Neutron star properties in the Thomas-Fermi model

The modern nucleon-nucleon interaction of Myers and Swiatecki, adjusted to the properties of finite nuclei, the parameters of the mass formula, and the behavior of the optical potential is used to calculate the properties of $\beta$--equilibrated neutron star matter, and to study the impact of this equation of state on the properties of (rapidly rotating) neutron stars and their cooling behavior. The results are in excellent agreement with the outcome of calculations performed for a broad collection of sophisticated nonrelativistic as well as relativistic models for the equation of state.Comment: 23 pages, LaTeX, 15 ps-figure

On the minimum and maximum mass of neutron stars and the delayed collapse

The minimum and maximum mass of protoneutron stars and neutron stars are investigated. The hot dense matter is described by relativistic (including hyperons) and non-relativistic equations of state. We show that the minimum mass ($\sim$ 0.88 - 1.28 M_{\sun}) of a neutron star is determined by the earliest stage of its evolution and is nearly unaffected by the presence of hyperons. The maximum mass of a neutron star is limited by the protoneutron star or hot neutron star stage. Further we find that the delayed collapse of a neutron star into a black hole during deleptonization is not only possible for equations of state with softening components, as for instance, hyperons, meson condensates etc., but also for neutron stars with a pure nucleonic-leptonic equation of state.Comment: 6 pages, 4 figures, using EDP Siences Latex A&A style, to be published in A&

Macroscopic Anisotropy and Symmetry Breaking in the Pyrochlore Antiferromagnet Gd2_{2}Ti2_{2}O7_{7}}

In the Heisenberg antiferromagnet $Gd_2Ti_2O_7$, the exchange interactions are geometrically frustrated by the pyrochlore lattice structure. This ESR study reveals a strong temperature dependent anisotropy with respect to a [111] body diagonal below a temperature $T_A=80$ K, despite the spin only nature of the $Gd^{3+}$ ion. Anisotropy and symmetry breaking can nevertheless appear through the superexchange interaction. The presence of short range planar correlation restricted to specific Kagom\'{e} planes is sufficient to explain the two ESR modes studied in this work.Comment: 4 pages, 5 figure

Observing the emergence of chaos in a many-particle quantum system

Accessing the connection between classical chaos and quantum many-body systems has been a long-standing experimental challenge. Here, we investigate the onset of chaos in periodically driven two-component Bose-Einstein condensates, whose small quantum uncertainties allow for exploring the phase space with high resolution. By analyzing the uncertainties of time-evolved many-body states, we find signatures of elliptic and hyperbolic periodic orbits generated according to the Poincar\'e-Birkhoff theorem, and the formation of a chaotic region at increasing driving strengths. The employed fluctuation analysis allows for probing the phase-space structure by use of only short-time quantum dynamics.Comment: 5+2 pages, 4 figure