Evolution from BCS to BKT superfluidity in one-dimensional optical lattices

We analyze the finite temperature phase diagram of fermion mixtures in one-dimensional optical lattices as a function of interaction strength. At low temperatures, the system evolves from an anisotropic three-dimensional Bardeen-Cooper-Schrieffer (BCS) superfluid to an effectively two-dimensional Berezinskii-Kosterlitz-Thouless (BKT) superfluid as the interaction strength increases. We calculate the critical temperature as a function of interaction strength, and identify the region where the dimensional crossover occurs for a specified optical lattice potential. Finally, we show that the dominant vortex excitations near the critical temperature evolve from multiplane elliptical vortex loops in the three-dimensional regime to planar vortex-antivortex pairs in the two-dimensional regime, and we propose a detection scheme for these excitations.Comment: 4 pages with 2 figure

Phase Fluctuations and Vortex Lattice Melting in Triplet Quasi-One-Dimensional Superconductors at High Magnetic Fields

Assuming that the order parameter corresponds to an equal spin triplet pairing symmetry state, we calculate the effect of phase fluctuations in quasi-one-dimensional superconductors at high magnetic fields applied along the y (b') axis. We show that phase fluctuations can destroy the theoretically predicted triplet reentrant superconducting state, and that they are responsible for melting the magnetic field induced Josephson vortex lattice above a magnetic field dependent melting temperature Tm.Comment: 4 pages (double column), 1 eps figur

Thermodynamically stable noncomposite vortices in mesoscopic two-gap superconductors

In mesoscopic two-gap superconductors with sizes of the order of the coherence length noncomposite vortices are found to be thermodynamically stable in a large domain of the $T - H$ phase diagram. In these phases the vortex cores of one condensate are spatially separated from the other condensate ones, and their respective distributions can adopt distinct symmetries. The appearance of these vortex phases is caused by a non-negligible effect of the boundary of the sample on the superconducting order parameter and represents therefore a genuine mesoscopic effect. For low values of interband Josephson coupling vortex patterns with $L_1 \neq L_2$ can arise in addition to the phases with $L_1 =L_2$, where $L_1$ and $L_2$ are total vorticities in the two condensates. The calculations show that noncomposite vortices could be observed in thin mesoscopic samples of MgB$_{2}$.Comment: 5 pages, 3 figures, to be published in Europhysics Letter

Nonzero orbital angular momentum superfluidity in ultracold Fermi gases

We analyze the evolution of superfluidity for nonzero orbital angular momentum channels from the Bardeen-Cooper-Schrieffer (BCS) to the Bose-Einstein condensation (BEC) limit in three dimensions. First, we analyze the low energy scattering properties of finite range interactions for all possible angular momentum channels. Second, we discuss ground state ($T = 0$) superfluid properties including the order parameter, chemical potential, quasiparticle excitation spectrum, momentum distribution, atomic compressibility, ground state energy and low energy collective excitations. We show that a quantum phase transition occurs for nonzero angular momentum pairing, unlike the s-wave case where the BCS to BEC evolution is just a crossover. Third, we present a gaussian fluctuation theory near the critical temperature ($T = T_{\rm c}$), and we analyze the number of bound, scattering and unbound fermions as well as the chemical potential. Finally, we derive the time-dependent Ginzburg-Landau functional near $T_{\rm c}$, and compare the Ginzburg-Landau coherence length with the zero temperature average Cooper pair size.Comment: 28 pages and 24 figure

Radiative accretion shocks along nonuniform stellar magnetic fields in classical T Tauri stars

(abridged) AIMS. We investigate the dynamics and stability of post-shock plasma streaming along nonuniform stellar magnetic fields at the impact region of accretion columns. We study how the magnetic field configuration and strength determine the structure, geometry, and location of the shock-heated plasma. METHODS. We model the impact of an accretion stream onto the chromosphere of a CTTS by 2D axisymmetric magnetohydrodynamic simulations. Our model takes into account the gravity, the radiative cooling, and the magnetic-field-oriented thermal conduction. RESULTS. The structure, stability, and location of the shocked plasma strongly depend on the configuration and strength of the magnetic field. For weak magnetic fields, a large component of B may develop perpendicular to the stream at the base of the accretion column, limiting the sinking of the shocked plasma into the chromosphere. An envelope of dense and cold chromospheric material may also develop around the shocked column. For strong magnetic fields, the field configuration determines the position of the shock and its stand-off height. If the field is strongly tapered close to the chromosphere, an oblique shock may form well above the stellar surface. In general, a nonuniform magnetic field makes the distribution of emission measure vs. temperature of the shocked plasma lower than in the case of uniform magnetic field. CONCLUSIONS. The initial strength and configuration of the magnetic field in the impact region of the stream are expected to influence the chromospheric absorption and, therefore, the observability of the shock-heated plasma in the X-ray band. The field strength and configuration influence also the energy balance of the shocked plasma, its emission measure at T > 1 MK being lower than expected for a uniform field. The above effects contribute in underestimating the mass accretion rates derived in the X-ray band.Comment: 11 pages, 11 Figures; accepted for publication on A&A. Version with full resolution images can be found at http://www.astropa.unipa.it/~orlando/PREPRINTS/sorlando_accretion_shocks.pd

Effects of a non-universal IMF and binary parameter correlations on compact binary mergers

Binary population synthesis provides a direct way of studying the effects of different choices of binary evolution models and initial parameter distributions on present-day binary compact merger populations, which can then be compared to empirical properties such as observed merger rates. Samples of zero-age main sequence binaries to be evolved by such codes are typically generated from an universal IMF and simple, uniform, distributions for orbital period $P$, mass ratio $q$ and eccentricity $e$. More recently, however, mounting observational evidence has suggested the non-universality of the IMF and the existence of correlations between binary parameters. In this study, we implement a metallicity- and redshift-dependent IMF alongside correlated distributions for $P$, $q$ and $e$ in order to generate representative populations of binaries at varying redshifts, which are then evolved with the COMPAS code in order to study the variations in merger rates and overall population properties.Comment: 5 pages, 5 figures, 1 table. Proceedings contribution to IWARA2022, held in Antigua, Guatemala, in September 2022. To be published by Astron. Nac

Ocorrência da mosca-da-carambola no estado do Amapá.

O presente trabalho reúne informações sobre a mosca-da-carambola e mostra a importância da pesquisa científica na geração de conhecimentos sobre a praga. Resultados preliminares das pesquisas de hospedeiros da praga no estado do Amapá são apresentados

Praga de importância quarentenária A2 na fruticultura brasileira.

1. Introdução: 1.1 Moscas-das-frutas, 1.2 Mosca-da-carambola, 1.3 Introdução no Brasil, 1.4 Hospedeiros, 1.5 Ações de prevenção e controle; Referências bibliográficas