DBI Galileon and Late time acceleration of the universe

We consider 1+3 dimensional maximally symmetric Minkowski brane embedded in a 1+4 dimensional maximally symmetric Minkowski background. The resulting 1+3 dimensional effective field theory is of DBI (Dirac-Born-Infeld) Galileon type. We use this model to study the late time acceleration of the universe. We study the deviation of the model from the concordance \Lambda CDM behaviour. Finally we put constraints on the model parameters using various observational data.Comment: 16 pages, 7 eps figures, Latex Style, new references added, corrected missing reference

Galileons as Wess-Zumino Terms

We show that the galileons can be thought of as Wess-Zumino terms for the spontaneous breaking of space-time symmetries. Wess-Zumino terms are terms which are not captured by the coset construction for phenomenological Lagrangians with broken symmetries. Rather they are, in d space-time dimensions, d-form potentials for (d+1)-forms which are non-trivial co-cycles in Lie algebra cohomology of the full symmetry group relative to the unbroken symmetry group. We introduce the galileon algebras and construct the non-trivial (d+1)-form co-cycles, showing that the presence of galileons and multi-galileons in all dimensions is counted by the dimensions of particular Lie algebra cohomology groups. We also discuss the DBI and conformal galileons from this point of view, showing that they are not Wess-Zumino terms, with one exception in each case.Comment: 49 pages. v2 minor changes, version appearing in JHE

Virus-Induced Cancers of the Skin and Mucosa:Are We Dealing with "Smoking Guns" or "Smoke and Mirrors" in the Operating Theatre?

Introduction: Human papillomavirus (HPV) alone is thought to cause ~610,000 cases of cancer per year, and is the dominant aetiological agent for ano-genital (esp. cervical) and head and neck cancers (esp. oropharyngeal). Merkel cell polyomavirus (MCV) is a more recently discovered virus which causes Merkel cell carcinoma, a rare but highly aggressive skin malignancy. Methods: We explored the available published evidence to see if transmission of live HPV or MCV virus in smoke generated by laser or diathermy was feasible, and would pose an infection risk. Long-term infection with such carcinogenic viruses would then pose an increased risk for the development of virus-induced cancers in medical personnel. Results: The morphological structures of both HPV and MCV are very similar, and the size, external capsids and genomic structures show striking similarity. Both viruses have a non-enveloped external protein capsid consisting of 72 capsomeres, and a double-stranded DNA core. Sizes of both viruses range from 50 to 60 nm. There are now recent data demonstrating live and infectious HPV in smoke, and that these viruses can be used to infect cells in vitro. Further, anecdotal reports of virus transmission leading to disease causation in the production of respiratory airway viral warts (benign disease), and, finally, reports of HPV-induced oropharyngeal carcinoma (malignant disease) in two gynaecological surgeons as an occupational health hazard have been published recently. Conclusion: There is now sufficient evidence to support the hypotheses that live infectious carcinogenic viruses can be transmitted via smoke generated from surgical procedures, and, in rare instances, actually cause significant disease. Protective measures such as smoke extraction and airway protection should be instituted for all healthcare personnel, particularly those with multiple repeated exposures such as gynaecological surgeons

Study of Foaming Properties and Effect of the Isomeric Distribution of Some Anionic Surfactants

Using different reaction conditions of photosulfochlorination of n-dodecane, two samples of anionic surfactants of sulfonate type are obtained. Their micellar behavior has been already reported and the relationship between their isomeric distribution and their chemical structures and micellar behaviors have been more thoroughly explored. In this investigation, we screened the foaming properties (foaming power and foam stability) by a standardized method very similar to the Ross–Miles foaming tests to identify which surfactants are suitable for applications requiring high foaming, or, alternatively, low foaming. The results obtained for the synthesized surfactants are compared to those obtained for an industrial sample of secondary alkanesulfonate (Hostapur 60) and to those of a commercial sample of sodium dodecylsulfate used as reference for anionic surfactants. The foam formation and foam stability of aqueous solutions of the two samples of dodecanesulfonate are compared as a function of their isomeric distribution. These compounds show good foaming power characterized in most cases by metastable or dry foams. The highest foaming power is obtained for the sample rich in primary isomers which also produces foam with a relatively high stability. For the sample rich in secondary isomers we observe under fixed conditions a comparable initial foam height but the foam stability turns out to be low. This property is interesting for applications requiring low foaming properties such as dishwashing liquid for machines. The best results are observed near and above the critical micellar concentrations and at 25 C for both the samples

