Data driving the top quark forward--backward asymmetry with a lepton-based handle

We propose that, within the standard model, the correlation between the $t\bar{t}$ forward--backward asymmetry $A_{t\bar t}$ and the corresponding lepton-based asymmetry $A_l$ -- at the differential level -- is strong and rather clean both theoretically and experimentally. Hence a combined measurement of the two distributions as a function of the lepton $p_T$, a direct and experimentally clean observable, would lead to a potentially unbiased and normalization-free test of the standard model prediction. To check the robustness of our proposal we study how the correlation is affected by mis-measurement of the $t\bar t$ system transverse momenta, acceptance cuts, scale dependence and compare the results of MCFM, POWHEG (with & without PYTHIA showering), and SHERPA's CSSHOWER in first-emission mode. We find that the shape of the relative differential distribution $A_{l} (p^{l}_{T}) [A_{t\bar{t}} (p^l_T)]$ is only moderately distorted hence supporting the usefulness of our proposal. Beyond the first emission, we find that the correlation is not accurately captured by lowest-order treatment. We also briefly consider other differential variables such as the system transverse mass and the canonical $t\bar t$ invariant mass. Finally, we study new physics scenarios where the correlation is significantly distorted and therefore can be more readily constrained or discovered using our method.Comment: 27 pages, 12 figure

Modelling fungal colonies and communities:challenges and opportunities

This contribution, based on a Special Interest Group session held during IMC9, focuses on physiological based models of filamentous fungal colony growth and interactions. Fungi are known to be an important component of ecosystems, in terms of colony dynamics and interactions within and between trophic levels. We outline some of the essential components necessary to develop a fungal ecology: a mechanistic model of fungal colony growth and interactions, where observed behaviour can be linked to underlying function; a model of how fungi can cooperate at larger scales; and novel techniques for both exploring quantitatively the scales at which fungi operate; and addressing the computational challenges arising from this highly detailed quantification. We also propose a novel application area for fungi which may provide alternate routes for supporting scientific study of colony behaviour. This synthesis offers new potential to explore fungal community dynamics and the impact on ecosystem functioning

The Wilsonian Renormalization Group in Randall-Sundrum 1

We find renormalization group transformations for the compactified Randall-Sundrum scenario by integrating out an infinitesimal slice of ultraviolet degrees of freedom near the Planck brane. Under these transformations the coefficients of operators on the Planck brane experience RG evolution. The extra-dimensional radius also scales, flowing to zero in the IR. We find an attractive fixed point in the context of a bulk scalar field theory. Calculations are simplified in the low energy effective theory as we demonstrate with the computation of a loop diagram.Comment: 19 pages, typos adde

A Krüppel-like transcription factor gene is involved in salt stress responses in Medicago spp.

Legume plants are able to fix nitrogen in symbiotic association with rhizobia and, like many crops, are sensitive to high salt conditions. However, very few molecular markers can be associated to stress tolerance in legume crops. A Kruppel-like transcription factor, Mtzpt2-1, required for the formation of the nitrogen-fixing region, confers salt tolerance to yeast cells. Here, legume responses to salt stresses were studied using alfalfa and its close relative Medicago truncatula, a model legume species. Salt stress induces the Mszpt2-1 gene both in roots and root harbouring nodules. In addition, Sinorhizobium meliloti strains tolerating up to 700 mM NaCl, were used in nodulation assays to assess salt tolerance of the symbiotic response of M. truncatula. Few nodules, mainly in the upper part of the root, could be detected in plants treated with 200 mM NaCl, suggesting that nodule initiation was particularly sensitive to salt stress. We have also defined for M. truncatula the threshold of NaCl tolerance after which recovery of stressed plants is irreversible under laboratory conditions. After analysing several times of salt treatment (150 mM NaCl), M. truncatula 108R plants stressed for 7 days could not recover (less than 5%), whereas a 4-day treatment allowed at least 75% recovery. Transgenic M. truncatula plants expressing Mtzpt2-1 in antisense configuration are more sensitive to `recover' from salt stress than the wild type. These results identify Mtzpt2-1 as a molecular marker potentially linked to stress tolerance in M. truncatula and suggest its participation in a transcriptional program induced in these plants to cope with salt stress.Facultad de Ciencias ExactasInstituto de Biotecnología y Biología Molecula

Local spinfoam expansion in loop quantum cosmology

The quantum dynamics of the flat Friedmann-Lemaitre-Robertson-Walker and Bianchi I models defined by loop quantum cosmology have recently been translated into a spinfoam-like formalism. The construction is facilitated by the presence of a massless scalar field which is used as an internal clock. The implicit integration over the matter variable leads to a nonlocal spinfoam amplitude. In this paper we consider a vacuum Bianchi I universe and show that by choosing an appropriate regulator a spinfoam expansion can be obtained without selecting a clock variable and that the resulting spinfoam amplitude is local.Comment: 12 page

Supersymmetric Extension of the Lorentz and CPT-Violating Maxwell-Chern-Simons Model

Focusing on gauge degrees of freedom specified by a 1+3 dimensions model hosting a Maxwell term plus a Lorentz and CPT non-invariant Chern-Simons-like contribution, we obtain a minimal extension of such a system to a supersymmetric environment. We comment on resulting peculiar self-couplings for the gauge sector, as well as on background contribution for gaugino masses. Furthermore, a non-polynomial generalization is presented.Comment: revtex4, 4 pages, no figure

Spin and a Running Radius in RS1

We develop a renormalization group formalism for the compactified Randall-Sundrum scenario wherein the extra-dimensional radius serves as the scaling parameter. Couplings on the hidden brane scale as we move within local effective field theories with varying size of the warped extra dimension. We consider this RG approach applied to U(1) gauge theories and gravity. We use this method to derive a low energy effective theory.Comment: 18 pages, minor changes, references adde

RS1, Higher Derivatives and Stability

We demonstrate the classical stability of the weak/Planck hierarchy within the Randall-Sundrum scenario, incorporating the Goldberger-Wise mechanism and higher-derivative interactions in a systematic perturbative expansion. Such higher-derivative interactions are expected if the RS model is the low-energy description of some more fundamental theory. Generically, higher derivatives lead to ill-defined singularities in the vicinity of effective field theory branes. These are carefully treated by the methods of classical renormalization.Comment: 30 page

Holography, Pade Approximants and Deconstruction

We investigate the relation between holographic calculations in 5D and the Migdal approach to correlation functions in large N theories. The latter employs Pade approximation to extrapolate short distance correlation functions to large distances. We make the Migdal/5D relation more precise by quantifying the correspondence between Pade approximation and the background and boundary conditions in 5D. We also establish a connection between the Migdal approach and the models of deconstructed dimensions.Comment: 28 page