543 research outputs found
The Non-Trapping Degree of Scattering
We consider classical potential scattering. If no orbit is trapped at energy
E, the Hamiltonian dynamics defines an integer-valued topological degree. This
can be calculated explicitly and be used for symbolic dynamics of
multi-obstacle scattering.
If the potential is bounded, then in the non-trapping case the boundary of
Hill's Region is empty or homeomorphic to a sphere.
We consider classical potential scattering. If at energy E no orbit is
trapped, the Hamiltonian dynamics defines an integer-valued topological degree
deg(E) < 2. This is calculated explicitly for all potentials, and exactly the
integers < 2 are shown to occur for suitable potentials.
The non-trapping condition is restrictive in the sense that for a bounded
potential it is shown to imply that the boundary of Hill's Region in
configuration space is either empty or homeomorphic to a sphere.
However, in many situations one can decompose a potential into a sum of
non-trapping potentials with non-trivial degree and embed symbolic dynamics of
multi-obstacle scattering. This comprises a large number of earlier results,
obtained by different authors on multi-obstacle scattering.Comment: 25 pages, 1 figure Revised and enlarged version, containing more
detailed proofs and remark
Large normally hyperbolic cylinders in a priori stable Hamiltonian systems
We prove the existence of normally hyperbolic invariant cylinders in nearly
integrable hamiltonian systems
A Large Scale Double Beta and Dark Matter Experiment: GENIUS
The recent results from the HEIDELBERG-MOSCOW experiment have demonstrated
the large potential of double beta decay to search for new physics beyond the
Standard Model. To increase by a major step the present sensitivity for double
beta decay and dark matter search much bigger source strengths and much lower
backgrounds are needed than used in experiments under operation at present or
under construction. We present here a study of a project proposed recently,
which would operate one ton of 'naked' enriched GErmanium-detectors in liquid
NItrogen as shielding in an Underground Setup (GENIUS). It improves the
sensitivity to neutrino masses to 0.01 eV. A ten ton version would probe
neutrino masses even down to 10^-3 eV. The first version would allow to test
the atmospheric neutrino problem, the second at least part of the solar
neutrino problem. Both versions would allow in addition significant
contributions to testing several classes of GUT models. These are especially
tests of R-parity breaking supersymmetry models, leptoquark masses and
mechanism and right-handed W-boson masses comparable to LHC. The second issue
of the experiment is the search for dark matter in the universe. The entire
MSSM parameter space for prediction of neutralinos as dark matter particles
could be covered already in a first step of the full experiment - with the same
purity requirements but using only 100 kg of 76Ge or even of natural Ge -
making the experiment competitive to LHC in the search for supersymmetry.
The layout of the proposed experiment is discussed and the shielding and
purity requirements are studied using GEANT Monte Carlo simulations. As a
demonstration of the feasibility of the experiment first results of operating a
'naked' Ge detector in liquid nitrogen are presented.Comment: 22 pages, 12 figures, see also
http://pluto.mpi-hd.mpg.de/~betalit/genius.htm
Latest Results from the Heidelberg-Moscow Double Beta Decay Experiment
New results for the double beta decay of 76Ge are presented. They are
extracted from Data obtained with the HEIDELBERG-MOSCOW, which operates five
enriched 76Ge detectors in an extreme low-level environment in the GRAN SASSO.
The two neutrino accompanied double beta decay is evaluated for the first time
for all five detectors with a statistical significance of 47.7 kg y resulting
in a half life of (T_(1/2))^(2nu) = [1.55 +- 0.01 (stat) (+0.19) (-0.15)
(syst)] x 10^(21) years. The lower limit on the half-life of the 0nu beta-beta
decay obtained with pulse shape analysis is (T_(1/2))^(0_nu) > 1.9 x 10^(25)
[3.1 x 10^(25)] years with 90% C.L. (68% C.L.) (with 35.5 kg y). This results
in an upper limit of the effective Majorana neutrino mass of 0.35 eV (0.27 eV).
