Seiberg–Witten monopole equations on noncommutative R4
It is well known that, due to vanishing theorems, there are no nontrivial finite action solutions to the Abelian Seiberg–Witten (SW) monopole equations on Euclidean four-dimensional space R4. We show that this is no longer true for the noncommutative version of these equations, i.e., on a noncommutative deformation Rθ4 of R4 there exist smooth solutions to the SW equations having nonzero topological charge. We introduce action functionals for the noncommutative SW equations and construct explicit regular solutions. All our solutions have finite energy. We also suggest a possible interpretation of the obtained solutions as codimension four vortex-like solitons representing D(p−4)- and D(p−4)¯-branes in a Dp-Dp¯ brane system in type II superstring theory.

title: Solutions of Yang-Mills and Yang-Mills-Higgs equations

title: Fundamental chiral strings
abstract: The problem of the non-uniqueness of the string theory in the space Rd-1,1 with d ≤ 10 and the procedure of the compactification and the deompactification are discussed. We consider a compact bosonic string defined as a closed string moving in the Lorentizian torus T25,1 and introduce fundamental chiral bosonic string (FCBS) as a universal cover of a compact string. It is shown that the Fock spaces of any standard strings are embedded into the Fock space of FCBS.

title: Noncommutative instantons in higher dimensions, vortices and topological K-cycles
abstract: We construct explicit BPS and non-BPS solutions of the U(2k) Yang-Mills equations on the noncommutative space 2nθ × S2 with finite energy and topological charge. By twisting with a Dirac multi-monopole bundle over S2, we reduce the Donaldson-Uhlenbeck-Yau equations on 2nθ × S2 to vortex-type equations for a pair of U(k) gauge fields and a bi-fundamental scalar field on 2nθ. In the SO(3)-invariant case the vortices on 2nθ determine multi-instantons on 2nθ × S2. We show that these solutions give natural physical realizations of Bott periodicity and vector bundle modification in topological K-homology, and can be interpreted as a blowing-up of D0-branes on 2nθ into spherical D2-branes on 2nθ × S2. In the generic case with broken rotational symmetry, we argue that the D0-brane charges on 2nθ × S2 provide a physical interpretation of the Adams operations in K-theory.

title: Solving string field equations: new uses for old tools
abstract: It is argued that the (NS-sector) superstring field equations are integrable, i.e. their solutions are obtainable from linear equations. We adapt the 25-year-old solution-generating “dressing” method and reduce the construction of nonperturbative superstring configurations to a specific cohomology problem. The application to vacuum superstring field theory is outlined.

title: On nonperturbative solutions of superstring field theory
abstract: Nonperturbative solutions to the nonlinear field equations in the NS sector of cubic as well as nonpolynomial superstring field theory can be obtained from a linear equation which includes a “spectral” parameter λ and a coboundary operator Q ( λ ). We borrow a simple ansatz from the dressing method (for generating solitons in integrable field theories) and show that classical superstring fields can be constructed from any string field  T subject merely to Q ( λ ) T =0. Following the decay of the non-BPS D9 brane in IIA theory and shifting the background to the tachyon vacuum, we repeat the arguments in vacuum superstring field theory and outline how to compute classical solutions explicitly.

title: Measurement of the differential cross section $d\sigma/dt$ in elastic $p\bar{p}$ scattering at $\sqrt{s}=1.96$ TeV
abstract: We present a measurement of the elastic differential cross section $d\sigma(p\bar{p}\rightarrow p\bar{p})/dt$ as a function of the four-momentum-transfer squared t. The data sample corresponds to an integrated luminosity of $\approx 31 nb^{-1}$ collected with the D0 detector using dedicated Tevatron $p\bar{p} $ Collider operating conditions at sqrt(s) = 1.96 TeV and covers the range $0.26 <|t|< 1.2 GeV^2$. For $|t|<0.6 GeV^2$, d\sigma/dt is described by an exponential function of the form $Ae^{-b|t|}$ with a slope parameter $ b = 16.86 \pm 0.10(stat) \pm 0.20(syst) GeV^{-2}$. A change in slope is observed at $|t| \approx 0.6 GeV^2$, followed by a more gradual |t| dependence with increasing values of |t|.

title: Exotic and q anti-q resonances in the pi+ pi- pi- system produced in pi- p collisions at 18-GeV/c/
abstract: A partial-wave analysis of the reaction pi(-)p-->pi(+)pi(-)pi(-)p at 18 GeV/c has been performed on a data sample of 250 000 events obtained in the Brookhaven experiment E852. The well-known a(1)(1260), a(2)(1320) and pi(2)(1670) resonant states are observed. The existence of the pi(1800), a(1)(1700) and a(4)(2040) states is confirmed. The a(3)(1874) state is also observed. The exotic 1(-+) pi(1)(1600) state produced in the natural parity exchange process is found to decay in the rho(770)pi(-) channel. A mass-dependent fit results in a resonance mass of 1593+/-8(-47)(+29) MeV/c(2) and a width of 168+/-20(-12)(+150) MeV/c(2).

title: Measurement of the forward-backward asymmetry in top quark-antiquark production in ppbar collisions using the lepton+jets channel
abstract: We present a measurement of the forward-backward asymmetry in top quark-antiquark production using the full Tevatron Run II data set collected by the D0 experiment at Fermilab. The measurement is performed in lepton + jets final states using a new kinematic fitting algorithm for events with four or more jets and a new partial reconstruction algorithm for events with only three jets. Corrected for detector acceptance and resolution effects, the asymmetry is evaluated to be A(FB) = (10.6 +/- 3.0)%. Results are consistent with the standard model predictions which range from 5.0% to 8.8%. We also present the dependence of the asymmetry on the invariant mass of the top quark-antiquark system and the difference in rapidities of the top quark and antiquark.

title: Search for production of single top quarks via tcg and tug flavor-changing-neutral-current couplings.
abstract: We search for the production of single top quarks via flavor-changing-neutral-current couplings of a gluon to the top quark and a charm (c) or up (u) quark. We analyze 230 pb{-1} of lepton+jets data from pp[over] collisions at a center of mass energy of 1.96 TeV collected by the D0 detector at the Fermilab Tevatron Collider. We observe no significant deviation from standard model predictions, and hence set upper limits on the anomalous coupling parameters kappa{g}{c}/Lambda and kappa{g}{u}/Lambda, where kappa{g} define the strength of tcg and tug couplings, and Lambda defines the scale of new physics. The limits at 95% C.L. are kappa{g}{c}/Lambda<0.15 TeV-1 and kappa{g}{u}/Lambda<0.037 TeV-1.

title: New results on searches for new physics beyond the standard model in the D0 experiment
abstract: The latest results obtained from searches for particles and phenomena beyond the Standard Model (new physics) in the D0 experiment at the Tevatron [Fermi National Accelerator Laboratory (FNAL), USA] on the basis of a statistical sample corresponding to an accumulated luminosity of 1 to 3 fb−1 in 2008 are considered.