Experimental discrimination between charge 2e/3 top quark and charge 4e/3 exotic quark production scenarios.
We present the first experimental discrimination between the 2e/3 and 4e/3 top quark electric charge scenarios, using top quark pairs (tt) produced in pp collisions at (square root) s = 1.96 TeV by the Fermilab Tevatron Collider. We use 370 pb;{-1} of data collected by the D0 experiment and select events with at least one high transverse momentum electron or muon, high transverse energy imbalance, and four or more jets. We discriminate between b- and b-quark jets by using the charge and momenta of tracks within the jet cones. The data are consistent with the expected electric charge, |q|=2e/3. We exclude, at the 92% C.L., that the sample is solely due to the production of exotic quark pairs QQ with |q|=4e/3. We place an upper limit on the fraction of QQ pairs rho<0.80 at the 90% C.L.

title: Search for long-lived particles decaying into electron or photon pairs with the D0 detector.
abstract: In this Letter we report on a search for long-lived particles that decay into final states with two electrons or photons. Such long-lived particles arise in a variety of theoretical models, such as hidden valleys and supersymmetry with gauge-mediated breaking. By precisely reconstructing the direction of the electromagnetic shower we are able to probe much longer lifetimes than previously explored. We see no evidence of the existence of such long-lived particles and interpret this search as a quasi model-independent limit on their production cross section, as well as a limit on a long-lived fourth generation quark.

title: Measurement of angular correlations of jets at s=1.96 TeV and determination of the strong coupling at high momentum transfers
abstract: We present a measurement of the average value of a new observable at hadron colliders that is sensitive to QCD dynamics and to the strong coupling constant, while being only weakly sensitive to parton distribution functions. The observable measures the angular correlations of jets and is defined as the number of neighboring jets above a given transverse momentum threshold which accompany a given jet within a given distance Delta-R in the plane of rapidity and azimuthal angle. The ensemble average over all jets in an inclusive jet sample is measured and the results are presented as a function of transverse momentum of the inclusive jets, in different regions of Delta-R and for different transverse momentum requirements for the neighboring jets. The measurement is based on a data set corresponding to an integrated luminosity of 0.7 fb-1 collected with the D0 detector at the Fermilab Tevatron Collider in pp-bar collisions at sqrt(s)=1.96 The results are well described by a perturbative QCD calculation in next-to-leading order in the strong coupling constant, corrected for non-perturbative effects. From these results, we extract the strong coupling and test the QCD predictions for its running over a range of momentum transfers of 50-400 GeV.

title: Precision measurement of the top quark mass in lepton + jets final States.
abstract: We measure the mass of the top quark in lepton+jets final states using the full sample of pp collision data collected by the D0 experiment in Run II of the Fermilab Tevatron Collider at sqrt[s] = 1.96 TeV, corresponding to 9.7 fb(-1) of integrated luminosity. We use a matrix element technique that calculates the probabilities for each event to result from tt production or background. The overall jet energy scale is constrained in situ by the mass of the W boson. We measure m(t) = 174.98 ± 0.76 GeV. This constitutes the most precise single measurement of the top-quark mass.

title: Jet energy scale determination in the D0 experiment
abstract: The calibration of jet energy measured in the DO detector is presented, based on p (p) over bar collisions at a center-of-mass energy of 1.96 TeV at the Fermilab Tevatron collider, jet energies are measured using a sampling calorimeter composed of uranium and liquid argon as the passive and active media, respectively. This paper describes the energy calibration of jets performed with gamma+jet, Z+jet and dilet events, with jet transverse momentum p(T) > 6 GeV and pseudorapidity range vertical bar eta vertical bar < 3.6, The corrections are measured separately for data and simulation, achieving a precision of 1.4-1.8% for jets in the central part of the calorimeter ancl up to 3.5% for the jets with pseudorapidity vertical bar eta vertical bar = 3.0. Specific corrections are extracted to enhance the description of jet energy in simulation and in particular of the effects due to the flavor of the parton originating the jet, correcting biases up to 3-4% in jets with low PT originating from gluons and up to 6-8% in jets from b quarks.

