7,884 research outputs found
Multiple Parton Interactions Studies at CMS
This paper summarizes the Multiple Parton Interactions studies in CMS,
focusing on the already performed low pT QCD measurements up to highest centre
of mass energies of 7 TeV and discussing the plans for the direct measurement
of the multiple high-pT scatterings. The underlying event in pp interactions is
studied measuring the charged multiplicity density and the charged energy
density in the transverse region, which is defined considering the azimuthal
distance of the reconstructed tracks with respect to the leading track-jet of
the event, defined from tracks according to a jet clustering algorithms. In
addition, we present the measurement of the underlying event using the
jet-area/median approach, demonstrating its sensitivity to different underlying
event scenarios. Observations in the central region are complemented by the
mea- surement of the energy flow in the forward direction for minimum bias and
central di-jet events. We compare our underlying event and forward results with
the predictions from different Monte Carlo event generators and tunes, aiming
to best parametrize the multiple parton interaction energy de- pendence
starting from the Monte Carlo tunes developed to best fit the charged particle
spectra measured at central rapidities. Finally we discuss the strategy to
directly measure the multiple particle interactions rate focusing on the
topologies with two hard scatterings in the same event
Time-dependent trading strategies in a continuous double auction
We model a continuous double auction with heterogenous agents and compute approximate optimal trading strategies using evolution strategies. Agents privately know their values and costs and have a limited time to transact. We focus on equilibrium strategies that are developed taking into account the number of traders that submitted orders previously, as well as the number of who will submit subsequently. We find that it is optimal to place increasingly aggressive orders, according to a roughly linear schedule, and test the resulting equilibrium for robustness and accuracy.Continuous double auction, equilibrium trading strategies, evolution strategies.
The density matrix renormalization group method. Application to the PPP model of a cyclic polyene chain
The density matrix renormalization group (DMRG) method introduced by White
for the study of strongly interacting electron systems is reviewed; the method
is variational and considers a system of localized electrons as the union of
two adjacent fragments A, B. A density matrix rho is introduced, whose
eigenvectors corresponding to the largest eigenvalues are the most significant,
the most probable states of A in the presence of B; these states are retained,
while states corresponding to small eigenvalues of rho are neglected. It is
conjectured that the decreasing behaviour of the eigenvalues is gaussian. The
DMRG method is tested on the Pariser-Parr-Pople Hamiltonian of a cyclic polyene
(CH)_N up to N=34. A Hilbert space of dimension 5 x 10^+18 is explored. The
ground state energy is 10^-3 eV within the full CI value in the case N=18. The
DMRG method compares favourably also with coupled cluster approximations. The
unrestricted Hartree-Fock solution (which presents spin density waves) is
briefly reviewed, and a comparison is made with the DMRG energy values.
Finally, the spin-spin and density-density correlation functions are computed;
the results suggest that the antiferromagnetic order of the exact solution does
not extend up to large distances but exists locally. No charge density waves
are present.Comment: 8 pages, RevTex, 2 figures, to be published in the Journal of
Chemical Physic
Generalized biodiversity assessment by Bayesian nested random effects models with spyke-and-slab priors
We analyze variations in alpha-diversity of benthic macroinvertebrate communities in an Italian lagoon system using Bayesian hierarchical models with nested random effects. Our aim is to understand how spatial scales influence microhabitat definition. Tsallis entropy measures diversity and spike-and-slab regression selects predictors
Siegert pseudostate perturbation theory: one- and two-threshold cases
Perturbation theory for the Siegert pseudostates (SPS) [Phys.Rev.A 58, 2077
(1998) and Phys.Rev.A 67, 032714 (2003)] is studied for the case of two
energetically separated thresholds. The perturbation formulas for the
one-threshold case are derived as a limiting case whereby we reconstruct More's
theory for the decaying states [Phys.Rev.A 3,1217(1971)] and amend an error.
The perturbation formulas for the two-threshold case have additional terms due
to the non-standard orthogonality relationship of the Siegert Pseudostates. We
apply the theory to a 2-channel model problem, and find the rate of convergence
of the perturbation expansion should be examined with the aide of the variance
instead of the real and imaginary parts of
the perturbation energy individually
Statistical VS Wave Realism in the Foundations of Quantum Mechanics
Different realistic attitudes towards wavefunctions and quantum states are as old as quantum theory itself. Recently Pusey, Barret and Rudolph (PBR) on the one hand, and Auletta and Tarozzi (AT) on the other, have proposed new interesting arguments in favor of a broad realistic interpretation of quantum mechanics that can be considered the modern heir to some views held by the fathers of quantum theory. In this paper we give a new and detailed presentation of such arguments, propose a new taxonomy of different realistic positions in the foundations of quantum mechanics and assess the scope, within this new taxonomy, of these realistic arguments
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