100 research outputs found
Einstein static universe as a brane in extra dimensions
We present a brane-world scenario in which two regions of space-time
are glued together along a 3-brane with constant positive curvature such that
{\em all} spatial dimensions form a compact manifold of topology . It
turns out that the induced geometry on the brane is given by Einstein's static
universe. It is possible to achieve an anisotropy of the manifold which allows
for a huge hierarchy between the size of the extra dimension and the size
of the observable universe at present. This anisotropy is also at the
origin of a very peculiar property of our model: the physical distance between
{\em any two points} on the brane is of the order of the size of the extra
dimension regardless of their distance measured with the use of the induced
metric on the brane. In an intermediate distance regime
gravity on the brane is shown to be effectively 4-dimensional, with
corresponding large distance corrections, in complete analogy with the
Randall-Sundrum II model. For very large distances we recover
gravity in Einstein's static universe. However, in contrast to the
Randall-Sundrum II model the difference in topology has the advantage of giving
rise to a geodesically complete space.Comment: 45 pages, 3 figure
Braneworlds in six dimensions: new models with bulk scalars
Six dimensional bulk spacetimes with 3-- and 4--branes are constructed using
certain non--conventional bulk scalars as sources. In particular, we
investigate the consequences of having the phantom (negative kinetic energy)
and the Brans--Dicke scalar in the bulk while obtaining such solutions. We find
geometries with 4--branes with a compact on--brane dimension (hybrid
compactification) which may be assumed to be small in order to realize a
3--brane world. On the other hand, we also construct, with similar sources,
bulk spacetimes where a 3--brane is located at a conical singularity.
Furthermore, we investigate the issue of localization of matter fields (scalar,
fermion, graviton, vector) on these 3-- and 4--branes and conclude with
comments on our six dimensional models.Comment: 24 pages, 1 figure, Replaced to match version published in Class.
Quant. Gra
Brane world in a texture
We study five dimensional brane physics induced by an O(2) texture formed in
one extra dimension. The model contains two 3-branes of nonzero tension, and
the extra dimension is compact. The symmetry-breaking scale of the texture
controls the particle hierarchy between the two branes. The TeV-scale particles
are confined to the negative-tension brane where the observer sees gravity as
essentially four dimensional. The effect of massive Kaluza-Klein gravitons is
suppressed.Comment: 25 pages, revtex, 5 eps figures, Significant changes have been made
for the tachyonic mode, One figure has been replaced, To appear in Physical
Review
Inflating magnetically charged braneworlds
Numerical solutions of Einstein, scalar, and gauge field equations are found
for static and inflating defects in a higher-dimensional spacetime. The defects
have -dimensional core and magnetic monopole configuration in
extra dimensions. For symmetry-breaking scale below the critical value
, the defects are characterized by a flat worldsheet geometry and
asymptotically flat extra dimensions. The critical scale is comparable
to the higher-dimensional Planck scale and has some dependence on the gauge and
scalar couplings. For , the extra dimensions degenerate into a
`cigar', and for all static solutions are singular. The
singularity can be removed if the requirement of staticity is relaxed and
defect cores are allowed to inflate. The inflating solutions have de Sitter
worldsheets and cigar geometry in the extra dimensions. Exact analytic
solutions describing the asymptotic behavior of these inflating monopoles are
found and the parameter space of these solutions is analyzed.Comment: 35 pages, revtex, 18 eps figure
Stability of inflating branes in a texture
We investigate the stability of inflating branes embedded in an O(2) texture
formed in one extra dimension. The model contains two 3-branes of nonzero
tension, and the extra dimension is compact. When the gravitational
perturbation is applied, the vacuum energy which is responsible for inflation
on the branes stabilizes the branes if the symmetry-breaking scale of the
texture is smaller than some critical value. This critical value is determined
by the particle-hierarchy scale between the two branes, and is smaller than the
5D Planck-mass scale. The scale of the vacuum energy can be considerably low in
providing the stability. This stability story is very different from the
flat-brane case which always suffers from the instability due to the
gravitational perturbation.Comment: 16 pages, 5 eps figures, revte
Localizing gravity on a 't Hooft-Polyakov monopole in seven dimensions
We present regular solutions for a brane world scenario in the form of a 't
Hooft-Polyakov monopole living in the three-dimensional spherical symmetric
transverse space of a seven-dimensional spacetime. In contrast to the cases of
a domain-wall in five dimensions and a string in six dimensions, there exist
gravity-localizing solutions for both signs of the bulk cosmological constant.
