20,561 research outputs found
Magnetic Field and Curvature Effects on Pair Production I: Scalars and Spinors
The pair production rates for spin-zero and spin- particles are
calculated on spaces of the form with
corresponding to (flat), (flat, compactified),
(positive curvature) and (negative curvature), with and without a
background magnetic field on . The motivation is to elucidate the effects of
curvature and background magnetic field. Contrasting effects for positive and
negative curvature on the two cases of spin are obtained. For positive
curvature, we find enhancement for spin-zero and suppression for
spin-, with the opposite effect for negative curvature.Comment: 28 pages, 10 figure
Magnetic Field and Curvature Effects on Pair Production II: Vectors and Implications for Chromodynamics
We calculate the pair production rates for spin- or vector particles on
spaces of the form with corresponding to
(flat), (positive curvature) and (negative
curvature), with and without a background (chromo)magnetic field on . Beyond
highlighting the effects of curvature and background magnetic field, this is
particularly interesting since vector particles are known to suffer from the
Nielsen-Olesen instability, which can dramatically increase pair production
rates. The form of this instability for and is obtained. We also
give a brief discussion of how our results relate to ideas about confinement in
nonabelian theories.Comment: 24 pages, 9 figure
The Isospin Asymmetry in Anomalous Fluid Dynamics
The dynamics of fluids in which the constituent particles carry nonabelian
charges can be described succinctly in terms of group-valued variables via a
generalization of the co-adjoint orbit action for particles. This formalism,
which is particularly suitable for incorporating anomalies, has previously been
used for the chiral magnetic and chiral vorticity effects. Here we consider the
similar effect for the isospin which corresponds to an angular asymmetry for
neutral pions.Comment: 12 page
Plasmon interactions in the quark-gluon plasma
Yang-Mills theory at finite temperature is rewritten as a theory of plasmons
which provides a Hamiltonian framework for perturbation theory with resummation
of hard thermal loops.Comment: 12 pages, LaTeX, minor typos corrected, discussion adde
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Comparison of the effects of high and low milk-replacer feeding regimens on health and growth of crossbred dairy heifers
Context: Pre-weaning growth in dairy heifers is highly dependent on the amount of milk fed. Both milk replacer (MR) and associated labour are costly, encouraging restricted milk rations and once-a-day feeding.
Aims: This study compared performance relating to the growth and health of calves receiving one of two commercial feeding regimens: High or Low.
Methods: All heifers born during the Spring (January–March) calving block on a commercial UK farm with mixed-breed genetics were recruited at birth, randomly assigned to the High (n = 104, receiving MR-A) or Low (n = 88, receiving MR-B) feed group and reared indoors on straw bedding, with free access to concentrate. Both groups initially received MR twice daily. The High group continued to receive MR twice daily throughout the experiment, whereas the Low group calves were reduced to a single MR feed daily during Weeks 4–8. Blood samples were taken in Weeks 1 and 6 to assess passive transfer and measure circulating insulin-like growth factor 1 (IGF1). The Wisconsin calf-scoring system was used to assess health of calves in Weeks 1, 2, 4, 6 and 8 and at 6 months and size was also measured at these times. Data were analysed by univariate and multivariate models.
Key results: Passive transfer was good in both groups (serum total protein (mean ± s.d.) 60.9 ± 9.1 mg/mL) with no differences in pre-weaning disease incidence; diarrhoea occurred in 64.5% and bovine respiratory disease in 26.3% of calves. High group calves were significantly heavier, taller and longer at all pre-weaning examinations except recruitment owing to more growth in the first month, and remained significantly larger at 6 months: weight 157 ± 8 vs 149 ± 7 kg, height 103 ± 5 vs 100 ± 5 cm, length 90 ± 4 vs 88 ± 5 cm. Plasma IGF1 concentrations at around Week 6 were doubled in the High group (101 ± 38.6 vs 55 ± 34.1 ng/mL). Bovine respiratory disease was associated with reduced weight gain. Heifers with diarrhoea were leaner at weaning. High feed group, weight at recruitment and good passive transfer were positively associated with weight at 6 months.
Conclusions: Higher feeding levels pre-weaning increased growth rates and IGF1, although the disease incidence was unaffected.
Implications: Previous studies have shown that more growth and higher IGF1 pre-weaning are associated with a lower age at first calving and an increased chance of reaching the end of first lactation. These in turn improve long-term performance
Control Synthesis for an Underactuated Cable Suspended System Using Dynamic Decoupling
This article studies the dynamics and control of a novel underactuated
system, wherein a plate suspended by cables and with a freely moving mass on
top, whose other ends are attached to three quadrotors, is sought to be
horizontally stabilized at a certain height, with the ball positioned at the
center of mass of the plate. The freely moving mass introduces a 2-degree of
underactuation into the system. The design proceeds through a decoupling of the
quadrotors and the plate dynamics. Through a partial feedback linearization
approach, the attitude of the plate and the translational height of the plate
is initially controlled, while maintaining a bounded velocity along the and
directions. These inputs are then synthesized through the quadrotors with a
backstepping and timescale separation argument based on Tikhonov's theorem
Effective Theory of Wilson Lines and Deconfinement
To study the deconfining phase transition at nonzero temperature, I outline
the perturbative construction of an effective theory for straight, thermal
Wilson lines. Certain large, time dependent gauge transformations play a
central role. They imply the existence of interfaces, which can be used to
determine the form of the effective theory as a gauged, nonlinear sigma model
of adjoint matrices. Especially near the transition, the Wilson line may
undergo a Higgs effect. As an adjoint field, this can generate eigenvalue
repulsion in the effective theory.Comment: 6 pages, LaTeX. Final, published version. Refs. 7, 39, and 40 added.
In Ref. 37, there is an expanded discussion of a "fuzzy" bag mode
Supersymmetry and Mass Gap in 2+1 Dimensions: A Gauge Invariant Hamiltonian Analysis
A Hamiltonian formulation of Yang-Mills-Chern-Simons theories with supersymmetry in terms of gauge-invariant variables is presented,
generalizing earlier work on nonsupersymmetric gauge theories. Special
attention is paid to the volume measure of integration (over the gauge orbit
space of the fields) which occurs in the inner product for the wave functions
and arguments relating it to the renormalization of the Chern-Simons level
number and to mass-gaps in the spectrum of the Hamiltonians are presented. The
expression for the integration measure is consistent with the absence of mass
gap for theories with extended supersymmetry (in the absence of additional
matter hypermultiplets and/or Chern-Simons couplings), while for the minimally
supersymmetric case, there is a mass-gap, the scale of which is set by a
renormalized level number, in agreement with indications from existing
literature. The realization of the supersymmetry algebra and the Hamiltonian in
terms of the gauge invariant variables is also presented.Comment: 31 pages, References added, typos correcte
Fuzzy spaces and new random matrix ensembles
We analyze the expectation value of observables in a scalar theory on the
fuzzy two sphere, represented as a generalized hermitian matrix model. We
calculate explicitly the form of the expectation values in the large-N limit
and demonstrate that, for any single kind of field (matrix), the distribution
of its eigenvalues is still a Wigner semicircle but with a renormalized radius.
For observables involving more than one type of matrix we obtain a new
distribution corresponding to correlated Wigner semicircles.Comment: 12 pages, 1 figure; version to appear in Phys. Rev.
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