183,899 research outputs found
BFKL Pomeron loop contribution in diffractive photoproduction and inclusive hadroproduction of and
We analyze contributions to the heavy vector meson production with large
transverse momentum in proton--proton and diffractive photon--proton scattering
driven by an exchange of two Balitsky--Fadin--Kuraev--Lipatov Pomerons in the
squared amplitudes. The Pomerons couple to a single parton and form a Pomeron
loop closed by the vector meson impact factors. For the photon--proton case the
diffractive cut of the Pomeron loop contributes, and for the inclusive
hadroproduction one finds the loop with two cut Pomerons. We compute both of
these Pomeron loop contributions and study in detail their properties. The
results are then used to calculate the cross sections for diffractive
photoproduction with large transverse momentum at HERA and the correlated two
Pomeron contribution for inclusive and production cross
sections at the LHC. Within a unified approach a good description of the
photoproduction data is found, but correlated two Pomeron mechanism gives only
a small contribution to hadroproduction of the vector mesons at the LHC.Comment: 34 pages, 16 figure
Plane-wave based electronic structure calculations for correlated materials using dynamical mean-field theory and projected local orbitals
The description of realistic strongly correlated systems has recently
advanced through the combination of density functional theory in the local
density approximation (LDA) and dynamical mean field theory (DMFT). This
LDA+DMFT method is able to treat both strongly correlated insulators and
metals. Several interfaces between LDA and DMFT have been used, such as (N-th
order) Linear Muffin Tin Orbitals or Maximally localized Wannier Functions.
Such schemes are however either complex in use or additional simplifications
are often performed (i.e., the atomic sphere approximation). We present an
alternative implementation of LDA+DMFT, which keeps the precision of the
Wannier implementation, but which is lighter. It relies on the projection of
localized orbitals onto a restricted set of Kohn-Sham states to define the
correlated subspace. The method is implemented within the Projector Augmented
Wave (PAW) and within the Mixed Basis Pseudopotential (MBPP) frameworks. This
opens the way to electronic structure calculations within LDA+DMFT for more
complex structures with the precision of an all-electron method. We present an
application to two correlated systems, namely SrVO3 and beta-NiS (a
charge-transfer material), including ligand states in the basis-set. The
results are compared to calculations done with Maximally Localized Wannier
functions, and the physical features appearing in the orbitally resolved
spectral functions are discussed.Comment: 15 pages, 17 figure
A cluster-based mean-field and perturbative description of strongly correlated fermion systems. Application to the 1D and 2D Hubbard model
We introduce a mean-field and perturbative approach, based on clusters, to
describe the ground state of fermionic strongly-correlated systems. In cluster
mean-field, the ground state wavefunction is written as a simple tensor product
over optimized cluster states. The optimization of the single-particle basis
where the cluster mean-field is expressed is crucial in order to obtain
high-quality results. The mean-field nature of the ansatz allows us to
formulate a perturbative approach to account for inter-cluster correlations;
other traditional many-body strategies can be easily devised in terms of the
cluster states. We present benchmark calculations on the half-filled 1D and
(square) 2D Hubbard model, as well as the lightly-doped regime in 2D, using
cluster mean-field and second-order perturbation theory. Our results indicate
that, with sufficiently large clusters or to second-order in perturbation
theory, a cluster-based approach can provide an accurate description of the
Hubbard model in the considered regimes. Several avenues to improve upon the
results presented in this work are discussed.Comment: 22 pages, 21 figure
Dynamical correlations in electronic transport through a system of coupled quantum dots
Current auto- and cross-correlations are studied in a system of two
capacitively coupled quantum dots. We are interested in a role of Coulomb
interaction in dynamical correlations, which occur outside the Coulomb blockade
region (for high bias). After decomposition of the current correlation
functions into contributions between individual tunneling events, we can show
which of them are relevant and lead to sub-/supper-Poissonian shot noise and
negative/positive cross-correlations. The results are differentiated for a weak
and strong inter-dot coupling. Interesting results are for the strong coupling
case when electron transfer in one of the channel is strongly correlated with
charge drag in the second channel. We show that cross-correlations are
non-monotonic functions of bias voltage and they are in general negative
(except some cases with asymmetric tunnel resistances). This is effect of local
potential fluctuations correlated by Coulomb interaction, which mimics the
Pauli exclusion principle
- …