295 research outputs found
A note on local BRST cohomology of Yang-Mills type theories with free abelian factors
We extend previous work on antifield dependent local BRST cohomology for
matter coupled gauge theories of Yang-Mills type to the case of gauge groups
that involve free abelian factors. More precisely, we first investigate in a
model independent way how the dynamics enters the computation of the cohomology
for a general class of Lagrangians in general spacetime dimensions. We then
discuss explicit solutions in the case of specific models. Our analysis has
implications for the structure of characteristic cohomology and for consistent
deformations of the classical models, as well as for divergences/counterterms
and for gauge anomalies that may appear during perturbative quantization.Comment: 31 page
An Exotic Theory of Massless Spin-Two Fields in Three Dimensions
It is a general belief that the only possible way to consistently deform the
Pauli-Fierz action, changing also the gauge algebra, is general relativity.
Here we show that a different type of deformation exists in three dimensions if
one allows for PT non-invariant terms. The new gauge algebra is different from
that of diffeomorphisms. Furthermore, this deformation can be generalized to
the case of a collection of massless spin-two fields. In this case it describes
a consistent interaction among them.Comment: 21+1 pages. Minor corrections and reference adde
Deformations of vector-scalar models
Abelian vector fields non-minimally coupled to uncharged scalar fields arise
in many contexts. We investigate here through algebraic methods their
consistent deformations ("gaugings"), i.e., the deformations that preserve the
number (but not necessarily the form or the algebra) of the gauge symmetries.
Infinitesimal consistent deformations are given by the BRST cohomology classes
at ghost number zero. We parametrize explicitly these classes in terms of
various types of global symmetries and corresponding Noether currents through
the characteristic cohomology related to antifields and equations of motion.
The analysis applies to all ghost numbers and not just ghost number zero. We
also provide a systematic discussion of the linear and quadratic constraints on
these parameters that follow from higher-order consistency. Our work is
relevant to the gaugings of extended supergravities.Comment: v2: references added, typos corrected, minor changes for clarit
Inconsistency of interacting, multi-graviton theories
We investigate, in any spacetime dimension >=3, the problem of consistent
couplings for a finite collection of massless, spin-2 fields described, in the
free limit, by a sum of Pauli-Fierz actions. We show that there is no
consistent (ghost-free) coupling, with at most two derivatives of the fields,
that can mix the various "gravitons". In other words, there are no
Yang-Mills-like spin-2 theories. The only possible deformations are given by a
sum of individual Einstein-Hilbert actions. The impossibility of
cross-couplings subsists in the presence of scalar matter. Our approach is
based on the BRST-based deformation point of view and uses results on the
so-called "characteristic cohomology" for massless spin-2 fields which are
explained in detail.Comment: 44+1 pages, no figures. Case of an infinite number of gravitons
treated more completely, comparison with work by Aragone and Deser on
gravitational coupling of a single massless spin-2 field discusse
A note on the uniqueness of D=4 N=1 Supergravity
We investigate in 4 spacetime dimensions, all the consistent deformations of
the lagrangian , which is the sum of the
Pauli-Fierz lagrangian for a free massless spin 2 field and the
Rarita-Schwinger lagrangian for a free massless spin 3/2
field. Using BRST cohomogical techniques, we show, under the assumptions of
locality, Poincar\'e invariance, conservation of the number of gauge symmetries
and the number of derivatives on each fields, that N=1 D=4 supergravity is the
only consistent interaction between a massless spin 2 and a massless spin 3/2
field. We do not assume general covariance. This follows automatically, as does
supersymmetry invariance. Various cohomologies related to conservations laws
are also given.Comment: 22+1 pages, LaTeX. References adde
Membrane recruitment of NOD2 in intestinal epithelial cells is essential for nuclear factorâÎșB activation in muramyl dipeptide recognition
Nucleotide oligomerization domain (NOD) 2 functions as a mammalian cytosolic pathogen recognition molecule, and mutant forms have been genetically linked to Crohn's disease (CD). NOD2 associates with the caspase activation and recruitment domain of RIP-like interacting caspase-like apoptosis regulatory protein kinase (RICK)/RIP2 and activates nuclear factor (NF)âÎșB in epithelial cells and macrophages, whereas NOD2 mutant 3020insC, which is associated with CD, shows an impaired ability to activate NF-ÎșB. To gain insight into the molecular mechanisms of NOD2 function, we performed a functional analysis of deletion and substitution NOD2 mutants. NOD2, but not NOD2 3020insC mutant, associated with cell surface membranes of intestinal epithelial cells. Membrane targeting and subsequent NF-ÎșB activation are mediated by two leucine residues and a tryptophan-containing motif in the COOH-terminal domain of NOD2. The membrane targeting of NOD2 is required for NF-ÎșB activation after the recognition of bacterial muramyl dipeptide in intestinal epithelial cells
Gauge invariants and Killing tensors in higher-spin gauge theories
In free completely symmetric tensor gauge field theories on Minkowski
space-time, all gauge invariant functions and Killing tensor fields are
computed, both on-shell and off-shell. These problems are addressed in the
metric-like formalisms.Comment: LaTeX, 24 pages, no figure. One reference added and one definition
corrected. Accepted for publication in NP
Gut microbiota imbalance and colorectal cancer.
