10,967 research outputs found
Exploring the Latest Union2 SNIa Dataset by Using Model-Independent Parametrization Methods
We explore the cosmological consequences of the recently released Union2
sample of 557 Type Ia supernovae (SNIa). Combining this latest SNIa dataset
with the Cosmic microwave background (CMB) anisotropy data from the Wilkinson
Microwave Anisotropy Probe 7 year (WMAP7) observations and the baryon acoustic
oscillation (BAO) results from the Sloan Digital Sky Survey (SDSS) Data Release
7 (DR7), we measure the dark energy density function as a free function of redshift. Two
model-independent parametrization methods (the binned parametrization and the
polynomial interpolation parametrization) are used in this paper. By using the
statistic and the Bayesian information criterion, we find that the
current observational data are still too limited to distinguish which
parametrization method is better, and a simple model has advantage in fitting
observational data than a complicated model. Moreover, it is found that all
these parametrizations demonstrate that the Union2 dataset is still consistent
with a cosmological constant at 1 confidence level. Therefore, the
Union2 dataset is different from the Constitution SNIa dataset, which more
favors a dynamical dark energy.Comment: 11 pages, 8 figures, 2 tables, accepted for publication in PR
K-essence Explains a Lorentz Violation Experiment
Recently, a state of the art experiment shows evidence for Lorentz violation
in the gravitational sector. To explain this experiment, we investigate a
spontaneous Lorentz violation scenario with a generalized scalar field. We find
that when the scalar field is nonminimally coupled to gravity, the Lorentz
violation induces a deformation in the Newtonian potential along the direction
of Lorentz violation.Comment: 8 pages, the final version, discussion and references adde
Shock Waves and Cosmological Matrix Models
We find the shock wave solutions in a class of cosmological backgrounds with
a null singularity, each of these backgrounds admits a matrix description. A
shock wave solution breaks all supersymmetry meanwhile indicates that the
interaction between two static D0-branes cancel, thus provides basic evidence
for the matrix description. The probe action of a D0-brane in the background of
another suggests that the usual perturbative expansion of matrix model breaks
down.Comment: 10 pages, harvmav, v2: some comments on instability added, v3:
version to appear in JHE
The transcription factors Egr2 and Egr3 are essential for the control of inflammation and antigen-induced proliferation of B and T cells
This article is available open access under a Creative Commons license (http://creativecommons.org/licenses/by-nc-nd/3.0/). Copyright @ 2012 Elsevier Inc.Lymphocytes provide optimal responses against pathogens with minimal inflammatory pathology. However, the intrinsic mechanisms regulating these responses are unknown. Here, we report that deletion of both transcription factors Egr2 and Egr3 in lymphocytes resulted in a lethal autoimmune syndrome with excessive serum proinflammatory cytokines but also impaired antigen receptor-induced proliferation of B and T cells. Egr2- and Egr3-defective B and T cells had hyperactive signal transducer and activator of transcription-1 (STAT1) and STAT3 while antigen receptor-induced activation of transcription factor AP-1 was severely impaired. We discovered that Egr2 and/or Egr3 directly induced expression of suppressor of cytokine signaling-1 (SOCS1) and SOCS3, inhibitors of STAT1 and STAT3, and also blocked the function of Batf, an AP-1 inhibitor, in B and T cells. Thus, Egr2 and Egr3 regulate B and T cell function in adaptive immune responses and homeostasis by promoting antigen receptor signaling and controlling inflammation.Arthritis Research U
Weak gravity conjecture in the asymptotical dS and AdS background
The cosmological observations provide a strong evidence that there is a
positive cosmological constant in our universe and thus the spacetime is
asymptotical de Sitter space. The conjecture of gravity as the weakest force in
the asymptotical dS space leads to a lower bound on the U(1) gauge coupling
, or equivalently, the positive cosmological constant gets an upper bound
in order that the U(1) gauge theory can survive in four
dimensions. This result has a simple explanation in string theory, i.e. the
string scale should not be greater than the size of the
cosmic horizon. Our proposal in string theory can be generalized to U(N) gauge
theory and gives a guideline to the microscopic explanation of the de Sitter
entropy. The similar results are also obtained in the asymptotical anti-de
Sitter space.Comment: 4 pages; version for publication in JHEP (title changed
PP-wave Black holes and The Matrix Model
We discuss the sizes of a black hole in the M theory pp-wave background, and
how the transverse size can be reproduced in the matrix model.Comment: 12 pages, harvmac. v2: final version to be published in JHEP, refs.
adde
High energy Scattering in 2+1 QCD: A Dipole Picture
A dipole picture of high energy scattering is developed in the 2+1
dimensional QCD, following Mueller. A generalized integral equation for the
dipole density with a given separation and center of mass position is derived,
and meson-meson non-forward scattering amplitude is therefore calculated. We
also calculate the amplitude due to two pomeron exchange, and the triple
pomeron coupling. We compare the result obtained by this method to our previous
result based on an effective action approach, and find the two results agree at
the one pomeron exchange level.Comment: minor typos corrected. Postscript files are available through
anonymous ftp quark.het.brown.edu, in the directory /pub/preprints, file name
is 9407299. Hard copy is available upon reques
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