G 4 flux, algebraic cycles and complex structure moduli stabilization

We construct G4 fluxes that stabilize all of the 426 complex structure moduli of the sextic Calabi-Yau fourfold at the Fermat point. Studying flux stabilization usually requires solving Picard-Fuchs equations, which becomes unfeasible for models with many moduli. Here, we instead start by considering a specific point in the complex structure moduli space, and look for a flux that fixes us there. We show how to construct such fluxes by using algebraic cycles and analyze flat directions. This is discussed in detail for the sextic Calabi-Yau fourfold at the Fermat point, and we observe that there appears to be tension between M2-tadpole cancellation and the requirement of stabilizing all moduli. Finally, we apply our results to show that even though symmetric fluxes allow to automatically solve several F-term equations, they typically lead to flat directions

Exclusive processes in position space and the pion distribution amplitude

We suggest to carry out lattice calculations of current correlators in position space, sandwiched between the vacuum and a hadron state (e.g. pion), in order to access hadronic light-cone distribution amplitudes (DAs). In this way the renormalization problem for composite lattice operators is avoided altogether, and the connection to the DA is done using perturbation theory in the continuum. As an example, the correlation function of two electromagnetic currents is calculated to the next-to-next-to-leading order accuracy in perturbation theory and including the twist-4 corrections. We argue that this strategy is fully competitive with direct lattice measurements of the moments of the DA, defined as matrix elements of local operators, and offers new insight in the space-time picture of hard exclusive reactions.Comment: 15 pages, 10 figure

Statistical hadronization of charmed quarks at SPS and RHIC

Production of open and hidden charm hadrons in heavy ion collisions is considered within the statistical coalescence model. The charmed quark-antiquark pairs are assumed to be created at the initial stage of the reaction in hard parton collisions. The number of these pairs is conserved during the evolution of the system. At the hadronization stage, the charmed (anti)quarks are distributed among open and hidden charm hadrons in accordance with the laws of statistical mechanics. The model is in agreement with the experimental data on J/psi to Drell-Yan ratio in Pb+Pb collisions at SPS. This agreement can be reached only if a rather strong enhancement of the open charm production in central Pb+Pb collisions is assumed. A possible mechanism of the charm enhancement is discussed. At the top RHIC energy, the model predicts an increase of J/psi to Drell-Yan ratio in more central nucleus-nucleus collisions with respect to less central ones.Comment: Presented at 16th International Conference "Quark Matter", Nantes (France), July 18-24, 2002; 4 pages, LaTeX, 2 PS-figure

Statistical Coalescence Model with Exact Charm Conservation

The statistical coalescence model for the production of open and hidden charm is considered within the canonical ensemble formulation. The data for the J/psi multiplicity in Pb+Pb collisions at 158 A GeV are used for the model prediction of the open charm yield which has not yet been measured in these reactions.Comment: 7 pages, Late

Heavy Flavor Enhancement as a Signal of Color Deconfinement

We argue that the color deconfinement in heavy ion collisions may lead to enhanced production of hadrons with open heavy flavor (charm or bottom). We estimate the upper bound of this enhancement.Comment: 7 pages, LaTeX, 3 PS-figure

New Host-plant Records For Neotropical Agromyzids (diptera: Agromyzidae) From Asteraceae Flower Heads

