3,064 research outputs found
Correlated fluctuations in the exciton dynamics and spectroscopy of DNA
The absorption of ultraviolet light creates excitations in DNA, which
subsequently start moving in the helix. Their fate is important for an
understanding of photo damage, and is determined by the interplay of electronic
couplings between bases and the structure of the DNA environment. We model the
effect of dynamical fluctuations in the environment and study correlation,
which is present when multiple base pairs interact with the same mode in the
environment. We find that the correlations strongly affect the exciton
dynamics, and show how they are observed in the decay of the anisotropy as a
function of a coherence and a population time in a non-linear optical
experiment
Nonlinear resonance reflection from and transmission through a dense glassy system built up of oriented linear Frenkel chains: two-level models
A theoretical study of the resonance optical response of assemblies of
oriented short (as compared to an optical wavelength) linear Frenkel chains is
carried out using a two-level model. We show that both transmittivity and
reflectivity of the film may behave in a bistable fashion and analyze how the
effects found depend on the film thickness and on the inhomogeneous width of
the exciton optical transition.Comment: 26 pages, 9 figure
Hard production of a Z boson plus heavy flavor jets at LHC and the intrinsic charm content of a proton
The cross section of associated production of a Z boson with heavy flavor
jets in collisions is calculated using the SHERPA Monte Carlo generator
and the analytical combined QCD approach based on kt-factorization at small x
and conventional collinear QCD at large x. A satisfactory description of the
ATLAS and CMS data on the spectra of Z bosons and c-jets in the whole
rapidity, y, region is shown. Searching for the intrinsic charm (IC)
contribution in these processes, which could be visible at large y > 1.5, we
study observables very sensitive to non-zero IC contributions and less affected
by theoretical QCD scale uncertainties. One of such observables is the
so-called double ratio: the ratio of the differential cross section of Z + c
production in the central region of |y| < 1.5 and in the forward region 1.5 <
|y| < 2.5, divided by the same ratio for Z + b production. These observables
could be more promising for the search of IC at LHC as compared to the
observables considered earlier.Comment: 18 pages, 7 figure
Statistics of low-energy levels of a one-dimensional weakly localized Frenkel exciton: A numerical study
Numerical study of the one-dimensional Frenkel Hamiltonian with on-site
randomness is carried out. We focus on the statistics of the energy levels near
the lower exciton band edge, i. e. those determining optical response. We found
that the distribution of the energy spacing between the states that are well
localized at the same segment is characterized by non-zero mean, i.e. these
states undergo repulsion. This repulsion results in a local discrete energy
structure of a localized Frenkel exciton. On the contrary, the energy spacing
distribution for weakly overlapping local ground states (the states with no
nodes within their localization segments) that are localized at different
segments has zero mean and shows almost no repulsion. The typical width of the
latter distribution is of the same order as the typical spacing in the local
discrete energy structure, so that this local structure is hidden; it does not
reveal itself neither in the density of states nor in the linear absorption
spectra. However, this structure affects the two-exciton transitions involving
the states of the same segment and can be observed by the pump-probe
spectroscopy. We analyze also the disorder degree scaling of the first and
second momenta of the distributions.Comment: 10 pages, 6 figure
Constraints on the intrinsic charm content of the proton from recent ATLAS data
Constraints on the intrinsic charm probability \wccm = P_{{\mathrm{c}\bar
\mathrm{c}} / \mathrm{p}} in the proton are obtained for the first time from
LHC measurements. The ATLAS Collaboration data for the production of prompt
photons, accompanied by a charm-quark jet in pp collisions at
TeV, are used. The upper limit \mbox{\wccm < 1.93~\%} is obtained at the
68~\% confidence level. This constraint is primarily determined from the
theoretical scale and systematical experimental uncertainties. Suggestions for
reducing these uncertainties are discussed. The implications of intrinsic heavy
quarks in the proton for future studies at the LHC are also discussed.Comment: 6 pages, 4 figure
Localization properties of a one-dimensional tight-binding model with non-random long-range inter-site interactions
We perform both analytical and numerical studies of the one-dimensional
tight-binding Hamiltonian with stochastic uncorrelated on-site energies and
non-fluctuating long-range hopping integrals . It was argued recently [A.
Rodriguez at al., J. Phys. A: Math. Gen. 33, L161 (2000)] that this model
reveals a localization-delocalization transition with respect to the disorder
magnitude provided . The transition occurs at one of the band edges (the upper
one for and the lower one for). The states at the other band edge are always
localized, which hints on the existence of a single mobility edge. We analyze
the mobility edge and show that, although the number of delocalized states
tends to infinity, they form a set of null measure in the thermodynamic limit,
i.e. the mobility edge tends to the band edge. The critical magnitude of
disorder for the band edge states is computed versus the interaction exponent
by making use of the conjecture on the universality of the normalized
participation number distribution at transition.Comment: 7 pages, 6 postscript figures, uses revtex
Linear optical properties of one-dimensional Frenkel exciton systems with intersite energy correlations
We analyze the effects of intersite energy correlations on the linear optical
properties of one-dimensional disordered Frenkel exciton systems. The
absorption line width and the factor of radiative rate enhancement are studied
as a function of the correlation length of the disorder. The absorption line
width monotonously approaches the seeding degree of disorder on increasing the
correlation length. On the contrary, the factor of radiative rate enhancement
shows a non-monotonous trend, indicating a complicated scenario of the exciton
localization in correlated systems. The concept of coherently bound molecules
is exploited to explain the numerical results, showing good agreement with
theory. Some recent experiments are discussed in the light of the present
theory.Comment: 18 pages, 3 figues, REVTeX, to appear in Physical Review
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