N-body simulations of gravitational dynamics

We describe the astrophysical and numerical basis of N-body simulations, both of collisional stellar systems (dense star clusters and galactic centres) and collisionless stellar dynamics (galaxies and large-scale structure). We explain and discuss the state-of-the-art algorithms used for these quite different regimes, attempt to give a fair critique, and point out possible directions of future improvement and development. We briefly touch upon the history of N-body simulations and their most important results.Comment: invited review (28 pages), to appear in European Physics Journal Plu

Holographic description of strongly correlated electrons in external magnetic fields

We study the Fermi level structure of (2+1)-dimensional strongly interacting electron systems in external magnetic field using the AdS/CFT correspondence. The gravity dual of a finite density fermion system is a Dirac field in the background of the dyonic AdS-Reissner-Nordstrom black hole. In the probe limit the magnetic system can be reduced to the non-magnetic one, with Landau-quantized momenta and rescaled thermodynamical variables. We find that at strong enough magnetic fields, the Fermi surface vanishes and the quasiparticle is lost either through a crossover to conformal regime or through a phase transition to an unstable Fermi surface. In the latter case, the vanishing Fermi velocity at the critical magnetic field triggers the non-Fermi liquid regime with unstable quasiparticles and a change in transport properties of the system. We associate it with a metal-"strange metal" phase transition. We compute the DC Hall and longitudinal conductivities using the gravity-dressed fermion propagators. As expected, the Hall conductivity is quantized according to integer Quantum Hall Effect (QHE) at weak magnetic fields. At strong magnetic fields, new plateaus typical for the fractional QHE appear. Our pattern closely resembles the experimental results on graphite which are described using the fractional filling factor proposed by Halperin.Comment: 39 pages, 11 figures, Ch. 21, Lect. Notes Phys. "Strongly interacting matter in magnetic fields" (Springer), edited by D. Kharzeev, K. Landsteiner, A. Schmitt, H.-U. Yee. arXiv admin note: substantial text overlap with arXiv:1011.405

Search for leptophobic Z ' bosons decaying into four-lepton final states in proton-proton collisions at root s=8 TeV

Peer reviewe

Search for black holes and other new phenomena in high-multiplicity final states in proton-proton collisions at root s=13 TeV

Peer reviewe

Search for heavy resonances decaying into a vector boson and a Higgs boson in final states with charged leptons, neutrinos, and b quarks

Peer reviewe

Search for high-mass diphoton resonances in proton-proton collisions at 13 TeV and combination with 8 TeV search

Peer reviewe

Measurements of differential production cross sections for a Z boson in association with jets in pp collisions at root s=8 TeV

Peer reviewe

Measurement of the inclusive 3-jet production differential cross section in proton-proton collisions at 7 TeV and determination of the strong coupling constant in the TeV range

This paper presents a measurement of the inclusive 3-jet production differential cross section at a proton–proton centre-of-mass energy of 7 TeV using data corresponding to an integrated luminosity of 5 fb-1 collected with the CMS detector. The analysis is based on the three jets with the highest transverse momenta. The cross section is measured as a function of the invariant mass of the three jets in a range of 445–3270 GeV and in two bins of the maximum rapidity of the jets up to a value of 2. A comparison between the measurement and the prediction from perturbative QCD at next-to-leading order is performed. Within uncertainties, data and theory are in agreement. The sensitivity of the observable to the strong coupling constant αS is studied. A fit to all data points with 3-jet masses larger than 664 GeV gives a value of the strong coupling constant of αS(MZ)=0.1171±0.0013(exp)-0.0047+0.0073(theo)

Search for heavy neutrinos and W bosons with right-handed couplings in proton - proton collisions at \sqrt = 8TeV

A search for heavy, right-handed neutrinos, Nℓ ( ℓ=e,μ ), and right-handed WR bosons, which arise in the left-right symmetric extensions of the standard model, has been performed by the CMS experiment. The search was based on a sample of two lepton plus two jet events collected in proton–proton collisions at a center-of-mass energy of 8 TeV corresponding to an integrated luminosity of 19.7 fb-1 . For models with strict left-right symmetry, and assuming only one Nℓ flavor contributes significantly to the WR decay width, the region in the two-dimensional (MWR,MNℓ) mass plane excluded at a 95 % confidence level extends to approximately MWR=3.0TeV and covers a large range of neutrino masses below the WR boson mass, depending on the value of MWR . This search significantly extends the (MWR,MNℓ) exclusion region beyond previous results. Electronic supplementary material The online version of this article (doi:10.1140/epjc/s10052-014-3149-z) contains supplementary material, which is available to authorized users

Measurement of the differential cross section for top quark pair production in pp collisions at √s=8 TeV

The normalized differential cross section for top quark pair (tt¯) production is measured in pp collisions at a centre-of-mass energy of 8TeV at the CERN LHC using the CMS detector in data corresponding to an integrated luminosity of 19.7fb-1. The measurements are performed in the lepton+jets (e/μ++jets) and in the dilepton e+e-, μ+μ-, and e±μ∓) decay channels. The tt¯ cross section is measured as a function of the kinematic properties of the charged leptons, the jets associated to b quarks, the top quarks, and the tt¯ system. The data are compared with several predictions from perturbative quantum chromodynamic up to approximate next-to-next-to-leading-order precision. No significant deviations are observed relative to the standard model predictions. © 2015, CERN for the benefit of the CMS collaboration