4,757 research outputs found
New visions for anaphylaxis: an iPAC summary and future trends
No full textAnaphylaxis is an increasing emergency in Western countries, especially in children. In the last decade, efforts have been attempted to widely understand anaphylaxis from several angles but at present, there are still numerous issues to be clarified and tackled for its earlier identification. The discrepancies in the operational definitions and diagnostic criteria of anaphylaxis represent one of the most controversial issues in casting light upon its epidemiology. Furthermore, the lack of reliable markers of the disease hampers its diagnosis. Further basic and clinical research is urgently needed to confirm the recent promising results derived from studies on animal models, and to clarify the key role of selected mediators and markers in the different steps of the reaction, in its severity and in the recurrences. The underuse of adrenaline is another important issue, as available data demonstrate physicians' preference for steroids and anti-histamines despite the current lack of evidence of their effectiveness. In the near future, the management of anaphylaxis will be strongly influenced by the development of a stepwise approach, as well as by the creation of a system improving transmission of good quality data between the emergency room, the allergist and the family doctor. This process will certainly be enhanced by the establishment of a network of Centres of Excellence collaborating for high quality research and care and involved in the dissemination of new knowledge at a primary care level. This review will seek to briefly overview our current knowledge and highlight the key questions that need to be addressed in the next decade to improve clinical care to children and will focus on the epidemiology of anaphylaxis, the identification of individuals at risk of anaphylaxis, the special issues related to infants, community management of children at risk of anaphylaxis and school related issue
One-loop quantum gravity from the N=4 spinning particle
Get PDFWe construct a spinning particle that reproduces the propagation of the graviton on those curved backgrounds which solve the Einstein equations, with or without cosmological constant, i.e. Einstein manifolds. It is obtained by modifying the N=4 supersymmetric spinning particle by relaxing the gauging of the full SO(4) R-symmetry group to a parabolic subgroup, and selecting suitable Chern-Simons couplings on the worldline. We test it by computing the correct one-loop divergencies of quantum gravity in D=4
Scattering Amplitudes of Massive N=2 Gauge Theories in Three Dimensions
Get PDFWe study the scattering amplitudes of mass-deformed Chern-Simons theories and Yang-Mills-Chern-Simons theories with N=2 supersymmetry in three dimensions. In particular, we derive the on-shell supersymmetry algebras which underlie the scattering matrices of these theories. We then compute various 3 and 4-point on-shell tree-level amplitudes in these theories. For the mass-deformed Chern-Simons theory, odd-point amplitudes vanish and we find that all of the 4-point amplitudes can be encoded elegantly in superamplitudes. For the Yang-Mills-Chern-Simons theory, we obtain all of the 4-point tree-level amplitudes using a combination of perturbative techniques and algebraic constraints and we comment on difficulties related to computing amplitudes with external gauge fields using Feynman diagrams. Finally, we propose a BCFW recursion relation for mass-deformed theories in three dimensions and discuss the applicability of this proposal to mass-deformed N=2 theories
Chirality of Gravitational Waves in Chern-Simons Gravity Cosmology
Get PDFIn this paper we shall consider an axionic Chern-Simons corrected
gravity theoretical framework, and we shall study the chirality of the
generated primordial gravitational waves. Particularly, we shall consider two
main axion models, the canonical misalignment axion model and the kinetic axion
model, both of which provide an interesting particle phenomenology, in the
presence of terms in the inflationary Lagrangian. The axion does not
affect significantly the background evolution during the inflationary era,
which is solely controlled by gravity. However, the due to the presence
of the Chern-Simons term, the tensor perturbations are directly affected, and
our aim is to reveal the extent of effects of the Chern-Simons term on the
gravitational waves modes, for both the axion models. We aim to produce
analytical descriptions of the primordial tensor modes behavior, and thus we
solve analytically the evolution equations of the tensor modes, for a nearly de
Sitter primordial evolution controlled by the gravity. We focus the
analytical study on superhorizon and subhorizon modes. For the misalignment
model, we were able to produce analytic solutions for both the subhorizon and
superhorizon modes, in which case we found the behavior of the circular
polarization function. Our results indicate that the produced tensor spectrum
is strongly chiral. For the kinetic axion model though, analytic solutions are
