Renyi Entropy and Parity Oscillations of the Anisotropic Spin-s Heisenberg Chains in a Magnetic Field

Using the density matrix renormalization group, we investigate the Renyi entropy of the anisotropic spin-s Heisenberg chains in a z-magnetic field. We considered the half-odd integer spin-s chains, with s=1/2,3/2 and 5/2, and periodic and open boundary conditions. In the case of the spin-1/2 chain we were able to obtain accurate estimates of the new parity exponents $p_{\alpha}^{(p)}$ and $p_{\alpha}^{(o)}$ that gives the power-law decay of the oscillations of the $\alpha-$Renyi entropy for periodic and open boundary conditions, respectively. We confirm the relations of these exponents with the Luttinger parameter $K$, as proposed by Calabrese et al. [Phys. Rev. Lett. 104, 095701 (2010)]. Moreover, the predicted periodicity of the oscillating term was also observed for some non-zero values of the magnetization $m$. We show that for $s>1/2$ the amplitudes of the oscillations are quite small, and get accurate estimates of $p_{\alpha}^{(p)}$ and $p_{\alpha}^{(o)}$ become a challenge. Although our estimates of the new universal exponents $p_{\alpha}^{(p)}$ and $p_{\alpha}^{(o)}$ for the spin-3/2 chain are not so accurate, they are consistent with the theoretical predictions.Comment: revised version, accepted to PRB. 9 pages, 3 Figures, 4 Table

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

Avaliação de regimes de temperatura no desenvolvimento da ferrugem-asiática da soja.

Com o objetivo de avaliar o impacto de cinco regimes de temperatura (28oC/ 20oC, 30oC/ 22oC, 32oC/ 24oC, 34oC/ 26oC e 36oC/ 28oC) no desenvolvimento da ferrugem-asiática da soja foram realizados ensaios em condições controladas. Plantas da cultivar CD 219 RR com a quarta folha expandida foram inoculadas com esporos do fungo Phakopsora pachyrhizi e mantidas nos diferentes regimes de temperatura. A severidade da ferrugem foi avaliada aos 16 dias após a inoculação. O regime de temperatura mais favorável para o desenvolvimento da ferrugem foi 28oC/ 20oC (média 24oC). A doença não se desenvolveu nos regimes de temperatura de 34oC/ 26oC e 36oC/ 28oC, com médias 30oC e 32oC, respectivamente

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

Dispersive fields in de Sitter space and event horizon thermodynamics

When Lorentz invariance is violated at high energy, the laws of black hole thermodynamics are apparently no longer satisfied. To shed light on this observation, we study dispersive fields in de Sitter space. We show that the Bunch-Davies vacuum state restricted to the static patch is no longer thermal, and that the Tolman law is violated. However we also show that, for free fields at least, this vacuum is the only stationary stable state, as if it were in equilibrium. We then present a precise correspondence between dispersive effects found in de Sitter and in black hole metrics. This indicates that the consequences of dispersion on thermodynamical laws could also be similar.Comment: 19 pages. Black and White version on Phys.Rev.D serve