1,734 research outputs found
Radiation zeros and scalar particles beyond the standard model
Standard radiation zeros arise from the factorization properties of
tree-level amplitudes involving a massless photon and can occur when all
charged particles in the initial and final state have the same sign. We
investigate how several different processes involving new scalar particles
beyond the standard model may exhibit radiation zeros and how this structure
might be exploited to probe their electromagnetic structure. We focus on (i)
unnoticed aspects of angular zeros in the process e- + e- --> Delta-- + gamma
for doubly charged Higgs boson (or any bilepton) production and (ii) the
process gamma + e- --> q + S/V for scalar (S) or vector (V) leptoquarks (LQs).
We also discuss how factorized amplitudes and radiation zeros may appear in the
gauge boson fusion production of non-conjugate leptoquark pairs via gamma + W
--> S_i + S_j* in high energy ee reactions and how the zeros affect the
production cross-sections for various types of scalar leptoquarks.Comment: 18 pages (LaTeX) plus 5 postscript figure
Pseudoseizure manifestations in two preschool age children
We report two patients with epilepsy with pseudoseizures at age 6 years. Both presented with intractable staring spells. Pseudoseizures were provoked and aborted by suggestion, leading to the diagnosis. In both patients, evidence of a neuropsychological disturbance was later found and psychotherapy started. Monitoring of intractable staring episodes is recommended prior to escalating antiepileptic drug levels or resorting to polytherapy. In addition, differentiation from other non-epileptic phenomena is necessary to initiate proper therapy
Polarization and `Model Independent' Extraction of from and
We briefly discuss the predictions of the heavy quark effective theory for
the semileptonic decays of a heavy pseudoscalar to a light one, or to a light
vector meson. We point out that measurement of combinations of differential
helicity decay rates at Cleo-c and the factories can provide a model
independent means of extracting the ratio
. We briefly discuss the corrections to this prediction.Comment: 8 pages, LaTeX, 1 figur
Measurements and modeling of Alfven eigenmode induced fast ion transport and loss in DIII-D and ASDEX Upgrade
Neutral beam injection into reversed magnetic shear DIII-D and ASDEX Upgrade plasmas
produces a variety of Alfve´nic activity including toroidicity-induced Alfve´n eigenmodes and
reversed shear Alfve´n eigenmodes (RSAEs). These modes are studied during the discharge current
ramp phase when incomplete current penetration results in a high central safety factor and
increased drive due to multiple higher order resonances. Scans of injected 80 keV neutral beam
power on DIII-D showed a transition from classical to AE dominated fast ion transport and, as
previously found, discharges with strong AE activity exhibit a deficit in neutron emission relative
to classical predictions. By keeping beam power constant and delaying injection during the current
ramp, AE activity was reduced or eliminated and a significant improvement in fast ion confinement
observed. Similarly, experiments in ASDEX Upgrade using early 60 keV neutral beam injection
drove multiple unstable RSAEs. Periods of strong RSAE activity are accompanied by a large (peak
dSn=Sn 60%) neutron deficit. Losses of beam ions modulated at AE frequencies were observed
using large bandwidth energy and pitch resolving fast ion loss scintillator detectors and clearly
identify their role in the process. Modeling of DIII-D loss measurements using guiding center
following codes to track particles in the presence of ideal magnetohydrodynamic (MHD)
calculated AE structures (validated by comparison to experiment) is able to reproduce the
dominant energy, pitch, and temporal evolution of these losses. While loss of both co and counter
current fast ions occurs, simulations show that the dominant loss mechanism observed is the mode induced transition of counter-passing fast ions to lost trapped orbits. Modeling also reproduces a coherent signature of AE induced losses and it was found that these coherent losses scale proportionally with the amplitude; an additional incoherent contribution scales quadratically with the mode amplitude. VC 2011 American Institute of Physics.US Department of Energy DE-FC02-04ER54698, SC-G903402, DE-AC02-99CH11466, DE-FG03-97ER54415, DE-FG02-89ER53296, DE-FG02-08ER5499
Beam ion losses due to energetic particle geodesic acoustic modes
We report the first experimental observations of fast-ion loss in a tokamak due to energetic particle driven geodesic acoustic modes (EGAMs). A fast-ion loss detector installed on the DIII-D tokamak observes bursts of beam ion losses coherent with the EGAM frequency. The EGAM activity results in a significant loss of beam ions, comparable to the first orbit losses. The pitch angles and energies of the measured fast-ion losses agree with predictions from a full orbit simulation code SPIRAL, which includes scattering and slowing-down.U.S. Department of Energy DE-FC02-04ER 54698, SC-G903402, DE-AC02-09CH1146
Alfven eigenmode stability and fast ion loss in DIII-D and ITER reversed magnetic shear plasmas
Neutral beam injection into reversed-magnetic shear DIII-D plasmas produces a variety of Alfvenic activity including ´
toroidicity-induced Alfven eigenmodes (TAEs) and reversed shear Alfv ´ en eigenmodes (RSAEs). With measured ´
equilibrium profiles as inputs, the ideal MHD code NOVA is used to calculate eigenmodes of these plasmas. The
postprocessor code NOVA-K is then used to perturbatively calculate the actual stability of the modes, including