No evidence for a Majoron emitting decay mode or for the neutrinoless mode is
observed.Comment: 14 pages, revtex, 6 figures, Talk was presented at third
International Conference ' Dark Matter in Astro and Particle Physics' -
DARK2000, to be publ. in Proc. of DARK2000, Springer (2000). Please look into
our HEIDELBERG Non-Accelerator Particle Physics group home page:
http://www.mpi-hd.mpg.de/non_acc
Double Beta Decay, Majorana Neutrinos, and Neutrino Mass
The theoretical and experimental issues relevant to neutrinoless double-beta
decay are reviewed. The impact that a direct observation of this exotic process
would have on elementary particle physics, nuclear physics, astrophysics and
cosmology is profound. Now that neutrinos are known to have mass and
experiments are becoming more sensitive, even the non-observation of
neutrinoless double-beta decay will be useful. If the process is actually
observed, we will immediately learn much about the neutrino. The status and
discovery potential of proposed experiments are reviewed in this context, with
significant emphasis on proposals favored by recent panel reviews. The
importance of and challenges in the calculation of nuclear matrix elements that
govern the decay are considered in detail. The increasing sensitivity of
experiments and improvements in nuclear theory make the future exciting for
this field at the interface of nuclear and particle physics.Comment: invited submission to Reviews of Modern Physics, higher resolution
figures available upon request from authors, Version 2 has fixed typos and
some changes after referee report
Limits on different Majoron decay modes of Mo and Se for neutrinoless double beta decays in the NEMO-3 experiment
The NEMO-3 tracking detector is located in the Fr\'ejus Underground
Laboratory. It was designed to study double beta decay in a number of different
isotopes. Presented here are the experimental half-life limits on the double
beta decay process for the isotopes Mo and Se for different
Majoron emission modes and limits on the effective neutrino-Majoron coupling
constants. In particular, new limits on "ordinary" Majoron (spectral index 1)
decay of Mo ( y) and Se ( y) have been obtained. Corresponding bounds on the
Majoron-neutrino coupling constant are
and .Comment: 23 pages includind 4 figures, to be published in Nuclear Physics
Isomerization dynamics of a buckled nanobeam
We analyze the dynamics of a model of a nanobeam under compression. The model
is a two mode truncation of the Euler-Bernoulli beam equation subject to
compressive stress. We consider parameter regimes where the first mode is
unstable and the second mode can be either stable or unstable, and the
remaining modes (neglected) are always stable. Material parameters used
correspond to silicon. The two mode model Hamiltonian is the sum of a
(diagonal) kinetic energy term and a potential energy term. The form of the
potential energy function suggests an analogy with isomerisation reactions in
chemistry. We therefore study the dynamics of the buckled beam using the
conceptual framework established for the theory of isomerisation reactions.
When the second mode is stable the potential energy surface has an index one
saddle and when the second mode is unstable the potential energy surface has an
index two saddle and two index one saddles. Symmetry of the system allows us to
construct a phase space dividing surface between the two "isomers" (buckled
states). The energy range is sufficiently wide that we can treat the effects of
the index one and index two saddles in a unified fashion. We have computed
reactive fluxes, mean gap times and reactant phase space volumes for three
stress values at several different energies. In all cases the phase space
volume swept out by isomerizing trajectories is considerably less than the
reactant density of states, proving that the dynamics is highly nonergodic. The
associated gap time distributions consist of one or more `pulses' of
trajectories. Computation of the reactive flux correlation function shows no
sign of a plateau region; rather, the flux exhibits oscillatory decay,
indicating that, for the 2-mode model in the physical regime considered, a rate
constant for isomerization does not exist.Comment: 42 pages, 6 figure
Nonlinear analysis of spacecraft thermal models
We study the differential equations of lumped-parameter models of spacecraft
thermal control. Firstly, we consider a satellite model consisting of two
isothermal parts (nodes): an outer part that absorbs heat from the environment
as radiation of various types and radiates heat as a black-body, and an inner
part that just dissipates heat at a constant rate. The resulting system of two
nonlinear ordinary differential equations for the satellite's temperatures is
analyzed with various methods, which prove that the temperatures approach a
steady state if the heat input is constant, whereas they approach a limit cycle
if it varies periodically. Secondly, we generalize those methods to study a
many-node thermal model of a spacecraft: this model also has a stable steady
state under constant heat inputs that becomes a limit cycle if the inputs vary
periodically. Finally, we propose new numerical analyses of spacecraft thermal
models based on our results, to complement the analyses normally carried out
with commercial software packages.Comment: 29 pages, 4 figure
Recent advances in neutrinoless double beta decay search
Even after the discovery of neutrino flavour oscillations, based on data from
atmospheric, solar, reactor, and accelerator experiments, many characteristics
of the neutrino remain unknown. Only the neutrino square-mass differences and
the mixing angle values have been estimated, while the value of each mass
eigenstate still hasn't. Its nature (massive Majorana or Dirac particle) is
still escaping. Neutrinoless double beta decay (-DBD) experimental
discovery could be the ultimate answer to some delicate questions of elementary
particle and nuclear physics. The Majorana description of neutrinos allows the
-DBD process, and consequently either a mass value could be measured or
the existence of physics beyond the standard should be confirmed without any
doubt. As expected, the -DBD measurement is a very difficult field of
application for experimentalists. In this paper, after a short summary of the
latest results in neutrino physics, the experimental status, the R&D projects,
and perspectives in -DBD sector are reviewed.Comment: 36 pages, 7 figures, To be publish in Czech Journal of Physic
A topological classification of convex bodies
The shape of homogeneous, generic, smooth convex bodies as described by the
Euclidean distance with nondegenerate critical points, measured from the center
of mass represents a rather restricted class M_C of Morse-Smale functions on
S^2. Here we show that even M_C exhibits the complexity known for general
Morse-Smale functions on S^2 by exhausting all combinatorial possibilities:
every 2-colored quadrangulation of the sphere is isomorphic to a suitably
represented Morse-Smale complex associated with a function in M_C (and vice
versa). We prove our claim by an inductive algorithm, starting from the path
graph P_2 and generating convex bodies corresponding to quadrangulations with
increasing number of vertices by performing each combinatorially possible
vertex splitting by a convexity-preserving local manipulation of the surface.
Since convex bodies carrying Morse-Smale complexes isomorphic to P_2 exist,
this algorithm not only proves our claim but also generalizes the known
classification scheme in [36]. Our expansion algorithm is essentially the dual
procedure to the algorithm presented by Edelsbrunner et al. in [21], producing
a hierarchy of increasingly coarse Morse-Smale complexes. We point out
applications to pebble shapes.Comment: 25 pages, 10 figure
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