Axel U. J. Lode
Physikalisch-Chemisches Institut
Universität Heidelberg

Alexej I. Streltsov
Physikalisch-Chemisches Institut
Universität Heidelberg

Kaspar Sakmann
Physikalisch-Chemisches Institut
Universität Heidelberg

Ofir E. Alon
Department of Physics
University of Haifa at Oranim, Israel

Lorenz S. Cederbaum
Physikalisch-Chemisches Institut
Universität Heidelberg

The tunneling process is a phenomenon which lies at the very heart of quantum mechanics. A rich variety of systems in nature undergo it - for many of them the characteristics of the process play a key role, e.g., alpha decay, fusion, fission, photoassociation, and -dissociation. The main aim of the study is to understand the process of quantum tunneling of initially-coherent ultracold one-dimensional many-boson systems with repulsive interactions to open space. We use the MCTDHB method ([Phys. Rev. Lett 99, 030402 (2007)], [Phys. Rev. A 77, 033613 (2008)] and http://MCTDHB.org) to solve the underlying many-boson time-dependent Schrödinger equation numerically exactly. The results reveal that the emission of the bosons to open space is accompanied by fragmentation - a dynamical loss of the coherence in a very non-trivial way - the source bosons remain coherent while the emitted ones do not. The mechanism behind the dynamical fragmentation is a quantum superposition of many single-particle processes taking place simultaneously. See Figure and arxiv:1202.3447 for more details. To assess the way of the loss of coherence during the dynamical fragmentation process, we provide a movie of the correlation function in momentum space around the emerging peak structure. It prooves that the coherence stays in the source while it is lost solely and quickly for the escaping particles. This is because only for the corresponding momenta the bosons become correlated and |g⁽¹⁾|²→ 0.

Link

• http://MCTDHB.org

Software

• OpenMPI, OpenMP, Gnuplot, Intel MKL, Intel Fortran

Publications

• Wave chaos as signature for depletion of a Bose-Einstein condensate, Iva Brezinova, Axel U. J. Lode, Alexej I. Streltsov, Ofir E. Alon, Lorenz S. Cederbaum, Joachim Burgdrfer, to appear in Phys. Rev. A. (2012). arxiv:1005.0093
• How does an interacting many-body system tunnel through a potential barrier to open space?, Axel U. J. Lode, Alexej I. Streltsov, Kaspar Sakmann, Ofir E. Alon, Lorenz S. Cederbaum, submitted to Proceedings of the National Academy of the Sciences (2012). arxiv:1202.3447
• Recursive formulation of the multiconfigurational time-dependent Hartree method for fermions, bosons and mixtures thereof in terms of one-body density operators, Ofir E. Alon, Alexej I. Streltsov, Kaspar Sakmann, Axel U.J. Lode, Julian Grond, Lorenz S. Cederbaum, J. Chem. Phys. (2011). http://dx.doi.org/10.1016/j.chemphys.2011.09.026
• The Multiconfigurational time-dependent Hartree for Bosons package, version 2.2, A. I. Streltsov, K. Sakmann, A. U. J. Lode, O. E. Alon, L. S. Cederbaum. http://MCTDHB.org
• Exact Decay and Tunneling of Interacting Few-Boson Systems, Poster at Center for Quantum Dynamics Poster Session, Heidelberg, Germany.
• Tunneling Dynamics of Open Ultracold Bosonic Systems, Poster at Quantum Science and Technologies, Rovereto, Italy.
• Tunneling Dynamics of Open Ultracold Bosonic Systems, Poster at Finite-Temperature Non-Equilibrium Superfluid Systems, Heidelberg, Germany.
• Recent Developments in the MCTDHB Package, Talk at Annual Colloquium of the HGS, Heidelberg, Germany.
• Tunneling Dynamics of Open Ultracold Bosonic Systems, Talk at Hybrid Quantum Systems, Heidelberg, Germany.

Lipi Thukral
Interdisciplinary Center for Scientific Computing (IWR)
University of Heidelberg

The folding mechanism of beta-hairpins, secondary structural elements in proteins, represents an issue of intense ongoing debate in current protein folding research. Small peptide folding simulations and experiments characterize the dynamics and molecular mechanisms of the early events of folding. Computationally, adequate sampling is required to cover the entire conformational space of the protein of interest. In our present work, we perform replica-exchange molecular dynamics (REMD) simulations of Peptide 1, a 15-residue beta-hairpin peptide.

We simulated ~650 ns each for 32 replica - for a total simulation time of 20.8 μs. The adjoining Figure shows the time evolution of conformational transitions at various temperatures. The map is colored according to R parameter, a conformational order parameter. A value of R ≈ 5 indicates formation of the native β-hairpin and a value ≈ 2-4 indicates an unfolded peptide. The trajectories were started from folded peptide and due to the inherent nature of REMD, the structures in each trajectory unfolds-folds again, providing multiple transitions.

