Towards finite density QCD with Taylor expansions

Convergence properties of Taylor expansions of observables, which are also used in lattice QCD calculations at non-zero chemical potential, are analyzed in an effective N_f = 2+1 flavor Polyakov-quark-meson model. A recently developed algorithmic technique allows the calculation of higher-order Taylor expansion coefficients in functional approaches. This novel technique is for the first time applied to an effective N_f = 2+1 flavor Polyakov-quark-meson model and the findings are compared with the full model solution at finite densities. The results are used to discuss prospects for locating the QCD phase boundary and a possible critical endpoint in the phase diagram.Comment: 11 pages, 6 figures; minor clarifying changes, version to be published in Phys. Lett.

Spontaneous parity and charge-conjugation violations at real isospin and imaginary baryon chemical potentials

The phase structure of two-flavor QCD is investigated at real isospin and imaginary quark chemical potentials by using the Polyakov-loop extended Nambu--Jona-Lasinio model. In the region, parity symmetry is spontaneously broken by the pion superfluidity phase transition, whereas charge-conjugation symmetry is spontaneously violated by the Roberge-Weiss transition. The chiral (deconfinement) crossover at zero isospin and quark chemical potentials is a remnant of the parity (charge-conjugation) violation. The interplay between the parity and charge-conjugation violations are analyzed, and it is investigated how the interplay is related to the correlation between the chiral and deconfinement crossovers at zero isospin and quark chemical potentials.Comment: 12 pages, 18 figures. Typos were revised. Symbols /P and /C were added in Figures 8a and 8b. Colors of the figures were changed. Some sentences were added and revise

Thermodynamics of the PNJL model

QCD thermodynamics is investigated by means of the Polyakov-loop-extended Nambu Jona-Lasinio (PNJL) model, in which quarks couple simultaneously to the chiral condensate and to a background temporal gauge field representing Polyakov loop dynamics. The behaviour of the Polyakov loop as a function of temperature is obtained by minimizing the thermodynamic potential of the system. A Taylor series expansion of the pressure is performed. Pressure difference and quark number density are then evaluated up to sixth order in quark chemical potential, and compared to the corresponding lattice data. The validity of the Taylor expansion is discussed within our model, through a comparison between the full results and the truncated ones.Comment: 6 pages, 5 figures, Talk given at the Workshop for Young Scientists on the Physics of Ultrarelativistic Nucleus-Nucleus Collisions (Hot Quarks 2006), Villasimius, Italy, 15-20 May 200

A Highly Drift-stable Atomic Magnetometer for Fundamental Physics Experiments

We report the design and performance of a non-magnetic drift stable optically pumped cesium magnetometer with a measured sensitivity of 35 fT at 200 s integration time and stability below 50 fT between 70 s and 600 s. To our knowledge this is the most stable magnetic field measurement to date. The sensor is based on the nonlinear magneto-optical rotation effect: in a Bell-Bloom configuration a higher order polarization moment (alignment) of Cs atoms is created with a pump laser beam in an anti-relaxation coated Pyrex cell under vacuum, filled with Cs vapor at room temperature. The polarization plane of light passing through the cell is modulated due the precession of the atoms in an external magnetic field of 2.1 muT, used to optically determine the Larmor precession frequency. Operation is based on a sequence of optical pumping and observation of freely precessing spins at a repetition rate of 8 Hz. This free precession decay readout scheme separates optical pumping and probing and thus ensures a systematically highly clean measurement. Due to the residual offset of the sensor of < 15 pT together with the cross-talk free operation of adjacent sensors, this device is uniquely suitable for a variety of experiments in low-energy particle physics with extreme precision, here as highly stable and systematically clean reference probe in search for time-reversal symmetry violating electric dipole moments.Comment: Submitted in AIP Applied Physics Lette