303 research outputs found
Second Order Noncommutative Corrections to Gravity
In this work, we calculate the leading order corrections to general
relativity formulated on a canonical noncommutative spacetime. These
corrections appear in the second order of the expansion in theta. First order
corrections can only appear in the gravity-matter interactions. Some
implications are briefly discussed.Comment: 10 page
Noncommutative General Relativity
We define a theory of noncommutative general relativity for canonical
noncommutative spaces. We find a subclass of general coordinate transformations
acting on canonical noncommutative spacetimes to be volume-preserving
transformations. Local Lorentz invariance is treated as a gauge theory with the
spin connection field taken in the so(3,1) enveloping algebra. The resulting
theory appears to be a noncommutative extension of the unimodular theory of
gravitation. We compute the leading order noncommutative correction to the
action and derive the noncommutative correction to the equations of motion of
the weak gravitation field.Comment: v2: 10 pages, Discussion on noncommutative coordinate transformations
has been changed. Corresponding changes have been made throughout the pape
Environmental Factors and Limbic Vulnerability in Childhood Autism
The rise in prevalence of autism spectrum disorders (ASD) is suggestive of a new etiology. Diagnostic substitution alone is unlikely to account for the increase, while genetic association with detoxification gene alleles points to an environmental contribution. Subtle structural anomalies in the ASD brain are widespread but limbic damage seems important for the development of behaviors diagnostic of ASD. The limbic brain is especially susceptible to environmental challenge: internal sensing, physiological feedback and neuroinflammatory processes may underlie this sensitivity to insult. Primary damage leading to ASD in later life is likely to take place in utero and/or in the immediate postnatal period. Despite evidence of heavy metal involvement, a causal connection may not yet be concluded because subjects exposed to metals tend to be exposed to other environmental agents. Because maternal minerals and lipids are supplied to the unborn child, historic toxic exposure of the mother may be pivotal. A two-hit combination of genetic susceptibility and environmental challenge is argued to underlie the rise in ASD
Unitarisation of EFT Amplitudes for Dark Matter Searches at the LHC
We propose a new approach to the LHC dark matter search analysis within the
effective field theory (EFT) framework by utilising the K-matrix unitarisation
formalism. This approach provides a reasonable estimate of the dark matter
production cross section at high energies, and hence allows reliable bounds to
be placed on the cut-off scale of relevant operators without running into the
problem of perturbative unitarity violation. We exemplify this procedure for
the effective operator D5 in monojet dark matter searches in the collinear
approximation. We compare our bounds to those obtained using the truncation
method and identify a parameter region where the unitarisation prescription
leads to more stringent bounds.Comment: 20 pages, 7 figures. References added and minor corrections made to
match published versio
New Solution to Doublet-Triplet Splitting Problem in SU(N) SUSY GUTs: Towards an Unification of Flavour
The missing VEV solution to the doublet-triplet splitting problem in general
SU(N) SUSY GUTs is found. Remarkably enough, it requires a strict equality of
numbers of the fundamental colours and flavours in SU(N) and for the even-order
groups (N=2k) gives the predominant breaking channel in the
parameter natural area. The flavour subsymmetry breaking owing to some generic
string inspired extra symmetries of the Higgs superpotential appears not to
affect markedly the basic adjoint vacuum configuration in the model. Thus the
both salient features of SM just as an interplay between colours and flavours
(or families for due assignment of quarks and leptons) so the doublet structure
of the weak interactions could be properly understood and accommodated in the
framework of the minimal SU(8) model. Among its predictions the most crucial
one belongs to the existence on the TeV scale just three families of
pseudo-Goldstone bosons and their superpartners 3(5+\bar 5) + SU(5)-singlets
which noticeably improve the unification picture of MSSM.Comment: 13 pages, LaTe
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