From Dimensional Reduction of 4d Spin Foam Model to Adding Non-Gravitational Fields to 3d Spin Foam Model

A Kaluza-Klein like approach for a 4d spin foam model is considered. By applying this approach to a model based on group field theory in 4d (TOCY model), and using the Peter-Weyl expansion of the gravitational field, reconstruction of new non gravitational fields and interactions in the action are found. The perturbative expansion of the partition function produces graphs colored with su(2) algebraic data, from which one can reconstruct a 3d simplicial complex representing space-time and its geometry; (like in the Ponzano-Regge formulation of pure 3d quantum gravity), as well as the Feynman graph for typical matter fields. Thus a mechanism for generation of matter and construction of new dimensions are found from pure gravity.Comment: 11 pages, no figure, to be published in International Journal of Geometric Methods in Modern Physic

The Derivation of Transfer Parameters in the Assessment of Radiological Impacts on Arctic Marine Biota

The initial stage of an environmental impact assessment requires quantification of radionuclide transfer in the study area. This paper evaluates the robustness of the concentration factor (CF) approach in assessing radiological impact on reference Arctic marine biota. By comparing region-specific data sets with recommended generic values for CFs, we tested the hypothesis that transfers to Arctic biota differ from transfers observed in temperate areas for 90Sr, 137Cs, 239, 240Pu and 99Tc. Despite the general paucity of data and great uncertainty regarding radionuclide CFs in reference biota, we conclude that the use of Arctic-specific CFs for Sr and Pu can be justified in some cases where differences from generic CFs seem apparent. Where CF data are absent, a biokinetic modelling approach with allometric considerations might be used to bridge data gaps. Such an approach has been used here to estimate the trophic transfer of 137Cs and 239Pu in a marine food chain consisting of four trophic levels. For the simulation concerning 137Cs, the preliminary results suggest that it takes more than five years to attain equilibrium for higher trophic levels (polar cod and harp seal). Biomagnification appears to occur at the lower trophic levels, but not at the highest (seal). For 239Pu, transfer to successively higher trophic levels is low: there is a fall of several orders of magnitude between primary producers, represented by phytoplankton, and polar cod, representing trophic levels 3 and 4. However, the model predicts that this decreasing trend in activity concentrations along the food chain is reversed for the highest trophic level, represented by seal. The simulated results for seal display equilibrium activity concentrations about two orders of magnitude higher than those observed for polar cod (one of its prey species). However, equilibrium (165 years) is not reached during the life span of a seal. The equilibrium 137Cs CFs are approximately 50 l/kg for zooplankton, 130l/kg for polar cod, and 70 l/kg for seal. The predicted equilibrium 239Pu CFs are 2.5·10³ l/kg for zooplankton and 25 l/kg for polar cod. For seal, following a one-year equilibration period, a CF of approximately 75 l/kg is predicted.Le stade initial d'une étude d'impact environnemental nécessite une évaluation quantitative du transfert de radionucléides dans la zone d'étude. Cet article évalue la robustesse de la méthode du facteur de concentration (FC) pour déterminer l'impact radiologique sur un biote marin arctique de référence. En comparant des ensembles de données spécifiques à une région avec des valeurs génériques recommandées pour les facteurs de concentration, on a testé l'hypothèse selon laquelle les transferts au biote arctique diffèrent des transferts observés dans des régions tempérées pour 90Sr, 137Cs, 239,240Pu et 99Tc. Malgré la pénurie générale de données et un haut niveau d'incertitude concernant les FC des radionucléides dans le biote de référence, on conclut que l'utilisation de FC spécifiques à l'Arctique pour Sr et Pu peut être justifiée dans certains cas où les différences d'avec les FC génériques semblent apparentes. Là où il n'existe pas de données sur les FC, on peut recourir à la modélisation biocinétique tenant compte des éléments allométriques afin de combler les lacunes dans les données. C'est cette approche que l'on a utilisée ici pour estimer le transfert trophique de 137Cs et de 239Pu dans une chaîne alimentaire marine comprenant quatre niveaux trophiques. Pour la simulation relative à 137Cs, les résultats préliminaires suggèrent qu'il faut plus de cinq ans pour atteindre l'équilibre aux niveaux trophiques supérieurs (morue polaire et phoque annelé). La bioamplification semble se produire aux niveaux trophiques inférieurs, mais pas au plus élevé (phoque). Pour 239Pu, le transfert aux niveaux trophiques supérieurs est faible: on constate une baisse de plusieurs ordres de grandeur entre les producteurs primaires, représentés par le phytoplancton, et la morue polaire, qui représente les niveaux trophiques 3 et 4. Le modèle prédit toutefois que cette tendance à la baisse dans l'activité volumique le long de la chaîne alimentaire s'inverse au niveau trophique le plus élevé, représenté par le phoque. Les résultats simulés pour le phoque affichent des activités volumiques à l'équilibre environ deux ordres de grandeur plus élevées que celles observées chez la morue polaire (l'une des espèces-proies du phoque). L'équilibre (165 ans) n'est cependant pas atteint durant la durée de vie du phoque. Les FC de 137Cs à l'équilibre sont environ de 50 l/kg pour le zooplancton, de 130 l/kg pour la morue polaire et de 70 l/kg pour le phoque. Les FC de 239Pu projetés à l'équilibre sont de 2,5·10³ l/kg pour le zooplancton et de 25 l/kg pour la morue polaire. Pour le phoque, après une période d'équilibre d'une année, on prédit un FC d'environ 75 l/kg

