is accurately taken into account, the leading
renormalon divergence in the resummed cross section is cancelled by
higher-order perturbative contributions in the exponent of the resummed cross
section. From this evidence, `higher twist' corrections to the hard cross
section in Drell-Yan production should therefore intervene only at order
\lqcd^2/((Q^2 (1-z)^2) in the entire perturbative domain Q (1-z) > \lqcd.
We compare this result with hadronic event shape variables, comment on the
potential universality of non-perturbative corrections to resummed cross
sections, and on possible implications for phenomenology.Comment: 37 pages, LATEX, 3 figures as uudecoded fil
QCD corrections to the longitudinally polarized Drell-Yan process
In this paper we calculate the O() corrections to the - and
-distributions of lepton pairs produced in collisions of longitudinally
polarized hadrons. The numerical importance of these corrections is studied and
consequences for the extraction of the polarized sea quark distributions from a
measurement of the longitudinally polarized Drell-Yan cross section are
discussed.Comment: 21 pages, LaTeX, 8 figures include
Calculating Dilepton Rates from Monte Carlo Simulations of Parton Production
To calculate dilepton rates in a Monte Carlo simulation of ultrarelativistic
heavy ion collisions, one usually scales the number of similar QCD processes by
a ratio of the corresponding differential probabilities. We derive the formula
for such a ratio especially for dilepton bremsstrahlung processes. We also
discuss the non-triviality of including higher order corrections to direct
Drell-Yan process. The resultant mass spectra from our Monte Carlo simulation
are consistent with the semi-analytical calculation using dilepton
fragmentation functions.Comment: 14 pages in RevTex, 3 figures in uuencoded files, LBL-3466
Correction Factors for Reactions involving Quark-Antiquark Annihilation or Production
In reactions with production or annihilation, initial-
and final-state interactions give rise to large corrections to the lowest-order
cross sections. We evaluate the correction factor first for low relative
kinetic energies by studying the distortion of the relative wave function. We
then follow the procedure of Schwinger to interpolate this result with the
well-known perturbative QCD vertex correction factors at high energies, to
obtain an explicit semi-empirical correction factor applicable to the whole
range of energies. The correction factor predicts an enhancement for
in color-singlet states and a suppression for color-octet states, the effect
increasing as the relative velocity decreases. Consequences on dilepton
production in the quark-gluon plasma, the Drell-Yan process, and heavy quark
production processes are discussed.Comment: 25 pages (REVTeX), includes 2 uuencoded compressed postscript figure
QCD and Yukawa corrections to single-top-quark production via q qbar -> t bbar
We calculate the O(alpha_s) and O(alpha_W m_t^2/M_W^2) corrections to the
production of a single top quark via the weak process q qbar -> t bbar at the
Fermilab Tevatron and the CERN Large Hadron Collider. An accurate calculation
of the cross section is necessary in order to extract |V_tb| from experiment.Comment: LaTeX, 13 pages, replaced with version to appear in Phys. Rev.
Predictions for Higgs production at the Tevatron and the associated uncertainties
We update the theoretical predictions for the production cross sections of
the Standard Model Higgs boson at the Fermilab Tevatron collider, focusing on
the two main search channels, the gluon-gluon fusion mechanism and
the Higgs-strahlung processes with , including all
relevant higher order QCD and electroweak corrections in perturbation theory.
We then estimate the various uncertainties affecting these predictions: the
scale uncertainties which are viewed as a measure of the unknown higher order
effects, the uncertainties from the parton distribution functions and the
related errors on the strong coupling constant, as well as the uncertainties
due to the use of an effective theory approach in the determination of the
radiative corrections in the process at next-to-next-to-leading
order. We find that while the cross sections are well under control in the
Higgs--strahlung processes, the theoretical uncertainties are rather large in
the case of the gluon-gluon fusion channel, possibly shifting the central
values of the next-to-next-to-leading order cross sections by more than
. These uncertainties are thus significantly larger than the
error assumed by the CDF and D0 experiments in their recent
analysis that has excluded the Higgs mass range 162-166 GeV at the 95%
confidence level. These exclusion limits should be, therefore, reconsidered in
the light of these large theoretical uncertainties.Comment: 40 pages, 12 figures. A few typos are corrected and some updated
numbers are provide
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