Currently, we are analyzing the data in detail to extract thermodynamic quantities like melting curve, enthalpy, entropy, free energies, etc. The data will also be validated with already published experimental data. The results presented here reveal large-scale protein folding simulations and the work will characterize thermodynamic properties of peptide folding in detail.

Software

• Gromacs

Publications

• Thermodynamic properties of a 15-residue peptide revealed using replica-exchange molecular dynamics simulations. Thukral L, Alekozai E, Smith JC, Daidone I. in preparation.

Prof. Steffen Schumann
II. Physikalisches Institut
Universitaet Goettingen

Monte Carlo event generators are an indispensable tool for the analysis and interpretation of experimental data from high-energy collider experiments, like the Fermilab Tevatron or the CERN LHC. We are concerned with the development of one such generator, called Sherpa.

Sherpa is a general-purpose tool for the simulation of particle collisions at high-energy colliders. It accounts for all aspects of individual scattering events including the hard-process generation, a parton-cascade simulation and phenomenological models for describing the parton-to-hadron transition. As a result Sherpa can be used to generate realistic, i.e. fully exclusive, pseudo-data for example for LHC collision events.
 
Meanwhile Sherpa represents one the standard tools to describe and interprete Tevatron and LHC collision data. It is widely used by the big Fermilab and CERN experimental collaborations as well as for state-of-the-art theoretical and phenomenological studies.

Link

• http://www.sherpa-mc.de/

Software

• C++, Sherpa, Rivet, Root

Publications

• A. Buckley et al., "General-purpose event generators for LHC physics", Phys. Rept. 504 (2011) 145. online
• T. Gleisberg, S. Hoeche, F. Krauss, M. Schonherr, S. Schumann, F. Siegert and J. Winter, "Event generation with SHERPA 1.1", JHEP 0902 (2009) 007. online
• S. Hoeche, F. Krauss, S. Schumann and F. Siegert, "QCD matrix elements and truncated showers", JHEP 0905 (2009) 053. online
• S. Hoeche, S. Schumann and F. Siegert, "Hard photon production and matrix-element parton-shower merging", Phys. Rev. D 81 (2010) 034026. online
• C. Englert, T. Plehn, P. Schichtel and S. Schumann, "Jets plus Missing Energy with an Autofocus", Phys. Rev. D 83 (2011) 095009. online
• S. Schumann, A. Renaud and D. Zerwas, "Hadronically decaying color-adjoint scalars at the LHC", JHEP 1109 (2011) 074. online
• E. Gerwick, T. Plehn and S. Schumann, "Understanding Jet Scaling and Jet Vetos in Higgs Searches", Phys. Rev. Lett. 108 (2012) 032003. online
• C. Englert, T. Plehn, P. Schichtel and S. Schumann, "Establishing Jet Scaling Patterns with a Photon", JHEP 1202 (2012) 030. online

Christoph Englert
IPPP
University Durham

Tilman Plehn
Institut für Theoretische Physik
Universität Heidelberg

Peter Schichtel
Institut für Theoretische Physik
Universität Heidelberg

Steffen Schumann
2. Physikalisches Institut
Universität Göttingen

We study the number of jets in LHC collisions to develop powerful tools in searches for new physics as well as to achieve a better understanding of QCD. In particular we observe two distinct patterns in QCD radiation: Staircase and Poisson scaling. Poisson processes are well understood as independent statistical processes, also known from QED. In contrast to that we can link the occurrence of staircase patterns to the gluon self interaction.

We use an analytical formalism to understand the jet radiation patterns in electron as well as proton colliders. These calculation we like to cross check against Monte Carlo simulations, which we know describe the data well. We are interested in how to translate our findings into the language of commonly used jet algorithms at the LHC.

The photon plus jets channel is one possibility to study the radiation patterns also in experimental data. It provides a clear standard model signature with a high cross section and is thus suitable even for early LHC studies. We identify kinematic regimes, where we expect either staircase or Poisson scaling to occur. The numbers we find translate to Z plus jets an important background to Higgs and new physics searches.

Once we understand the radiation pattern, e.g. the number of jets distribution we use it for physic searches. In Higgs searches the usual Weak Boson Fusion cuts drive the backgrounds into the Poisson regime, while the signal processes stay in the staircase regime. In this way we can understand the jet veto probabilities, which are important in those search strategies. In new physics searches we are interested in heavy colored states, which decay to dark matter candidates. These introduce two interesting new features: additional jets from their decay, as well as a mass scale ink the event. In understanding the jet radiation patterns we are able to get information about the color structure of those particles and we can restrict the uncertainties of other multi-jet observables, which are usually very notorious. The so called effective mass then yields the information about the mass scale. Thus we use these two observables to perform a log-likelihood analysis. As we use only very generic cuts the analysis automatically focuses on the interesting regions in phase space, giving information about the color structure and the mass scale.

