2,858 research outputs found
What do -ray bursts look like?
There have been great and rapid progresses in the field of -ray
bursts (denoted as GRBs) since BeppoSAX and other telescopes discovered their
afterglows in 1997. Here, we will first give a brief review on the
observational facts of GRBs and direct understanding from these facts, which
lead to the standard fireball model. The dynamical evolution of the fireball is
discussed, especially a generic model is proposed to describe the whole
dynamical evolution of GRB remnant from highly radiative to adiabatic, and from
ultra-relativistic to non-relativistic phase. Then, Various deviations from the
standard model are discussed to give new information about GRBs and their
environment. In order to relax the energy crisis, the beaming effects and their
possible observational evidences are also discussed in GRB's radiations.Comment: 10 pages, Latex. Invited talk at the Pacific Rim Conference on
Stellar Astrophysics, Hong Kong, China, Aug. 199
Bridging flavour violation and leptogenesis in SU(3) family models
We reconsider basic, in the sense of minimal field content, Pati-Salam x
SU(3) family models which make use of the Type I see-saw mechanism to reproduce
the observed mixing and mass spectrum in the neutrino sector. The goal of this
is to achieve the observed baryon asymmetry through the thermal decay of the
lightest right-handed neutrino and at the same time to be consistent with the
expected experimental lepton flavour violation sensitivity. This kind of models
have been previously considered but it was not possible to achieve a
compatibility among all of the ingredients mentioned above. We describe then
how different SU(3) messengers, the heavy fields that decouple and produce the
right form of the Yukawa couplings together with the scalars breaking the SU(3)
symmetry, can lead to different Yukawa couplings. This in turn implies
different consequences for flavour violation couplings and conditions for
realizing the right amount of baryon asymmetry through the decay of the
lightest right-handed neutrino. Also a highlight of the present work is a new
fit of the Yukawa textures traditionally embedded in SU(3) family models.Comment: 26 pages, 5 figures, Some typos correcte
R-parity violation in SU(5)
We show that judiciously chosen R-parity violating terms in the minimal
renormalizable supersymmetric SU(5) are able to correct all the
phenomenologically wrong mass relations between down quarks and charged
leptons. The model can accommodate neutrino masses as well. One of the most
striking consequences is a large mixing between the electron and the Higgsino.
We show that this can still be in accord with data in some regions of the
parameter space and possibly falsified in future experiments.Comment: 30 pages, 1 figure. Revised version. To appear in JHE
Goldstone Fermion Dark Matter
We propose that the fermionic superpartner of a weak-scale Goldstone boson
can be a natural WIMP candidate. The p-wave annihilation of this `Goldstone
fermion' into pairs of Goldstone bosons automatically generates the correct
relic abundance, whereas the XENON100 direct detection bounds are evaded due to
suppressed couplings to the Standard Model. Further, it is able to avoid
indirect detection constraints because the relevant s-wave annihilations are
small. The interactions of the Goldstone supermultiplet can induce non-standard
Higgs decays and novel collider phenomenology.Comment: 25 pages, 6 figures. References added, minor typos corrected.
Submitted to JHE
Supernova Remnants as Clues to Their Progenitors
Supernovae shape the interstellar medium, chemically enrich their host
galaxies, and generate powerful interstellar shocks that drive future
generations of star formation. The shock produced by a supernova event acts as
a type of time machine, probing the mass loss history of the progenitor system
back to ages of 10 000 years before the explosion, whereas supernova
remnants probe a much earlier stage of stellar evolution, interacting with
material expelled during the progenitor's much earlier evolution. In this
chapter we will review how observations of supernova remnants allow us to infer
fundamental properties of the progenitor system. We will provide detailed
examples of how bulk characteristics of a remnant, such as its chemical
composition and dynamics, allow us to infer properties of the progenitor
evolution. In the latter half of this chapter, we will show how this exercise
may be extended from individual objects to SNR as classes of objects, and how
there are clear bifurcations in the dynamics and spectral characteristics of
core collapse and thermonuclear supernova remnants. We will finish the chapter
by touching on recent advances in the modeling of massive stars, and the
implications for observable properties of supernovae and their remnants.Comment: A chapter in "Handbook of Supernovae" edited by Athem W. Alsabti and
Paul Murdin (18 pages, 6 figures
Decitabine impact on the endocytosis regulator RhoA, the folate carriers RFC1 and FOLR1, and the glucose transporter GLUT4 in human tumors.
BackgroundIn 31 solid tumor patients treated with the demethylating agent decitabine, we performed tumor biopsies before and after the first cycle of decitabine and used immunohistochemistry (IHC) to assess whether decitabine increased expression of various membrane transporters. Resistance to chemotherapy may arise due to promoter methylation/downregulation of expression of transporters required for drug uptake, and decitabine can reverse resistance in vitro. The endocytosis regulator RhoA, the folate carriers FOLR1 and RFC1, and the glucose transporter GLUT4 were assessed.ResultsPre-decitabine RhoA was higher in patients who had received their last therapy >3 months previously than in patients with more recent prior therapy (P = 0.02), and varied inversely with global DNA methylation as assessed by LINE1 methylation (r = -0.58, P = 0.006). Tumor RhoA scores increased with decitabine (P = 0.03), and RFC1 also increased in patients with pre-decitabine scores ≤150 (P = 0.004). Change in LINE1 methylation with decitabine did not correlate significantly with change in IHC scores for any transporter assessed. We also assessed methylation of the RFC1 gene (alias SLC19A1). SLC19A1 methylation correlated with tumor LINE1 methylation (r = 0.45, P = 0.02). There was a small (statistically insignificant) decrease in SLC19A1 methylation with decitabine, and there was a trend towards change in SLC19A1 methylation with decitabine correlating with change in LINE1 methylation (r = 0.47, P <0.15). While SLC19A1 methylation did not correlate with RFC1 scores, there was a trend towards an inverse correlation between change in SLC19A1 methylation and change in RFC1 expression (r = -0.45, P = 0.19).ConclusionsIn conclusion, after decitabine administration, there was increased expression of some (but not other) transporters that may play a role in chemotherapy uptake. Larger patient numbers will be needed to define the extent to which this increased expression is associated with changes in DNA methylation
Frequency and predictors of the lupus low disease activity state in a multi-national and multi-ethnic cohort
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