32,483 research outputs found
Gluon Correlators in the Kogan-Kovner Model
The Lorentz-invariant gluon correlation functions, corresponding to scalar
and pseudo-scalar glueballs, are calculated for Kogan's and Kovner's
variational ansatz for the pure SU(N) Yang-Mills wavefunctional.
One expects that only one dynamical mass scale should be present in QCD; the
ansatz generates the expected scale for both glueballs, as well as an
additional scale for the scalar glueball. The additional mass scale must
therefore vanish, or be close to the expected one. This is shown to constrain
the nature of the phase transition in the Kogan-Kovner ansatz.Comment: 9 pages, no figure
The impact of stochastic physics on climate sensitivity in EC-Earth
Stochastic schemes, designed to represent unresolved sub-grid scale
variability, are frequently used in short and medium-range weather forecasts,
where they are found to improve several aspects of the model. In recent years,
the impact of stochastic physics has also been found to be beneficial for the
model's long term climate. In this paper, we demonstrate for the first time
that the inclusion of a stochastic physics scheme can notably affect a model's
projection of global warming, as well as its historical climatological global
temperature. Specifically, we find that when including the 'stochastically
perturbed parametrisation tendencies' scheme (SPPT) in the fully coupled
climate model EC-Earth v3.1, the predicted level of global warming between 1850
and 2100 is reduced by 10% under an RCP8.5 forcing scenario. We link this
reduction in climate sensitivity to a change in the cloud feedbacks with SPPT.
In particular, the scheme appears to reduce the positive low cloud cover
feedback, and increase the negative cloud optical feedback. A key role is
played by a robust, rapid increase in cloud liquid water with SPPT, which we
speculate is due to the scheme's non-linear interaction with condensation.Comment: Under review in Journal of Geophysical Research: Atmosphere
Quasi-hermitian Quantum Mechanics in Phase Space
We investigate quasi-hermitian quantum mechanics in phase space using
standard deformation quantization methods: Groenewold star products and Wigner
transforms. We focus on imaginary Liouville theory as a representative example
where exact results are easily obtained. We emphasize spatially periodic
solutions, compute various distribution functions and phase-space metrics, and
explore the relationships between them.Comment: Accepted by Journal of Mathematical Physic
The shape of primordial non-Gaussianity and the CMB bispectrum
We present a set of formalisms for comparing, evolving and constraining
primordial non-Gaussian models through the CMB bispectrum. We describe improved
methods for efficient computation of the full CMB bispectrum for any general
(non-separable) primordial bispectrum, incorporating a flat sky approximation
and a new cubic interpolation. We review all the primordial non-Gaussian models
in the present literature and calculate the CMB bispectrum up to l <2000 for
each different model. This allows us to determine the observational
independence of these models by calculating the cross-correlation of their CMB
bispectra. We are able to identify several distinct classes of primordial
shapes - including equilateral, local, warm, flat and feature (non-scale
invariant) - which should be distinguishable given a significant detection of
CMB non-Gaussianity. We demonstrate that a simple shape correlator provides a
fast and reliable method for determining whether or not CMB shapes are well
correlated. We use an eigenmode decomposition of the primordial shape to
characterise and understand model independence. Finally, we advocate a
standardised normalisation method for based on the shape
autocorrelator, so that observational limits and errors can be consistently
compared for different models.Comment: 32 pages, 20 figure
Primordial non-Gaussianity and the CMB bispectrum
We present a new formalism, together with efficient numerical methods, to
directly calculate the CMB bispectrum today from a given primordial bispectrum
using the full linear radiation transfer functions. Unlike previous analyses
which have assumed simple separable ansatze for the bispectrum, this work
applies to a primordial bispectrum of almost arbitrary functional form, for
which there may have been both horizon-crossing and superhorizon contributions.
We employ adaptive methods on a hierarchical triangular grid and we establish
their accuracy by direct comparison with an exact analytic solution, valid on
large angular scales. We demonstrate that we can calculate the full CMB
bispectrum to greater than 1% precision out to multipoles l<1800 on reasonable
computational timescales. We plot the bispectrum for both the superhorizon
('local') and horizon-crossing ('equilateral') asymptotic limits, illustrating
its oscillatory nature which is analogous to the CMB power spectrum
Radiation from an accelerated quark via AdS/CFT
In this paper we investigate radiation by an accelerated quark in a strongly
coupled gauge theory via AdS/CFT correspondence. According to AdS/CFT
dictionary, we can read off energy density or energy flux of the radiation from
asymptotic gravitational field in AdS bulk sourced by an accelerated string
trailing behind the quark. In the case of an oscillating quark with frequency
, we show that the time averaged energy density is asymptotically
isotropic and it falls off as with
distance from the source. In a toy model of a scattered quark by an
external field, we simply estimate Poynting vector by the bremsstrahlung
radiation and show that the energy flux is anisotropic outgoing radiation.
Based on these investigations, we discuss the properties of strongly coupled
gauge theory radiation in comparison with electromagnetic radiation.Comment: 16 pages, no figures, accepted for publication in Phys. Rev.
Universal relaxational dynamics of gapped one dimensional models in the quantum sine-Gordon universality class
A semiclassical approach to the low-temperature real time dynamics of generic
one-dimensional, gapped models in the sine-Gordon model universality class is
developed. Asymptotically exact universal results for correlation functions are
obtained in the temperature regime T << Delta, where Delta is the energy gap.Comment: 4 pages, 1 figur
The Cauchy Problem for the Wave Equation in the Schwarzschild Geometry
The Cauchy problem is considered for the scalar wave equation in the
Schwarzschild geometry. We derive an integral spectral representation for the
solution and prove pointwise decay in time.Comment: 33 page
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