8,997 research outputs found
Upper bounds on all R-parity-violating \lambda\lambda'' combinations from proton stability
In an R-parity-violating supersymmetric theory, we derive upper bounds on all
the \lambda''_{ijk}\lambda_{i'j'k'}-type combinations from the consideration of
proton stability, where \lambda''_{ijk} are baryon-number-violating couplings
involving three baryonic fields and \lambda_{i'j'k'} are
lepton-number-violating couplings involving three leptonic fields.Comment: 5 pages, Latex, uses axodraw.sty; minor changes in the text. Final
versio
Measurement of Double-Polarization asymmetries in the Quasi-Elastic He→ 3 (e→, e′ p) Process
We report on a precise measurement of double-polarization asymmetries in electron-induced breakup of 3He proceeding to pd and ppn final states, performed in quasi-elastic kinematics at Q2 = 0.25 (GeV/c)2 for missing momenta up to 250 MeV/c. These observables represent highly sensitive tools to investigate the electromagnetic and spin structure of 3He and the relative importance of two- and three-body effects involved in the breakup reaction dynamics. The measured asymmetries cannot be satisfactorily reproduced by state-of-the-art calculations of 3He unless their three-body segment is adjusted, indicating that the spin-dependent part of the nuclear interaction governing the three-body breakup process is much smaller than previously thought
Measurement of Double-Polarization asymmetries in the Quasi-Elastic He→ 3 (e→, e′ p) Process
We report on a precise measurement of double-polarization asymmetries in electron-induced breakup of 3He proceeding to pd and ppn final states, performed in quasi-elastic kinematics at Q2 = 0.25 (GeV/c)2 for missing momenta up to 250 MeV/c. These observables represent highly sensitive tools to investigate the electromagnetic and spin structure of 3He and the relative importance of two- and three-body effects involved in the breakup reaction dynamics. The measured asymmetries cannot be satisfactorily reproduced by state-of-the-art calculations of 3He unless their three-body segment is adjusted, indicating that the spin-dependent part of the nuclear interaction governing the three-body breakup process is much smaller than previously thought
Acceleressence: Dark Energy from a Phase Transition at the Seesaw Scale
Simple models are constructed for "acceleressence" dark energy: the latent
heat of a phase transition occurring in a hidden sector governed by the seesaw
mass scale v^2/M_Pl, where v is the electroweak scale and M_Pl the
gravitational mass scale. In our models, the seesaw scale is stabilized by
supersymmetry, implying that the LHC must discover superpartners with a
spectrum that reflects a low scale of fundamental supersymmetry breaking.
Newtonian gravity may be modified by effects arising from the exchange of
fields in the acceleressence sector whose Compton wavelengths are typically of
order the millimeter scale. There are two classes of models. In the first class
the universe is presently in a metastable vacuum and will continue to inflate
until tunneling processes eventually induce a first order transition. In the
simplest such model, the range of the new force is bounded to be larger than 25
microns in the absence of fine-tuning of parameters, and for couplings of order
unity it is expected to be \approx 100 microns. In the second class of models
thermal effects maintain the present vacuum energy of the universe, but on
further cooling, the universe will "soon" smoothly relax to a matter dominated
era. In this case, the range of the new force is also expected to be of order
the millimeter scale or larger, although its strength is uncertain. A firm
prediction of this class of models is the existence of additional energy
density in radiation at the eV era, which can potentially be probed in
precision measurements of the cosmic microwave background. An interesting
possibility is that the transition towards a matter dominated era has occurred
in the very recent past, with the consequence that the universe is currently
decelerating.Comment: 10 pages, references adde
C1q deficiency leads to the defective suppression of IFN-α in response to nucleoprotein containing immune complexes
Almost all humans with homozygous deficiency of C1q develop systemic lupus erythematosus (SLE). The precise cellular mechanism (s) by which C1q prevents the development of SLE remains unclear. In this study, we tested the role of C1q in the regulation of IFN-α induced by immune complexes (ICs) in vitro, as well as the consequences of lack of C1q in vivo. Our experiments revealed that C1q preferentially promotes the binding of SLE ICs to monocytes rather than plasmacytoid dendritic cells, but this inhibition was not due to the induction of inhibitory soluble factors. The presence of C1q also altered the trafficking of ICs within monocytes such that ICs persisted in early endosomes. In patients with C1q deficiency, serum and cerebrospinal fluid levels of IFN-α and IFN-γ–inducible protein-10 levels were elevated and strongly correlated with Ro autoantibodies, demonstrating the clinical significance of these observations. These studies therefore associate C1q deficiency with defective regulation of IFN-α and provide a better understanding of the cellular mechanisms by which C1q prevents the development of IC-stimulated autoimmunity
Gravitational decays of heavy particles in large extra dimensions
In the framework of quantum gravity propagating in large extra dimensions, we
analyze the inclusive radiative emission of Kaluza-Klein spin-2 gravitons in
the two-fermions decays of massive gauge bosons, heavy quarks, Higgs bosons,
and in the two-massive gauge bosons decay of Higgs bosons. We provide
analytical expressions for the square modulus of amplitudes summed over
polarizations, and numerical results for the widths and branching ratios. The
corresponding decays in the Z, top quark, and Higgs boson sectors of the
standard model are analyzed in the light of present and future experiments.Comment: 29 pages, 4 figures, notation slightly changed, a few comments adde
Young Stellar Object Candidates in IC 417
IC 417 is in the Galactic Plane, and likely part of the Aur OB2 association;
it is ~2 kpc away. Stock 8 is one of the densest cluster constituents; off of
it to the East, there is a 'Nebulous Stream' (NS) that is dramatic in the
infrared (IR). We have assembled a list of literature-identified young stellar
objects (YSOs), new candidate YSOs from the NS, and new candidate YSOs from IR
excesses. We vetted this list via inspection of the images, spectral energy
distributions (SEDs), and color-color/color-magnitude diagrams. We placed the
710 surviving YSOs and candidate YSOs in ranked bins, nearly two-thirds of
which have more than 20 points defining their SEDs. The lowest-ranked bins
include stars that are confused, or likely carbon stars. There are 503 in the
higher-ranked bins; half are SED Class III, and 40\% are SED Class II.
Our results agree with the literature in that we find that the NS and Stock 8
are at about the same distance as each other (and as the rest of the YSOs), and
that the NS is the youngest region, with Stock 8 a little older. We do not find
any evidence for an age spread within the NS, consistent with the idea that the
star formation trigger came from the north. We do not find that the other
literature-identified clusters here are as young as either the NS or Stock 8;
at best they are older than Stock 8, and they may not all be legitimate
clusters.Comment: Accepted by AAS Journal
Recent Nuclear Astrophysics Measurements using the TwinSol Separator
Many astrophysical events, such as novae and X-ray bursts, are powered by reactions with radioactive nuclei. Studying the properties of these nuclei in the laboratory can therefore further our understanding of these astrophysical explosions. The TwinSol separator at the University of Notre Dame has recently been used to produce intense (∼106 pps) beams of 17F. In this article, some of the first measurements with these beams are discussed
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