Software

• Sherpa, MadGraph, Pythia, HepMC, Fastjet, Root

Publications

• Jets plus Missing Energy with an Autofocus. Christoph Englert, Tilman Plehn, Peter Schichtel, Steffen Schumann. Published in Phys.Rev. D83 (2011) 095009, e-Print: arXiv:1102.4615 [hep-ph]
• Establishing Jet Scaling Patterns with a Photon. Christoph Englert, Tilman Plehn, Peter Schichtel, Steffen Schumann. Published in JHEP 1202 (2012) 030, e-Print: arXiv:1108.5473 [hep-ph]

Uzma Habib
Anorganisch-Chemisches Institut
Universität Heidelberg

Nitrate reductase (Nars), a molybdoenzyme, belongs to the DMSO reductase family. The first W-containing nitrate reductase was isolated from Pyrobaculum aerophilum, a hyperthermophilic denitrifying archeon. It contains W as the metal cofactor but is otherwise identical to Mo-Nar previously purified from Pyrobaculum aerophilum grown at low tungstate concentration.  It demonstrates that the type of the metal cofactor is dependent on the environmental metal concentration. Several studies show that W can replace Mo as the active site metal in E.coli TMAO reductase, the Desulfovibrio alaskensis formate dehydrogenase, and the Rhodobacter capsulatus DMSO reductase. Active site model complexes, derived from the protein X-ray crystal structure of the E.coli NarGH enzyme, are under investigations to find: (i) The Effect on the reduction of nitrate when W replaces the Mo. (ii) The Energy barriers on the potential energy surface. (iii) The reason for the activity loss of Nars in the presence of W.

Software

• Gaussian

Publications

• Poster presentation, "Effect of Molybdenum and Tungsten on the reduction of nitrate in Nitrate Reductase, a DFT study", MOLMOD 2011 "Modeling of Molecular Properties", Heidelberg University, Heidelberg, Germany.

Riccardo Catena
Institut für Theoretische Physik
Universität Heidelberg

The dark matter (DM) direct detection technique has played a major role in the quest for the identification of the DM component of the Universe. The goal is measure the recoil energy due to the scatterings on a target material of the particles forming the Milky Way DM halo. The interpretation of a count rate or an annual modulation effect in a given experiment in terms of properties of DM particles depend on a number of assumptions implemented  in the analysis of the data. Besides issues regarding understanding the target material, such as nuclear form factors or whether channeling occurs, and the performance of the detector,  such as determining the energy threshold, the quenching factors and background rejection/contamination, there are uncertainties related to the DM signal itself. First of all there is an uncertainty in the normalization of the incident DM particle flux, which scales with the local halo density, often quoted to be unknown within a factor of 2 or so. Large uncertainties also affect the energy spectrum of the DM particles in the detector frame, in turn connected to their velocity distribution in the Galactic frame and to the proper motion of the Sun/Earth system. Concerning these, the vast majority of the analyses adopt a standard paradigm in which the velocity distribution is assumed to be Maxwell-Boltzmann  truncated to the value assumed for the escape velocity. The Maxwellian distribution is the configuration maximizing the entropy for a self-gravitating collisionless system and is associated to the spherical isothermal sphere density profile, which declines as r to the −2 at large radii and hence supports a flat rotation curve. It is a well-motivated form but unlikely a fair description of the Milky Way DM halo. In particular cosmological N-body simulations find that DM halos have density profiles falling more rapidly at large radii, as r to the −3, and velocity distributions showing significant departures from the Maxwell-Boltzmann shape.

Our project aims at reducing the present uncertainties in the local DM density and velocity distribution function (the product of which is defined as the DM phase-space density) in order to be able to more clearly interpret the results of a next generation of DM direct detection experiments. In a recent series of works, we presented a new determination of the local dark matter phase-space density. This result has been obtained implementing, in the limit of isotropic velocity distribution and spherical symmetry, Eddington’s inversion formula, which links univocally the DM distribution function to the DM density profile. This analyses required the implementation, within a Bayesian framework, of a Markov Chain Monte Carlo algorithm to sample mass models for the Milky Way against a broad and variegated sample of dynamical constraints. The Figure shows the mean dark matter phase-space density as a function of the detector rest frame velocity. The four curves correspond to our results (three colored lines) obtained for three different choices of DM profile and to the usual Maxwell-Boltzmann approximation (black line) associated with a local circular velocity equal to 220 km/s, local escape velocity equal to 544 km/s and local dark matter density equal to 0.3 GeV per cubic cm.


