TeV resonances in top physics at the LHC

We consider the possibility of studying novel particles at the TeV scale with enhanced couplings to the top quark via top quark pair production at the LHC and VLHC. In particular we discuss the case of neutral scalar and vector resonances associated with a strongly interacting electroweak symmetry breaking sector. We constrain the couplings of these resonances by imposing appropriate partial wave unitarity conditions and known low energy constraints. We evaluate the new physics signals via WW -> tt~ for various models without making approximation for the initial state W bosons, and optimize the acceptance cuts for the signal observation. We conclude that QCD backgrounds overwhelm the signals in both the LHC and a 200 TeV VLHC, making it impossible to study this type of physics in the tt~ channel at those machines.Comment: 15p, add. comments to clarify model, +2 ref., version to appear PR

Inevitability of Plate Tectonics on Super-Earths

The recent discovery of super-Earths (masses less or equal to 10 earth-masses) has initiated a discussion about conditions for habitable worlds. Among these is the mode of convection, which influences a planet's thermal evolution and surface conditions. On Earth, plate tectonics has been proposed as a necessary condition for life. Here we show, that super-Earths will also have plate tectonics. We demonstrate that as planetary mass increases, the shear stress available to overcome resistance to plate motion increases while the plate thickness decreases, thereby enhancing plate weakness. These effects contribute favorably to the subduction of the lithosphere, an essential component of plate tectonics. Moreover, uncertainties in achieving plate tectonics in the one earth-mass regime disappear as mass increases: super-Earths, even if dry, will exhibit plate tectonic behaviour.Comment: 13 pages, 2 figures and 1 table; in press in ApJ

An analysis of the Sargasso Sea resource and the consequences for database composition

Background: The environmental sequencing of the Sargasso Sea has introduced a huge new resource of genomic information. Unlike the protein sequences held in the current searchable databases, the Sargasso Sea sequences originate from a single marine environment and have been sequenced from species that are not easily obtainable by laboratory cultivation. The resource also contains very many fragments of whole protein sequences, a side effect of the shotgun sequencing method.These sequences form a significant addendum to the current searchable databases but also present us with some intrinsic difficulties. While it is important to know whether it is possible to assign function to these sequences with the current methods and whether they will increase our capacity to explore sequence space, it is also interesting to know how current bioinformatics techniques will deal with the new sequences in the resource.Results: The Sargasso Sea sequences seem to introduce a bias that decreases the potential of current methods to propose structure and function for new proteins. In particular the high proportion of sequence fragments in the resource seems to result in poor quality multiple alignments.Conclusion: These observations suggest that the new sequences should be used with care, especially if the information is to be used in large scale analyses. On a positive note, the results may just spark improvements in computational and experimental methods to take into account the fragments generated by environmental sequencing techniques

T-odd correlations from CP violating anomalous top-quark couplings revisited

We revisit the effect of CP violating anomalous top-quark couplings in $t\bar{t}$ production and decay. We consider $t\bar{t}$ production through gluon fusion (and light $q{\bar q}$ annihilation) followed by top-quark decay into $bW$ or $b\ell\nu$. We find explicit analytic expressions for all the triple products generated by the anomalous couplings that fully incorporate all spin correlations. Our results serve as a starting point for numerical simulations for the LHC.Comment: minor typos correcte

The Interior Dynamics of Water Planets

The ever-expanding catalog of detected super-Earths calls for theoretical studies of their properties in the case of a substantial water layer. This work considers such water planets with a range of masses and water mass fractions (2 to 5 M_Earth, 0.02% to 50% H2 O). First, we model the thermal and dynamical structure of the near-surface for icy and oceanic surfaces, finding separate regimes where the planet is expected to maintain a subsurface liquid ocean and where it is expected to exhibit ice tectonics. Newly discovered exoplanets may be placed into one of these regimes given estimates of surface temperature, heat flux, and gravity. Second, we construct a parameterized convection model for the underlying ice mantle of higher ice phases, finding that materials released from the silicate iron core should traverse the ice mantle on the timescale of 0.1 to 100 megayears. We present the dependence of the overturn times of the ice mantle and the planetary radius on total mass and water mass fraction. Finally, we discuss the implications of these internal processes on atmospheric observables.Comment: 9 page 4 figure

On the Expressiveness of Spatial Constraint Systems

In this paper we shall report on our progress using spatial constraint system as an abstract representation of modal and epistemic behaviour. First we shall give an introduction as well as the background to our work. Then, we present our preliminary results on the representation of modal behaviour by using spatial constraint systems. Then, we present our ongoing work on the characterization of the epistemic notion of knowledge. Finally, we discuss about the future work of our research