Masses and magnetic moments of pentaquarks

We discuss the spectroscopy of pentaquarks. The quantum numbers of the ground state depend on the interplay between spin-flavor and orbital contributions to the energy. The magnetic moments of the lowest pentaquark state with negative and positive parity are found to be 0.382 \mu_N and 0.089 \mu_n, respectively.Comment: 15 pages, 4 figures, 3 tables (text rewritten, extra figure added, essential results unchanged

Mass spectrum of pentaquarks

We discuss the properties of the pentaquark in a collective stringlike model with a nonplanar configuration of the four quarks and the antiquark. In an application to the mass spectrum of exotic Theta baryons, we find that the ground state pentaquark has angular momentum and parity J(p)=1/2(-) and a small magnetic moment of 0.382 nuclear magnetons. The decay width is suppressed by the spatial overlap with the decay products.Comment: 8 pages, 3 figures, 1 table, invited talk at 23rd International Workshop on Nuclear Theory, June 14-19, 2004, Rila, Bulgari

The effects of retardation on the topological plasmonic chain: plasmonic edge states beyond the quasistatic limit

We study a one-dimensional plasmonic system with non-trivial topology: a chain of metallic nanoparticles with alternating spacing, which is the plasmonic analogue to the Su-Schreiffer-Heeger model. We extend previous efforts by including long range hopping with retardation and radiative damping, which leads to a non-Hermitian Hamiltonian with frequency dependence. We calculate band structures numerically and show that topological features such as quantised Zak phase persist due to chiral symmetry. This predicts parameters leading to topologically protected edge modes, which allows for positioning of disorder-robust hotspots at topological interfaces, opening up novel nanophotonics applications

Collective Gradient Sensing in Fish Schools

Throughout the animal kingdom, animals frequently benefit from living in groups. Models of collective behaviour show that simple local interactions are sufficient to generate group morphologies found in nature (swarms, flocks and mills). However, individuals also interact with the complex noisy environment in which they live. In this work, we experimentally investigate the group performance in navigating a noisy light gradient of two unrelated freshwater species: golden shiners (Notemigonuscrysoleucas) and rummy nose tetra (Hemigrammus bleheri). We find that tetras outperform shiners due to their innate individual ability to sense the environmental gradient. Using numerical simulations, we examine how group performance depends on the relative weight of social and environmental information. Our results highlight the importance of balancing of social and environmental information to promote optimal group morphologies and performance

Towards a better classification of unclear eruptive variables: the cases of V2492 Cyg, V350 Cep, and ASASSN-15qi

Eruptive variables are young stars that show episodic variations of brightness: EXors/FUors variations are commonly associated with enhanced accretion outbursts occurring at intermittent cadence of months/years (EXors) and decades/centuries (FUors). Variations that can be ascribed to a variable extinction along their line of sight are instead classified as UXors. We aim at investigating the long-term photometric behaviour of three sources classified as eruptive variables. We present data from the archival plates of the Asiago Observatory relative to the fields where the targets are located. For the sake of completeness we have also analysed the Harvard plates of the same regions that cover a much longer historical period, albeit at a lower sensitivity, however we are only able to provide upper limits. A total of 273 Asiago plates were investigated, providing a total of more than 200 magnitudes for the three stars, which cover a period of about 34 yr between 1958 and 1991. We have compared our data with more recently collected literature data. Our plates analysis of V2492 Cyg provides historical upper limits that seem not to be compatible with the level of the activity monitored during the last decade. Therefore, recently observed accretion phenomena could be associated with the outbursting episodes, more than repetitive obscuration. While a pure extinction does not seem the only mechanism responsible for the ASASSN-15qi fluctuations, it can account quite reasonably for the recent V350 Cep variations.Comment: 12 pages, accepted by A&

X-ray and HeI 1.0830 mu emission from protostellar jets

Context. The high energies of protostellar jets, implied by recent observations of X-rays from such flows, came very much as a surprise. Inferred shock velocities are considerably higher than what was previously known, hence putting even larger energy demands on the driving sources of the jets. The statistics of X-ray emitting jets are still poor, yet a few cases exist which seem to imply a correlation between the presence of HeI 1.0830 mu emission and X-ray radiation in a given source. Aims. This tentative correlation needs confirmation and explanation. If the jet regions of HeI 1.0830 mu emission are closely associated with those producing X-rays, high resolution infared spectroscopy can be used to observationally study the velocity fields in the hot plasma regions of the jets. This would provide the necessary evidence to test and further develop theoretical models of intermediately fast (> 500 - 1500 km/s) interstellar shock waves. Methods. The HH 154 jet flow from the embedded protostellar binary L 1551 IRS 5 provides a case study, since adequate IR and X-ray spectroscopic data are in existence. The thermal X-ray spectrum is fed into a photoionization code to compute, in particular, the line emission of HeI and HI and to account for the observed unusual line intensity ratios. Results. The advanced model is capable of accounting for most observables, but shows also major weaknesses. It seems not unlikely that these could, in principle, be overcome by a time dependent hydrodynamical calculation with self-consistent cooling. However, such sophisticated model development is decisively beyond the scope of the present work. Conclusions. Continued X-ray observations, coordinated with simultaneous high resolution infrared spectroscopy, are highly desirable.Comment: 5 pages, 4 Postscript figures, 3 in color. accepted for publication in Astronomy and Astrophysic

IR diagnostics of embedded jets: velocity resolved observations of the HH34 and HH1 jets

We present VLT-ISAAC medium resolution spectroscopy of the HH34 and HH1 jets. Our aim is to derive the kinematics and the physical parameters and to study how they vary with jet velocity. We use several important diagnostic lines such as [FeII] 1.644um, 1.600um and H2 2.122um. In the inner jet region of HH34 we find that both the atomic and molecular gas present two components at high and low velocity. The [FeII] LVC in HH34 is detected up to large distances from the source (>1000 AU), at variance with TTauri jets. In H2 2.122um, the LVC and HVC are spatially separated. We detect, for the first time, the fainter red-shifted counterpart down to the central source. In HH1, we trace the jet down to ~1" from the VLA1 driving source: the kinematics of this inner region is again characterised by the presence of two velocity components, one blue-shifted and one red-shifted with respect to the source LSR velocity. In the inner HH34 jet region, ne increases with decreasing velocity. Up to ~10" from the driving source, and along the whole HH1 jet an opposite behaviour is observed instead, with ne increasing with velocity. In both jets the mass flux is carried mainly by the high-velocity gas. A comparison between the position velocity diagrams and derived electron densities with models for MHD jet launching mechanisms has been performed for HH34. While the kinematical characteristics of the line emission at the jet base can be, at least qualitatively, reproduced by both X-winds and disc-wind models, none of these models can explain the extent of the LVC and the dependence of electron density with velocity that we observe. It is possible that the LVC in HH34 represents gas not directly ejected in the jet but instead denser ambient gas entrained by the high velocity collimated jet.Comment: A&A accepte