1,126 research outputs found
Gauging CSO groups in N=4 Supergravity
We investigate a class of CSO-gaugings of N=4 supergravity coupled to six
vector multiplets. Using the CSO-gaugings we do not find a vacuum that is
stable against all scalar perturbations at the point where the matter fields
are turned off. However, at this point we do find a stable cosmological scaling
solution.Comment: 21 page
Group Manifold Reduction of Dual N=1 d=10 Supergravity
We perform a group manifold reduction of the dual version of N=1 d=10
supergravity to four dimensions. The effects of the 3- and 4-form gauge fields
in the resulting gauged N=4 d=4 supergravity are studied in particular. The
example of the group manifold SU(2)xSU(2) is worked out in detail, and we
compare for this case the four-dimensional scalar potential with gauged N=4
supergravity.Comment: 22 pages, revised section 3, typos corrected. Published versio
De Sitter solutions in N=4 matter coupled supergravity
We investigate the scalar potential of gauged N=4 supergravity with matter.
The extremum in the SU(1,1)/U(1) scalars is obtained for an arbitrary number of
matter multiplets. The constraints on the matter scalars are solved in terms of
an explicit parametrisation of an
SO(6,6+n) element. For the case of six matter multiplets we discuss both
compact and noncompact gauge groups.
In an example involving noncompact groups and four scalars we find a
potential with an absolute minimum and a positive cosmological constant.Comment: 14 page
Scaling solutions and geodesics in moduli space
In this paper we consider cosmological scaling solutions in general
relativity coupled to scalar fields with a non-trivial moduli space metric. We
discover that the scaling property of the cosmology is synonymous with the
scalar fields tracing out a particular class of geodesics in moduli space -
those which are constructed as integral curves of the gradient of the log of
the potential. Given a generic scalar potential we explicitly construct a
moduli metric that allows scaling solutions, and we show the converse - how one
can construct a potential that allows scaling once the moduli metric is known.Comment: 10 pages, 3 figure
Potential and mass-matrix in gauged N=4 supergravity
We discuss the potential and mass-matrix of gauged N=4 matter coupled
supergravity for the case of six matter multiplets, extending previous work by
considering the dependence on all scalars. We consider all semi-simple gauge
groups and analyse the potential and its first and second derivatives in the
origin of the scalar manifold. Although we find in a number of cases an
extremum with a positive cosmological constant, these are not stable under
fluctuations of all scalar fields.Comment: 28 pages, LaTe
Dynamics of Generalized Assisted Inflation
We study the dynamics of multiple scalar fields and a barotropic fluid in an
FLRW-universe. The scalar potential is a sum of exponentials. All critical
points are constructed and these include scaling and de Sitter solutions. A
stability analysis of the critical points is performed for generalized assisted
inflation, which is an extension of assisted inflation where the fields
mutually interact. Effects in generalized assisted inflation which differ from
assisted inflation are emphasized. One such a difference is that an
(inflationary) attractor can exist if some of the exponential terms in the
potential are negative.Comment: 27 page
Cas3 is a limiting factor for CRISPR-Cas immunity in Escherichia coli cells lacking H-NS
Background: CRISPR-Cas systems provide adaptive immunity to mobile genetic elements in prokaryotes. In many bacteria, including E. coli, a specialized ribonucleoprotein complex called Cascade enacts immunity by “an interference reaction" between CRISPR encoded RNA (crRNA) and invader DNA sequences called “protospacers”. Cascade recognizes invader DNA via short “protospacer adjacent motif” (PAM) sequences and crRNA-DNA complementarity. This triggers degradation of invader DNA by Cas3 protein and in some circumstances stimulates capture of new invader DNA protospacers for incorporation into CRISPR as “spacers” by Cas1 and Cas2 proteins, thus enhancing immunity. Co-expression of Cascade, Cas3 and crRNA is effective at giving E. coli cells resistance to phage lysis, if a transcriptional repressor of Cascade and CRISPR, H-NS, is inactivated (Δhns). We present further genetic analyses of the regulation of CRISPR-Cas mediated phage resistance in Δhns E. coli cells.
Results: We observed that E. coli Type I-E CRISPR-Cas mediated resistance to phage λ was strongly temperature dependent, when repeating previously published experimental procedures. Further genetic analyses highlighted the importance of culture conditions for controlling the extent of CRISPR immunity in E. coli. These data identified that expression levels of cas3 is an important limiting factor for successful resistance to phage. Significantly, we describe the new identification that cas3 is also under transcriptional control by H-NS but that this is exerted only in stationary phase cells.
Conclusions: Regulation of cas3 is responsive to phase of growth, and to growth temperature in E. coli, impacting on the efficacy of CRISPR-Cas immunity in these experimental systems
Scaling Cosmologies of N=8 Gauged Supergravity
We construct exact cosmological scaling solutions in N=8 gauged supergravity.
We restrict to solutions for which the scalar fields trace out geodesic curves
on the scalar manifold. Under these restrictions it is shown that the axionic
scalars are necessarily constant. The potential is then a sum of exponentials
and has a very specific form that allows for scaling solutions. The scaling
solutions describe eternal accelerating and decelerating power-law universes,
which are all unstable. An uplift of the solutions to 11-dimensional
supergravity is carried out and the resulting timedependent geometries are
discussed. In the discussion we briefly comment on the fact that N=2 gauged
supergravity allows stable scaling solutions.Comment: 17 pages; referenced added, reportnr changed and some corrections in
section
A String Field Theory based on Causal Dynamical Triangulations
We formulate the string field theory in zero-dimensional target space
corresponding to the two-dimensional quantum gravity theory defined through
Causal Dynamical Triangulations. This third quantization of the quantum gravity
theory allows us in principle to calculate the transition amplitudes of
processes in which the topology of space changes in time, and to include
non-trivial topologies of space-time. We formulate the corresponding
Dyson-Schwinger equations and illustrate how they can be solved iteratively.Comment: 29 pages, 4 figure
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