15,785 research outputs found

### Scale invariant forces in 1d shuffled lattices

In this paper we present a detailed and exact study of the probability
density function $P(F)$ of the total force $F$ acting on a point particle
belonging to a perturbed lattice of identical point sources of a power law pair
interaction. The main results concern the large $F$ tail of $P(F)$ for which
two cases are mainly distinguished: (i) Gaussian-like fast decreasing $P(F)$
for lattice with perturbations forbidding any pair of particles to be found
arbitrarily close to one each other; (ii) L\'evy-like power law decreasing
$P(F)$ when this possibility is instead permitted. It is important to note that
in the second case the exponent of the power law tail of $P(F)$ is the same for
all perturbation (apart from very singular cases), and is in an one to one
correspondence with the exponent characterizing the behavior of the pair
interaction with the distance between the two particles.Comment: 10 pages, revtex4 forma

### Polymeric Phase of Simplicial Quantum Gravity

We deduce the appearance of a polymeric phase in 4-dimensional simplicial
quantum gravity by varying the values of the coupling constants and discuss the
geometric structure of the phase in terms of ergodic moves. A similar result is
true in 3-dimensions.Comment: 6 pages, revte

### Point processes and stochastic displacement fields

The effect of a stochastic displacement field on a statistically independent
point process is analyzed. Stochastic displacement fields can be divided into
two large classes: spatially correlated and uncorrelated. For both cases exact
transformation equations for the two-point correlation function and the power
spectrum of the point process are found, and a detailed study of them with
important paradigmatic examples is done. The results are general and in any
dimension. A particular attention is devoted to the kind of large scale
correlations that can be introduced by the displacement field, and to the
realizability of arbitrary ``superhomogeneous'' point processes.Comment: 17 pages, 7 figure

### Chemical etching of a disordered solid: from experiments to field theory

We present a two-dimensional theoretical model for the slow chemical
corrosion of a thin film of a disordered solid by suitable etching solutions.
This model explain different experimental results showing that the corrosion
stops spontaneously in a situation in which the concentration of the etchant is
still finite while the corrosion surface develops clear fractal features. We
show that these properties are strictly related to the percolation theory, and
in particular to its behavior around the critical point. This task is
accomplished both by a direct analysis in terms of a self-organized version of
the Gradient Percolation model and by field theoretical arguments.Comment: 7 pages, 3 figure

### A radiatively improved fermiophobic Higgs boson scenario

The naive fermiophobic scenario is unstable under radiative corrections, due
to the chiral-symmetry breaking induced by fermion mass terms. In a recent
study, the problem of including the radiative corrections has been tackled via
an effective field theory approach. The renormalized Yukawa couplings are
assumed to vanish at a high energy scale $\Lambda$, and their values at the
electroweak scale are computed via modified Renormalization Group Equations. We
show that, in case a fermiophobic Higgs scenario shows up at the LHC, a linear
collider program will be needed to accurately measure the radiative Yukawa
structure, and consequently constrain the $\Lambda$ scale.Comment: 7 pages, 3 figures, Proceedings of the 2011 International Workshop on
Future Linear Colliders (LCWS11), Granada (Spain), 26-30 September 201

### Clustering and coalescence from multiplicative noise: the Kraichnan ensemble

We study the dynamics of the two-point statistics of the Kraichnan ensemble
which describes the transport of a passive pollutant by a stochastic turbulent
flow characterized by scale invariant structure functions. The fundamental
equation of this problem consists in the Fokker-Planck equation for the
two-point correlation function of the density of particles performing spatially
correlated Brownian motions with scale invariant correlations. This problem is
equivalent to the stochastic motion of an effective particle driven by a
generic multiplicative noise. In this paper we propose an alternative and more
intuitive approach to the problem than the original one leading to the same
conclusions. The general features of this new approach make possible to fit it
to other more complex contexts.Comment: IOP-LaTeX, 17 pages J. Phys. A: Theor. Mat. 2008 in pres

### Voronoi and Voids Statistics for Super-homogeneous Point Processes

We study the Voronoi and void statistics of super-homogeneous (or
hyperuniform) point patterns in which the infinite-wavelength density
fluctuations vanish. Super-homogeneous or hyperuniform point patterns arise in
one-component plasmas, primordial density fluctuations in the Universe, and in
jammed hard-particle packings. We specifically analyze a certain
one-dimensional model by studying size fluctuations and correlations of the
associated Voronoi cells. We derive exact results for the complete joint
statistics of the size of two Voronoi cells. We also provide a sum rule that
the correlation matrix for the Voronoi cells must obey in any space dimension.
In contrast to the conventional picture of super-homogeneous systems, we show
that infinitely large Voronoi cells or voids can exist in super-homogeneous
point processes in any dimension.
We also present two heuristic conditions to identify and classify any
super-homogeneous point process in terms of the asymptotic behavior of the void
size distribution.Comment: 27 pages, and 4 figure

### Testing PVLAS axions with resonant photon splitting

The photon splitting gamma -> gamma gamma in a time-independent and
inhomogeneous magnetized background is considered when neutral and ultralight
spin-0 particles are coupled to two-photons. Depending on the inhomogeneity
scale of the external field, resonant photon splitting can occur. If an optical
laser crosses a magnetic field of few Tesla with typical inhomogeneity scale of
the order of the meter, a potentially observable rate of photon splittings is
expected for the PVLAS range of couplings and masses.Comment: 7 pages, 2 included eps figures, two references added, minor typos
correcte

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