title: Observation and properties of the orbitally excited B_(s2)(*) meson.
abstract: We report the direct observation of the excited L=1 state B_(s2)(*) in fully reconstructed decays to B+K-. The mass of the B_(s2)(*) meson is measured to be 5839.6+/-1.1(stat)+/-0.7(syst) MeV/c(2), and its production rate relative to the B+ meson is measured to be [1.15+/-0.23(stat)+/-0.13(syst)]%.

title: Spontaneous compactification of d=11 supergravity due to Rarita-Schwinger fields
abstract: A characteristic feature of all the spontaneous compactification mechanisms so far proposed has been the consideration of only the boson sector of the theories being compactified, i.e., the vacuum values of the Fermi fields were assumed to be zero. Thus, in d = 11 supergravity one uses the Freund-Rubin mechanism of compactification due to antisymmetric tensor fields F/sub MNPQ/. This mechanism yielded in particular compactifications onto the round, squashed, and squashed with torsion seven-dimensional spheres. In the present paper, the Freund-Rubin mechanism is generalized to nonvanishing vacuum values of a Rarita-Schwinger field and is used to obtain a new solution of d = 11 supergravity

title: Instantons on Special Holonomy Manifolds
abstract: We consider cones over manifolds admitting real Killing spinors and instanton equations on connections on vector bundles over these manifolds. Such cones are manifolds with special (reduced) holonomy. We generalize the scalar ansatz for a connection proposed by Harland and Nolle in such a way that instantons are parameterized by constrained matrix-valued functions. Our ansatz reduces instanton equations to a matrix model equations which can be further reduced to Newtonian mechanics with particle trajectories obeying first-order gradient flow equations. Generalizations to Kaehler-Einstein manifolds and resolved Calabi-Yau cones are briefly discussed. Our construction allows one to associate quiver gauge theories with special holonomy manifolds.

title: Yang-Mills Flows on Nearly Kähler Manifolds and G2-Instantons
abstract: We consider Lie(G)-valued G-invariant connections on bundles over spaces $${G/H,\, \mathbb{R}\times G/H\, {\rm and}\, \mathbb{R}^2\times G/H}$$, where G/H is a compact nearly Kähler six-dimensional homogeneous space, and the manifolds $${\mathbb{R}\times G/H}$$ and $${\mathbb{R}^2\times G/H}$$ carry G2- and Spin(7)-structures, respectively. By making a G-invariant ansatz, Yang-Mills theory with torsion on $${\mathbb{R}\times G/H}$$ is reduced to Newtonian mechanics of a particle moving in a plane with a quartic potential. For particular values of the torsion, we find explicit particle trajectories, which obey first-order gradient or hamiltonian flow equations. In two cases, these solutions correspond to anti-self-dual instantons associated with one of two G2-structures on $${\mathbb{R}\times G/H}$$. It is shown that both G2-instanton equations can be obtained from a single Spin(7)-instanton equation on $${\mathbb{R}^2\times G/H}$$.

title: Supertwistors and cubic string field theory for open N=2 strings
abstract: The known Lorentz invariant string field theory for open N = 2 strings is combined with a generalization of the twistor description of anti-self-dual (super-)Yang–Mills theories. We introduce a Chern–Simons-type Lagrangian containing twistor variables and derive the Berkovits–Siegel covariant string field equations of motion via the twistor correspondence. Both the purely bosonic and the maximally space–time supersymmetric cases are considered.

title: Instantons and Yang–Mills Flows on Coset Spaces
abstract: We consider the Yang–Mills flow equations on a reductive coset space G/H and the Yang–Mills equations on the manifold $${\mathbb{R}\times G/H}$$. On non-symmetric coset spaces G/H one can introduce geometric fluxes identified with the torsion of the spin connection. The condition of G-equivariance imposed on the gauge fields reduces the Yang–Mills equations to $${\phi^4}$$-kink equations on $${\mathbb{R}}$$. Depending on the boundary conditions and torsion, we obtain solutions to the Yang–Mills equations describing instantons, chains of instanton–anti-instanton pairs or modifications of gauge bundles. For Lorentzian signature on $${\mathbb{R}\times G/H}$$, dyon-type configurations are constructed as well. We also present explicit solutions to the Yang–Mills flow equations and compare them with the Yang–Mills solutions on $${\mathbb{R}\times G/H}$$.