4,842 research outputs found
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 , 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 scale.Comment: 7 pages, 3 figures, Proceedings of the 2011 International Workshop on
Future Linear Colliders (LCWS11), Granada (Spain), 26-30 September 201
Etching of random solids: hardening dynamics and self-organized fractality
When a finite volume of an etching solution comes in contact with a
disordered solid, a complex dynamics of the solid-solution interface develops.
Since only the weak parts are corroded, the solid surface hardens
progressively. If the etchant is consumed in the chemical reaction, the
corrosion dynamics slows down and stops spontaneously leaving a fractal solid
surface, which reveals the latent percolation criticality hidden in any random
system. Here we introduce and study, both analytically and numerically, a
simple model for this phenomenon. In this way we obtain a detailed description
of the process in terms of percolation theory. In particular we explain the
mechanism of hardening of the surface and connect it to Gradient Percolation.Comment: Latex, aipproc, 6 pages, 3 figures, Proceedings of 6th Granada
Seminar on Computational Physic
Looking for anomalous gamma-gamma-H and Z-gamma-H couplings at future linear collider
We consider the possibility of studying anomalous contributions to the
gamma-gamma-H and Z-gamma-H vertices through the process e-gamma--> e-H at
future e-gamma linear colliders, with Sqrt(S)=500-1500 GeV. We make a model
independent analysis based on SU(2)xU(1) invariant effective operators of dim=6
added to the standard model lagrangian. We consider a light Higgs boson (mostly
decaying in bar(b)-b pairs), and include all the relevant backgrounds. Initial
e-beam polarization effects are also analyzed. We find that the process
e-gamma--> e-H provides an excellent opportunity to strongly constrain both the
CP-even and the CP-odd anomalous contributions to the gamma-gamma-H and
Z-gamma-H vertices.Comment: LaTeX, 33 pages, 16 eps figures, extended section
Force distribution in a randomly perturbed lattice of identical particles with pair interaction
We study the statistics of the force felt by a particle in the class of
spatially correlated distribution of identical point-like particles,
interacting via a pair force (i.e. gravitational or Coulomb), and
obtained by randomly perturbing an infinite perfect lattice. In the first part
we specify the conditions under which the force on a particle is a well defined
stochastic quantity. We then study the small displacements approximation,
giving both the limitations of its validity, and, when it is valid, an
expression for the force variance. In the second part of the paper we extend to
this class of particle distributions the method introduced by Chandrasekhar to
study the force probability density function in the homogeneous Poisson
particle distribution. In this way we can derive an approximate expression for
the probability distribution of the force over the full range of perturbations
of the lattice, i.e., from very small (compared to the lattice spacing) to very
large where the Poisson limit is recovered. We show in particular the
qualitative change in the large-force tail of the force distribution between
these two limits. Excellent accuracy of our analytic results is found on
detailed comparison with results from numerical simulations. These results
provide basic statistical information about the fluctuations of the
interactions (i) of the masses in self-gravitating systems like those
encountered in the context of cosmological N-body simulations, and (ii) of the
charges in the ordered phase of the One Component Plasma.Comment: 23 pages, 10 figure
A SUSY Inspired Simplified Model for the 750 GeV Diphoton Excess
The evidence for a new singlet scalar particle from the 750 GeV diphoton
excess, and the absence of any other signal of new physics at the LHC so far,
suggest the existence of new coloured scalars. To study this possibility, we
propose a supersymmetry inspired simplified model, extending the Standard Model
with a singlet scalar and with heavy scalar fields carrying both colour and
electric charges -- the `squarks'. To allow the latter to decay, and to
generate the dark matter of the Universe, we also add a neutral fermion to the
particle content. We show that this model provides a two-parameter fit to the
observed diphoton excess consistently with cosmology, while the allowed
parameter space is bounded by the consistency of the model. In the context of
our simplified model this implies the existence of other supersymmetric
particles accessible at the LHC, rendering this scenario falsifiable. If this
excess persists, it will imply a paradigm shift in assessing supersymmetry
breaking and the role of scalars in low scale physics.Comment: 7 pages, 2 figures, SUSY incarnat
Quasi-stationary states and the range of pair interactions
"Quasi-stationary" states are approximately time-independent out of
equilibrium states which have been observed in a variety of systems of
particles interacting by long-range interactions. We investigate here the
