233,267 research outputs found
Squark Production and Decay matched with Parton Showers at NLO
Extending previous work on the predictions for the production of
supersymmetric (SUSY) particles at the LHC, we present the fully differential
calculation of the next-to-leading order (NLO) SUSY-QCD corrections to the
production of squark and squark-antisquark pairs of the first two generations.
The NLO cross sections are combined with the subsequent decay of the final
state (anti)squarks into the lightest neutralino and (anti)quark at NLO
SUSY-QCD. No assumptions on the squark masses are made, and the various
subchannels are taken into account independently. In order to obtain realistic
predictions for differential distributions the fixed-order calculations have to
be combined with parton showers. Making use of the Powheg method we have
implemented our results in the Powheg-Box framework and interfaced the NLO
calculation with the parton shower Monte Carlo programs Pythia6 and Herwig++.
The code is publicly available and can be downloaded from the Powheg-Box
webpage. The impact of the NLO corrections on the differential distributions is
studied and parton shower effects are investigated for different benchmark
scenarios.Comment: 36 pages, 10 figure
New Constraints on the Star Formation History of the Star Cluster NGC 1856
We use the Wide Field Camera 3 onboard the Hubble Space Telescope to obtain
deep, high-resolution photometry of the young (age ~ 300 Myr) star cluster
NGC1856 in the Large Magellanic Cloud. We compare the observed colour-magnitude
diagram (CMD), after having applied a correction for differential reddening,
with Monte Carlo simulations of simple stellar populations (SSPs) of various
ages. We find that the main sequence turn-off (MSTO) region is wider than that
derived from the simulation of a single SSP. Using constraints based on the
distribution of stars in the MSTO region and the red clump, we find that the
CMD is best reproduced using a combination of two different SSPs with ages
separated by 80 Myr (0.30 and 0.38 Gyr, respectively). However, we can not
formally exclude that the width of the MSTO could be due to a range of stellar
rotation velocities if the efficiency of rotational mixing is higher than
typically assumed. Using a King-model fit to the surface number density profile
in conjunction with dynamical evolution models, we determine the evolution of
cluster mass and escape velocity from an age of 10 Myr to the present age,
taking into account the possible effects of primordial mass segregation. We
find that the cluster has an escape velocity Vesc ~ 17 km/s at an age of 10
Myr, and it remains high enough during a period of ~ 100 Myr to retain material
ejected by slow winds of first-generation stars. Our results are consistent
with the presence of an age spread in NGC1856, in contradiction to the results
of Bastian & Silva-Villa (2013).Comment: 17 pages, 14 figures. Re-submitted to MNRAS after addressing all the
comments by the refere
Optimisation of electricity energy markets and assessment of CO2 trading on their structure : a stochastic analysis of the greek power sector
Power production was traditionally dominated by monopolies. After a long period of research and organisational advances in international level, electricity markets have been deregulated allowing customers to choose their provider and new producers to compete the former Public Power Companies. Vast changes have been made in the European legal framework but still, the experience gathered is not sufficient to derive safe conclusions regarding the efficiency and reliability of deregulation. Furthermore, emissions' trading progressively becomes a reality in many respects, compliance with Kyoto protocol's targets is a necessity, and stability of the national grid's operation is a constraint of vital importance. Consequently, the production of electricity should not rely solely in conventional energy sources neither in renewable ones but on a mixed structure. Finding this optimal mix is the primary objective of the study. A computational tool has been created, that simulates and optimises the future electricity generation structure based on existing as well as on emerging technologies. The results focus on the Greek Power Sector and indicate a gradual decreasing of anticipated CO2 emissions while the socioeconomic constraints and reliability requirements of the system are met. Policy interventions are pointed out based on the numerical results of the model. (C) 2010 Elsevier Ltd. All rights reserved
Minimum-time trajectory generation for quadrotors in constrained environments
In this paper, we present a novel strategy to compute minimum-time
trajectories for quadrotors in constrained environments. In particular, we
consider the motion in a given flying region with obstacles and take into
account the physical limitations of the vehicle. Instead of approaching the
optimization problem in its standard time-parameterized formulation, the
proposed strategy is based on an appealing re-formulation. Transverse
coordinates, expressing the distance from a frame path, are used to
parameterise the vehicle position and a spatial parameter is used as
independent variable. This re-formulation allows us to (i) obtain a fixed
horizon problem and (ii) easily formulate (fairly complex) position
constraints. The effectiveness of the proposed strategy is proven by numerical
computations on two different illustrative scenarios. Moreover, the optimal
trajectory generated in the second scenario is experimentally executed with a
real nano-quadrotor in order to show its feasibility.Comment: arXiv admin note: text overlap with arXiv:1702.0427
Matching pre-equilibrium dynamics and viscous hydrodynamics
We demonstrate how to match pre-equilibrium dynamics of a 0+1 dimensional
quark gluon plasma to 2nd-order viscous hydrodynamical evolution. The matching
allows us to specify the initial values of the energy density and shear tensor
at the initial time of hydrodynamical evolution as a function of the lifetime
of the pre-equilibrium period. We compare two models for the pre-equilibrium
quark-gluon plasma, longitudinal free streaming and collisionally-broadened
longitudinal expansion, and present analytic formulas which can be used to fix
the necessary components of the energy-momentum tensor. The resulting dynamical
models can be used to assess the effect of pre-equilibrium dynamics on
quark-gluon plasma observables. Additionally, we investigate the dependence of
entropy production on pre-equilibrium dynamics and discuss the limitations of
the standard definitions of the non-equilibrium entropy.Comment: 24 pages, 5 figures,v2: minor modifications and updated references.
Accepted for publication in Phys. Rev.
Precision calculations for h->WW/ZZ->4 fermions in the Two-Higgs-Doublet Model with PROPHECY4F
We have calculated the next-to-leading-order electroweak and QCD corrections
to the decay processes h -> WW/ZZ -> 4 fermions of the light CP-even Higgs
boson h of various types of Two-Higgs-Doublet Models (Types I and II,
"lepton-specific" and "flipped" models). The input parameters are defined in
four different renormalization schemes, where parameters that are not directly
accessible by experiments are defined in the MSbar scheme. Numerical results
are presented for the corrections to partial decay widths for various benchmark
scenarios previously motivated in the literature, where we investigate the
dependence on the MSbar renormalization scale and on the choice of the
renormalization scheme in detail. We find that it is crucial to be precise with
these issues in parameter analyses, since parameter conversions between
different schemes can involve sizeable or large corrections, especially in
scenarios that are close to experimental exclusion limits or theoretical
bounds. It even turns out that some renormalization schemes are not applicable
in specific regions of parameter space. Our investigation of differential
distributions shows that corrections beyond the Standard Model are mostly
constant offsets induced by the mixing between the light and heavy CP-even
Higgs bosons, so that differential analyses of h -> 4f decay observables do not
help to identify Two-Higgs-Doublet Models. Moreover, the decay widths do not
significantly depend on the specific type of those models. The calculations are
implemented in the public Monte Carlo generator PROPHECY4F and ready for
application.Comment: 56 pages, 39 figure
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