239 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
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
Equation of state in the PNJL model with the entanglement interaction
The equation of state and the phase diagram in two-flavor QCD are
investigated by the Polyakov-loop extended Nambu--Jona-Lasinio (PNJL) model
with an entanglement vertex between the chiral condensate and the
Polyakov-loop. The entanglement-PNJL (EPNJL) model reproduces LQCD data at zero
and finite chemical potential better than the PNJL model. Hadronic degrees of
freedom are taken into account by the free-hadron-gas (FHG) model with the
volume-exclusion effect due to the hadron generation. The EPNJL+FHG model
improves agreement of the EPNJL model with LQCD data particularly at small
temperature. The quarkyonic phase survives, even if the correlation between the
chiral condensate and the Polyakov loop is strong and hadron degrees of freedom
are taken into account. However, the location of the quarkyonic phase is
sensitive to the strength of the volume exclusion.Comment: 9 pages, 7 figure
Observational Constraints on Accelerating Brane Cosmology with Exchange between the Bulk and Brane
We explore observational constraints on a cosmological brane-world scenario
in which the bulk is not empty. Rather, exchange of mass-energy between the
bulk and the bane is allowed. The evolution of matter fields to an observer on
the brane is then modified due to new terms in the energy momentum tensor
describing this exchange. We investigate the constraints from various
cosmological observations on the flow of matter from the bulk into the brane.
Interestingly, we show that it is possible to have a cosmology to
an observer in the brane which satisfies standard cosmological constraints
including the CMB temperature fluctuations, Type Ia supernovae at high
redshift, and the matter power spectrum. This model even accounts for the
observed suppression of the CMB power spectrum at low multipoles. In this
cosmology, the observed cosmic acceleration is attributable to the flow of
matter from the bulk to the brane. A peculiar aspect of this cosmology is that
the present dark-matter content of the universe may be significantly larger
than that of a CDM cosmology. Its influence, however, is offset by the
dark-radiation term. Possible additional observational tests of this new
cosmological paradigm are suggested.Comment: 11 pages, 5 figures, 1 tabl
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.
Spontaneous parity and charge-conjugation violations at real isospin and imaginary baryon chemical potentials
The phase structure of two-flavor QCD is investigated at real isospin and
imaginary quark chemical potentials by using the Polyakov-loop extended
Nambu--Jona-Lasinio model. In the region, parity symmetry is spontaneously
broken by the pion superfluidity phase transition, whereas charge-conjugation
symmetry is spontaneously violated by the Roberge-Weiss transition. The chiral
(deconfinement) crossover at zero isospin and quark chemical potentials is a
remnant of the parity (charge-conjugation) violation. The interplay between the
parity and charge-conjugation violations are analyzed, and it is investigated
how the interplay is related to the correlation between the chiral and
deconfinement crossovers at zero isospin and quark chemical potentials.Comment: 12 pages, 18 figures. Typos were revised. Symbols /P and /C were
added in Figures 8a and 8b. Colors of the figures were changed. Some
sentences were added and revise
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
Scalar kinks and fermion localisation in warped spacetimes
Scalar kinks propagating along the bulk in warped spacetimes provide a thick
brane realisation of the braneworld. We consider here, a class of such exact
solutions of the full Einstein-scalar system with a sine-Gordon potential and a
negative cosmological constant. In the background of the kink and the
corresponding warped geometry, we discuss the issue of localisation of spin
half fermions (with emphasis on massive ones) on the brane in the presence of
different types of kink-fermion Yukawa couplings. We analyse the possibility of
quasi-bound states for large values of the Yukawa coupling parameter
(with , the warp factor parameter kept fixed) using appropriate, recently
developed, approximation methods. In particular, the spectrum of the low--lying
states and their lifetimes are obtained, with the latter being exponentially
enhanced for large . Our results indicate quantitatively, within
this model, that it is possible to tune the nature of warping and the strength
and form of the Yukawa interaction to obtain trapped massive fermion states on
the brane, which, however, do have a finite (but very small) probability of
escaping into the bulk.Comment: 22 pages, 4 figures, RevTex
Chaotic scalar fields as models for dark energy
We consider stochastically quantized self-interacting scalar fields as
suitable models to generate dark energy in the universe. Second quantization
effects lead to new and unexpected phenomena is the self interaction strength
is strong. The stochastically quantized dynamics can degenerate to a chaotic
dynamics conjugated to a Bernoulli shift in fictitious time, and the right
amount of vacuum energy density can be generated without fine tuning. It is
numerically observed that the scalar field dynamics distinguishes fundamental
parameters such as the electroweak and strong coupling constants as
corresponding to local minima in the dark energy landscape. Chaotic fields can
offer possible solutions to the cosmological coincidence problem, as well as to
the problem of uniqueness of vacua.Comment: 30 pages, 3 figures. Replaced by final version accepted by Phys. Rev.
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