conditions of their occurrence for a generic pair interaction V(r \rightarrow
\infty) \sim 1/r^a with a > 0, in d>1 dimensions. We generalize analytic
calculations known for gravity in d=3 to determine the scaling parametric
dependences of their relaxation rates due to two body collisions, and report
extensive numerical simulations testing their validity. Our results lead to the
conclusion that, for a < d-1, the existence of quasi-stationary states is
ensured by the large distance behavior of the interaction alone, while for a >
d-1 it is conditioned on the short distance properties of the interaction,
requiring the presence of a sufficiently large soft-core in the interaction
potential.Comment: 5 pages, 3 figures; final version to appear in Phys. Rev. Let
Surface Hardening and Self-Organized Fractality Through Etching of Random Solids
When a finite volume of etching solution is in contact with a disordered
solid, complex dynamics of the solid-solution interface develop. If the etchant
is consumed in the chemical reaction, the dynamics stop spontaneously on a
self-similar fractal surface. As only the weakest sites are corroded, the solid
surface gets progressively harder and harder. At the same time it becomes
rougher and rougher uncovering the critical spatial correlations typical of
percolation. From this, the chemical process reveals the latent percolation
criticality hidden in any random system. Recently, a simple minimal model has
been introduced by Sapoval et al. to describe this phenomenon. Through analytic
and numerical study, we obtain a detailed description of the process. The time
evolution of the solution corroding power and of the distribution of resistance
of surface sites is studied in detail. This study explains the progressive
hardening of the solid surface. Finally, this dynamical model appears to belong
to the universality class of Gra dient Percolation.Comment: 14 pages, 15 figures (1457 Kb
Anisotropic Anomalous Diffusion assessed in the human brain by scalar invariant indices
A new method to investigate anomalous diffusion in human brain is proposed.
The method has been inspired by both the stretched-exponential model proposed
by Hall and Barrick (HB) and DTI. Quantities extracted using HB method were
able to discriminate different cerebral tissues on the basis of their
complexity, expressed by the stretching exponent gamma and of the anisotropy of
gamma across different directions. Nevertheless, these quantities were not
defined as scalar invariants like mean diffusivity and fractional anisotropy,
which are eigenvalues of the diffusion tensor. We hypotesize instead that the
signal may be espressed as a simple stretched-exponential only along the
principal axes of diffusion, while in a generic direction the signal is modeled
as a combination of three different stretched-exponentials. In this way, we
derived indices to quantify both the tissue anomalous diffusion and its
anisotropy, independently of the reference frame of the experiment. We tested
and compare our new method with DTI and HB approaches applying them to 10
healty subjects brain at 3T. Our experimental results show that our parameters
are highly correlated to intrinsic local geometry when compared to HB indices.
Moreover, they offer a different kind of contrast when compared to DTI outputs.
Specifically, our indices show a higher capability to discriminate among
different areas of the corpus callosum, which are known to be associated to
different axonal densities.Comment: 21 pages, 6 figures, 2 table
Combinatorics of lattice paths with and without spikes
We derive a series of results on random walks on a d-dimensional hypercubic
lattice (lattice paths). We introduce the notions of terse and simple paths
corresponding to the path having no backtracking parts (spikes). These paths
label equivalence classes which allow a rearrangement of the sum over paths.
The basic combinatorial quantities of this construction are given. These
formulas are useful when performing strong coupling (hopping parameter)
expansions of lattice models. Some applications are described.Comment: Latex. 25 page
Clausius inequality and optimality of quasi static transformations for nonequilibrium stationary states
Nonequilibrium stationary states of thermodynamic systems dissipate a
positive amount of energy per unit of time. If we consider transformations of
such states that are realized by letting the driving depend on time, the amount
of energy dissipated in an unbounded time window becomes then infinite.
Following the general proposal by Oono and Paniconi and using results of the
macroscopic fluctuation theory, we give a natural definition of a renormalized
work performed along any given transformation. We then show that the
renormalized work satisfies a Clausius inequality and prove that equality is
achieved for very slow transformations, that is in the quasi static limit. We
finally connect the renormalized work to the quasi potential of the macroscopic
fluctuation theory, that gives the probability of fluctuations in the
stationary nonequilibrium ensemble
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