2,288 research outputs found
Gastric LTi cells promote lymphoid follicle formation but are limited by IRAK-M and do not alter microbial growth.
Lymphoid tissue inducer (LTi) cells are activated by accessory cell IL-23, and promote lymphoid tissue genesis and antibacterial peptide production by the mucosal epithelium. We investigated the role of LTi cells in the gastric mucosa in the context of microbial infection. Mice deficient in IRAK-M, a negative regulator of TLR signaling, were investigated for increased LTi cell activity, and antibody mediated LTi cell depletion was used to analyze LTi cell dependent antimicrobial activity. H. pylori infected IRAK-M deficient mice developed increased gastric IL-17 and lymphoid follicles compared to wild type mice. LTi cells were present in naive and infected mice, with increased numbers in IRAK-M deficient mice by two weeks. Helicobacter and Candida infection of LTi cell depleted rag1(-/-) mice demonstrated LTi-dependent increases in calprotectin but not RegIII proteins. However, pathogen and commensal microbiota populations remained unchanged in the presence or absence of LTi cell function. These data demonstrate LTi cells are present in the stomach and promote lymphoid follicle formation in response to infection, but are limited by IRAK-M expression. Additionally, LTi cell mediated antimicrobial peptide production at the gastric epithelium is less efficacious at protecting against microbial pathogens than has been reported for other tissues
Constraining Proton Lifetime in SO(10) with Stabilized Doublet-Triplet Splitting
We present a class of realistic unified models based on supersymmetric SO(10)
wherein issues related to natural doublet-triplet (DT) splitting are fully
resolved. Using a minimal set of low dimensional Higgs fields which includes a
single adjoint, we show that the Dimopoulos--Wilzcek mechanism for DT splitting
can be made stable in the presence of all higher order operators without having
pseudo-Goldstone bosons and flat directions. The \mu term of order TeV is found
to be naturally induced. A Z_2-assisted anomalous U(1)_A gauge symmetry plays a
crucial role in achieving these results. The threshold corrections to
alpha_3(M_Z), somewhat surprisingly, are found to be controlled by only a few
effective parameters. This leads to a very predictive scenario for proton
decay. As a novel feature, we find an interesting correlation between the d=6
(p\to e^+\pi^0) and d=5 (p\to \nu-bar K+) decay amplitudes which allows us to
derive a constrained upper limit on the inverse rate of the e^+\pi^0 mode. Our
results show that both modes should be observed with an improvement in the
current sensitivity by about a factor of five to ten.Comment: 21 pages LaTeX, 2 figures, Few explanatory sentences and three new
references added, minor typos corrected
Experimental observation of the optical spin transfer torque
The spin transfer torque is a phenomenon in which angular momentum of a spin
polarized electrical current entering a ferromagnet is transferred to the
magnetization. The effect has opened a new research field of electrically
driven magnetization dynamics in magnetic nanostructures and plays an important
role in the development of a new generation of memory devices and tunable
oscillators. Optical excitations of magnetic systems by laser pulses have been
a separate research field whose aim is to explore magnetization dynamics at
short time scales and enable ultrafast spintronic devices. We report the
experimental observation of the optical spin transfer torque, predicted
theoretically several years ago building the bridge between these two fields of
spintronics research. In a pump-and-probe optical experiment we measure
coherent spin precession in a (Ga,Mn)As ferromagnetic semiconductor excited by
circularly polarized laser pulses. During the pump pulse, the spin angular
momentum of photo-carriers generated by the absorbed light is transferred to
the collective magnetization of the ferromagnet. We interpret the observed
optical spin transfer torque and the magnetization precession it triggers on a
quantitative microscopic level. Bringing the spin transfer physics into optics
introduces a fundamentally distinct mechanism from the previously reported
thermal and non-thermal laser excitations of magnets. Bringing optics into the
field of spin transfer torques decreases by several orders of magnitude the
timescales at which these phenomena are explored and utilized.Comment: 11 pages, 4 figure
A Simple Grand Unified Relation between Neutrino Mixing and Quark Mixing
It is proposed that all flavor mixing is caused by the mixing of the three
quark and lepton families with vectorlike fermions in 5 + 5-bar multiplets of
SU(5). This simple assumption implies that both V_{CKM} and U_{MNS} are
generated by a single matrix. The entire 3-by-3 complex mass matrix of the
neutrinos M_{nu} is then found to have a simple expression in terms of two
complex parameters and an overall scale. Thus, all the presently unknown
