Coexistence of Pairing Tendencies and Ferromagnetism in a Doped Two-Orbital Hubbard Model on Two-Leg Ladders

Using the Density Matrix Renormalization Group and two-leg ladders, we investigate an electronic two-orbital Hubbard model including plaquette diagonal hopping amplitudes. Our goal is to search for regimes where charges added to the undoped state form pairs, presumably a precursor of a superconducting state.For the electronic density $\rho=2$, i.e. the undoped limit, our investigations show a robust $(\pi,0)$ antiferromagnetic ground state, as in previous investigations. Doping away from $\rho=2$ and for large values of the Hund coupling $J$, a ferromagnetic region is found to be stable. Moreover, when the interorbital on-site Hubbard repulsion is smaller than the Hund coupling, i.e. for $U'<J$ in the standard notation of multiorbital Hubbard models, our results indicate the coexistence of pairing tendencies and ferromagnetism close to $\rho=2$. These results are compatible with previous investigations using one dimensional systems. Although further research is needed to clarify if the range of couplings used here is of relevance for real materials, such as superconducting heavy fermions or pnictides, our theoretical results address a possible mechanism for pairing that may be active in the presence of short-range ferromagnetic fluctuations.Comment: 8 pages, 4 Fig

Chaotic motion of charged particles in toroidal magnetic configurations

We study the motion of a charged particle in a tokamak magnetic field and discuss its chaotic nature. Contrary to most of recent studies, we do not make any assumption on any constant of the motion and solve numerically the cyclotron gyration using Hamiltonian formalism. We take advantage of a symplectic integrator allowing us to make long-time simulations. First considering an idealized magnetic configuration, we add a non generic perturbation corresponding to a magnetic ripple, breaking one of the invariant of the motion. Chaotic motion is then observed and opens questions about the link between chaos of magnetic field lines and chaos of particle trajectories. Second, we return to a axi-symmetric configuration and tune the safety factor (magnetic configuration) in order to recover chaotic motion. In this last setting with two constants of the motion, the presence of chaos implies that no third global constant exists, we highlight this fact by looking at variations of the first order of the magnetic moment in this chaotic setting. We are facing a mixed phase space with both regular and chaotic regions and point out the difficulties in performing a global reduction such as gyrokinetics

Vortex distribution in the Lowest Landau Level

We study the vortex distribution of the wave functions minimizing the Gross Pitaevskii energy for a fast rotating condensate in the Lowest Landau Level (LLL): we prove that the minimizer cannot have a finite number of zeroes thus the lattice is infinite, but not uniform. This uses the explicit expression of the projector onto the LLL. We also show that any slow varying envelope function can be approximated in the LLL by distorting the lattice. This is used in particular to approximate the inverted parabola and understand the role of ``invisible'' vortices: the distortion of the lattice is very small in the Thomas Fermi region but quite large outside, where the "invisible" vortices lie.Comment: 4 pages, 1 figur

Birationality of \'etale morphisms via surgery

We use a counting argument and surgery theory to show that if $D$ is a sufficiently general algebraic hypersurface in $\Bbb C^n$, then any local diffeomorphism $F:X \to \Bbb C^n$ of simply connected manifolds which is a $d$-sheeted cover away from $D$ has degree $d=1$ or $d=\infty$ (however all degrees $d > 1$ are possible if $F$ fails to be a local diffeomorphism at even a single point). In particular, any \'etale morphism $F:X \to \Bbb C^n$ of algebraic varieties which covers away from such a hypersurface $D$ must be birational.Comment: 17 pages. Replaced to add further references and make language more consistent with the literatur

Coquetel biológico (EM) no crescimento de mudas de Ocimum basilicum L.

O estudo objetivou avaliar os efeitos de diferentes dosagens de EM (Microorganismos Eficazes) na germinação, emergência, crescimento e qualidade de mudas de manjericão Ocimum basilicum L. As plantas foram cultivadas em bandejas com capacidade para 576 tubetes, em um viveiro localizado no Assentamento Taquaral, Corumbá, MS. O delineamento utilizado foi inteiramente casualizado com quatro tratamentos e cinco repetições. Os tratamentos consistiram em uma base formada por areia, vermicomposto e terra. Essa base recebeu doses crescentes de EM (que é uma combinação de vários microorganismos benéficos, tanto aeróbicos quanto anaeróbicos, que cumprem diferentes funções), que foram preparadas em solução aquosa misturadas ao substrato na proporção 10 ml (0,1%), 30 ml (0,3%) e 60 ml (0,6%). O tratamento a 0,3% (30 ml) apresentou melhor resultado na emergência e no crescimento do manjericão. The study aimed to evaluate the effects of different concentrations doses of EM (Effective Microorganisms) on growth of basil, Ocimum basilicum L. We grow plants in trays with capacity of 576 tubes, in a greenhouse located in Taquaral, Corumbá, Mato Grosso do Sul State. The experimental design was completely randomized, with four treatments, and five repetitions. The substrate was a combination of sand, humus and soil. The treatments consisted of increasing doses of EM in the substrate, which is a combination of several beneficial microorganisms, both aerobic and anaerobic, fulfilling different functions. We prepared in aqueous solution mixed with substrate in proportions 10 ml (0.1%), 30 ml (0.3%) and 60 ml (0.6%). Treatment of 0.3% showed better results in the emergence and growth of basil.Também em: SEMINÁRIO DE AGROECOLOGIA DE MATO GROSSO DO SUL, 4.; ENCONTRO DE PRODUTORES AGROECOLÓGICOS DE MS, 3., 2012, Glória de Dourados. O saber tradicional e o científico: a interação encurtando caminhos para o desenvolvimento sustentável: anais. Brasília, DF: Embrapa, 2012. 1 CD-ROM. Editado por: Leandro Fávio Carneiro, Milton Parron Padovan

Detection of gravitational waves from the QCD phase transition with pulsar timing arrays

If the cosmological QCD phase transition is strongly first order and lasts sufficiently long, it generates a background of gravitational waves which may be detected via pulsar timing experiments. We estimate the amplitude and the spectral shape of such a background and we discuss its detectability prospects.Comment: 7 pages, 5 figs. Version accepted by PR