2,403 research outputs found
The Role of CP violation in D0 anti-D0 Mixing
In current searches for D0 anti-D0 mixing, the time evolution of
``wrong-sign'' decays is used to distinguish between a potential mixing signal
and the dominant background from doubly-Cabibbo-suppressed decays. A term
proportional to in the expression for the time evolution is often
neglected in theoretical discussions and experimental analyses of these
processes. We emphasize that, in general, this term does not vanish even in the
case of CP invariance. Furthermore, CP invariance is likely to be violated if
the rate of D0 anti-D0 mixing is close to the experimental bound. The
consequence of either of these two facts is that the strongest existing
measured bound is not applicable for constraining New Physics.Comment: 14 pages, uuencoded gzip-compressed postscript (84 kB
Probing Supersymmetric Flavor Models with
We discuss the supersymmetric contribution to in various
supersymmetric flavor models. We find that in alignment models the
supersymmetric contribution could be significant while in heavy squark models
it is expected to be small. The situation is particularly interesting in models
that solve the flavor problems by either of the above mechanisms and the
remaining CP problems by means of approximate CP, that is, all CP violating
phases are small. In such models, the standard model contributions cannot
account for and a failure of the supersymmetric
contributions to do so would exclude the model. In models of alignment and
approximate CP, the supersymmetric contributions can account for
only if both the supersymmetric model parameters and the
hadronic parameters assume rather extreme values. Such models are then strongly
disfavored by the measurements. Models of heavy squarks
and approximate CP are excluded.Comment: 16 pages, harvmac. v2: We added a discussion of the intriguing
implications that would follow if a recent lattice result is confirme
A Porosity-Length Formalism for Photon-Tiring-Limited Mass Loss from Stars Above the Eddington Limit
We examine radiatively driven mass loss from stars near and above the
Eddington limit (Ledd). We begin by reviewing the instabilities that are
expected to form extensive structure near Ledd. We investigate how this
"porosity" can reduce the effective coupling between the matter and radiation.
Introducing a new "porosity-length'' formalism, we derive a simple scaling for
the reduced effective opacity, and use this to derive an associated scaling for
the porosity-moderated, continuum-driven mass loss rate from stars that
formally exceed Ledd. For a simple super-Eddington model with a single porosity
length that is assumed to be on the order of the gravitational scale height,
the overall mass loss is similar to that derived in previous porosity work.
This is much higher than is typical of line-driven winds, but is still only a
few percent of the photon tiring limit--for which the luminosity becomes
insufficient to carry the flow out of the gravitational potential. To obtain
still stronger mass loss that approaches observationally inferred values near
this limit, we introduce a power-law-porosity model in which the associated
structure has a broad range of scales. We show that the mass loss rate can be
enhanced by a factor that increases with the Eddington parameter Gamma, such
that for moderately large Gamma (> 3-4), mass loss rates could approach the
photon tiring limit. Together with the ability to drive quite fast outflow
speeds, the derived mass loss could explain the large inferred mass loss and
flow speeds of giant outbursts in eta Carinae and other LBV stars.Comment: 17 pages, 6 figures, to appear in Ap
Effect of P-wave interaction in 6He and 6Li photoabsorption
The total photoabsorption cross sections of six-body nuclei are calculated
including complete final state interaction via the Lorentz Integral Transform
method. The effect of nucleon-nucleon central P-wave forces is investigated.
Comparing to results with central potentials containg S-wave forces only one
finds considerably more strength in the low-energy cross sections and a rather
strong improvement in comparison with experimental data, in particular for 6Li.Comment: 11 pages with 4 figure
Signatures of Strong Momentum Localization via Translational-Internal Entanglement
We show that atoms or molecules subject to fields that couple their internal
and translational (momentum) states may undergo a crossover from randomization
(diffusion) to strong localization (sharpening) of their momentum distribution.
The predicted crossover should be manifest by a drastic change of the
interference pattern as a function of the coupling fields.Comment: 4 pages, 3 figure
Recommended from our members
Functional interpretation of single cell similarity maps.
We present Vision, a tool for annotating the sources of variation in single cell RNA-seq data in an automated and scalable manner. Vision operates directly on the manifold of cell-cell similarity and employs a flexible annotation approach that can operate either with or without preconceived stratification of the cells into groups or along a continuum. We demonstrate the utility of Vision in several case studies and show that it can derive important sources of cellular variation and link them to experimental meta-data even with relatively homogeneous sets of cells. Vision produces an interactive, low latency and feature rich web-based report that can be easily shared among researchers, thus facilitating data dissemination and collaboration
Long-Range Acoustic Interactions in Insect Swarms: An Adaptive Gravity Model
The collective motion of groups of animals emerges from the net effect of the interactions between individual members of the group. In many cases, such as birds, fish, or ungulates, these interactions are mediated by sensory stimuli that predominantly arise from nearby neighbors. But not all stimuli in animal groups are short range. Here, we consider mating swarms of midges, which are thought to interact primarily via long-range acoustic stimuli. We exploit the similarity in form between the decay of acoustic and gravitational sources to build a model for swarm behavior. By accounting for the adaptive nature of the midges\u27 acoustic sensing, we show that our \u27adaptive gravity\u27 model makes mean-field predictions that agree well with experimental observations of laboratory swarms. Our results highlight the role of sensory mechanisms and interaction range in collective animal behavior. Additionally, the adaptive interactions that we present here open a new class of equations of motion, which may appear in other biological contexts
Long-range Acoustic Interactions in Insect Swarms: An Adaptive Gravity Model
The collective motion of groups of animals emerges from the net effect of the
interactions between individual members of the group. In many cases, such as
birds, fish, or ungulates, these interactions are mediated by sensory stimuli
that predominantly arise from nearby neighbors. But not all stimuli in animal
groups are short range. Here, we consider mating swarms of midges, which
interact primarily via long-range acoustic stimuli. We exploit the similarity
in form between the decay of acoustic and gravitational sources to build a
model for swarm behavior. By accounting for the adaptive nature of the midges'
acoustic sensing, we show that our "adaptive gravity" model makes mean-field
predictions that agree well with experimental observations of laboratory
swarms. Our results highlight the role of sensory mechanisms and interaction
range in collective animal behavior. The adaptive interactions that we present
here open a new class of equations of motion, which may appear in other
biological contexts.Comment: 25 pages, 15 figure
Flavor Changing Processes in Supersymmetric Models with Hybrid Gauge- and Gravity-Mediation
We consider supersymmetric models where gauge mediation provides the dominant
contributions to the soft supersymmetry breaking terms while gravity mediation
provides sub-dominant yet non-negligible contributions. We further assume that
the gravity-mediated contributions are subject to selection rules that follow
from a Froggatt-Nielsen symmetry. This class of models constitutes an example
of viable and natural non-minimally flavor violating models. The constraints
from mixing in the neutral K system imply that the modifications to the
Standard Model predictions for mixing in the neutral B_d and B_s systems are
generically at most at the percent level, but can be of order ten percent for
large . The modifications for the neutral D system mixing are
generically at most of order a few percent, but in a special subclass of models
they can be of order one. We point out processes relevant for
flavor violation in hybrid mediation.Comment: 30 pages, 3 figure
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