952 research outputs found
Short-range correlations and neutrinoless double beta decay
In this work we report on the effects of short-range correlations upon the
matrix elements of neutrinoless double beta decay. We focus on the calculation
of the matrix elements of the neutrino-mass mode of neutrinoless double beta
decays of 48Ca and 76Ge. The nuclear-structure components of the calculation,
that is the participant nuclear wave functions, have been calculated in the
shell-model scheme for 48Ca and in the proton-neutron quasiparticle
random-phase approximation (pnQRPA) scheme for 76Ge. We compare the traditional
approach of using the Jastrow correlation function with the more complete
scheme of the unitary correlation operator method (UCOM). Our results indicate
that the Jastrow method vastly exaggerates the effects of short-range
correlations on the neutrinoless double beta decay nuclear matrix elements.Comment: 12 pages, 3 figures, to appear in Physics Letters B (2007
Chaperone-assisted translocation of flexible polymers in three dimensions
Polymer translocation through a nanometer-scale pore assisted by chaperones
binding to the polymer is a process encountered in vivo for proteins. Studying
the relevant models by computer simulations is computationally demanding.
Accordingly, previous studies are either for stiff polymers in three dimensions
or flexible polymers in two dimensions. Here, we study chaperone-assisted
translocation of flexible polymers in three dimensions using Langevin dynamics.
We show that differences in binding mechanisms, more specifically, whether a
chaperone can bind to a single or multiple sites on the polymer, lead to
substantial differences in translocation dynamics in three dimensions. We show
that the single-binding mode leads to dynamics that is very much like that in
the constant-force driven translocation and accordingly mainly determined by
tension propagation on the cis side. We obtain for the
exponent for the scaling of the translocation time with polymer length. This
fairly low value can be explained by the additional friction due to binding
particles. The multiple-site binding leads to translocation whose dynamics is
mainly determined by the trans side. For this process we obtain . This value can be explained by our derivation of for
constant-bias translocation, where translocated polymer segments form a globule
on the trans side. Our results pave the way for understanding and utilizing
chaperone-assisted translocation where variations in microscopic details lead
to rich variations in the emerging dynamics.Comment: 10 pages, 12 figure
Dynamics of polymer ejection from capsid
Polymer ejection from a capsid through a nanoscale pore is an important
biological process with relevance to modern biotechnology. Here, we study
generic capsid ejection using Langevin dynamics. We show that even when the
ejection takes place within the drift-dominated region there is a very high
probability for the ejection process not to be completed. Introducing a small
aligning force at the pore entrance enhances ejection dramatically. Such a pore
asymmetry is a candidate for a mechanism by which a viral ejection is
completed. By detailed high-resolution simulations we show that such capsid
ejection is an out-of-equilibrium process that shares many common features with
the much studied driven polymer translocation through a pore in a wall or a
membrane. We find that the escape times scale with polymer length, . We show that for the pore without the asymmetry the previous
predictions corroborated by Monte Carlo simulations do not hold. For the pore
with the asymmetry the scaling exponent varies with the initial monomer density
(monomers per capsid volume) inside the capsid. For very low densities
the polymer is only weakly confined by the capsid, and we
measure , which is close to obtained for polymer
translocation. At intermediate densities the scaling exponents
and for and , respectively. These scalings are in
accord with a crude derivation for the lower limit . For the
asymmetrical pore precise scaling breaks down, when the density exceeds the
value for complete confinement by the capsid, . The
high-resolution data show that the capsid ejection for both pores, analogously
to polymer translocation, can be characterized as a multiplicative stochastic
process that is dominated by small-scale transitions.Comment: 10 pages, 6 figure
Improved short-range correlations and 0nbb nuclear matrix elements of 76Ge and 82Se
We calculate the nuclear matrix elements of the neutrinoless double beta
() decays of Ge and Se for the light-neutrino
exchange mechanism. The nuclear wave functions are obtained by using realistic
two-body forces within the proton-neutron quasiparticle random-phase
approximation (pnQRPA). We include the effects that come from the finite size
of a nucleon, from the higher-order terms of nucleonic weak currents, and from
the nucleon-nucleon short-range correlations. Most importantly, we improve on
the presently available calculations by replacing the rudimentary Jastrow
short-range correlations by the more advanced unitary correlation operator
method (UCOM). The UCOM corrected matrix elements turn out to be notably larger
in magnitude than the Jastrow corrected ones. This has drastic consequences for
the detectability of decay in the present and future double
beta experiments.Comment: 5 pages, 2 figures, to appear in Physical Review C (Rapid
Communication) 200
Nuclear matrix elements of neutrinoless double beta decay with improved short-range correlations
Nuclear matrix elements of the neutrinoless double beta decays of 96Zr,
100Mo, 116Cd, 128Te, 130Te and 136Xe are calculated for the light-neutrino
exchange mechanism by using the proton-neutron quasiparticle random-phase
approximation (pnQRPA) with a realistic nucleon-nucleon force. The g_pp
parameter of the pnQRPA is fixed by the data on the two-neutrino double beta
decays and single beta decays. The finite size of a nucleon, the higher-order
terms of nucleonic weak currents, and the nucleon-nucleon short-range
correlations (s.r.c) are taken into account. The s.r.c. are computed by the
traditional Jastrow method and by the more advanced unitary correlation
operator method (UCOM). Comparison of the results obtained by the two methods
is carried out. The UCOM computed matrix elements turn out to be considerably
larger than the Jastrow computed ones. This result is important for the
assessment of the neutrino-mass sensitivity of the present and future double
beta experiments.Comment: Two figures, to be published in Physical Review C (2007) as a regular
articl
On nuclear matrix element uncertainties in short range 0vBB decay
The evaluation of short range contributions to neutrinoless double beta decay
has been challenged due to critics of the ansatz of the nuclear matrix element
calculations. We comment on the critics and uncertainties of these calculations
and the effect on the derived limits.Comment: 3 pages, Latex, new arguments adde
Double beta decay versus cosmology: Majorana CP phases and nuclear matrix elements
We discuss the relation between the absolute neutrino mass scale, the
effective mass measured in neutrinoless double beta decay, and the Majorana CP
phases. Emphasis is placed on estimating the upper bound on the nuclear matrix
element entering calculations of the double beta decay half life. Consequently,
one of the Majorana CP phases can be constrained when combining the claimed
evidence for neutrinoless double beta decay with the neutrino mass bound from
cosmology.Comment: 11 pages, 3 figure
Extended shell-model calculation for even N=82 isotones with realistic effective interactions
The shell model within the shell is applied to
calculate nuclear structure properties of the even Z=52 - 62, N=82 isotones.
The results are compared with experimental data and with the results of a
quasiparticle random-phase approximation (QRPA) calculation. The interaction
used in these calculations is a realistic two-body G-matrix interaction derived
from modern meson-exchange potential models for the nucleon-nucleon
interaction. For the shell model all the two-body matrix elements are
renormalized by the -box method whereas for the QRPA the effective
interaction is defined by the G-matrix.Comment: 25 pages, Elsevier latex style. Submitted to Nuclear Physics
- …