6,246 research outputs found
Structure and three-body decay of Be resonances
The complex-rotated hyperspherical adiabatic method is used to study the
decay of low-lying Be resonances into one neutron and two
-particles. We investigate the six resonances above the break-up
threshold and below 6 MeV: , and . The
short-distance properties of each resonance are studied, and the different
angular momentum and parity configurations of the Be and He two-body
substructures are determined. We compute the branching ratio for sequential
decay via the Be ground state which qualitatively is consistent with
measurements. We extract the momentum distributions after decay directly into
the three-body continuum from the large-distance asymptotic structures. The
kinematically complete results are presented as Dalitz plots as well as
projections on given neutron and -energy. The distributions are
discussed and in most cases found to agree with available experimental data.Comment: 12 pages, 10 figures. To appear in Physical Review
alpha particle momentum distributions from 12C decaying resonances
The computed particle momentum distributions from the decay of
low-lying C resonances are shown. The wave function of the decaying
fragments is computed by means of the complex scaled hyperspherical adiabatic
expansion method. The large-distance part of the wave functions is crucial and
has to be accurately calculated. We discuss energy distributions, angular
distributions and Dalitz plots for the , and states of
C.Comment: 6 pages, 4 figures. Proceedings of the SOTANCP2008 conference held in
Strasbourg in May 200
Momentum distributions of -particles from decaying low-lying C-resonances
The complex scaled hyperspherical adiabatic expansion method is used to
compute momentum and energy distributions of the three -particles
emerging from the decay of low-lying C-resonances. The large distance
continuum properties of the wave functions are crucial and must be accurately
calculated. We discuss separately decays of natural parity states: two ,
one , three , one , two , one , and one of each of
unnatural parity, , , , . The lowest natural parity state
of each decays predominantly sequentially via the Be ground
state whereas other states including unnatural parity states predominantly
decay directly to the continuum. We present Dalitz plots and systematic
detailed momentum correlations of the emerging -particles.Comment: 11 pages, 7 figures, accepted for publication in Physical Review
Decay of low-lying 12C resonances within a 3alpha cluster model
We compute energy distributions of three -particles emerging from the
decay of C resonances by means of the hyperspherical adiabatic expansion
method combined with complex scaling. The large distance continuum properties
of the wave functions are crucial and must be accurately calculated. The
substantial changes from small to large distances determine the decay
mechanisms. We illustrate by computing the energy distributions from decays of
the and -resonances in C. These states are dominated by
direct and sequential decays into the three-body continuum respectively.Comment: 5 pages, 3 figures. Proceedings of the Clusters '07 conference held
in Stratford-upon-Avon in September 200
Three-body decays: structure, decay mechanism and fragment properties
We discuss the three-body decay mechanisms of many-body resonances. R-matrix
sequential description is compared with full Faddeev computation. The role of
the angular momentum and boson symmetries is also studied. As an illustration
we show the computed -particle energy distribution after the decay of
12C(1^+) resonance at 12.7 MeV.Comment: 4 pages, 3 figures. Proceedings of the workshop "Critical Stability
of Few-Body Quantum Systems" 200
Gamow-Teller strength distributions in Xe isotopes
The energy distributions of the Gamow-Teller strength are studied for
even-even Xe isotopes with mass numbers from 124 to 142. A self-consistent
microscopic formalism is used to generate the single particle basis, using a
deformed Skyrme Hartree-Fock mean field with pairing correlations in BCS
approximation. The Gamow-Teller transitions are obtained within a quasiparticle
random phase approximation (QRPA) approach using a residual spin-isospin
interaction in the particle-hole and particle-particle channels. We then
discuss the pairing BCS treatment and the determination of the ph and pp
residual interaction coupling constants. We study the GT+ and GT- strength
distributions for the equilibrium nuclear shapes, which are an essential
information for studies of charge-exchange reactions and double-beta processes
involving these isotopes.Comment: 15 pages, 5 figures. To appear in Phys Rev
Refining the associations of the Fermi Large Area Telescope Source Catalogs
The Fermi-Large Area Telescope (LAT) First Source Catalog (1FGL) was released
in February 2010 and the Fermi-LAT 2-Year Source Catalog (2FGL) appeared in
April 2012, based on data from 24 months of operation. Since their releases,
many follow up observations of unidentified gamma-ray sources (UGSs) were
performed and new procedures to associate gamma-ray sources with potential
counterparts at other wavelengths were developed. Here we review and
characterize all the associations as published in the 1FGL and 2FGL catalog on
the basis of multifrequency archival observations. In particular we located 177
spectra for the low-energy counterparts that were not listed in the previous
Fermi catalogs, and in addition we present new spectroscopic observations of 8
gamma-ray blazar candidates. Based on our investigations, we introduce a new
counterpart category of "candidate associations" and propose a refined
classification for the candidate low-energy counterparts of the Fermi sources.
We compare the 1FGL-assigned counterparts with those listed in the 2FGL to
determine which unassociated sources became associated in later releases of the
Fermi catalogs. We also search for potential counterparts to all the remaining
unassociated Fermi sources. Finally, we prepare a refined and merged list of
all the associations of the 1FGL plus 2FGL catalogs that includes 2219 unique
Fermi objects. This is the most comprehensive and systematic study of all the
associations collected for the gamma-ray sources available to date. We conclude
that 80% of the Fermi sources have at least one known plausible gamma-ray
emitter within their positional uncertainty regions.Comment: 26 pages, 24 figures, 7 tables, ApJS accepted for publication
(pre-proof version uploaded
An effective theory of accelerated expansion
We work out an effective theory of accelerated expansion to describe general
phenomena of inflation and acceleration (dark energy) in the Universe. Our aim
is to determine from theoretical grounds, in a physically-motivated and model
independent way, which and how many (free) parameters are needed to broadly
capture the physics of a theory describing cosmic acceleration. Our goal is to
make as much as possible transparent the physical interpretation of the
parameters describing the expansion. We show that, at leading order, there are
five independent parameters, of which one can be constrained via general
relativity tests. The other four parameters need to be determined by observing
and measuring the cosmic expansion rate only, H(z). Therefore we suggest that
future cosmology surveys focus on obtaining an accurate as possible measurement
of to constrain the nature of accelerated expansion (dark energy and/or
inflation).Comment: In press; minor changes, results unchange
Filling minimality of Finslerian 2-discs
We prove that every Riemannian metric on the 2-disc such that all its
geodesics are minimal, is a minimal filling of its boundary (within the class
of fillings homeomorphic to the disc). This improves an earlier result of the
author by removing the assumption that the boundary is convex. More generally,
we prove this result for Finsler metrics with area defined as the
two-dimensional Holmes-Thompson volume. This implies a generalization of Pu's
isosystolic inequality to Finsler metrics, both for Holmes-Thompson and
Busemann definitions of Finsler area.Comment: 16 pages, v2: improved introduction and formattin
Summability of the perturbative expansion for a zero-dimensional disordered spin model
We show analytically that the perturbative expansion for the free energy of
the zero dimensional (quenched) disordered Ising model is Borel-summable in a
certain range of parameters, provided that the summation is carried out in two
steps: first, in the strength of the original coupling of the Ising model and
subsequently in the variance of the quenched disorder. This result is
illustrated by some high-precision calculations of the free energy obtained by
a straightforward numerical implementation of our sequential summation method.Comment: LaTeX, 12 pages and 4 figure
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