Spontaneous Symmetry Breaking and Nambu–Goldstone Bosons in Quantum Many-Body Systems
- 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
- 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
Philipp K. Kählitz
Yvonne C. Pachmayer
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
Rita De Masi
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
- 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
- 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
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
Maria Paola Lombardo
- 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
Bastian B. Brandt
- 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
- 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.