7,722 research outputs found
R-symmetry breaking, runaway directions and global symmetries in O'Raifeartaigh models
We discuss O'Raifeartaigh models with general R-charge assignments,
introduced by Shih to break R-symmetry spontaneously. We argue that most of
these models have runaway directions related to the R-symmetry. In addition, we
study the simplest model with a U(N) global symmetry and show that in a range
of parameters R-symmetry is spontaneously broken in a metastable vacuum.Comment: 16 pages, 1 figur
Solitonic supersymmetry restoration
Q-balls are a possible feature of any model with a conserved, global U(1)
symmetry and no massless, charged scalars. It is shown that for a broad class
of models of metastable supersymmetry breaking they are extremely influential
on the vacuum lifetime and make seemingly viable vacua catastrophically short
lived. A net charge asymmetry is not required as there is often a significant
range of parameter space where statistical fluctuations alone are sufficient.
This effect is examined for two supersymmetry breaking scenarios. It is found
that models of minimal gauge mediation (which necessarily have a messenger
number U(1)) undergo a rapid, supersymmetry restoring phase transition unless
the messenger mass is greater than 10^8 GeV. Similarly the ISS model, in the
context of direct mediation, quickly decays unless the perturbative
superpotential coupling is greater than the Standard Model gauge couplings.Comment: 17 pages, 3 figures, minor comments added, accepted for publication
in JHE
Plasmodium yoelii infection of BALB/c mice results in expansion rather than induction of CD4+ Foxp3+ regulatory T cells
Recently, we demonstrated elevated numbers of CD4(+) Foxp3(+) regulatory T (Treg) cells in Plasmodium yoeliiâinfected mice contributing to the regulation of antiâmalarial immune response. However, it remains unclear whether this increase in Treg cells is due to thymusâderived Treg cell expansion or induction of Treg cells in the periphery. Here, we show that the frequency of Foxp3(+) Treg cells expressing neuropilinâ1 (Nrpâ1) decreased at early timeâpoints during P. yoelii infection, whereas percentages of Helios(+) Foxp3(+) Treg cells remained unchanged. Both Foxp3(+) Nrpâ1(+) and Foxp3(+) Nrpâ1(â) Treg cells from P. yoeliiâinfected mice exhibited a similar Tâcell receptor VÎČ chain usage and methylation pattern in the Tregâspecific demethylation region within the foxp3 locus. Strikingly, we did not observe induction of Foxp3 expression in Foxp3(â) T cells adoptively transferred to P. yoeliiâinfected mice. Hence, our results suggest that P. yoelii infection triggered expansion of naturally occurring Treg cells rather than de novo induction of Foxp3(+) Treg cells
Pattern Dynamics of Vortex Ripples in Sand: Nonlinear Modeling and Experimental Validation
Vortex ripples in sand are studied experimentally in a one-dimensional setup
with periodic boundary conditions. The nonlinear evolution, far from the onset
of instability, is analyzed in the framework of a simple model developed for
homogeneous patterns. The interaction function describing the mass transport
between neighboring ripples is extracted from experimental runs using a
recently proposed method for data analysis, and the predictions of the model
are compared to the experiment. An analytic explanation of the wavelength
selection mechanism in the model is provided, and the width of the stable band
of ripples is measured.Comment: 4 page
Meta-Stable Brane Configuration with Orientifold 6 Plane
We present the intersecting brane configuration of type IIA string theory
corresponding to the meta-stable nonsupersymmetric vacua in four dimensional
N=1 supersymmetric SU(N_c) gauge theory with a symmetric flavor, a conjugate
symmetric flavor and fundamental flavors. By studying the previously known
supersymmetric M5-brane curve, the M-theory lift for this type IIA brane
configuration, which consists of NS5-branes, D4-branes, D6-branes and an
orientifold 6-plane, is analyzed.Comment: 21 pp, 3 colored figures; stability arguments added in page 11 and
12, a typo in figure 3 corrected, and to appear in JHE
Protein Clusters on the T Cell Surface May Suppress Spurious Early Signaling Events
T cells play an important role in the adaptive immune system, quickly activating effector functions in response to small numbers of antigenic peptides but rarely activating in response to constant interaction with most endogenous peptides. Emerging experimental evidence suggests that key membrane-bound signaling proteins such as the T cell receptor and the adaptor protein Lat are spatially organized into small clusters on the T cell membrane. We use spatially resolved, stochastic computer simulations to study how the inhomogeneous distribution of molecules affects the portion of the T cell signaling network in which the kinase ZAP-70, originating in T cell receptor clusters, phosphorylates Lat. To gain insight into the effects of protein clustering, we compare the signaling response from membranes with clustered proteins to the signaling response from membranes with homogeneously distributed proteins. Given a fixed amount of ZAP-70 (a proxy for degree of TCR stimulation) that must diffuse into contact with Lat molecules, the spatially homogeneous system responds faster and results in higher levels of phosphorylated Lat. Analysis of the spatial distribution of proteins demonstrates that, in the homogeneous system, nearest ZAP-70 and Lat proteins are closer on average and fewer Lat molecules share the same closest ZAP-70 molecule, leading to the faster response time. The results presented here suggest that spatial clustering of proteins on the T cell membrane may suppress the propagation of signal from ZAP-70 to Lat, thus providing a regulatory mechanism by which T cells suppress transient, spurious signals induced by stimulation of T cell receptors by endogenous peptides. Because this suppression of spurious signals may occur at a cost to sensitivity, we discuss recent experimental results suggesting other potential mechanisms by which ZAP-70 and Lat may interact to initiate T cell activation.United States. National Institutes of Health (Grant 1P01AI091580-01
A natural renormalizable model of metastable SUSY breaking
We propose a model of metastable dynamical supersymmetry breaking in which
all scales are generated dynamically. Our construction is a simple variant of
the Intriligator-Seiberg-Shih model, with quark masses induced by
renormalizable couplings to an auxiliary supersymmetric QCD sector. Since all
scales arise from dimensional transmutation, the model has no fundamental
dimensionful parameters. It also does not rely on higher-dimensional operators.Comment: 9 pages; v2: typos correcte
Cosmological evolution of scalar fields and gravitino dark matter in gauge mediation at low reheating temperatures
We consider the dynamics of the supersymmetry-breaking scalar field and the
production of dark matter gravitinos via its decay in a gauge-mediated
supersymmetry breaking model with metastable vacuum. We find that the scalar
field amplitude and gravitino density are extremely sensitive to the parameters
of the hidden sector. For the case of an O'Raifeartaigh sector, we show that
the observed dark matter density can be explained by gravitinos even for low
reheating temperatures T_{R} < 10 GeV. Such low reheating temperatures may be
implied by detection of the NLSP at the LHC if its thermal freeze-out density
is in conflict with BBN.Comment: 11 pages RevTex. Extended discussion and minor corrections,
conclusions unaltered. Version to be published in JCA
Common Weeds as a Cause of Perirenal Edema In Swine
The disease problem described here has been diagnosed with increased frequency in Iowa during the last few years. The literature contains very few references to perirenal edema as a lesion in swine, and even fewer references to the condition as a distinct disease syndrome
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