neutrino parameters are predicted. The best fits are for theta_{atm} less than
or approximately 40 degrees. The leptonic Dirac CP phase is found to be
somewhat greater than pi radians.Comment: 10 pages, 4 figures, one table. Typos correcte
Half-Metallic Graphene Nanoribbons
Electrical current can be completely spin polarized in a class of materials
known as half-metals, as a result of the coexistence of metallic nature for
electrons with one spin orientation and insulating for electrons with the
other. Such asymmetric electronic states for the different spins have been
predicted for some ferromagnetic metals - for example, the Heusler compounds-
and were first observed in a manganese perovskite. In view of the potential for
use of this property in realizing spin-based electronics, substantial efforts
have been made to search for half-metallic materials. However, organic
materials have hardly been investigated in this context even though
carbon-based nanostructures hold significant promise for future electronic
device. Here we predict half-metallicity in nanometre-scale graphene ribbons by
using first-principles calculations. We show that this phenomenon is realizable
if in-plane homogeneous electric fields are applied across the zigzag-shaped
edges of the graphene nanoribbons, and that their magnetic property can be
controlled by the external electric fields. The results are not only of
scientific interests in the interplay between electric fields and electronic
spin degree of freedom in solids but may also open a new path to explore
spintronics at nanometre scale, based on graphene
Flagellin-Deficient Legionella Mutants Evade Caspase-1- and Naip5-Mediated Macrophage Immunity
Macrophages from C57BL/6J (B6) mice restrict growth of the intracellular bacterial pathogen Legionella pneumophila. Restriction of bacterial growth requires caspase-1 and the leucine-rich repeat-containing protein Naip5 (Birc1e). We identified mutants of L. pneumophila that evade macrophage innate immunity. All mutants were deficient in expression of flagellin, the primary flagellar subunit, and failed to induce caspase-1-mediated macrophage death. Interestingly, a previously isolated flagellar mutant (fliI) that expresses, but does not assemble, flagellin did not replicate in macrophages, and induced macrophage death. Thus, flagellin itself, not flagella or motility, is required to initiate macrophage innate immunity. Immunity to Legionella did not require MyD88, an essential adaptor for toll-like receptor 5 (TLR5) signaling. Moreover, flagellin of Legionella and Salmonella induced cytotoxicity when delivered to the macrophage cytosol using Escherichia coli as a heterologous host. It thus appears that macrophages sense cytosolic flagellin via a TLR5-independent pathway that leads to rapid caspase-1-dependent cell death and provides defense against intracellular bacterial pathogens
Evolution of Landau Levels into Edge States at an Atomically Sharp Edge in Graphene
The quantum-Hall-effect (QHE) occurs in topologically-ordered states of
two-dimensional (2d) electron-systems in which an insulating bulk-state
coexists with protected 1d conducting edge-states. Owing to a unique
topologically imposed edge-bulk correspondence these edge-states are endowed
with universal properties such as fractionally-charged quasiparticles and
interference-patterns, which make them indispensable components for QH-based
quantum-computation and other applications. The precise edge-bulk
correspondence, conjectured theoretically in the limit of sharp edges, is
difficult to realize in conventional semiconductor-based electron systems where
soft boundaries lead to edge-state reconstruction. Using scanning-tunneling
microscopy and spectroscopy to follow the spatial evolution of bulk
Landau-levels towards a zigzag edge of graphene supported above a graphite
substrate we demonstrate that in this system it is possible to realize
atomically sharp edges with no edge-state reconstruction. Our results single
out graphene as a system where the edge-state structure can be controlled and
the universal properties directly probed.Comment: 16 pages, 4 figure
First direct observation of Dirac fermions in graphite
Originating from relativistic quantum field theory, Dirac fermions have been
recently applied to study various peculiar phenomena in condensed matter
physics, including the novel quantum Hall effect in graphene, magnetic field
driven metal-insulator-like transition in graphite, superfluid in 3He, and the
exotic pseudogap phase of high temperature superconductors. Although Dirac
fermions are proposed to play a key role in these systems, so far direct
experimental evidence of Dirac fermions has been limited. Here we report the
first direct observation of massless Dirac fermions with linear dispersion near
the Brillouin zone (BZ) corner H in graphite, coexisting with quasiparticles
with parabolic dispersion near another BZ corner K. In addition, we report a
large electron pocket which we attribute to defect-induced localized states.
