Trimers, molecules and polarons in imbalanced atomic Fermi gases

We consider the ground state of a single "spin-down" impurity atom interacting attractively with a "spin-up" atomic Fermi gas. By constructing variational wave functions for polarons, molecules and trimers, we perform a detailed study of the transitions between each of these dressed bound states as a function of mass ratio $r=m_\uparrow/m_\downarrow$ and interaction strength. We find that the presence of a Fermi sea enhances the stability of the $p$-wave trimer, which can be viewed as a Fulde-Ferrell-Larkin-Ovchinnikov (FFLO) molecule that has bound an additional majority atom. For sufficiently large $r$, we find that the transitions lie outside the region of phase separation in imbalanced Fermi gases and should thus be observable in experiment, unlike the well-studied equal-mass case.Comment: 5 pages, 2 figure

Enlarging and cooling the N\'eel state in an optical lattice

We propose an experimental scheme to favor both the realization and the detection of the N\'eel state in a two-component gas of ultracold fermions in a three-dimensional simple-cubic optical lattice. By adding three compensating Gaussian laser beams to the standard three pairs of retroreflected lattice beams, and adjusting the relative waists and intensities of the beams, one can significantly enhance the size of the N\'eel state in the trap, thus increasing the signal of optical Bragg scattering. Furthermore, the additional beams provide for adjustment of the local chemical potential and the possibility to evaporatively cool the gas while in the lattice. Our proposals are relevant to other attempts to realize many-body quantum phases in optical lattices.Comment: 8 pages, 10 figures (significantly revised text and figures

Phase separation and collapse in Bose-Fermi mixtures with a Feshbach resonance

We consider a mixture of single-component bosonic and fermionic atoms with an interspecies interaction that is varied using a Feshbach resonance. By performing a mean-field analysis of a two-channel model, which describes both narrow and broad Feshbach resonances, we find an unexpectedly rich phase diagram at zero temperature: Bose-condensed and non-Bose-condensed phases form a variety of phase-separated states that are accompanied by both critical and tricritical points. We discuss the implications of our results for the experimentally observed collapse of Bose-Fermi mixtures on the attractive side of the Feshbach resonance, and we make predictions for future experiments on Bose-Fermi mixtures close to a Feshbach resonance.Comment: 7 pages, 3 figures. Extended versio

Maximizing the Neel temperature of fermions in a simple-cubic optical lattice

For a simple-cubic optical lattice with lattice spacing d, occupied by two species of fermionic atoms of mass m that interact repulsively, we ask what conditions maximize the Neel temperature in the Mott insulating phase at density one atom per site, with equal numbers of the two species. This maximum occurs near the edge of the regime where the system is well-approximated by the usual Hubbard model. The correction to the Hubbard-model approximation that produces a "direct" ferromagnetic interaction between atoms in nearest-neighbor Wannier orbitals is the leading term that limits how high the Neel temperature can be made.Comment: 4 pages, 3 figures, minor changes. A new paper, arXiv:0903.0108, expands on this paper and contains most of its result

Trade, Exchange Rate Regimes and Output Co-Movement: Evidence from the Great Depression

A large body of cross-country empirical evidence identifies monetary policy and trade integration as key determinants of business cycle co-movement. Partially consistent with this, many argue that the re-emergence of the gold standard allowed for the global transmission of a deflationary shock in 1929 that culminated in the Great Depression. It is puzzling then to see decreased co-movement between 1920 and 1927 when international integration increased and nations returned to the gold standard. Fixed exchange rates and global trade were also on the rise after 1932, but co-movement declined again. Our empirical results shows that exchange rate regimes and trade were associated with higher co-movement at the bilateral level while common shocks and exchange control policies also mattered. Much of the fall after 1932 was driven by the rise of smaller blocs of monetary and trade cooperation and an inter-bloc fall in co-movement.

