243 research outputs found
The collective quantization of three-flavored Skyrmions revisited
A self-consistent large approach is developed for the collective
quantization of SU(3) flavor hedgehog solitons, such as the Skyrmion. The key
to this analysis is the determination of all of the zero modes associated with
small fluctuations around the hedgehog. These are used in the conventional way
to construct collective coordinates. This approach differs from previous work
in that it does not implicitly assume that each static zero mode is associated
with a dynamical zero mode. It is demonstrated explicitly in the context of the
Skyrmion that there are fewer dynamical zero modes than static ones due to the
Witten-Wess-Zumino term in the action. Group-theoretic methods are employed to
identify the physical states resulting from canonical quantization of the
collectively rotating soliton. The collective states fall into representations
of SU(3) flavor labeled by and are given by
where is the spin of the collective state. States with
strangeness do not arise as collective states from this procedure; thus
the (pentaquark) resonance does not arise as a collective
excitation in models of this type.Comment: 12 pages; uses package "youngtab
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Scalable continuous evolution for the generation of diverse enzyme variants encompassing promiscuous activities
Enzyme orthologs sharing identical primary functions can have different promiscuous activities. While it is possible to mine this natural diversity to obtain useful biocatalysts, generating comparably rich ortholog diversity is difficult, as it is the product of deep evolutionary processes occurring in a multitude of separate species and populations. Here, we take a first step in recapitulating the depth and scale of natural ortholog evolution on laboratory timescales. Using a continuous directed evolution platform called OrthoRep, we rapidly evolve the Thermotoga maritima tryptophan synthase β-subunit (TmTrpB) through multi-mutation pathways in many independent replicates, selecting only on TmTrpB’s primary activity of synthesizing L-tryptophan from indole and L-serine. We find that the resulting sequence-diverse TmTrpB variants span a range of substrate profiles useful in industrial biocatalysis and suggest that the depth and scale of evolution that OrthoRep affords will be generally valuable in enzyme engineering and the evolution of biomolecular functions
Asymmetric WIMP dark matter
In existing dark matter models with global symmetries the relic abundance of
dark matter is either equal to that of anti-dark matter (thermal WIMP), or
vastly larger, with essentially no remaining anti-dark matter (asymmetric dark
matter). By exploring the consequences of a primordial asymmetry on the coupled
dark matter and anti-dark matter Boltzmann equations we find large regions of
parameter space that interpolate between these two extremes. Interestingly,
this new asymmetric WIMP framework can accommodate a wide range of dark matter
masses and annihilation cross sections. The present-day dark matter population
is typically asymmetric, but only weakly so, such that indirect signals of dark
matter annihilation are not completely suppressed. We apply our results to
existing models, noting that upcoming direct detection experiments will
constrain a large region of the relevant parameter space.Comment: 32 pages, 6 figures, updated references, updated XENON100 bounds,
typo in figure caption correcte
Phenological corrections to a field-scale, ET-based crop stress indicator: An application to yield forecasting across the U.S. Corn Belt
Soil moisture deficiency is a major factor in determining crop yields in water-limited agricultural production regions. Evapotranspiration (ET), which consists of crop water use through transpiration and water loss through direct soil evaporation, is a good indicator of soil moisture availability and vegetation health. ET therefore has been an integral part of many yield estimation efforts. The Evaporative Stress Index (ESI) is an ET-based crop stress indicator that describes temporal anomalies in a normalized evapotranspiration metric as derived from satellite remote sensing. ESI has demonstrated the capacity to explain regional yield variability in water-limited regions. However, its performance in some regions where the vegetation cycle is intensively managed appears to be degraded due to interannual phenological variability. This investigation selected three study sites across the U.S. Corn Belt – Mead, NE, Ames, IA and Champaign, IL – to investigate the potential operational value of 30-m resolution, phenologically corrected ESI datasets for yield prediction. The analysis was conducted over an 8-year period from 2010 to 2017, which included both drought and pluvial conditions as well as a broad range in yield values. Detrended yield anomalies for corn and soybean were correlated with ESI computed using annual ET curves temporally aligned based on (1) calendar date, (2) crop emergence date, and (3) a growing degree day (GDD) scaled time axis. Results showed that ESI has good correlations with yield anomalies at the county scale and that phenological corrections to the annual temporal alignment of the ET timeseries improve the correlation, especially when the time axis is defined by GDD rather than the calendar date. Peak correlations occur in the silking stage for corn and the reproductive stage for soybean – phases when these crops are particularly sensitive to soil moisture deficiencies. Regression equations derived at the time of peak correlation were used to estimate yields at county scale using a leave-one-out cross-validation strategy. The ESI-based yield estimates agree well with the USDA National Agricultural Statistics Service (NASS) county-level crop yield data, with correlation coefficients ranging from 0.79 to 0.93 and percent root-mean-square errors of 5–8%. These results demonstrate that remotely sensed ET at high spatiotemporal resolution can convey valuable water stress information for forecasting crop yields across the Corn Belt if interannual phenological variability is considered
