8,251 research outputs found
Fractional Lindstedt series
The parametric equations of the surfaces on which highly resonant
quasi-periodic motions develop (lower-dimensional tori) cannot be analytically
continued, in general, in the perturbation parameter, i.e. they are not
analytic functions of the perturbation parameter. However rather generally
quasi-periodic motions whose frequencies satisfy only one rational relation
("resonances of order 1") admit formal perturbation expansions in terms of a
fractional power of the perturbation parameter, depending on the degeneration
of the resonance. We find conditions for this to happen, and in such a case we
prove that the formal expansion is convergent after suitable resummation.Comment: 40 pages, 6 figure
Fermionic Corrections to Fluid Dynamics from BTZ Black Hole
We reconstruct the complete fermionic orbit of the non-extremal BTZ black
hole by acting with finite supersymmetry transformations. The solution
satisfies the exact supergravity equations of motion to all orders in the
fermonic expansion and the final result is given in terms of fermionic
bilinears. By fluid/gravity correspondence, we derive linearized Navier-Stokes
equations and a set of new differential equations from Rarita-Schwinger
equation. We compute the boundary energy-momentum tensor and we interpret the
result as a perfect fluid with a modified definition of fluid velocity.
Finally, we derive the modified expression for the entropy of the black hole in
terms of the fermionic bilinears.Comment: 21 pages, Latex2e, no figure
Fermionic Wigs for BTZ Black Holes
We compute the wig for the BTZ black hole, namely the complete non-linear
solution of supergravity equations with all fermionic zero modes. We use a
"gauge completion" method starting from AdS_3 Killing spinors to generate the
gravitinos fields associated to the BH and we compute the back-reaction on the
metric. Due to the anticommutative properties of the fermionic hairs the
resummation of these effects truncates at some order. We illustrate the
technique proposed in a precedent paper in a very explicit and analytical form.
We also compute the mass, the angular momentum and other charges with their
corrections.Comment: 11 pages, no figure
Fermions, Wigs, and Attractors
We compute the modifications to the attractor mechanism due to fermionic
corrections. In N=2, D=4 supergravity, at the fourth order, we find a new
contribution to the horizon values of the scalar fields of the vector
multiplets.Comment: v2 : 1+11 pages; paper reorganized in Sections; Sec. 5 added, with
detailed treatment of the axion-dilaton model; some typos fixed and
references adde
Resummation of perturbation series and reducibility for Bryuno skew-product flows
We consider skew-product systems on T^d x SL(2,R) for Bryuno base flows close
to constant coefficients, depending on a parameter, in any dimension d, and we
prove reducibility for a large measure set of values of the parameter. The
proof is based on a resummation procedure of the formal power series for the
conjugation, and uses techniques of renormalisation group in quantum field
theory.Comment: 30 pages, 12 figure
Localized exciton-polariton modes in dye-doped nanospheres: a quantum approach
We model a dye-doped polymeric nanosphere as an ensemble of quantum emitters
and use it to investigate the localized exciton-polaritons supported by such a
nanosphere. By determining the time evolution of the density matrix of the
collective system, we explore how an incident laser field may cause transient
optical field enhancement close to the surface of such nanoparticles. Our
results provide further evidence that excitonic materials can be used to good
effect in nanophotonics.Comment: 16 pages, 4 figure
The use of the McIlwain L-parameter to estimate cosmic ray vertical cutoff rigidities for different epochs of the geomagnetic field
Secular changes in the geomagnetic field between 1955 and 1980 have been large enough to produce significant differences in both the verical cutoff rigidities and in the L-value for a specified position. A useful relationship employing the McIlwain L-parameter to estimate vertical cutoff rigidities has been derived for the twenty-five year period
Estimating the change in asymptotic direction due to secular changes in the geomagnetic field
The concept of geomagnetic optics, as described by the asymptotic directions of approach, is extremely useful in the analysis of cosmic radiation data. However, when changes in cutoff occur as a result of evolution in the geomagnetic field, there are corresponding changes in the asymptotic cones of acceptance. A method is introduced of estimating the change in the asymptotic direction of approach for vertically incident cosmic ray particles from a reference set of directions at a specific epoch by considering the change in the geomagnetic cutoff
The Herschel exploitation of local galaxy Andromeda (HELGA) V: Strengthening the case for substantial interstellar grain growth
In this paper we consider the implications of the distributions of dust and
metals in the disc of M31. We derive mean radial dust distributions using a
dust map created from Herschel images of M31 sampling the entire far-infrared
(FIR) peak. Modified blackbodies are fit to approximately 4000 pixels with a
varying, as well as a fixed, dust emissivity index (beta). An overall metal
distribution is also derived using data collected from the literature. We use a
simple analytical model of the evolution of the dust in a galaxy with dust
contributed by stellar sources and interstellar grain growth, and fit this
model to the radial dust-to-metals distribution across the galaxy. Our analysis
shows that the dust-to-gas gradient in M31 is steeper than the metallicity
gradient, suggesting interstellar dust growth is (or has been) important in
M31. We argue that M31 helps build a case for cosmic dust in galaxies being the
result of substantial interstellar grain growth, while the net dust production
from stars may be limited. We note, however, that the efficiency of dust
production in stars, e.g., in supernovae (SNe) ejecta and/or stellar
atmospheres, and grain destruction in the interstellar medium (ISM) may be
degenerate in our simple model. We can conclude that interstellar grain growth
by accretion is likely at least as important as stellar dust production
channels in building the cosmic dust component in M31.Comment: 12 pages, 7 figures. Published in MNRAS 444, 797. This version is
updated to match the published versio
A rigorous implementation of the Jeans--Landau--Teller approximation
Rigorous bounds on the rate of energy exchanges between vibrational and
translational degrees of freedom are established in simple classical models of
diatomic molecules. The results are in agreement with an elementary
approximation introduced by Landau and Teller. The method is perturbative
theory ``beyond all orders'', with diagrammatic techniques (tree expansions) to
organize and manipulate terms, and look for compensations, like in recent
studies on KAM theorem homoclinic splitting.Comment: 23 pages, postscrip
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