21,565 research outputs found
Large N_c in chiral perturbation theory
The construction of the effective Lagrangian relevant for the mesonic sector
of QCD in the large N_c limit meets with a few rather subtle problems. We
thoroughly examine these and show that, if the variables of the effective
theory are chosen suitably, the known large N_c counting rules of QCD can
unambiguously be translated into corresponding counting rules for the effective
coupling constants. As an application, we demonstrate that the Kaplan-Manohar
transformation is in conflict with these rules and is suppressed to all orders
in 1/N_c. The anomalous dimension of the axial singlet current generates an
additional complication: The corresponding external field undergoes
nonmultiplicative renormalization. As a consequence, the Wess-Zumino-Witten
term, which accounts for the U(3)_R x U(3)_L anomalies in the framework of the
effective theory, contains pieces that depend on the running scale of QCD. The
effect only shows up at nonleading order in 1/N_c, but requires specific
unnatural parity contributions in the effective Lagrangian that restore
renormalization group invariance.Comment: 56 page
Driven collective instabilities in magneto-optical traps: a fluid-dynamical approach
We present a theoretical model to describe an instability mechanism in
ultra-cold gases, where long-range interactions are taken into account.
Focusing on the nonlinear coupling between the collective (plasma-like) and the
center-of-mass modes, we show that the resulting dynamics is governed by a
parametric equation of the generalized Mathieu type and compute the
corresponding stability chart. We apply our model to typical ranges of
magneto-optical traps (MOT) parameters and find a good agreement with previous
experimental observations.Comment: 4 pages, 3 figures. Some minor changes in the published version
Priming by recombinant chicken interleukin-2 induces selective expression of IL-8 and IL-18 mRNA in chicken heterophils during receptor-mediated phagocytosis of opsonized and nonopsonized Salmonella enterica serovar enteritidis
Inflationary paradigm after Planck 2013
Models of cosmic inflation posit an early phase of accelerated expansion of
the universe, driven by the dynamics of one or more scalar fields in curved
spacetime. Though detailed assumptions about fields and couplings vary across
models, inflation makes specific, quantitative predictions for several
observable quantities, such as the flatness parameter ()
and the spectral tilt of primordial curvature perturbations (), among others---predictions that match the latest
observations from the {\it Planck} satellite to very good precision. In the
light of data from {\it Planck} as well as recent theoretical developments in
the study of eternal inflation and the multiverse, we address recent criticisms
of inflation by Ijjas, Steinhardt, and Loeb. We argue that their conclusions
rest on several problematic assumptions, and we conclude that cosmic inflation
is on a stronger footing than ever before.Comment: 11 pages, no figures; added references, and brief additions to
Footnote 1, Section VI, and the Acknowledgment
Relativistic Corrections to Nonrelativistic Effective Field Theories
In this paper we develop a formalism for studying the nonrelativistic limit
of relativistic field theories in a systematic way. By introducing a simple,
nonlocal field redefinition, we transform a given relativistic theory,
describing a real, self-interacting scalar field, into an equivalent theory,
describing a complex scalar field that encodes at each time both the original
field and its conjugate momentum. Our low-energy effective theory incorporates
relativistic corrections to the kinetic energy as well as the backreaction of
fast-oscillating terms on the behavior of the dominant, slowly varying
component of the field. Possible applications of our new approach include axion
dark matter, though the methods developed here should be applicable to the
low-energy limits of other field theories as well.Comment: 31pp. References added, and 3 appendices added, showing (a) how to
implement the field redefinition as a canonical transformation, (b) how to
develop the effective field theory using a local field redefinition, and (c)
how to use a further field redefinition to compare our results with those of
Mukaida, Takimoto, and Yamad
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