Fachspezifischer Anhang zur SPoL (Teil III): Studienfach Physik im Studiengang L3
Fachspezifischer Anhang zur SPoL (Teil III): Studienfach Physik in den Studiengängen L2 und L5
Ordnung für den Bachelor- und den Masterstudiengang Physik der Johann Wolfgang Goethe-Universität vom 26.02.2008 : genehmigt durch Beschluss des Präsidiums der Johann Wolfgang Goethe-Universität vom 25.03.2008
The finite-temperature phase structure of lattice QCD with twisted-mass Wilson fermions
Maria Paola Lombardo
- We report progress in our exploration of the finite-temperature phase structure of two-flavour lattice
QCD with twisted-mass Wilson fermions and a tree-level Symanzik-improved gauge action
for a temporal lattice size Nt = 8. Extending our investigations to a wider region of parameter
space we gain a global view of the rich phase structure. We identify the finite temperature transition/
crossover for a non-vanishing twisted-mass parameter in the neighbourhood of the zerotemperature
critical line at sufficiently high b . Our findings are consistent with Creutz’s conjecture
of a conical shape of the finite temperature transition surface. Comparing with NLO lattice
cPT we achieve an improved understanding of this shape.
The adjoint potential in the pseudoparticle approach: string breaking and Casimir scaling
- We perform a detailed study of the adjoint static potential in the pseudoparticle approach, which
is a model for SU(2) Yang-Mills theory. We find agreement with the Casimir scaling hypothesis
and there is clear evidence for string breaking. At the same time the potential in the fundamental
representation is linear for large separations. Our results are in qualitative agreement with results
from lattice computations.
Status of ETMC simulations with Nf = 2+1+1 twisted mass fermions
Enno E. Scholz
- We present the status of runs performed in the twisted mass formalism with Nf =2+1+1 flavours
of dynamical fermions: a degenerate light doublet and a mass split heavy doublet. The procedure
for tuning to maximal twist will be described as well as the current status of the runs using both
thin and stout links. Preliminary results for a few observables obtained on ensembles at maximal
twist will be given. Finally, a reweighting procedure to tune to maximal twist will be described.
Static-light meson masses from twisted mass lattice QCD
- We compute the static-light meson spectrum using two-flavor Wilson twisted mass lattice
QCD. We have considered five different values for the light quark mass corresponding to
300MeV<~ mPS<~ 600MeV. We have extrapolated our results, to make predictions regarding the
spectrum of B and Bs mesons.
Probing the composition of sub-millisecond rotating compact stars by r-modes instability
- We investigate the implications of the r-modes instability on the composition of a compact star
rotating at a sub-millisecond period. In particular, the only viable astrophysical scenario for
such an object, wich might present inside the Low Mass X-ray Binary associated with the x-ray
transient XTE J1739-285, is that it has a strangeness content. Since previous analysis indicate that
hyperonic stars or stars containing a kaon condensate are unlikely because of the mass-shedding
constraint, the only remaining possibility is that such an object is either a strange quark star or a
hybrid quark-hadron star.
Astrophysical Implications of the QCD phase transition
- The possible role of a first order QCD phase transition at nonvanishing quark chemical potential
and temperature for cold neutron stars and for supernovae is delineated. For cold neutron stars,
we use the NJL model with nonvanishing color superconducting pairing gaps, which describes
the phase transition to the 2SC and the CFL quark matter phases at high baryon densities. We
demonstrate that these two phase transitions can both be present in the core of neutron stars and
that they lead to the appearance of a third family of solution for compact stars. In particular, a core
of CFL quark matter can be present in stable compact star configurations when slightly adjusting
the vacuum pressure to the onset of the chiral phase transition from the hadronicmodel to the NJL
model. We show that a strong first order phase transition can have strong impact on the dynamics
of core collapse supernovae. If the QCD phase transition sets in shortly after the first bounce, a
second outgoing shock wave can be generated which leads to an explosion. The presence of the
QCD phase transition can be read off from the neutrino and antineutrino signal of the supernova.
Impact of an electric field on P-type ATPases
- P-type ATPases are membrane proteins acting as ion pumps that drive an active transport of cations across the membrane against a concentration gradient. The required energy for the ion transport is provided by binding and hydrolysis of ATP. A reaction mechanism of ion transport and energy transduction is assumed to be common for all P-type ATPases and generally described by the Post-Albers cycle. Transient currents and charge translocation of P-type ATPases were extensively investigated by electrical measurements that apply voltage jumps to initiate the reaction cycle. In this study, we simulate an applied voltage across the membrane by an electric field and perform electrostatic calculations in order to verify the experimentally-driven hypothesis that the energy transduction mechanism is regulated by specific structural elements. Side chain conformational and ionization changes induced by the electric field are evaluated for each transmembrane helix and the selectivity in response is qualitatively analyzed for the Ca2+-ATPase as well as for structural models of the Na+/K+-ATPase. Helix M5 responds with more conformer changes as compared to the other transmembrane helices what is even more emphasized when the stalk region is included. Thus our simulations support experimental results and indicate a crucial role for the highly conserved transmembrane helix M5 in the energy transduction mechanism of P-type ATPases.