36,549 research outputs found
Non-perturbative double scaling limits
Recently, the author has proposed a generalization of the matrix and vector
models approach to the theory of random surfaces and polymers. The idea is to
replace the simple matrix or vector (path) integrals by gauge theory or
non-linear sigma model (path) integrals. We explain how this solves one of the
most fundamental limitation of the classic approach: we automatically obtain
non-perturbative definitions in non-Borel summable cases. This is exemplified
on the simplest possible examples involving O(N) symmetric non-linear sigma
models with N-dimensional target spaces, for which we construct (multi)critical
metrics. The non-perturbative definitions of the double scaled, manifestly
positive, partition functions rely on remarkable identities involving (path)
integrals.Comment: 18 pages, one figur
Raman Fingerprint of Charged Impurities in Graphene
We report strong variations in the Raman spectra for different single-layer
graphene samples obtained by micromechanical cleavage, which reveals the
presence of excess charges, even in the absence of intentional doping. Doping
concentrations up to ~10^13 cm-2 are estimated from the G peak shift and width,
and the variation of both position and relative intensity of the second order
2D peak. Asymmetric G peaks indicate charge inhomogeneity on the scale of less
than 1 micron.Comment: 3 pages, 5 figure
Multiple merging events in Abell 521
We present a detailed spatial and dynamical analysis of the central
~2.2~\h~Mpc region of the galaxy cluster Abell~521 (z=0.247), based on
238 spectra obtained at the 3.6~m Telescope of ESO and at the CFHT. From the
analysis of the 125 galaxies confirmed members of the cluster, we derive a mean
velocity of km/s and detect a complex velocity
distribution with high velocity dispersion, km/s), but
clear departure from a single gaussian component. The general structure of the
cluster follows a NW/SE direction, crossed by a perpendicular high density
``ridge'' of galaxies in the core region. The northern region of the cluster is
characterized by a lower velocity dispersion as compared to the whole cluster
value; it hosts the BCG and a dynamically bound complex of galaxies, and it is
associated to a group detected in X-ray (Arnaud et al 2000). This region could
be in pre-merger stage onto the main cluster nearly in the plane of the sky.
These results, taken together with the fact that most of the clumps detected on
the isodensity maps, as well as the early type galaxies and the brightest ones
are aligned, suggest that this NW/SE direction is the preferred one for the
formation of this cluster. The central high dense region shows a lower velocity
location ( km/s) and significantly higher scale ( km/s) as compared to the whole cluster values. This is due to
the presence of a low-velocity group of galaxies with a high fraction of
emission line objects. This can be explained in a scenario in which a merging
of subclusters has recently occurred along the direction of the ``ridge'' with
a significant component along the line of sight.Comment: 21 pages, 32 figures, uses aa.cls style, Latex. Accepted for
publication in A&
Speedy motions of a body immersed in an infinitely extended medium
We study the motion of a classical point body of mass M, moving under the
action of a constant force of intensity E and immersed in a Vlasov fluid of
free particles, interacting with the body via a bounded short range potential
Psi. We prove that if its initial velocity is large enough then the body
escapes to infinity increasing its speed without any bound "runaway effect".
Moreover, the body asymptotically reaches a uniformly accelerated motion with
acceleration E/M. We then discuss at a heuristic level the case in which Psi(r)
diverges at short distances like g r^{-a}, g,a>0, by showing that the runaway
effect still occurs if a<2.Comment: 15 page
The effect of ram pressure on the star formation, mass distribution and morphology of galaxies
We investigate the dependence of star formation and the distribution of the
components of galaxies on the strength of ram pressure. Several mock
observations in X-ray, H and HI wavelength for different ram-pressure
scenarios are presented. By applying a combined N-body/hydrodynamic description
(GADGET-2) with radiative cooling and a recipe for star formation and stellar
feedback 12 different ram-pressure stripping scenarios for disc galaxies were
calculated. Special emphasis was put on the gas within the disc and in the
surroundings. All gas particles within the computational domain having the same
mass resolution. The relative velocity was varied from 100 km/s to 1000 km/s in
different surrounding gas densities in the range from to
g/cm. The temperature of the surrounding gas was
initially K. The star formation of a galaxy is enhanced by more
than a magnitude in the simulation with a high ram-pressure (
dyn/cm) in comparison to the same system evolving in isolation. The
enhancement of the star formation depends more on the surrounding gas density
than on the relative velocity. Up to 95% of all newly formed stars can be found
in the wake of the galaxy out to distances of more than 350 kpc behind the
stellar disc. Continuously stars fall back to the old stellar disc, building up
a bulge-like structure. Young stars can be found throughout the stripped wake
with surface densities locally comparable to values in the inner stellar disc.
Ram-pressure stripping can shift the location of star formation from the disc
into the wake on very short timescales. (Abridged)Comment: 19 pages, 25 figures, A&A accepted, high resolution version can be
found at http://astro.uibk.ac.at/~wolfgang/kapferer_rps_galaxies.pd
model in aether-superspace
In this paper we study the dynamical generation of mass in the
Lorentz-violating model defined in two and three-dimensional
aether-superspace. We show that even though the model presents a phase
structure similar to the usual, Lorentz invariant case, the dynamically
generated mass by quantum corrections has a dependence on the Lorentz violating
background properties, except for spacelike LV vector parameter. This is to be
contrasted with the behavior of the quantum electrodynamics in the
two-dimensional aether-superspace, where the dynamical generation of mass was
shown to exhibit an explicit dependence on the aether parameters in every
possible case.Comment: 18 pages, 4 figure
Dynamical aspects of inextensible chains
In the present work the dynamics of a continuous inextensible chain is
studied. The chain is regarded as a system of small particles subjected to
constraints on their reciprocal distances. It is proposed a treatment of
systems of this kind based on a set Langevin equations in which the noise is
characterized by a non-gaussian probability distribution. The method is
explained in the case of a freely hinged chain. In particular, the generating
functional of the correlation functions of the relevant degrees of freedom
which describe the conformations of this chain is derived. It is shown that in
the continuous limit this generating functional coincides with a model of an
inextensible chain previously discussed by one of the authors of this work.
Next, the approach developed here is applied to a inextensible chain, called
the freely jointed bar chain, in which the basic units are small extended
objects. The generating functional of the freely jointed bar chain is
constructed. It is shown that it differs profoundly from that of the freely
hinged chain. Despite the differences, it is verified that in the continuous
limit both generating functionals coincide as it is expected.Comment: 15 pages, LaTeX 2e + various packages, 3 figures. The title has been
changed and three references have been added. A large part of the manuscript
has been rewritten to improve readability. Chapter 4 has been added. It
contains the construction of the generating functional without the
shish-kebab approximation and a new derivation of the continuous limit of the
freely jointed bar chai
Intermixture of extended edge and localized bulk energy levels in macroscopic Hall systems
We study the spectrum of a random Schroedinger operator for an electron
submitted to a magnetic field in a finite but macroscopic two dimensional
system of linear dimensions equal to L. The y direction is periodic and in the
x direction the electron is confined by two smooth increasing boundary
potentials. The eigenvalues of the Hamiltonian are classified according to
their associated quantum mechanical current in the y direction. Here we look at
an interval of energies inside the first Landau band of the random operator for
the infinite plane. In this energy interval, with large probability, there
exist O(L) eigenvalues with positive or negative currents of O(1). Between each
of these there exist O(L^2) eigenvalues with infinitesimal current
O(exp(-cB(log L)^2)). We explain what is the relevance of this analysis to the
integer quantum Hall effect.Comment: 29 pages, no figure
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