Noether Symmetry Approach in "Cosmic Triad" Vector Field Scenario
To realize the accelerations in the early and late periods of our universe,
we need to specify potentials for the dominant fields. In this paper, by using
the Noether symmetry approach, we try to find suitable potentials in the
"cosmic triad" vector field scenario. Because the equation of state parameter
of dark energy has been constrained in the range of by observations, we derive the Noether conditions for the vector field
in quintessence, phantom and quintom models, respectively. In the first two
cases, constant potential solutions have been obtained. What is more, a fast
decaying point-like solution with power-law potential is also found for the
vector field in quintessence model. For the quintom case, we find an
interesting constraint on the field potentials,
where and are constants related to the Noether symmetry.Comment: 15 pages, no figures, accepted by Classical and Quantum Gravity
Chiral U(1) flavor models and flavored Higgs doublets: the top FB asymmetry and the Wjj
We present U(1) flavor models for leptophobic Z' with flavor dependent
couplings to the right-handed up-type quarks in the Standard Model, which can
accommodate the recent data on the top forward-backward (FB) asymmetry and the
dijet resonance associated with a W boson reported by CDF Collaboration. Such
flavor-dependent leptophobic charge assignments generally require extra chiral
fermions for anomaly cancellation. Also the chiral nature of U(1)' flavor
symmetry calls for new U(1)'-charged Higgs doublets in order for the SM
fermions to have realistic renormalizable Yukawa couplings. The stringent
constraints from the top FB asymmetry at the Tevatron and the same sign top
pair production at the LHC can be evaded due to contributions of the extra
Higgs doublets. We also show that the extension could realize cold dark matter
candidates.Comment: 40 pages, 10 figures, added 1 figure and extended discussion,
accepted for publication in JHE
Faith Integration in the Classroom: A Plural View
The topic of faith integration has been of interest to the higher education community for almost two centuries. Ten professors from ten different business schools collaborated during a Best Practices in College Teaching course to discuss faith integration, its importance in Christian universities, and ideas on implementation. Their writings on the topic were combined to form a guide to operationalizing faith integration. The resulting article seeks to demonstrate the imperative nature of integration within religious universities, focusing on schools of business. Practical ways of incorporating faith are also discussed, including three dimensions of integration. Assessment ideas and project proposals are included as well to aid professors in implementation
What the Tevatron Found?
The CDF collaboration has reported a 4.1\sigma\ excess in their lepton,
missing energy, and dijets channel. This excess, which takes the form of an
approximately Gaussian peak centered at a dijet invariant mass of 147 GeV, has
provoked a great deal of experimental and theoretical interest. Although the
D\O\ collaboration has reported that they do not observe a signal consistent
with CDF, there is currently no widely accepted explanation for the discrepancy
between these two experiments. A resolution of this issue is of great
importance---not least because it may teach us lessons relevant for future
searches at the LHC---and it will clearly require additional information. In
this paper, we consider the ability of the Tevatron and LHC detectors to
observe evidence associated with the CDF excess in a variety of channels. We
also discuss the ability of selected kinematic distributions to distinguish
between Standard Model explanations of the observed excess and various new
physics scenarios.Comment: 14 pages, 4 figures, 2 tables. Accepted for publication by JHEP. v2:
minor changes to text and figure
The other Higgses, at resonance, in the Lee-Wick extension of the Standard Model
Within the framework of the Lee Wick Standard Model (LWSM) we investigate
Higgs pair production , and top pair
production at the Large Hadron Collider (LHC), where the
neutral particles from the Higgs sector (, and )
appear as possible resonant intermediate states. We investigate the signal and we find that the LW Higgs,
depending on its mass-range, can be seen not long after the LHC upgrade in
2012. More precisely this happens when the new LW Higgs states are below the
top pair threshold. In the LW states, due to the wrong-sign
propagator and negative width, lead to a dip-peak structure instead of the
usual peak-dip structure which gives a characteristic signal especially for
low-lying LW Higgs states. We comment on the LWSM and the forward-backward
asymmetry in view of the measurement at the TeVatron. Furthermore, we present a
technique which reduces the hyperbolic diagonalization to standard
diagonalization methods. We clarify issues of spurious phases in the Yukawa
sector.Comment: 36 pages, 16 figures, 3 table
Statistical Anisotropy from Anisotropic Inflation
We review an inflationary scenario with the anisotropic expansion rate. An
anisotropic inflationary universe can be realized by a vector field coupled
with an inflaton, which can be regarded as a counter example to the cosmic
no-hair conjecture. We show generality of anisotropic inflation and derive a
universal property. We formulate cosmological perturbation theory in
anisotropic inflation. Using the formalism, we show anisotropic inflation gives
rise to the statistical anisotropy in primordial fluctuations. We also explain
a method to test anisotropic inflation using the cosmic microwave background
radiation (CMB).Comment: 32 pages, 5 figures, invited review for CQG, published versio
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