759 research outputs found
Evaluation of Effective Astrophysical S factor for Non-Resonant Reactions
We derived analytic formulas of the effective S astrophysical S factor,S^eff
for a non-resonant reaction of charged particles using a Taylor expension of
the astrophysical S factor and a uniform approximation.The formulas will be
able to generate generate more accurate approximation to S^eff than previous
ones
Addendum: Attenuation of the intensity within a superdeformed band
We investigate a random matrix model [Phys. Rev. C {\bf 65} 024302 (2002] for
the decay-out of a superdeformed band as a function of the parameters:
, , and . Here
is the spreading width for the mixing of an SD state
with a normally deformed (ND) doorway state , and
are the electromagnetic widths of the the SD and ND states respectively, is
the mean level spacing of the compound ND states and is the energy
difference between and . The maximum possible effect of an
order-chaos transition is inferred from analytical and numerical calculations
of the decay intensity in the limiting cases for which the ND states obey
Poisson and GOE statistics. Our results show that the sharp attenuation of the
decay intensity cannot be explained solely by an order-chaos transition.Comment: 4 pages, 4 figures, submitted to Physical Review
Symmetry Breaking Study with Deformed Ensembles
A random matrix model to describe the coupling of m-fold symmetry in
constructed. The particular threefold case is used to analyze data on
eigenfrequencies of elastomechanical vibration of an anisotropic quartz block.
It is suggested that such experimental/theoretical study may supply powerful
means to discern intrinsic symmetries in physical systems.Comment: 12 pages, 5 figure
Energy averages over regular and chaotic states in the decay out of superdeformed bands
We describe the decay out of a superdeformed band using the methods of
reaction theory. Assuming that decay-out occurs due to equal coupling (on
average) to a sea of equivalent chaotic normally deformed (ND) states, we
calculate the average intraband decay intensity and show that it can be written
as an ``optical'' background term plus a fluctuation term, in total analogy
with average nuclear cross sections. We also calculate the variance in closed
form. We investigate how these objects are modified when the decay to the ND
states occurs via an ND doorway and the ND states' statistical properties are
changed from chaotic to regular. We show that the average decay intensity
depends on two dimensionless variables in the first case while in the second
case, four variables enter the picture.Comment: 8 pages, 1 figure, presented at FUSION03, Matsushima, Miyagi, Japan,
Nov 12-15, 2003, to appear in Progress of Theoretical Physics; corrected
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Thermal Relics in Modified Cosmologies: Bounds on Evolution Histories of the Early Universe and Cosmological Boosts for PAMELA
Alternative cosmologies, based on extensions of General Relativity, predict
modified thermal histories in the Early Universe during the pre Big Bang
Nucleosynthesis (BBN) era, epoch which is not directly constrained by
cosmological observations. When the expansion rate is enhanced with respect to
the standard case, thermal relics typically decouple with larger relic
abundances. The correct value of the relic abundance is therefore obtained for
larger annihilation cross--sections, as compared to standard cosmology. A
direct consequence is that indirect detection rates are enhanced. Extending
previous analyses of ours, we derive updated astrophysical bounds on the dark
matter annihilation cross sections and use them to constrain alternative
cosmologies in the pre--BBN era. We also determine the characteristics of these
alternative cosmologies in order to provide the correct value of relic
abundance for a thermal relic for the (large) annihilation cross--section
required to explain the PAMELA results on the positron fraction, therefore
providing a "cosmological boost" solution to the dark matter interpretation of
the PAMELA data.Comment: 19 pages, 27 figures, matches published versio
Entanglement of pseudo-Hermitian random states
In a recent paper (arXiv:1905.07348v1), Dyson scheme to deal with density
matrix of non-Hermitian Hamiltonians has been used to investigate the
entanglement of states of a PT-symmetric bosonic system. They found that von
Neumann entropy can show a different behavior in the broken and unbroken
regime. We show that their results can be recast in terms of an abstract model
of pseudo-Hermitian random matrices. It is found however that, although the
formalism is practically the same, the entanglement is not of Fock states but
of Bell states.Comment: 15 pages, 2 figure
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