Recent developments in research into the Cyathostominae and Anoplocephala perfoliata

Intestinal helminths are an important cause of equine disease. Of these parasites, the Cyathostominae are the commonest group that infect horses. These nematodes consist of a complex tribe of 51 species, although individual horses tend to harbour 10 or so common species, in addition to a few rarer species. The Cyathostominae can be extremely pathogenic, and high levels of infection result in clinical symptoms ranging from chronic weight loss to colic, diarrhoea and death. As part of their life cycle, immature cyathostomins penetrate the large intestinal wall, where they can enter a state of inhibited larval development. These larvae can exist in this state for months to years, after which they subsequently re-emerge. If larvae re-emerge in large numbers (i.e. several million), severe pathological consequences ensue. The inhibited larvae are also relatively refractory to several of the currently available anthelmintics, so that horses treated previously with anthelmintics can still carry life-threatening burdens of these parasitic stages. Little is known about the cyathostomin larvae during their mucosal phase, and current research efforts are focused on investigating the biology of these stages. Much of the research described here highlights this area of research and details studies aimed at investigating the host immune responses that the mucosal larvae invoke. As part of this research effort, molecular tools have been developed to facilitate the identification of larval and egg stages of cyathostomins. These molecular tools are now proving very useful in the investigation of the relative contributions that individual, common cyathostomin species make to the pathology and epidemiology of mixed helminth infections. At the more applied level, research is also in progress to develop an immunodiagnostic test that will allow numbers of mucosal larvae to be estimated. This test utilises antigen-specific IgG(T) serum antibody responses as markers of infection. As anthelmintic resistance will be the major constraint on the future control of the Cyathostominae, researchers are now actively investigating this area and studies aimed at elucidating the molecular mechanisms of drug resistance are described. Another parasite which has assumed a clinically important role in horses is the tapeworm, Anoplocephala perfoliata. This parasite is prevalent world-wide and has been shown to be a significant cause of equine colic. Because previous methods of estimating the infection intensity of tapeworm were inaccurate, recent research has been directed at developing an immunodiagnostic ELISA for these cestodes. Specific IgG(T) responses to antigens secreted by adult tapeworms have been shown to provide a reasonable indication of infection intensity. An ELISA based on these responses is now commercially available. The steps involved in the development of this ELISA are described here. In addition to these recent advances in research, this review also outlines the principle areas for future research into these important equine parasites

Spin foams with timelike surfaces

Spin foams of 4d gravity were recently extended from complexes with purely spacelike surfaces to complexes that also contain timelike surfaces. In this article, we express the associated partition function in terms of vertex amplitudes and integrals over coherent states. The coherent states are characterized by unit 3--vectors which represent normals to surfaces and lie either in the 2--sphere or the 2d hyperboloids. In the case of timelike surfaces, a new type of coherent state is used and the associated completeness relation is derived. It is also shown that the quantum simplicity constraints can be deduced by three different methods: by weak imposition of the constraints, by restriction of coherent state bases and by the master constraint.Comment: 22 pages, no figures; v2: remarks on operator formalism added in discussion; correction: the spin 1/2 irrep of the discrete series does not appear in the Plancherel decompositio