Thus, graphite presents a novel system where massless Dirac fermions,
quasiparticles with finite effective mass, and defect states all contribute to
the low energy electronic dynamics.Comment: Nature Physics, in pres
Natural Islands for a 125 GeV Higgs in the scale-invariant NMSSM
We study whether a 125 GeV standard model-like Higgs boson can be
accommodated within the scale-invariant NMSSM in a way that is natural in all
respects, i.e., not only is the stop mass and hence its loop contribution to
Higgs mass of natural size, but we do not allow significant tuning of NMSSM
parameters as well. We pursue as much as possible an analytic approach which
gives clear insights on various ways to accommodate such a Higgs mass, while
conducting complementary numerical analyses. We consider both scenarios with
singlet-like state being heavier and lighter than SM-like Higgs. With A-terms
being small, we find for the NMSSM to be perturbative up to GUT scale, it is
not possible to get 125 GeV Higgs mass, which is true even if we tune
parameters of NMSSM. If we allow some of the couplings to become
non-perturbative below the GUT scale, then the non-tuned option implies that
the singlet self-coupling, kappa, is larger than the singlet-Higgs coupling,
lambda, which itself is order 1. This leads to a Landau pole for these
couplings close to the weak scale, in particular below ~10^4 TeV. In both the
perturbative and non-perturbative NMSSM, allowing large A_lambda, A_kappa gives
"more room" to accommodate a 125 GeV Higgs, but a tuning of these A-terms may
be needed. In our analysis we also conduct a careful study of the constraints
on the parameter space from requiring global stability of the desired vacuum
fitting a 125 GeV Higgs, which is complementary to existing literature. In
particular, as the singlet-Higgs coupling lambda increases, vacuum stability
becomes more serious of an issue.Comment: 34 pages, 4 figures, references added, minor corrections to text and
figures, version to be published in JHE
Singlet-doublet Higgs mixing and its implications on the Higgs mass in the PQ-NMSSM
We examine the implications of singlet-doublet Higgs mixing on the properties
of a Standard Model (SM)-like Higgs boson within the Peccei-Quinn invariant
extension of the NMSSM (PQ-NMSSM). The SM singlet added to the Higgs sector
connects the PQ and visible sectors through a PQ-invariant non-renormalizable
K\"ahler potential term, making the model free from the tadpole and domain-wall
problems. For the case that the lightest Higgs boson is dominated by the
singlet scalar, the Higgs mixing increases the mass of a SM-like Higgs boson
while reducing its signal rate at collider experiments compared to the SM case.
The Higgs mixing is important also in the region of parameter space where the
NMSSM contribution to the Higgs mass is small, but its size is limited by the
experimental constraints on the singlet-like Higgs boson and on the lightest
neutralino constituted mainly by the singlino whose Majorana mass term is
forbidden by the PQ symmetry. Nonetheless the Higgs mixing can increase the
SM-like Higgs boson mass by a few GeV or more even when the Higgs signal rate
is close to the SM prediction, and thus may be crucial for achieving a 125 GeV
Higgs mass, as hinted by the recent ATLAS and CMS data. Such an effect can
reduce the role of stop mixing.Comment: 26 pages, 3 figures; published in JHE
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