Nonequilibrium dynamical mean-field theory for bosonic lattice models

We develop the nonequilibrium extension of bosonic dynamical mean field theory (BDMFT) and a Nambu real-time strong-coupling perturbative impurity solver. In contrast to Gutzwiller mean-field theory and strong coupling perturbative approaches, nonequilibrium BDMFT captures not only dynamical transitions, but also damping and thermalization effects at finite temperature. We apply the formalism to quenches in the Bose-Hubbard model, starting both from the normal and Bose-condensed phases. Depending on the parameter regime, one observes qualitatively different dynamical properties, such as rapid thermalization, trapping in metastable superfluid or normal states, as well as long-lived or strongly damped amplitude oscillations. We summarize our results in non-equilibrium "phase diagrams" which map out the different dynamical regimes.Comment: 18 pages, 8 figure

Exploring quark transverse momentum distributions with lattice QCD

We discuss in detail a method to study transverse momentum dependent parton distribution functions (TMDs) using lattice QCD. To develop the formalism and to obtain first numerical results, we directly implement a bi-local quark-quark operator connected by a straight Wilson line, allowing us to study T-even, "process-independent" TMDs. Beyond results for x-integrated TMDs and quark densities, we present a study of correlations in x and transverse momentum. Our calculations are based on domain wall valence quark propagators by the LHP collaboration calculated on top of gauge configurations provided by MILC with 2+1 flavors of asqtad-improved staggered sea quarks.Comment: 36 pages, 24 figures; revised version of May 2011, one appendix adde

Strong interference effects in the resonant Auger decay of atoms induced by intense X-Ray fields

The theory of resonant Auger decay of atoms in a high intensity coherent X-ray pulse is presented. The theory includes the coupling between the ground state and the resonance due to an intense X-ray pulse, taking into account the decay of the resonance and the direct photoionization of the ground state, both populating the final ionic states coherently. The theory also considers the impact of the direct photoionization of the resonance state itself which typically populates highly-excited ionic states. The combined action of the resonant decay and of the direct ionization of the ground state in the field induces a non-hermitian time-dependent coupling between the ground and the 'dressed' resonance stats. The impact of these competing processes on the total electron yield and on the 2s$^2$2p$^{4}(^1\mathrm{D})$3p $^2$P spectator and 2s$^1$2p$^{6}$ $^2$S participator Auger decay spectra of the Ne 1s$\to$3p resonance is investigated. The role of the direct photoionization of the ground state and of the resonance increases dramatically with the field intensity. This results in strong interference effects with distinct patterns in the electron spectra, different for the participator and spectator final states.Comment: 31 pages, 6 figure

Measurement of the Top Quark Mass at D0 Run II with the Matrix Element Method in the Lepton+Jets Final State

The mass of the top quark is a fundamental parameter of the Standard Model. Its precise knowledge yields valuable insights into unresolved phenomena in and beyond the Standard Model. A measurement of the top quark mass with the matrix element method in the lepton+jets final state in D0 Run II is presented. Events are selected requiring an isolated energetic charged lepton (electron or muon), significant missing transverse energy, and exactly four calorimeter jets. For each event, the probabilities to originate from the signal and background processes are calculated based on the measured kinematics, the object resolutions and the respective matrix elements. The jet energy scale is known to be the dominant source of systematic uncertainty. The reference scale for the mass measurement is derived from Monte Carlo events. The matrix element likelihood is defined as a function of both, mtop and jet energy scale JES, where the latter represents a scale factor with respect to the reference scale. The top mass is obtained from a two-dimensional correlated fit, and the likelihood yields both the statistical and jet energy scale uncertainty. Using a dataset of 320 pb-1 of D0 Run II data, the mass of the top quark is measured to be mtop (ljets) = 169.5 +/- 4.4(stat.+JES) +1.7-1.6(syst.) GeV mtop (ejets) = 168.8 +/- 6.0(stat.+JES) +1.9-1.9(syst.) GeV mtop (mujets)= 172.3 +/- 9.6(stat.+JES) +3.4-3.3(syst.) GeV The jet energy scale measurement in the lepton+jets sample yields JES=1.034 +/- 0.034, suggesting good consistency of the data with the simulation. The measurement forecasts significant improvements to the total top mass uncertainty during Run II before the startup of the LHC, as the data sample will grow by a factor of ten and D0's tracking capabilities will be employed in jet energy reconstruction and flavor identification.Die Masse des Top-Quarks ist ein fundamentaler Parameter des Standard-Modells. Ihre genaue Kenntnis liefert wertvolle Aufschlüsse bezüglich unverstandener Phänomene im Standard-Model und darüber hinaus. Die Messung der Top-Quark-Masse mit der Matrixelement-Methode im Lepton+Jets Zerfallskanal in Run II des D0 Experiments wird präsentiert. Ereignisse werden selektiert, wenn sie ein isoliertes Lepton (Elektron oder Myon), signifikante fehlende transversale Energie und genau vier Kalorimeter-Jets aufweisen. Für jedes Ereignis werden die Wahrscheinlichkeiten berechnet, dass das Ereignis durch den Signal- bzw. Untergrund-Prozess produziert worden ist, basierend auf der gemessenen Kinematik, den Auflösungen der rekonstrierten Objekte und der prozess-spezifischen Matrixelemente. Die Kenntnis der Jet Energie Skala ist die dominierende Quelle systematischer Unsicherheit dieser Messung. Die Referenz-Skala wird in Monte Carlo Ereignissen bestimmt. Die Matrixelement-Likelihood wird definiert als Funktion beider Variablen, mtop und JES, wobei letzterer einen Skalierungs-Faktor bezüglich der Referenzskala beschreibt. Die Topmasse wird mittels eines zweidimensionalen korrelierten Fits bestimmt, wobei der Likelihood sowohl den statistischen Fehler als auch den Fehler durch Jet Energie Skala liefert. Die Methode wird auf einen D0 Run II Datensatz angewandt, der einer integrierten Luminosität von 320 pb-1 entspricht, und die Messung ergibt mtop (ljets) = 169.5 +/- 4.4(stat.+JES) +1.7-1.6(syst.) GeV mtop (ejets) = 168.8 +/- 6.0(stat.+JES) +1.9-1.9(syst.) GeV mtop (mujets)= 172.3 +/- 9.6(stat.+JES) +3.4-3.3(syst.) GeV Die Messung der Jet Energie Skala im lepton+jets Datensatz ergibt JES=1.034 +/- 0.034, was auf gute Übereinstimmung der Daten mit der Simulation hinweist. Die vorliegende Messung verspricht signifikante Verbesserungen des Gesamtfehlers der Topmasse in Run II noch vor dem Start des LHC, wenn der Datensatz sich verzehnfachen und D0's Spurvermessung in die Rekonstruktion von Jet Energien und die Identifikation von b-Jets einbezogen werden