International audienceThe gut microbiota acts as a real organ. The symbiotic interactions between resident micro-organisms and the digestive tract highly contribute to maintain the gut homeostasis. However, alterations to the microbiome caused by environmental changes (e.g., infection, diet and/or lifestyle) can disturb this symbiotic relationship and promote disease, such as inflammatory bowel diseases and cancer. Colorectal cancer is a complex association of tumoral cells, non-neoplastic cells and a large amount of micro-organisms, and the involvement of the microbiota in colorectal carcinogenesis is becoming increasingly clear. Indeed, many changes in the bacterial composition of the gut microbiota have been reported in colorectal cancer, suggesting a major role of dysbiosis in colorectal carcinogenesis. Some bacterial species have been identified and suspected to play a role in colorectal carcinogenesis, such as Streptococcus bovis, Helicobacter pylori, Bacteroides fragilis, Enterococcus faecalis, Clostridium septicum, Fusobacterium spp. and Escherichia coli. The potential pro-carcinogenic effects of these bacteria are now better understood. In this review, we discuss the possible links between the bacterial microbiota and colorectal carcinogenesis, focusing on dysbiosis and the potential pro-carcinogenic properties of bacteria, such as genotoxicity and other virulence factors, inflammation, host defenses modulation, bacterial-derived metabolism, oxidative stress and anti-oxidative defenses modulation. We lastly describe how bacterial microbiota modifications could represent novel prognosis markers and/or targets for innovative therapeutic strategies
Abnormally expressed ER stress response chaperone Gp96 in CD favours adherent-invasive Escherichia coli invasion
Background and aims Crohn's disease (CD) ileal lesions are colonised by pathogenic adherent-invasive Escherichia coli (AIEC) producing outer membrane vesicles (OMVs) that contribute to the bacterial invasion process. In addition, increased expression of endoplasmic reticulum (ER)-localised stress response proteins, due to ER stress, is observed in patients with CD. The expression of the ER-localised stress response protein Gp96 in patients with CD and its biological role with regards to the ability of AIEC to invade intestinal epithelial cells were analysed.Methods and results Immunohistochemistry on tissue arrays showed that, together with CEACAM6 (carcinoembryonic antigen-related cell adhesion molecule 6) or the ER stress protein Grp78, Gp96 is also strongly expressed at the apical plasma membrane of the ileal epithelial cells of 50% of patients with CD. Invasion experiments in the presence of antibodies raised against Gp96, or after transfection of Intestine-407 cells with gp96 small interfering RNA (siRNA), indicated that Gp96 is essential to promote AIEC LF82 invasion, allowing, via the recognition of the outer membrane protein OmpA, OMVs to fuse with intestinal epithelial cells.Conclusions Gp96 is overexpressed on the apical surface of ileal epithelial cells in patients with CD and acts as a host cell receptor for OMVs, promoting AIEC invasion. From the results shown here, it is speculated that AIEC could take advantage of the abnormal expression of Gp96 in patients with CD to invade the ileal mucosa
A minimal BV action for Vasiliev's four-dimensional higher spin gravity
The action principle for Vasiliev's four-dimensional higher-spin gravity
proposed recently by two of the authors, is converted into a minimal BV master
action using the AKSZ procedure, which amounts to replacing the classical
differential forms by vectorial superfields of fixed total degree given by the
sum of form degree and ghost number. The nilpotency of the BRST operator is
achieved by imposing boundary conditions and choosing appropriate gauge
transitions between charts leading to a globally-defined formulation based on a
principal bundle.Comment: 39 pages, 1 figure. Additional comments in the conclusion
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