35 research outputs found
Allowed slepton intergenerational mixing in light of light element abundances
We studied allowed region on the intergenerational mixing parameters of
sleptons from a viewpoint of big-bang nucleosynthesis in a slepton-neutralino
coannihilation scenario. In this scenario, Li and Li problems can be
solved by considering exotic reactions caused by bound-state effects with a
long-lived slepton. Light element abundances are calculated as functions of the
relic density and lifetime of the slepton which considerably depend on the
intergenerational mixing parameters. Compared with observational light element
abundances, we obtain allowed regions on the intergenerational mixing. Ratio of
selectron component to stau component, , is allowed in with solving both the Li and Li
problems. Similarly, the ratio for smuon, , is allowed in for mass difference between
slepton and neutralino, which is smaller than muon mass, and for the mass difference in
range between muon mass and 125 MeV. We also discuss collider signatures of the
slepton decays. We find characteristic double peaks in momentum distribution of
event number of the slepton decays with allowed mixing parameters. Discoveries
of the double peaks at future collider experiments should confirm our scenario.Comment: 10 pages, 6 figure
Stau relic density at the Big-Bang nucleosynthesis era consistent with the abundance of the light element nuclei in the coannihilation scenario
We calculate the relic density of stau at the beginning of the Big-Bang
Nucleosynthesis (BBN) era in the coannihilation scenario of minimal
supersymmetric standard model (MSSM). In this scenario, stau can be long-lived
and form bound states with nuclei. We put constraints on the parameter space of
MSSM by connecting the calculation of the relic density of stau to the
observation of the light elements abundance, which strongly depends on the
relic density of stau. Consistency between the theoretical prediction and the
observational result, both of the dark matter abundance and the light elements
abundance, requires the mass difference between the lighter stau and the
lightest neutralino to be around 100MeV, the stau mass to be 300 -- 400 GeV,
and the mixing angle of the left and right-handed staus to be
.Comment: 9 pages, 5 figures, figure 5 correcte
Possible solution to the Li problem by the long lived stau
Modification of standard big-bang nucleosynthesis is considered in the
minimal supersymmetric standard model to resolve the excessive theoretical
prediction of the abundance of primordial lithium 7. We focus on the stau as a
next-lightest superparticle, which is long lived due to its small mass
difference with the lightest superparticle. It provides a number of additional
decay processes of and . A particularly
important process is the internal conversion in the stau-nucleus bound state,
which destroys the and effectively. We show
that the modification can lead to a prediction consistent with the observed
abundance of .Comment: 6 pages, 5 figure
Big-bang nucleosynthesis and the relic abundance of dark matter in a stau-neutralino coannihilation scenario
A scenario of the Big-Bang Nucleosynthesis is analyzed within the Minimal
Supersymmetric Standard Model which is consistent with a stau-neutralino
coannihilation scenario to explain the relic abundance of dark matter. We find
that we can account for the possible descrepancy of the abundance of
between the observation and the prediction of the Big-Bang
Nucleosynthesis by taking the mass of the neutralino as and
the mass difference between the stau and the neutralino as .
We can therefore simultaneously explain the abundance of the dark matter and
that of by these values of parameters. The lifetime of staus
in this scenario is predicted to be .Comment: 9 pages, 2 figure
Characterization of Mesenchymal Stem Cell-Like Cells Derived From Human iPSCs via Neural Crest Development and Their Application for Osteochondral Repair
Mesenchymal stem cells (MSCs) derived from induced pluripotent stem cells (iPSCs) are a promising cell source for the repair of skeletal disorders. Recently, neural crest cells (NCCs) were reported to be effective for inducing mesenchymal progenitors, which have potential to differentiate into osteochondral lineages. Our aim was to investigate the feasibility of MSC-like cells originated from iPSCs via NCCs for osteochondral repair. Initially, MSC-like cells derived from iPSC-NCCs (iNCCs) were generated and characterized in vitro. These iNCC-derived MSC-like cells (iNCMSCs) exhibited a homogenous population and potential for osteochondral differentiation. No upregulation of pluripotent markers was detected during culture. Second, we implanted iNCMSC-derived tissue-engineered constructs into rat osteochondral defects without any preinduction for specific differentiation lineages. The implanted cells remained alive at the implanted site, whereas they failed to repair the defects, with only scarce development of osteochondral tissue in vivo. With regard to tumorigenesis, the implanted cells gradually disappeared and no malignant cells were detected throughout the 2-month follow-up. While this study did not show that iNCMSCs have efficacy for repair of osteochondral defects when implanted under undifferentiated conditions, iNCMSCs exhibited good chondrogenic potential in vitro under appropriate conditions. With further optimization, iNCMSCs may be a new source for tissue engineering of cartilage.Peer Reviewe
Scaffold-free tissue engineering for injured joint surface restoration
Abstract Articular cartilage does not heal spontaneously due to its limited healing capacity, and thus effective treatments for cartilage injuries has remained challenging. Since the first report by Brittberg et al. in 1994, autologous chondrocyte implantation (ACI) has been introduced into the clinic. Recently, as an alternative for chondrocyte-based therapy, mesenchymal stem cell (MSC)-based therapy has received considerable research attention because of the relative ease in handling for tissue harvest, and subsequent cell expansion and differentiation. In this review, we discuss the latest developments regarding stem cell-based therapies for cartilage repair, with special focus on recent scaffold-free approaches