212 research outputs found
Application of Absorbing Boundary Condition to Nuclear Breakup Reactions
Absorbing boundary condition approach to nuclear breakup reactions is
investigated. A key ingredient of the method is an absorbing potential outside
the physical area, which simulates the outgoing boundary condition for
scattered waves. After discretizing the radial variables, the problem results
in a linear algebraic equation with a sparse coefficient matrix, to which
efficient iterative methods can be applicable. No virtual state such as
discretized continuum channel needs to be introduced in the method. Basic
aspects of the method are discussed by considering a nuclear two-body
scattering problem described with an optical potential. We then apply the
method to the breakup reactions of deuterons described in a three-body direct
reaction model. Results employing the absorbing boundary condition are found to
accurately coincide with those of the existing method which utilizes
discretized continuum channels.Comment: 21 pages, 5 figures, RevTeX
Coupled-channels effects in elastic scattering and near-barrier fusion induced by weakly bound nuclei and exotic halo nuclei
The influence on fusion of coupling to the breakup process is investigated
for reactions where at least one of the colliding nuclei has a sufficiently low
binding energy for breakup to become an important process. Elastic scattering,
excitation functions for sub-and near-barrier fusion cross sections, and
breakup yields are analyzed for Li+Co. Continuum-Discretized
Coupled-Channels (CDCC) calculations describe well the data at and above the
barrier. Elastic scattering with Li (as compared to Li) indicates
the significant role of breakup for weakly bound projectiles. A study of
He induced fusion reactions with a three-body CDCC method for the
He halo nucleus is presented. The relative importance of breakup and
bound-state structure effects on total fusion is discussed.Comment: 29 pages, 9 figure
Localization of Gravity on Brane Embedded in and
We address the localization of gravity on the Friedmann-Robertson-Walker type
brane embedded in either or bulk space,and derive two
definite limits between which the value of the bulk cosmological constant has
to lie in order to localize the graviton on the brane.The lower limit implies
that the brane should be either or 4d Minkowski in the
bulk.The positive upper limit indicates that the gravity can be trapped also on
curved brane in the bulk space.Some implications to recent
cosmological scenarios are also discussed.Comment: 18 pages, 3 figures, Latex fil
Coulomb and nuclear breakup of B
The cross sections for the (B,Be-) breakup reaction on Ni
and Pb targets at the beam energies of 25.8 MeV and 415 MeV have been
calculated within a one-step prior-form distorted-wave Born approximation. The
relative contributions of Coulomb and nuclear breakup of dipole and quadrupole
multipolarities as well as their interference have been determined. The nuclear
breakup contributions are found to be substantial in the angular distributions
of the Be fragment for angles in the range of 30 - 80 at
25.8 MeV beam energy. The Coulomb-nuclear interference terms make the dipole
cross section larger than that of quadrupole even at this low beam energy.
However, at the incident energy of 415 MeV, these effects are almost negligible
in the angular distributions of the (Be-p) coincidence cross sections at
angles below 4.Comment: Revised version, accepted for publication in Phys. Rev.
Evolution of Thick Walls in Curved Spacetimes
We generalize our previous thick shell formalism to incorporate any
codimension-1 thick wall with a peculiar velocity and proper thickness bounded
by arbitrary spacetimes. Within this new formulation we obtain the equation of
motion of a spherically symmetric dust thick shell immersed in vacuum as well
as in Friedmann-Robertson-Walker spacetimes.Comment: 8 pages, 1 figur
Non-adiabatic corrections to elastic scattering of halo nuclei
We derive the formalism for the leading order corrections to the adiabatic
approximation to the scattering of composite projectiles. Assuming a two-body
projectile of core plus loosely-bound valence particle and a model (the core
recoil model) in which the interaction of the valence particle and the target
can be neglected, we derive the non-adiabatic correction terms both exactly,
using a partial wave analysis, and using the eikonal approximation. Along with
the expected energy dependence of the corrections, there is also a strong
dependence on the valence-to-core mass ratio and on the strength of the
imaginary potential for the core-target interaction, which relates to
absorption of the core in its scattering by the target. The strength and
diffuseness of the core-target potential also determine the size of the
corrections. The first order non-adiabatic corrections were found to be smaller
than qualitative estimates would expect. The large absorption associated with
the core-target interaction in such halo nuclei as Be11 kills off most of the
non-adiabatic corrections. We give an improved estimate for the range of
validity of the adiabatic approximation when the valence-target interaction is
neglected, which includes the effect of core absorption. Some consideration was
given to the validity of the eikonal approximation in our calculations.Comment: 14 pages with 10 figures, REVTeX4, AMS-LaTeX v2.13, submitted to
Phys. Rev.
Effective action and brane running
We address the renormalized effective action for a Randall-Sundrum brane
running in 5d bulk space. The running behavior of the brane action is obtained
by shifting the brane-position without changing the background and the
fluctuations. After an appropriate renormalization, we obtain an effective, low
energy braneworld action, in which the effective 4d Planck mass is independent
of the running-position. We address some implications of this effective action.Comment: 15 pages, no figur
Improved +He potentials by inversion, the tensor force and validity of the double folding model
Improved potential solutions are presented for the inverse scattering problem
for +He data. The input for the inversions includes both the data of
recent phase shift analyses and phase shifts from RGM coupled-channel
calculations based on the NN Minnesota force. The combined calculations provide
a more reliable estimate of the odd-even splitting of the potentials than
previously found, suggesting a rather moderate role for this splitting in
deuteron-nucleus scattering generally. The approximate parity-independence of
the deuteron optical potentials is shown to arise from the nontrivial
interference between antisymmetrization and channel coupling to the deuteron
breakup channels. A further comparison of the empirical potentials established
here and the double folding potential derived from the M3Y effective NN force
(with the appropriate normalisation factor) reveals strong similarities. This
result supports the application of the double folding model, combined with a
small Majorana component, to the description even of such a loosely bound
projectile as the deuteron. In turn, support is given for the application of
iterative-perturbative inversion in combination with the double folding model
to study fine details of the nucleus-nucleus potential. A -He tensor
potential is also derived to reproduce correctly the negative Li quadrupole
moment and the D-state asymptotic constant.Comment: 22 pages, 12 figures, in Revte
Disappearing Dark Matter in Brane World Cosmology: New Limits on Noncompact Extra Dimensions
We explore cosmological implications of dark matter as massive particles
trapped on a brane embedded in a Randall-Sundrum noncompact higher dimension
space. It is an unavoidable consequence of this cosmology that massive
particles are metastable and can disappear into the bulk dimension. Here, we
show that a massive dark matter particle (e.g. the lightest supersymmetric
particle) is likely to have the shortest lifetime for disappearing into the
bulk. We examine cosmological constraints on this new paradigm and show that
disappearing dark matter is consistent (at the 95% confidence level) with all
cosmological constraints, i.e. present observations of Type Ia supernovae at
the highest redshift, trends in the mass-to-light ratios of galaxy clusters
with redshift, the fraction of X-ray emitting gas in rich clusters, and the
spectrum of power fluctuations in the cosmic microwave background. A best concordance region is identified corresponding to a mean lifetime for
dark matter disappearance of Gyr. The implication
of these results for brane-world physics is discussed.Comment: 7 pages, 7 figures, new cosmological constraints added, accepted for
publication in PR
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