Software

• MPI, C, MKL

Publications

• R. Catena and P. Ullio; A novel determination of the local dark matter density; JCAP 1008 (2010) 004.
• R. Catena and P. Ullio; The local dark matter phase-space density and impact on WIMP direct detection; arXiv:1111.3556, to be published in JCAP.

Christoph Nagel
Center for Doctoral Studies in Economics (CDSE), Fakultät für VWL, Lehrstuhl für Statistik
Universität Mannheim

Für dieses Projekt wurde ein neues tagesaktuelles nationales Haushaltspanel für Deutschland mit 15000 Teilnehmern mit einer Laufzeit von 2 Jahren verwendet. Die Waschmittelkäufe der Haushalte und ihre exakten Kontakte mit TV Werbung sind enthalten.
Der Datensatz wird zur Schätzung von zwei unterschiedlichen Nachfragemodellen mit vertikaler Differenzierung verwendet. Die Schätzungen sämtlicher RC Mixed Logit Modelle wäre ohne den Einsatz des BW-Grids nicht möglich gewesen. Der Speicher universitätsüblicher Rechner ist nicht ausreichend und die Schätzung einer Spezifikation über Simulated Maximum Likelihood beschäftigt einen modernen PC (Intel Core 2 Duo) bis zu 10 Tage.

Modell 1 Ergebnis: Die Preisendogenitätskorrektur nach Petrin und Train (2006) lässt wichtige Endogenitätsgründe außer Acht. Insgesamt zeigt sich, dass in Modellen nur mit der Preisendogenitätskorrektur die Preiselastizitäten unterschätzt werden, wenn man das Ergebnis mit der Schätzung unter Berücksichtigung aller Endogenitätsgründe vergleicht. Die quantitativ wichtigsten Endogenitätsgründe sind Zustandsabhängigkeit/Gewohnheiten und die Produktdetails.

Die Verwendung eines nationalen Split Samples mit Hausman Instrumenten ist ein erfolgreicher Ersatz für fehlende Großhandelspreis-Instrumente. TV Werbung und Haushaltslager sind neutral in Beug auf die Korrektur. Dieses Ergebnis ist neu in der Literatur, in der TV Werbung als beliebtes Beispiel für Preisendogenität genannt wird. TV Werbung erhöht die Preiselastizität nur geringfügig. Wenn Produktdetails vollständig modelliert sind, sinken die Preiselastizitäten. Zustandsabhängigkeit/Gewohnheiten verstärken Preiselastizitäten.

Modell 2 Ergebnis: Lokale TV Werbung und lokale Einzelhandelsaktivität sind auf Marktebene in einem Logit Market Modell "robust" signifikant und erklären Unterschiede zwischen den geographischen Märkten. "Robust" meint, dass dabei 120 verschiedene Datensetups mit mehreren Modellen ausgewertet wurden, um diese Ergebnisse erzielen. Dabei ist die Anzahl der Werbekontakte, nicht aber der Werbedruck (Kontakte relativ zur zeitgleichen Gesamtkonkurrenz) das beste Werbemaß.
Für 4 Datensetups wird in einem Random Coefficients Market Modell die Werbesignifikanz bestätigt und Evidenz für eine heterogene Reaktion der Teilmärkte auf Werbung gefunden.

Link

• http://madoc.bib.uni-mannheim.de/madoc/volltexte/2011/3052/

Software

• Stata, Matlab

Publications

• Nagel; Demand Models with Price Endogeneity and Advertising; Disseration, Universität Mannheim, 2010; pdf

Georg Duernecker
Fakultät für VWL
Universität Mannheim

We propose a stylised dynamic model to understand the role of social networks in the phenomenon we call 'globalization'. This term refers to the process by which even agents who are geographically far apart come to interact, thus overcoming what would otherwise be a fast saturation of local opportunities. A key feature of our model is that the social network is the main channel through which agents search and exploit new opportunities. Thus only if the social network becomes global (heuristically, reaches far) can global interaction be steadily sustained. To shed light on the conditions under which such a transformation may, or may not, take place is the main objective of the paper. One of our interesting insights is that in order for a local social network to turn global, the economy needs to display a degree of geographical cohesion that is neither too high (for then global opportunities simply do not arise) nor too low (in which case there is too little social structure for the process to take off). And if globalization does arise, we show that it often occurs abruptly and consolidates as a robust state of affairs. We also show how it is affected by improvements in the flow at which information travels in the network, or the range at which the social network helps to monitor behavior.

Link

• http://www.vwl.uni-mannheim.de/duernecker

Software

• Matlab

Publications

• G. Duernecker and F. Vega-Redondo; Social networks and the process of globalization; 2012, submitted pdf