OPUS 4 | Universitätspublikationen

Spontaneous Symmetry Breaking and Nambu–Goldstone Bosons in Quantum Many-Body Systems (2010)

Tomáš Brauner

Spontaneous symmetry breaking is a general principle that constitutes the underlying concept of a vast number of physical phenomena ranging from ferromagnetism and superconductivity in condensed matter physics to the Higgs mechanism in the standard model of elementary particles. I focus on manifestations of spontaneously broken symmetries in systems that are not Lorentz invariant, which include both nonrelativistic systems as well as relativistic systems at nonzero density, providing a self-contained review of the properties of spontaneously broken symmetries specific to such theories. Topics covered include: (i) Introduction to the mathematics of spontaneous symmetry breaking and the Goldstone theorem. (ii) Minimization of Higgs-type potentials for higher-dimensional representations. (iii) Counting rules for Nambu–Goldstone bosons and their dispersion relations. (iv) Construction of effective Lagrangians. Specific examples in both relativistic and nonrelativistic physics are worked out in detail.

A demonstrator for the Micro-Vertex-Detector of the CBM experiment (2010)

Christoph Schrader Samir Amar-Youcef Norbert Bialas Michael Deveaux Ingo Fröhlich Christian Müntz Selim Seddiki Tobias Tischler Joachim Stroth

CMOS sensors are the most promising candidates for the Micro-Vertex-Detector (MVD) of the CBM experiment at GSI, as they provide an unprecedented compromise between spatial resolution, low material budget, adequate radiation tolerance and readout speed. To study the integration of these sensors into a detector module, a so-called MVD-demonstrator has been developed. The demonstrator and its in-beam performance will be presented and discussed in this work.

A versatile method for simulating pp -> ppe+e- and dp -> pne+e-p_spec reactions (2010)

Frank Dohrmann Ingo Fröhlich Tetyana Galatyuk Romain Holzmann Philipp K. Kählitz Burkhard Kämpfer Emilie Moriniere Yvonne C. Pachmayer Beatrice Ramstein Piotr Salabura Joachim Stroth Radoslaw Trebacz Jacques Van de Wiele

We have developed a versatile software package for the simulation of di-electron production in pp and dp collisions at moderate beam kinetic energies (1-2GeV). Particular attention has been paid to incorporate different descriptions of the Dalitz decay Δ rightarrow Ne + e - via a common interface. In addition, suitable parameterizations for the virtual bremsstrahlung process NN rightarrow NNe + e - based on one-boson exchange models have been implemented. Such simulation tools with high flexibility of the framework are important for the interpretation of the di-electron data taken with the HADES spectrometer and demonstrates the wide applicability within the field of nuclear and hadronic physics.

Status of the Micro Vertex Detector of the Compressed Baryonic Matter Experiment (2010)

Michael Deveaux Samir Amar-Youcef Norbert Bialas Dennis Doering Melissa Domachowski Horst Düring Ingo Fröhlich Tetyana Galatyuk Jan Michael Christian Müntz Sarah Ottersbach Paul Scharrer Christoph Schrader Joachim Stroth Tobias Tischler Christian Trageser Bernhard Wiedemann Jérome Baudot Grégory Bertolone Nathalie Chon-Sen Claude Colledani Rita De Masi Andrei Dorokhov Wojchiech Dulinski Jean-Charles Fontaine Mathieu Goffe Abdelkader Himmi Christine Hu Kimmo Jaaskelainen Michal Koziel Frédéric Morel Fouad Rami Mathieu Specht Isabelle Valin Marc Winter Christina Dritsa Selim Seddiki Franz M. Wagner

The CBM experiment will investigate heavy-ion collisions at beam energies from 8 to 45 AGeV at the future accelerator facility FAIR. The goal of the experiment is to study the QCD phase diagram in the vincinity of the QCD critical point. To do so, CBM aims at measuring rare probes among them open charm. In order to identify those rare and short lived particles despite the rich combinatorial background generated in heavy ion collisions, a micro vertex detector (MVD) providing an unprecedented combination of high rate capability and radiation hardness, very light material budget and excellent granularity is required. In this work, we will discuss the concept of this detector and summarize the status of the R&D.

