1,067 research outputs found
Weak Decay of Hypernuclei
The focus of these Lectures is on the weak decay modes of hypernuclei, with
special attention to Lambda-hypernuclei. The subject involves many fields of
modern theoretical and experimental physics, from nuclear structure to the
fundamental constituents of matter and their interactions. The various weak
decay modes of Lambda-hypernuclei are described: the mesonic mode and the
non-mesonic ones. The latter are the dominant decay channels of medium--heavy
hypernuclei, where, on the contrary, the mesonic decay is disfavoured by Pauli
blocking effect on the outgoing nucleon. In particular, one can distinguish
between one-body and two-body induced decays. Theoretical models employed to
evaluate the (partial and total) decay widths of hypernuclei are illustrated,
and their results compared with existing experimental data. Open problems and
recent achievements are extensively discussed, in particular the determination
of the ratio Gamma_n/Gamma_p, possible tests of the Delta I=1/2 rule in
non-mesonic decays and the puzzling asymmetric non-mesonic decay of polarized
hypernuclei.Comment: 59 pages, 13 figures Lectures given at the International School of
Physics "Enrico Fermi" Course on: HADRON PHYSICS, Varenna (Lake Como), June
22nd - July 2nd, 200
Static properties of nuclear matter within the Boson Loop Expansion
The use of the Boson Loop Expansion is proposed for investigating the static
properties of nuclear matter. We explicitly consider a schematic dynamical
model in which nucleons interact with the scalar-isoscalar sigma meson. The
suggested approximation scheme is examined in detail at the mean field level
and at the one- and two-loop orders. The relevant formulas are provided to
derive the binding energy per nucleon, the pressure and the compressibility of
nuclear matter. Numerical results of the binding energy at the one-loop order
are presented for Walecka's sigma-omega model in order to discuss the degree of
convergence of the Boson Loop Expansion.Comment: 40 pages, 13 figure
Weak decays of medium and heavy Lambda-hypernuclei
We have made a new evaluation of the Lambda decay width in nuclear matter
within the Propagator Method. Through the Local Density Approximation it is
possible to obtain results in finite nuclei. We have also studied the
dependence of the widths on the N-N and Lambda-N short range correlations.
Using reasonable values for the parameters that control these correlations, as
well as realistic nuclear densities and Lambda wave functions, we reproduce,
for the first time, the experimental non-mesonic widths in a wide range of mass
numbers (from medium to heavy hypernuclei).Comment: 22 pages, including 5 figure
A new loveringite occurrence: : oriented rods from the foltea lherzolite, South Carpathians, Romania
Exchange terms in the two--nucleon induced non--mesonic weak decay of --hypernuclei
The contribution of Pauli exchange terms to the two--nucleon induced
non--mesonic weak decay of C hypernuclei,
( or ), is studied within a nuclear matter formalism implemented in a
local density approximation. We have adopted a weak transition potential
including the exchange of the complete octets of pseudoscalar and vector mesons
as well as a residual strong interaction modeled on the Bonn potential. The
introduction of exchange terms turns out to reduce the two--nucleon induced
non--mesonic rate by 18% and, jointly with an increase in the one--nucleon
induced rate by the same magnitude, reveals to be significant for an accurate
determination of the full set of hypernuclear non--mesonic decay widths in
theoretical and experimental analyses.Comment: 14 pages, 3 figure
The semi-classical approach to the exclusive electron scattering
The semiclassical approach, successfully applied in the past to the
inelastic, inclusive electron scattering off nuclei, is extended to the
treatment of exclusive processes. The final states interaction is accounted for
in the mean field approximation, respecting the Pauli principle. The impact on
the exclusive cross section of the shape of the potential binding the nucleons
into the nucleus and of the distortion of the outgoing nucleon wave are
explored. The exclusive scattering is found to be quite sensitive to the mean
field final states interaction, unlike the inclusive one. Indeed we verify that
the latter is not affected, as implied by unitarity, by the distortion of the
outgoing nucleon wave except for the effect of relativity, which is modest in
the range of momenta up to about 500 MeV/c. Furthermore, depending upon the
correlations between the directions of the outgoing and of the initial nucleon,
the exclusive cross-section turns out to be remarkably sensitive to the shape
of the potential binding the nucleons. These correlations also critically
affect the domain in the missing energy-- missing momentum plane where the
exclusive process occurs.Comment: 39 pages, latex, including 9 figures (fig.ps
Functional approach to the non-mesonic decay of Lambda-hypernuclei
We present an evaluation of the non-mesonic decay widths for
Lambda-hypernuclei (Lambda N --> NN, Lambda NN --> NNN) within the framework of
the polarization propagator method. The full Lambda self-energy is evaluated
microscopically in nuclear matter by using the functional approach, which
supplies a theoretically well grounded approximation scheme for the
classification of the relevant diagrams, according to the prescriptions of the
bosonic loop expansion. We employ average Fermi momenta, suitably adapted to
different mass number regions (medium-light, medium and heavy hypernuclei).
Moreover, we study the dependence of the decay rates on the NN and Lambda-N
short range correlations. With a proper choice of the parameters which control
these correlations in the new approximation scheme, it is possible to reproduce
the experimental decay widths for A > 10 hypernuclei.Comment: 25 pages, 8 figure
On the Relativistic Description of the Nucleus
We present here a formalism able to generalise to a relativistically
covariant scheme the standard nuclear shell model. We show that, using some
generalised nuclear Green's functions and their Lehmann representation we can
define the relativistic equivalent of the non relativistic single particle wave
function (not loosing, however, the physical contribution of other degrees of
freedom, like mesons and antinucleons). It is shown that the mass operator
associated to the nuclear Green's function can be approximated with the
equivalent of a shell-model potential and that the corresponding ``single
particle wave functions'' can be easily derived in a specified frame of
reference and then boosted to any other system, thus fully restoring the
Lorentz covarianc
Distinguishing Supersymmetry From Universal Extra Dimensions or Little Higgs Models With Dark Matter Experiments
There are compelling reasons to think that new physics will appear at or
below the TeV-scale. It is not known what form this new physics will take,
however. Although The Large Hadron collider is very likely to discover new
particles associated with the TeV-scale, it may be difficult for it to
determine the nature of those particles, whether superpartners, Kaluza-Klein
modes or other states. In this article, we consider how direct and indirect
dark matter detection experiments may provide information complementary to
hadron colliders, which can be used to discriminate between supersymmetry,
models with universal extra dimensions, and Little Higgs theories. We find
that, in many scenarios, dark matter experiments can be effectively used to
distinguish between these possibilities.Comment: 23 pages, 7 figures, references added in version
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