261 research outputs found
Molecular mechanisms of human prion diseases
No full textAfter having proof of its transmissibility, the mysterious agent of human transmissible encephalopathies was considered for decades an unconventional invader. The subsequent characterization of a host amyloidogenic protein, segregating with infectivity, and the discovery of its encoding gene, led to the hypothesis that the infectious agent, termed prion, is a misfolded self-replicating protein. Prions are both infectious and neurotoxic, and recent evidence suggests that these properties segregate with distinct molecular forms of this protein. © 2005 Elsevier Ltd. All rights reserved
Molecular pathogenesis of prion diseases
No full textIntroduction: Prion diseases or transmissible spongiform encephalopathies (TSEs) are rare, fatal and
incurable neurodegenerative disorders of humans and animals (Prusiner, 1998).
In humans, prion diseases occur with unique aetiology as sporadic, genetic or infectious
disorders. Sporadic cases of prion diseases, which account for the majority of casualties (up
to 85% of all cases), are of unknown origin; the genetic forms are less frequent (up to 15%),
while the infectious cases are extremely rare with an incidence of less than 1% (Prusiner,
2001). Creutzfeldt-Jakob disease (CJD), Gerstmann-Sträussler-Scheinker (GSS) syndrome,
Fatal Familial Insomnia (FFI) are examples of human prion diseases. In animals the disease
is mostly infectious and the mode of transmission is horizontal. Prion diseases include
scrapie in sheep and goats, bovine spongiform encephalopathy (BSE) in cattle, and chronic
wasting disease of deer, elk, and moose (Williams, 2005).
The agents responsible for prion diseases are infectious proteins named prions. The term
‘prion’ was coined when Stanley B. Prusiner introduced the concept of proteinaceous
infectious particles (Prusiner, 1982). Since the introduction of this once heretical notion,
mounting evidence has strengthened its validity.
In the next sections of this chapter we present and discuss the peculiar complexity of the
molecular pathogenesis of prion diseases in humans and animals
Asymptotic safety in einstein gravity and scalar-fermion matter
No full textWithin the functional renormalization group approach we study the effective quantum field theory of Einstein gravity and one self-interacting scalar coupled to Nf Dirac fermions. We include in our analysis the matter anomalous dimensions induced by all the interactions and analyze the highly nonlinear beta functions determining the renormalization flow. We find the existence of a nontrivial fixed point structure both for the gravity and the matter sector, besides the usual Gaussian matter one. This suggests that asymptotic safety could be realized in the gravitational sector and in the standard model. Nontriviality in the Higgs sector might involve gravitational interactions. © 2010 The American Physical Society
Conformally covariant operators of mixed-symmetry tensors and MAGs
No full textWe compute conformally covariant actions and operators for tensors with mixed symmetries in arbitrary dimension d. Our results complete the classification of conformal actions that are quadratic on arbitrary tensors with three indices, which allows to write corresponding conformal actions for all tensor species that appear in the decomposition of the distorsion tensor of an arbitrary metric-affine theory of gravity including both torsion and nonmetricity. We also discuss the degrees of freedom that such theories are propagating, as well as interacting metric-affine theories that enjoy the conformal actions in the Gaussian limit
Crossover exponents, fractal dimensions and logarithms in Landau–Potts field theories
No full textWe compute the crossover exponents of all quadratic and cubic deformations of critical field theories with permutation symmetry in (Landau–Potts field theories) and (hypertetrahedral models) up to three loops. We use our results to determine the -expansion of the fractal dimension of critical clusters in the most interesting cases, which include spanning trees and forests (), and bond percolations (). We also explicitly verify several expected degeneracies in the spectrum of relevant operators for natural values of q upon analytic continuation, which are linked to logarithmic corrections of CFT correlators, and use the -expansion to determine the universal coefficients of such logarithms
Functional perturbative RG and CFT data in the ϵ -expansion
No full textAbstract We show how the use of standard perturbative RG in dimensional regularization allows for a renormalization group-based computation of both the spectrum and a family of coefficients of the operator product expansion (OPE) for a given universality class. The task is greatly simplified by a straightforward generalization of perturbation theory to a functional perturbative RG approach. We illustrate our procedure in the ϵ -expansion by obtaining the next-to-leading corrections for the spectrum and the leading corrections for the OPE coefficients of Ising and Lee-Yang universality classes and then give several results for the whole family of renormalizable multi-critical models ϕ2n . Whenever comparison is possible our RG results explicitly match the ones recently derived in CFT frameworks
New universality class in three dimensions: The critical Blume-Capel model
No full textWe study the Blume-Capel universality class in d=103-ε dimensions. The renormalization group flow is extracted by looking at poles in fractional dimension of three loop diagrams using MS. The theory is the only nontrivial universality class which admits an expansion to three dimensions with ε=13<1. We compute the relevant scaling exponents and estimate some of the operator product expansion coefficients to the leading order. Our findings agree with and complement conformal field theory results. Finally we discuss a family of nonunitary multicritical models which includes the Lee-Yang and Blume-Capel classes as special cases
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