Agromyzidae is a large and cosmopolitan fly family with approximately 2,500 known species. Here we present 22 new records of agromyzid-host plant associations. Plants were sampled from 2002 to 2005 in São Paulo state, Brazil. A total of eight agromyzid species were reared from 18 Asteraceae host species. The genus Melanagromyza Hendel was the commonest. This is the first detailed study reporting associations between non-leafmining Agromyzidae and their host plants in Brazil.3719799Almeida, A.M., C.R. Fonsceca, P.I. Prado, M. Almeida Neto, S. Diniz, U. Kubota, M.R. Braun, R.L.G. Raimundo, L.A. Anjos, T.G. Mendonça, S.M. Futada & T.M. Lewinsohn. 2005. Diversidade e ocorrência de Asteraceae em cerrados de São Paulo. Biota Neotrop. 5: http://www.biotaneotropica. org.br/v5n2/pt/abstract?article+BN00105022005 . ISSN 1676-0603Andersen, A., Sjursen, H., Rafoss, T., Biodiversity of Agromizydae (Diptera) and biologically and conventionally grown spring barley and grass field (2004) Biol. Agric. Hortic, 22, pp. 143-155Benavent-Corai, J., Martinez, M., Jimenez Peydró, R., Catalogue of the host-plants of the world Agromyzidae (Diptera) (2005) Boll. Zool. Agrar. Bachic. Serie II, 37, pp. 1-97Bremer, K., (1994) Asteraceae: Cladistics and classification, , Timber Press, Portland, 752pChen, X., Lang, F., Xu, Z., He, J., Ma, Y., The occurrence of leafminers and their parasitoids on vegetables and weeds in Hangzhou area, Southeast China (2003) BioControl, 48, pp. 515-527Eiten, G., Cerrado vegetation of Brazil (1972) Bot. Rev, 38, pp. 201-341Fonseca, C.R., Prado, P.I., Almeida Neto, M., Kubota, U., Lewinsohn, T.M., Flower heads, herbivores, and their parasitoids: Food web structure along a fertility gradient (2005) Ecol. Entomol, 30, pp. 36-46Gagné, R.J., (1994) The gall midges of the Neotropical region, , Cornell Univ. Press, Ithaca, 352pLewinsohn, T.M. 1991. Insects in flower heads of Asteraceae in southeast Brazil: a case study on tropical species richness, p.525-560. In P.W. Price, T.M. Lewinsohn, G.W. Fernandes & W.W. Benson (eds.). Plant-animal interactions: Evolutionary ecology in tropical and temperate regions. John Wiley & Sons, Inc., New York, 639pLewinsohn, T.M., Novotny, V., Basset, Y., Insects on plants: Diversity of herbivore assemblages revisited (2005) Annu. Rev. Ecol. Syst, 36, pp. 597-620Schuster, D.J., Gilreath, J.P., Wharton, R.A., Seymour, P.R., Agromyzidae (Diptera) leafminers and their parasitoids in weeds associated with potato in Florida (1991) Environ. Entomol, 20, pp. 720-723Spencer, K.A., Notes on the Neotropical Agromyzidae (Diptera) (1966) Pap. Avulsos Zool, 19, pp. 142-150Spencer, K.A., The Agromyzidae of Canada and Alaska (1969) Mem. Entomol. Soc. Can, 64, pp. 1-311Spencer, K.A. 1973a. Agromyzidae (Diptera) of economic importance. Dr. W. Junk B. V. The Hague, Serie Entomologica, 418pSpencer, K.A., The Agromyzidae (Diptera) of Venezuela. Rev. Fac. Agrom (1973), pp. 5-107. , Mar. VIIISpencer, K.A., (1990) Host specialization in the world Agromyzidae, , Diptera, Kluwer Academic Publishers, Dordrecht, 444pSpencer, K.A. 1996. Australasian/Oceanian Diptera Catalog - Web Version. URL: http://hbs.bishopmuseum.org/aocat/agromyzidae.html. Accessed in 12/09/2006Spencer, K.A. & C.E. Stegmaier. 1973. Arthropods of Florida (EUA) and neighboring land areas, v. 7. Agromyzidae of Florida (USA) with a Supplement on Species from the Caribbean. Fla. Dep. Agri. Cons. Serv., Gainesville, 205pSpencer, K.A. & G.C. Steyskal. 1986. Manual of the Agromyzidae (Diptera) of the United States. U. S. Department of Agriculture, Agriculture Handbook. n. 638. Washington, U.S.ASpencer, K.A., Martinez, M., Etienne, J., Les Agromyzidae (Diptera) de Guadeloupe. (1992) Ann. Soc. Entomol. Fr, 28, pp. 251-302Zwölfer, H. 1988. Species richness, species packing, and evolution in insect-plant systems, p.301-319. In E.D. Schulze & H. Zwölfer (eds.), Potentials and limitations of ecosystem analysis. Springer-Verlag. Berlin, 435

BOLLOCKS!! Designing pervasive games that play with the social rules of built environments

We propose that pervasive games designed with mechanics that are specifically in opposition with, or disruptive of, social rules of the environment in which they are played, have unique potential to provide interesting, provocative experiences for players. We explore this concept through the design and evaluation of an experimental game prototype, Shhh!, inspired by the juvenile game Bollocks, and implemented on Android mobile devices, which challenges players to make loud noises in libraries. Six participants played the game before engaging in semi-structured interviews, explored through inductive thematic analysis. Results suggest that the game provoked in players a heightened awareness of social rules, as well as a complex social dilemma of whether or not to act. We conclude by presenting a model for designing games that play with the social, as well as physical, rules of the environments in which they are set

Fluctuations and Instabilities of Ferromagnetic Domain Wall pairs in an External Magnetic Field

Soliton excitations and their stability in anisotropic quasi-1D ferromagnets are analyzed analytically. In the presence of an external magnetic field, the lowest lying topological excitations are shown to be either soliton-soliton or soliton-antisoliton pairs. In ferromagnetic samples of macro- or mesoscopic size, these configurations correspond to twisted or untwisted pairs of Bloch walls. It is shown that the fluctuations around these configurations are governed by the same set of operators. The soliton-antisoliton pair has exactly one unstable mode and thus represents a critical nucleus for thermally activated magnetization reversal in effectively one-dimensional systems. The soliton-soliton pair is stable for small external fields but becomes unstable for large magnetic fields. From the detailed expression of this instability threshold and an analysis of nonlocal demagnetizing effects it is shown that the relative chirality of domain walls can be detected experimentally in thin ferromagnetic films. The static properties of the present model are equivalent to those of a nonlinear sigma-model with anisotropies. In the limit of large hard-axis anisotropy the model reduces to a double sine-Gordon model.Comment: 15 pages RevTex 3.0 (twocolumn), 9 figures available on request, to appear in Phys Rev B, Dec (1994

D7-Brane Moduli vs. F-Theory Cycles in Elliptically Fibred Threefolds

We study the space of geometric and open string moduli of type IIB compactifications from the perspective of complex structure deformations of F-theory. In order to find a correspondence, we work in the weak coupling limit and for simplicity focus on compactifications to 6 dimensions. Starting from the topology of D7-branes and O7-planes, we construct the 3-cycles of the F-theory threefold. We achieve complete agreement between the degrees of freedom of the Weierstrass model and the complex structure deformations of the elliptic Calabi-Yau. All relevant quantities are expressed in terms of the topology of the base space, allowing us to formulate our results for general base spaces.Comment: 40 pages, 15 figures, references adde

The Small-x Behaviour of the Singlet Polarized Structure Function g_2 in the Double Logarithmic Approximation

The small-x behavior of the singlet contributions to the polarized structure function g_2(x,Q^2) is calculated in the double-logarithmic approximation of perturbative QCD. The dominant contribution is due to the gluons which, in contrast to the unpolarized case, mix with the fermions also in the small-x domain. We find a power-like growth in 1/x in the odd-signature parts of the amplitude with the same power as in the singlet function g_1(x,Q^2) at x<< 1.Comment: 20 pages, latex, 3 ps figure