Search for weak M1 transitions in 48^{48}Ca with inelastic proton scattering

The spinflip M1 resonance in the doubly magic nucleus $^{48}$Ca, dominated by a single transition, serves as a reference case for the quenching of spin-isospin modes in nuclei. The aim of the present work is a search for weak M1 transitions in $^{48}$Ca with a high-resolution (p,p') experiment at 295 MeV and forward angles including 0 degree and a comparison to results from a similar study using backward-angle electron scattering at low momentum transfers in order to estimate their contribution to the total B(M1) strength. M1 cross sections of individual peaks in the spectra are deduced with a multipole decomposition analysis. The corresponding reduced B(M1) transition strengths are extracted following the approach outlined in J. Birkhan et al., Phys. Rev. C 93, 041302(R) (2016). In total, 29 peaks containing a M1 contribution are found in the excitation energy region 7 - 13 MeV. The resulting B(M1) strength distribution compares well to the electron scattering results considering different factors limiting the sensitivity in both experiments and the enhanced importance of mechanisms breaking the proportionality of nuclear cross sections and electromagnetic matrix elements for weak transitions as studied here. The total strength of 1.19(6) $\mu_N^2$ deduced assuming a non-quenched isoscalar part of the (p,p') cross sections agrees with the (e,e') result of 1.21(13) $\mu_N^2$. A binwise analysis above 10 MeV provides an upper limit of 1.62(23) $\mu_N^2$. The present results confirm that weak transitions contribute about 25% to the total B(M1) strength in $^{48}$Ca and the quenching factors of GT and spin-M1 strength are comparable in fp-shell nuclei. Thus, the role of of meson exchange currents seems to be neglible, in contrast to sd-shell nuclei.Comment: 11 pages, 9 figures, revised analysis with oxygen contamination remove

Defect mediated melting and the breaking of quantum double symmetries

In this paper, we apply the method of breaking quantum double symmetries to some cases of defect mediated melting. The formalism allows for a systematic classification of possible defect condensates and the subsequent confinement and/or liberation of other degrees of freedom. We also show that the breaking of a double symmetry may well involve a (partial) restoration of an original symmetry. A detailed analysis of a number of simple but representative examples is given, where we focus on systems with global internal and external (space) symmetries. We start by rephrasing some of the well known cases involving an Abelian defect condensate, such as the Kosterlitz-Thouless transition and one-dimensional melting, in our language. Then we proceed to the non-Abelian case of a hexagonal crystal, where the hexatic phase is realized if translational defects condense in a particular rotationally invariant state. Other conceivable phases are also described in our framework.Comment: 10 pages, 4 figures, updated reference

Galactosylsphingamides : new α-GalCer analogues to probe the F’-pocket of CD1d

Invariant Natural Killer T-cells (iNKT-cells) are an attractive target for immune response modulation, as upon CD1d-mediated stimulation with KRN7000, a synthetic alpha-galactosylceramide, they produce a vast amount of cytokines. Here we present a synthesis that allows swift modification of the phytosphingosine side chain by amidation of an advanced methyl ester precursor. The resulting KRN7000 derivatives, termed alpha-galactosylsphingamides, were evaluated for their capacity to stimulate iNKT-cells. While introduction of the amide-motif in the phytosphingosine chain is tolerated for CD1d binding and TCR recognition, the studied alpha-galactosylsphingamides showed compromised antigenic properties

Protective activity of propofol, Diprivan and intralipid against active oxygen species.

We separately studied the antioxidant properties of propofol (PPF), Diprivan (the commercial form of PPF) and intralipid (IL) (the vehicle solution of PPF in Diprivan) on active oxygen species produced by phorbol myristate acetate (10(-6) M)-stimulated human polymorphonuclear leukocytes (PMN: 5 x 10(5) cells/assay), human endothelial cells (5 x 10(5) cells/assay) or cell-free systems (NaOCl or H2O2/peroxidase systems), using luminol (10(-4) M)-enhanced chemiluminescence (CL). We also studied the protective effects of Diprivan on endothelial cells submitted to an oxidant stress induced by H2O2/MPO system: cytotoxicity was assessed by the release of preincorporated 51Cr. Propofol inhibited the CL produced by stimulated PMN in a dose dependent manner (until 5 x 10(-5) M, a clinically relevant concentration), while Diprivan and IL were not dose-dependent inhibitors. The CL produced by endothelial cells was dose-dependently inhibited by Diprivan and PPF, and weakly by IL (not dose-dependent). In cell free systems, dose-dependent inhibitions were obtained for the three products with a lower effect for IL. Diprivan efficaciously protected endothelial cells submitted to an oxidant stress, while IL was ineffective. By HPLC, we demonstrated that PPF was not incorporated into the cells. The drug thus acted by scavenging the active oxygen species released in the extracellular medium. IL acted in the same manner, but was a less powerful antioxidant