Canonical formalism for simplicial gravity

We summarise a recently introduced general canonical formulation of discrete systems which is fully equivalent to the covariant formalism. This framework can handle varying phase space dimensions and is applied to simplicial gravity in particular.Comment: 4 pages, 5 figures, based on a talk given at Loops '11 in Madrid, to appear in Journal of Physics: Conference Series (JPCS

Resonant Auger decay of the core-excited C∗^\astO molecule in intense X-ray laser fields

The dynamics of the resonant Auger (RA) process of the core-excited C$^\ast$O(1s$^{-1}\pi^\ast,v_r=0$) molecule in an intense X-ray laser field is studied theoretically. The theoretical approach includes the analogue of the conical intersections of the complex potential energy surfaces of the ground and `dressed' resonant states due to intense X-ray pulses, taking into account the decay of the resonance and the direct photoionization of the ground state, both populating the same final ionic states coherently, as well as the direct photoionization of the resonance state itself. The light-induced non-adiabatic effect of the analogue of the conical intersections of the resulting complex potential energy surfaces gives rise to strong coupling between the electronic, vibrational and rotational degrees of freedom of the diatomic CO molecule. The interplay of the direct photoionization of the ground state and of the decay of the resonance increases dramatically with the field intensity. The coherent population of a final ionic state via both the direct photoionization and the resonant Auger decay channels induces strong interference effects with distinct patterns in the RA electron spectra. The individual impact of these physical processes on the total electron yield and on the CO$^+(A^2\Pi)$ electron spectrum are demonstrated.Comment: 13 figs, 1 tabe

Bosonic self-energy functional theory

We derive the self-energy functional theory for bosonic lattice systems with broken U(1) symmetry by parametrizing the bosonic Baym-Kadanoff effective action in terms of one- and two-point self-energies. The formalism goes beyond other approximate methods such as the pseudoparticle variational cluster approximation, the cluster composite boson mapping, and the Bogoliubov+U theory. It simplifies to bosonic dynamical-mean-field theory when constraining to local fields, whereas when neglecting kinetic contributions of noncondensed bosons, it reduces to the static mean-field approximation. To benchmark the theory, we study the Bose-Hubbard model on the two- and three-dimensional cubic lattice, comparing with exact results from path integral quantum Monte Carlo. We also study the frustrated square lattice with next-nearest-neighbor hopping, which is beyond the reach of Monte Carlo simulations. A reference system comprising a single bosonic state, corresponding to three variational parameters, is sufficient to quantitatively describe phase boundaries and thermodynamical observables, while qualitatively capturing the spectral functions, as well as the enhancement of kinetic fluctuations in the frustrated case. On the basis of these findings, we propose self-energy functional theory as the omnibus framework for treating bosonic lattice models, in particular, in cases where path integral quantum Monte Carlo methods suffer from severe sign problems (e.g., in the presence of nontrivial gauge fields or frustration). Self-energy functional theory enables the construction of diagrammatically sound approximations that are quantitatively precise and controlled in the number of optimization parameters but nevertheless remain computable by modest means