Analysis of a hybrid TATA box binding protein originating from mesophilic and thermophilic donor organisms (2010)

Annette Kopitz Jörg Soppa Karin Hauser

The TATA Box Binding Protein (TBP) is a 20 kD protein that is essential and universally conserved in eucarya and archaea. Especially among archaea, organisms can be found that live below 0°C as well as organisms that grow above 100°C. The archaeal TBPs show a high sequence identity and a similar structure consisting of α-helices and β-sheets that are arranged in a saddle-shape 2-symmetric fold. In previous studies, we have characterized the thermal stability of thermophilic and mesophilic archaeal TBPs by infrared spectroscopy and showed the correlation between the transition temperature (Tm) and the optimal growth temperature (OGT) of the respective donor organism. In this study, a “new” mutant TBP has been constructed, produced, purified and analyzed for a deeper understanding of the molecular mechanisms of thermoadaptation. The β-sheet part of the mutant consists of the TBP from Methanothermobacter thermoautotrophicus (OGT 65°C, MtTBP65) whose α-helices have been exchanged by those of Methanosarcina mazei (OGT 37°C, MmTBP37). The Hybrid-TBP irreversibly aggregates after thermal unfolding just like MmTBP37 and MtTBP65, but the Tm lies between that of MmTBP37 and MtTBP65 indicating that the interaction between the α-helical and β-sheet part of the TBP is crucial for the thermal stability. The temperature stability is probably encoded in the variable α-helices that interact with the highly conserved and DNA binding β-sheets.

The QCD phase diagram at low baryon density from lattice simulations (2010)

Owe Philipsen

The QCD phase diagram as a function of temperature, T, and chemical potential for baryon number, mB, is still unknown today, due to the sign problem, which prohibits direct Monte Carlo simulations for non-vanishing baryon density. Investigations in models sharing chiral symmetry with QCD predict a phase diagram, in which the transition corresponds to a smooth crossover at zero density, but which is strengthened by chemical potential to turn into a first order transition beyond some second order critical point. This contribution reviews the lattice evidence in favour and against the existence of a critical point.

Constraints for the QCD phase diagram from imaginary chemical potential (2010)

Owe Philipsen Philippe de Forcrand

We present unambiguous evidence from lattice simulations of Nf = 3 QCD for two tricritical points in the (T;m) phase diagram at fixed imaginary m=T = ip=3 mod. 2p=3, one in the light and one in the heavy quark regime. Together with similar results in the literature for Nf = 2 this implies the existence of a chiral and of a deconfinement tricritical line at those values of imaginary chemical potentials. These tricritical lines represent the boundaries of the analytically continued chiral and deconfinement critical surfaces, respectively, which delimit the parameter space with first order phase transitions. It is demonstrated that the shape of the deconfinement critical surface is dictated by tricritical scaling and implies the weakening of the deconfinement transition with real chemical potential. A qualitatively similar effect holds for the chiral critical surface.

Thermal transition temperature from twisted mass QCD (2010)

Florian Burger Malik Kirchner Michael Müller-Preussker Ernst-Michael Ilgenfritz Maria Paola Lombardo Owe Philipsen Lars Zeidlewicz Carsten Urbach

We present the current status of lattice simulations with Nf = 2 maximally twisted mass Wilson fermions at finite temperature. In particular, the determination of the thermal transition tempera- ture is discussed.

Towards the Nf = 2 deconfinement transition temperature with O(a) improved Wilson fermions (2010)

Bastian B. Brandt Hartmut Wittig Owe Philipsen Lars Zeidlewicz

A lot of effort in lattice simulations over the last years has been devoted to studies of the QCD deconfinement transition. Most state-of-the-art simulations use rooted staggered fermions, while Wilson fermions are affected by large systematic uncertainties, such as coarse lattices or heavy sea quarks. Here we report on an ongoing study of the transition, using two degenerate flavours of nonperturbatively O(a) improved Wilson fermions. We start with Nt = 12 and 16 lattices and pion masses of 600 to 450 MeV, aiming at chiral and continuum limits with light quarks.

The spectrum of static-light baryons in twisted mass lattice QCD (2010)

Marc Wagner Christian Wiese

We compute the static-light baryon spectrum with Nf = 2 flavors of sea quarks using Wilson twisted mass lattice QCD. As light valence quarks we consider quarks, which have the same mass as the sea quarks with corresponding pion masses in the range 340MeV<∼ mPS<∼ 525MeV, as well as partially quenched quarks, which have the mass of the physical s quark. We extract masses of states with isospin I = 0,1/2,1, with strangeness S = 0,−1,−2, with angular momentum of the light degrees of freedom j = 0,1 and with parity P = +,−. We present a preliminary extrapolation in the light u/d and an interpolation in the heavy b quark mass to the physical point and compare with available experimental results.

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