finite orbit width and finite Larmor radius effects, and reasonable agreement with the spectrum of observed modes
is found. Using experimentally measured mode amplitudes, fast ion orbit following simulations have been carried
out in the presence of the NOVA calculated eigenmodes and are found to reproduce the dominant energy, pitch
and temporal evolution of the losses measured using a large bandwidth scintillator diagnostic. The same analysis
techniques applied to a DT 8 MA ITER steady-state plasma scenario with reversed-magnetic shear and both beam
ion and alpha populations show Alfven eigenmode instability. Both RSAEs and TAEs are found to be unstable ´
with maximum growth rates occurring for toroidal mode number n = 6 and the majority of the drive coming from
fast ions injected by the 1 MeV negative ion beams. AE instability due to beam ion drive is confirmed by the non-perturbative code TAEFL. Initial fast ion orbit following simulations using the unstable modes with a range of amplitudes (δB/B = 10−5–10−3) have been carried out and show negligible fast ion loss. The lack of fast ion loss is a result of loss boundaries being limited to large radii and significantly removed from the actual modes themselves.US Department of Energy DE-FC02-04ER54698, DE-AC02-09CH11466, SC-G903402, DE-AC05-00OR22725, DE-FG03-97ER5441
Fast ion transport during applied 3D magnetic perturbations on DIII-D
Measurements show fast ion losses correlated with applied three-dimensional (3D) fields in
a variety of plasmas ranging from L-mode to resonant magnetic perturbation (RMP) edge
localized mode (ELM) suppressed H-mode discharges. In DIII-D L-mode discharges with a
slowly rotating n = 2 magnetic perturbation, scintillator detector loss signals synchronized
with the applied fields are observed to decay within one poloidal transit time after beam turnoff indicating they arise predominantly from prompt loss orbits. Full orbit following using
M3D-C1 calculations of the perturbed fields and kinetic profiles reproduce many features of
the measured losses and points to the importance of the applied 3D field phase with respect
to the beam injection location in determining the overall impact on prompt beam ion loss.
Modeling of these results includes a self-consistent calculation of the 3D perturbed beam ion
birth profiles and scrape-off-layer ionization, a factor found to be essential to reproducing the
experimental measurements. Extension of the simulations to full slowing down timescales,
including fueling and the effects of drag and pitch angle scattering, show the applied n = 3
RMPs in ELM suppressed H-mode plasmas can induce a significant loss of energetic
particles from the core. With the applied n = 3 fields, up to 8.4% of the injected beam power
is predicted to be lost, compared to 2.7% with axisymmetric fields only. These fast ions,
originating from minor radii ρ > 0.7, are predicted to be primarily passing particles lost to
the divertor region, consistent with wide field-of-view infrared periscope measurements of
wall heating in n = 3 RMP ELM suppressed plasmas. Edge fast ion Dα (FIDA) measurements
also confirm a large change in edge fast ion profile due to the n = 3 fields, where the effect
was isolated by using short 50ms RMP-off periods during which ELM suppression was
maintained yet the fast ion profile was allowed to recover. The role of resonances between
fast ion drift motion and the applied 3D fields in the context of selectively targeting regions
of fast ion phase space is also discussed
Brane World Susy Breaking from String/M Theory
String and M-theory realizations of brane world supersymmetry breaking
scenarios are considered in which visible sector Standard Model fields are
confined on a brane, with hidden sector supersymmetry breaking isolated on a
distant brane. In calculable examples with an internal manifold of any volume
the Kahler potential generically contains brane--brane non-derivative contact
interactions coupling the visible and hidden sectors and is not of the no-scale
sequestered form. This leads to non-universal scalar masses and without
additional assumptions about flavor symmetries may in general induce dangerous
sflavor violation even though the Standard Model and supersymmetry branes are
physically separated. Deviations from the sequestered form are dictated by bulk
supersymmetry and can in most cases be understood as arising from exchange of
bulk supergravity fields between branes or warping of the internal geometry.
Unacceptable visible sector tree-level tachyons arise in many models but may be
avoided in certain classes of compactifications. Anomaly mediated and gaugino
mediated contributions to scalar masses are sub-dominant except in special
circumstances such as a flat or AdS pure five--dimensional bulk geometry
without bulk vector multiplets.Comment: Latex, 83 pages, references adde
New Charged Dilaton Solutions in 2+1 Dimensions and Solutions with Cylindrical Symmetry in 3+1 Dimensions
We report a new family of solutions to Einstein-Maxwell-dilaton gravity in
2+1 dimensions and Einstein-Maxwell gravity with cylindrical symmetry in 3+1
dimensions. A set of static charged solutions in 2+1 dimensions are obtained by
a compactification of charged solutions in 3+1 dimensions with cylindrical
symmetry. These solutions contain naked singularities for certain values of the
parameters considered. New rotating charged solutions in 2+1 dimensions and 3+1
dimensions are generated treating the static charged solutions as seed metrics
and performing transformations.Comment: Latex. No figure
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