obtained only for the superhorizon modes. In order to have a grasp of the
behavior of the chirality of the tensor modes, we studied the chirality of the
superhorizon modes, however a more complete study is needed, which is
impossible to do analytically though.Comment: PRD Accepte
Einstein-Chern-Simons equations on the 3-brane world
Get PDFIn this article it is studied the 3-brane world in the context of
five-dimensional Einstein-Chern-Simons gravity. We started by considering
Israel's junction condition for AdS-Chern-Simons gravity. Using the S-expansion
procedure, we mapped the AdS-Chern-Simons junction conditions to
Einstein-Chern-Simons gravity, allowing us to derive effective four-dimensional
Einstein-Chern-Simons field equations
Higher dimensional abelian Chern-Simons theories and their link invariants
No full text40 pagesInternational audienceThe role played by Deligne-Beilinson cohomology in establishing the relation between Chern-Simons theory and link invariants in dimensions higher than three is investigated. Deligne-Beilinson cohomology classes provide a natural abelian Chern-Simons action, non trivial only in dimensions , whose parameter is quantized. The generalized Wilson -loops are observables of the theory and their charges are quantized. The Chern-Simons action is then used to compute invariants for links of -loops, first on closed -manifolds through a novel geometric computation, then on through an unconventional field theoretic computation
Solitons in low-dimensional sigma models
Get PDFThe aim of this thesis is to study topological soliton solutions in classical field theories, called sigma models, on a three-dimensional space. In chapter 1 we review the general field-theoretical framework of classical soliton solutions and exemplify it on the main features of the 0(3) σ-model and the Abehan Higgs model in (2+1) dimensions. In chapter 2 a U(l)-gauged 0(3) σ-model is discussed, where the behaviour of the gauge field is determined by a Chern-Simons term in the action. We find numerical solutions for radially symmetric fields and discuss those of degree one and two. They carry a non-vanishing angular momentum and can be interpreted as classical anyons. A similar model is studied in chapter 3. Here the potential is of Higgs-type and chosen to produce a Bogomol'nyi model where the energy is bounded from below by a linear combination of the topological degree of the matter fields and the local U(l)-charge. Depending on internal parameters, the solutions are solitons or vortices. We study them numerically and prove for a certain range of the matter field's vacuum value that there cannot be a 1-soliton.In chapter 4 we discuss a modified 0(3) σ-model in (3+0) dimensions. The topological stability of the solitons is here imphed by the degree of the map S(^3) → S(^2), which provides a lower boundon the potential energy of the configuration. Numerical solutions are obtained for configurations of azimuthal symmetry and the spectrum of slowly rotating solitons is approximated. Chapter 5 deals with a theory where the fields are maps IR(^2+1) → CP(^2). The Lagrangian includes a potential and a fourth-order term in the field-gradient. We find a family of static analytic solutions of degree one and study the 2-soIiton configuration numerically by using a gradient-flow equation on the moduli space of solutions. We conclude this thesis with a brief summary and give an outlook to open questions
Some comments on Chern-Simons gauge theory
No full textFollowing M. F. Atiyah and R. Bott [AB] and E. Witten [W], we consider the space of flat connections on the trivial SU(2) bundle over a surface M, modulo the space of gauge transformations. We describe on this quotient space a natural hermitian line-bundle with connection and prove that if the surface M is now endowed with a complex structure, this line bundle is isomorphic to the determinant bundle. We show heuristically how path-integral quantisation of the Chern-Simons action yields holomorphic sections of this bundle
A note on amplitudes in N=6 superconformal Chern-Simons theory
No full textThis is the accepted version of an article subsequently published in Journal of High Energy Physics July 2012, 2012:160. The original publication is available at www.springerlink.com http://link.springer.com/article/10.1007%2FJHEP07%282012%29160This version deposited to arXiv 30-07-12 arXiv:1205.6705v3 [hep-th
Topological gauge fixing II: a homotopy formulation
No full textInternational audienceWe revisit the implementation of the metric-independent Fock-Schwinger gauge in the abelian Chern-Simons field theory defined in by means of a homotopy condition. This leads to the lagrangian in terms of curvatures and of the Poincar\'e homotopy operator . The corresponding field theory provides the same link invariants as the abelian Chern-Simons theory. Incidentally the part of the gauge field propagator which yields the link invariants of the Chern-Simons theory in the Fock-Schwinger gauge is recovered without any computation
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