25,336 research outputs found
Modelling the Kinked Jet of the Crab Nebula
We investigate the dynamical propagation of the South-East jet from the Crab
pulsar interacting with supernova ejecta by means of three-dimensional
relativistic MHD numerical simulations with the PLUTO code.
The initial jet structure is set up from the inner regions of the Crab
Nebula.
We study the evolution of hot, relativistic hollow outflows initially
carrying a purely azimuthal magnetic field.
Our jet models are characterized by different choices of the outflow
magnetization ( parameter) and the bulk Lorentz factor ().
We show that the jet is heavily affected by the growth of current-driven kink
instabilities causing considerable deflection throughout its propagation
length.
This behavior is partially stabilized by the combined action of larger flow
velocities and/or reduced magnetic field strengths.
We find that our best jet models are characterized by relatively large values
of () and small values of .
Our results are in good agreement with the recent X-ray (\textit{Chandra})
data of the Crab Nebula South-East jet indicating that the jet changes
direction of propagation on a time scale of the order of few years.
The 3D models presented here may have important implications in the
investigation of particle acceleration in relativistic outflows.Comment: 15 pages, 20 figure
Geometry of contours and Peierls estimates in d=1 Ising models
Following Fr\"ohlich and Spencer, we study one dimensional Ising spin systems
with ferromagnetic, long range interactions which decay as ,
. We introduce a geometric description of the spin
configurations in terms of triangles which play the role of contours and for
which we establish Peierls bounds. This in particular yields a direct proof of
the well known result by Dyson about phase transitions at low temperatures.Comment: 28 pages, 3 figure
On the asymmetric zero-range in the rarefaction fan
We consider the one-dimensional asymmetric zero-range process starting from a
step decreasing profile. In the hydrodynamic limit this initial condition leads
to the rarefaction fan of the associated hydrodynamic equation. Under this
initial condition and for totally asymmetric jumps, we show that the weighted
sum of joint probabilities for second class particles sharing the same site is
convergent and we compute its limit. For partially asymmetric jumps we derive
the Law of Large Numbers for the position of a second class particle under the
initial configuration in which all the positive sites are empty, all the
negative sites are occupied with infinitely many first class particles and with
a single second class particle at the origin. Moreover, we prove that among the
infinite characteristics emanating from the position of the second class
particle, this particle chooses randomly one of them. The randomness is given
in terms of the weak solution of the hydrodynamic equation through some sort of
renormalization function. By coupling the zero-range with the exclusion process
we derive some limiting laws for more general initial conditions.Comment: 22 pages, to appear in Journal of Statistical Physic
Resonances Width in Crossed Electric and Magnetic Fields
We study the spectral properties of a charged particle confined to a
two-dimensional plane and submitted to homogeneous magnetic and electric fields
and an impurity potential. We use the method of complex translations to prove
that the life-times of resonances induced by the presence of electric field are
at least Gaussian long as the electric field tends to zero.Comment: 3 figure
Solving the solar neutrino problem with kamLAND and BOREXINO
We analyze the expected signals of two future neutrino experiments, kamLAND
and BOREXINO. We show that with just these experiments, we will hopefully be
able to determine which of the existing solutions to the solar neutrino problem
is the real solution. We also analyze existing solar neutrino data and
determine the best-fit points in the oscillation-parameter space finding that
with the inclusion of SNO-charged current, the global-rates analysis gives a
favored LMA solution with a goodness of fit (g.o.f) of just 32.63%, whereas the
g.o.f of the SMA solution is 9.83%. Nonetheless, maximal and quasi-maximal
mixing is not favored. If we include the Superkamiokande spectrum in our \chi^2
analysis, we obtain a LMA solution with a g.o.f. of 84.38%.Comment: 4 pages, 5 figures, Talk given at 37th Rencontres de Moriond on
Electroweak Interactions and Unified Theories, Les Arcs, France, 9-16 Mar
200
The solar neutrino puzzle: present situation and future scenarios
We present a short review of the existing evidence in favor of neutrino mass
and neutrino oscillations which come from different kinds of experiments. We
focus our attention in particular on solar neutrinos, presenting a global
updated phenomenological analysis of all the available data and we comment on
different possible future scenarios.Comment: 22 pp. Expanded version of the contribution to appear in the
Proceedings of ``Les Rencontres de Physique de la Vallee d'Aoste'', February
200
- …