Lorentzian spin foam amplitudes: graphical calculus and asymptotics

The amplitude for the 4-simplex in a spin foam model for quantum gravity is defined using a graphical calculus for the unitary representations of the Lorentz group. The asymptotics of this amplitude are studied in the limit when the representation parameters are large, for various cases of boundary data. It is shown that for boundary data corresponding to a Lorentzian simplex, the asymptotic formula has two terms, with phase plus or minus the Lorentzian signature Regge action for the 4-simplex geometry, multiplied by an Immirzi parameter. Other cases of boundary data are also considered, including a surprising contribution from Euclidean signature metrics.Comment: 30 pages. v2: references now appear. v3: presentation greatly improved (particularly diagrammatic calculus). Definition of "Regge state" now the same as in previous work; signs change in final formula as a result. v4: two references adde

Neutral B-meson mixing from full lattice QCD at the physical point

We calculate the bag parameters for neutral $B$-meson mixing in and beyond the Standard Model, in full four-flavour lattice QCD for the first time. We work on gluon field configurations that include the effect of $u$, $d$, $s$ and $c$ sea quarks with the Highly Improved Staggered Quark (HISQ) action at three values of the lattice spacing and with three $u/d$ quark masses going down to the physical value. The valence $b$ quarks use the improved NRQCD action and the valence light quarks, the HISQ action. Our analysis was blinded. Our results for the bag parameters for all five operators are the most accurate to date. For the Standard Model operator between $B_s$ and $B_d$ mesons we find: $\hat{B}_{B_s}=1.232(53)$, $\hat{B}_{B_d}=1.222(61)$. Combining our results with lattice QCD calculations of the decay constants using HISQ quarks from the Fermilab/MILC collaboration and with experimental values for $B_s$ and $B_d$ oscillation frequencies allows determination of the CKM elements $V_{ts}$ and $V_{td}$. We find $V_{ts} = 0.04189(93)$, $V_{td} = 0.00867(23)$ and $V_{ts}/V_{td} = 0.2071(27)$. Our results agree well (within $2\sigma$) with values determined from CKM unitarity constraints based on tree-level processes (only). Using a ratio to $\Delta M$ in which CKM elements cancel in the Standard Model, we determine the branching fractions ${\text{Br}}(B_s\rightarrow \mu^+\mu^-) = 3.81(18) \times 10^{-9}$ and ${\text{Br}}(B_d\rightarrow \mu^+\mu^-) = 1.031(54) \times 10^{-10}$. We also give results for matrix elements of the operators $R_0$, $R_1$ and $\tilde{R}_1$ that contribute to neutral $B$-meson width differences.This work was funded by STFC, the Royal Society, the Wolfson Foundation and the US DOE and National Science Foundation

Generating Functions for Coherent Intertwiners

We study generating functions for the scalar products of SU(2) coherent intertwiners, which can be interpreted as coherent spin network evaluations on a 2-vertex graph. We show that these generating functions are exactly summable for different choices of combinatorial weights. Moreover, we identify one choice of weight distinguished thanks to its geometric interpretation. As an example of dynamics, we consider the simple case of SU(2) flatness and describe the corresponding Hamiltonian constraint whose quantization on coherent intertwiners leads to partial differential equations that we solve. Furthermore, we generalize explicitly these Wheeler-DeWitt equations for SU(2) flatness on coherent spin networks for arbitrary graphs.Comment: 31 page

Effective action and semiclassical limit of spin foam models

We define an effective action for spin foam models of quantum gravity by adapting the background field method from quantum field theory. We show that the Regge action is the leading term in the semi-classical expansion of the spin foam effective action if the vertex amplitude has the large-spin asymptotics which is proportional to an exponential function of the vertex Regge action. In the case of the known three-dimensional and four-dimensional spin foam models this amounts to modifying the vertex amplitude such that the exponential asymptotics is obtained. In particular, we show that the ELPR/FK model vertex amplitude can be modified such that the new model is finite and has the Einstein-Hilbert action as its classical limit. We also calculate the first-order and some of the second-order quantum corrections in the semi-classical expansion of the effective action.Comment: Improved presentation, 2 references added. 15 pages, no figure