Massive Gravity on de Sitter and Unique Candidate for Partially Massless Gravity

We derive the decoupling limit of Massive Gravity on de Sitter in an arbitrary number of space-time dimensions d. By embedding d-dimensional de Sitter into d+1-dimensional Minkowski, we extract the physical helicity-1 and helicity-0 polarizations of the graviton. The resulting decoupling theory is similar to that obtained around Minkowski. We take great care at exploring the partially massless limit and define the unique fully non-linear candidate theory that is free of the helicity-0 mode in the decoupling limit, and which therefore propagates only four degrees of freedom in four dimensions. In the latter situation, we show that a new Vainshtein mechanism is at work in the limit m^2\to 2 H^2 which decouples the helicity-0 mode when the parameters are different from that of partially massless gravity. As a result, there is no discontinuity between massive gravity and its partially massless limit, just in the same way as there is no discontinuity in the massless limit of massive gravity. The usual bounds on the graviton mass could therefore equivalently well be interpreted as bounds on m^2-2H^2. When dealing with the exact partially massless parameters, on the other hand, the symmetry at m^2=2H^2 imposes a specific constraint on matter. As a result the helicity-0 mode decouples without even the need of any Vainshtein mechanism.Comment: 30 pages. Some clarifications and references added. New subsection 'Symmetry and Counting in the Full Theory' added. New appendix 'St\"uckelberg fields in the Na\"ive approach' added. Matches version published in JCA

CEP162 is an axoneme-recognition protein promoting ciliary transition zone assembly at the cilia base

The transition zone (TZ) is a specialized compartment found at the base of cilia, adjacent to the centriole distal end, where axonemal microtubules (MTs) are heavily cross-linked to the surrounding membrane to form a barrier that gates the ciliary compartment. A number of ciliopathy molecules have been found to associate with the TZ, but factors that directly recognize axonemal MTs to specify TZ assembly at the cilia base remain unclear. Here, through quantitative centrosome proteomics, we identified an axoneme-associated protein, CEP162, tethered specifically at centriole distal ends to promote TZ assembly. CEP162 interacts with core TZ components, and mediates their association with MTs. Loss of CEP162 arrests ciliogenesis at the stage of TZ assembly. Abolishing its centriolar tethering, however, allows CEP162 to stay on the growing end of the axoneme, and ectopically assemble TZ components at cilia tips. This generates extra-long cilia with strikingly swollen tips that actively release ciliary contents into the extracellular environment. CEP162 is thus an axoneme-recognition protein “pre-tethered” at centriole distal ends prior to ciliogenesis to promote and restrict TZ formation specifically at the cilia base

Generalizing Galileons

The Galileons are a set of terms within four-dimensional effective field theories, obeying symmetries that can be derived from the dynamics of a 3+1-dimensional flat brane embedded in a 5-dimensional Minkowski Bulk. These theories have some intriguing properties, including freedom from ghosts and a non-renormalization theorem that hints at possible applications in both particle physics and cosmology. In this brief review article, we will summarize our attempts over the last year to extend the Galileon idea in two important ways. We will discuss the effective field theory construction arising from co-dimension greater than one flat branes embedded in a flat background - the multiGalileons - and we will then describe symmetric covariant versions of the Galileons, more suitable for general cosmological applications. While all these Galileons can be thought of as interesting four-dimensional field theories in their own rights, the work described here may also make it easier to embed them into string theory, with its multiple extra dimensions and more general gravitational backgrounds.Comment: 16 pages; invited brief review article for a special issue of Classical and Quantum Gravity. Submitted to CQ

de Sitter Galileon

We generalize the Galileon symmetry and its relativistic extension to a de Sitter background. This is made possible by studying a probe-brane in a flat five-dimensional bulk using a de Sitter slicing. The generalized Lovelock invariants induced on the probe brane enjoy the induced Poincar\'e symmetry inherited from the bulk, while living on a de Sitter geometry. The non-relativistic limit of these invariants naturally maintain a generalized Galileon symmetry around de Sitter while being free of ghost-like pathologies. We comment briefly on the cosmology of these models and the extension to the AdS symmetry as well as generic FRW backgrounds

Interacting Spin-2 Fields

We construct consistent theories of multiple interacting spin-2 fields in arbitrary spacetime dimensions using a vielbein formulation. We show that these theories have the additional primary constraints needed to eliminate potential ghosts, to all orders in the fields, and to all orders beyond any decoupling limit. We postulate that the number of spin-2 fields interacting at a single vertex is limited by the number of spacetime dimensions. We then show that, for the case of two spin-2 fields, the vielbein theory is equivalent to the recently proposed theories of ghost-free massive gravity and bi-metric gravity. The vielbein formulation greatly simplifies the proof that these theories have an extra primary constraint which eliminates the Boulware-Deser ghost.Comment: 42 pages, 3 figures. v3 alternative argument using constrained spatial vielbeins has been removed (see footnote 3