Mutual entropy production in bipartite systems

in Journal of Statistical Mechanics: Theory and Experiment (2014)

It was recently shown by Barato et al (2013 Phys. Rev. E 87 042104) that the mutual information at the trajectory level of a bipartite Markovian system is not bounded by the entropy production. In the ... [more ▼]

It was recently shown by Barato et al (2013 Phys. Rev. E 87 042104) that the mutual information at the trajectory level of a bipartite Markovian system is not bounded by the entropy production. In the same way as Gaspard showed (2004 J. Stat. Phys. 117 599) that the entropy production is not directly related to the Shannon entropy at the trajectory level but is in fact equal to its difference from the so-called time-reversed Shannon entropy, we show in this paper that the difference between the mutual information and its time-reversed form is equal to the mutual entropy production (MEP), i.e. the difference between the full entropy production and that of the two marginal processes. Evaluation of the MEP is in general a difficult task due to non-Markovian effects. For bipartite systems, we provide closed expressions in various limiting regimes which we verify by numerical simulations. [less ▲]

Missing energy and jets for supersymmetry searches

in Physical Review. D (2013), 87(3), 034026

We extend our investigation of backgrounds to new physics signals, following CMS’s data-driven search for supersymmetry at the LHC. The aim is to use different sets of cuts in γ+3-jet production to ... [more ▼]

We extend our investigation of backgrounds to new physics signals, following CMS’s data-driven search for supersymmetry at the LHC. The aim is to use different sets of cuts in γ+3-jet production to predict the irreducible Z+3-jet background (with the Z boson decaying to neutrinos) to searches with E̸T+3-jet signal topologies. We compute ratios of Z+3-jet to γ+3-jet production cross sections and kinematic distributions at next-to-leading order (NLO) in αs. We compare these ratios with those obtained using a parton shower matched to leading-order matrix elements (ME+PS). This study extends our previous work [Bern et al., Phys. Rev. D 84 114002 (2011)] on the Z+2-jet to γ+2-jet ratio. We find excellent agreement with the ratio determined from the earlier NLO results involving two instead of three jets, and agreement to within 10% between the NLO and ME+PS results for the ratios. We also examine the possibility of large QCD logarithms in these processes. Ratios of Z+n-jet to γ+n-jet cross sections are plausibly less sensitive to such corrections than the cross sections themselves. Their effect on estimates of Z+3-jet to γ+3-jet ratios can be assessed experimentally by measuring the γ+3-jet to γ+2-jet production ratio in search regions. We partially address the question of potentially large electroweak logarithms by computing the real-emission part of the electroweak corrections to the ratio using ME+PS and find that it is 1% or less. Our estimate of the remaining theoretical uncertainties in the Z to γ ratio is in agreement with our earlier study. [less ▲]

NLO vector boson production with light jets

in Il Nuovo Cimento (2012), 35(3), 25-28

In this contribution we present recent progress in the computation of next-to-leading order (NLO) QCD corrections for the production of an electroweak vector boson in association with jets at hadron ... [more ▼]

In this contribution we present recent progress in the computation of next-to-leading order (NLO) QCD corrections for the production of an electroweak vector boson in association with jets at hadron colliders. We focus on results obtained using the virtual matrix element library BlackHat [1] in conjunction with SHERPA [2, 3, 4], focusing on results relevant to understanding the background to top production. [less ▲]

Driving missing data at next-to-leading order

in Physical Review. D (2011), 84(11), 114002

The prediction of backgrounds to new-physics signals in topologies with large missing transverse energy and jets is important to new-physics searches at the LHC. Following a CMS study, we investigate ... [more ▼]

The prediction of backgrounds to new-physics signals in topologies with large missing transverse energy and jets is important to new-physics searches at the LHC. Following a CMS study, we investigate theoretical issues in using measurements of γ+2-jet production to predict the irreducible background to searches for missing energy plus two jets that originates from Z+2-jet production where the Z boson decays to neutrinos. We compute ratios of γ+2-jet to Z+2-jet production cross sections and kinematic distributions at next-to-leading order in αs, as well as using a parton shower matched to leading-order matrix elements. The former ratios rely on the first next-to-leading-order calculation of γ+2-jet production at a hadron collider. We find that the ratios obtained in the two approximations are quite similar, making γ+2-jet production a theoretically reliable estimator for the missing energy plus two jets background. We employ a Frixione-style photon isolation, but we also show that for isolated prompt-photon production at high transverse momentum the difference between this criterion and the standard-cone isolation used by CMS is small. [less ▲]

High-energy resummation in direct photon production

in Nuclear Physics B (2010), 824(1), 154--167

We present the computation of the direct photon production cross-section in perturbative QCD to all orders in the limit of high partonic center-of-mass energy. We show how the high-energy resummation can ... [more ▼]

We present the computation of the direct photon production cross-section in perturbative QCD to all orders in the limit of high partonic center-of-mass energy. We show how the high-energy resummation can be performed consistently in the presence of a collinear singularity in the final state, we compare our results to the fixed order NLO cross-section in MS scheme, and we provide predictions at NNLO and beyond. [less ▲]

Expansion of a Fermi cloud in the BCS-BEC crossover

in Physical Review. A (2006), 73(6), 065601

We study the free expansion of a dilute two-component Fermi gas with attractive interspecies interaction in the BCS-BEC crossover. We apply a time-dependent parameter-free density-functional theory by ... [more ▼]

We study the free expansion of a dilute two-component Fermi gas with attractive interspecies interaction in the BCS-BEC crossover. We apply a time-dependent parameter-free density-functional theory by using two choices of the equation of state: an analytic formula based on Monte Carlo data and the mean-field equation of state resulting from the extended BCS equations. The calculated axial and transverse radii and the aspect ratio of the expanding cloud are compared to experimental data on vapors of 6 Li atoms. Remarkably, the mean-field theory shows a better agreement with the experiments than the theory based on the Monte Carlo equation of state. Both theories predict a measurable dependence of the aspect ratio on expansion time and on scattering length. [less ▲]