A detailed discussion of the parameter space that leads to localization of
gravity is given. A point-like monopole limit is discussed.Comment: 29 pages, 17 figure
Isospin breaking corrections to low-energy pi-K scattering
We evaluate the matrix elements for the processes pi^0 K^0 -> pi^0 K^0 and
pi^- K^+ -> pi^0 K^0 in the presence of isospin breaking terms at leading and
next-to-leading order. As a direct application the releveant combination of the
S-wave scattering lengths involved in the pion-kaon atom lifetime is
determined. We discuss the sensitivity of the results with respect to the input
parameters.Comment: 33 pages, plain latex, 2 figure
B-physics from Nf=2 tmQCD: the Standard Model and beyond
We present a lattice QCD computation of the b-quark mass, the B and B_s decay constants, the B-mixing bag parameters for the full four-fermion operator basis as well as determinations for \xi and f_{Bq}\sqrt{B_i^{(q)}} extrapolated to the continuum limit and to the physical pion mass. We used N_f = 2 twisted mass Wilson fermions at four values of the lattice spacing with pion masses ranging from 280 to 500 MeV. Extrapolation in the heavy quark mass from the charm to the bottom quark region has been carried out on ratios of physical quantities computed at nearby quark masses, exploiting the fact that they have an exactly known infinite mass limit. Our results are m_b(m_b, \overline{\rm{MS}})=4.29(12) GeV, f_{Bs}=228(8) MeV, f_{B}=189(8) MeV and f_{Bs}/f_B=1.206(24). Moreover with our results for the bag-parameters we find \xi=1.225(31), B_1^{(s)}/B_1^{(d)}=1.01(2), f_{Bd}\sqrt{\hat{B}_{1}^{(d)}} = 216(10) MeV and f_{Bs}\sqrt{\hat{B}_{1}^{(s)}} = 262(10) MeV. We also computed the bag parameters for the complete basis of the four-fermion operators which are required in beyond the SM theories. By using these results for the bag parameters we are able to provide a refined Unitarity Triangle analysis in the presence of New Physics, improving the bounds coming from B_{(s)}-\bar B_{(s)} mixing
The Expression of a Xylanase Targeted to ER-Protein Bodies Provides a Simple Strategy to Produce Active Insoluble Enzyme Polymers in Tobacco Plants
Background
Xylanases deserve particular attention due to their potential application in the feed, pulp bleaching and paper industries. We have developed here an efficient system for the production of an active xylanase in tobacco plants fused to a proline-rich domain (Zera) of the maize storage protein γ-zein. Zera is a self-assembling domain able to form protein aggregates in vivo packed in newly formed endoplasmic reticulum-derived organelles known as protein bodies (PBs).
Methodology/Principal Findings
Tobacco leaves were transiently transformed with a binary vector containing the Zera-xylanase coding region, which was optimized for plant expression, under the control of the 35S CaMV promoter. The fusion protein was efficiently expressed and stored in dense PBs, resulting in yields of up to 9% of total protein. Zera-xylanase was post-translationally modified with high-mannose-type glycans. Xylanase fused to Zera was biologically active not only when solubilized from PBs but also in its insoluble form. The resistance of insoluble Zera-xylanase to trypsin digestion demonstrated that the correct folding of xylanase in PBs was not impaired by Zera oligomerization. The activity of insoluble Zera-xylanase was enhanced when substrate accessibility was facilitated by physical treatments such as ultrasound. Moreover, we found that the thermostability of the enzyme was improved when Zera was fused to the C-terminus of xylanase.
Conclusion/Significance
In the present work we have successfully produced an active insoluble aggregate of xylanase fused to Zera in plants. Zera-xylanase chimeric protein accumulates within ER-derived protein bodies as active aggregates that can easily be recovered by a simple density-based downstream process. The production of insoluble active Zera-xylanase protein in tobacco outlines the potential of Zera as a fusion partner for producing enzymes of biotechnological relevance. Zera-PBs could thus become efficient and low-cost bioreactors for industrial purposes.This work was mainly supported by ERA Biotech (www.erabiotech.com). Additional support was supplied by grant SGR 2009/703 funded by the Generalitat de Catalunya (www10.gencat.net) and grants CDS2007/00036 of Consolider Ingenio program and TRA 2009/0124 of TRACE program funded by Ministerio de Ciencia e Inovación (MICINN, www.micinn.es). The funders had no role in study design, data collection and analysis, decision to publish, or preparation of the manuscript.Peer reviewe
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