1,025 research outputs found
Near-BPS Skyrmions: Non-shell configurations and Coulomb effects
The relatively small binding energy in nuclei suggests that they may be well
represented by near-BPS Skyrmions since their mass is roughly proportional to
the baryon number For that purpose, we propose a generalization of the
Skyrme model with terms up to order six in derivatives of the pion fields and
treat the nonlinear and Skyrme terms as small perturbations. For our
special choice of mass term (or potential) , we obtain well-behaved
analytical BPS-type solutions with non-shell configurations for the baryon
density, as opposed to the more complex shell-like configurations found in most
extensions of the Skyrme model . Along with static and (iso)rotational
energies, we add to the mass of the nuclei the often neglected Coulomb energy
and isospin breaking term. Fitting the four model parameters, we find a
remarkable agreement for the binding energy per nucleon with respect to
experimental data. These results support the idea that nuclei could be near-BPS
Skyrmions.Comment: Correction of minors errors, references adde
A supersymmetric model of gamma ray bursts
We propose a model for gamma ray bursts in which a star subject to a high
level of fermion degeneracy undergoes a phase transition to a supersymmetric
state. The burst is initiated by the transition of fermion pairs to sfermion
pairs which, uninhibited by the Pauli exclusion principle, can drop to the
ground state of minimum momentum through photon emission. The jet structure is
attributed to the Bose statistics of sfermions whereby subsequent sfermion
pairs are preferentially emitted into the same state (sfermion amplification by
stimulated emission). Bremsstrahlung gamma rays tend to preserve the
directional information of the sfermion momenta and are themselves enhanced by
stimulated emission.Comment: published versio
Compound nuclear decay and the liquid to vapor phase transition: a physical picture
Analyses of multifragmentation in terms of the Fisher droplet model (FDM) and
the associated construction of a nuclear phase diagram bring forth the problem
of the actual existence of the nuclear vapor phase and the meaning of its
associated pressure. We present here a physical picture of fragment production
from excited nuclei that solves this problem and establishes the relationship
between the FDM and the standard compound nucleus decay rate for rare particles
emitted in first-chance decay. The compound thermal emission picture is
formally equivalent to a FDM-like equilibrium description and avoids the
problem of the vapor while also explaining the observation of Boltzmann-like
distribution of emission times. In this picture a simple Fermi gas thermometric
relation is naturally justified and verified in the fragment yields and time
scales. Low energy compound nucleus fragment yields scale according to the FDM
and lead to an estimate of the infinite symmetric nuclear matter critical
temperature between 18 and 27 MeV depending on the choice of the surface energy
coefficient of nuclear matter.Comment: Five page two column pages, four figures, submitted to Phys. Rev.
Searching for cavities of various densities in the Earth's crust with a low-energy electron-antineutrino beta-beam
We propose searching for deep underground cavities of different densities in
the Earth's crust using a long-baseline electron-antineutrino disappearance
experiment, realized through a low-energy beta-beam with highly-enhanced
luminosity. We focus on four cases: cavities with densities close to that of
water, iron-banded formations, heavier mineral deposits, and regions of
abnormal charge accumulation that have been posited to appear prior to the
occurrence of an intense earthquake. The sensitivity to identify cavities
attains confidence levels higher than and for exposures
times of 3 months and 1.5 years, respectively, and cavity densities below 1 g
cm or above 5 g cm, with widths greater than 200 km. We
reconstruct the cavity density, width, and position, assuming one of them known
while keeping the other two free. We obtain large allowed regions that improve
as the cavity density differs more from the Earth's mean density. Furthermore,
we demonstrate that knowledge of the cavity density is important to obtain
O(10%) error on the width. Finally, we introduce an observable to quantify the
presence of a cavity by changing the orientation of the electron-antineutrino
beam, with which we are able to identify the presence of a cavity at the
to C.L.Comment: 7 pages, 5 figures; matches published versio
Local Projections of Low-Momentum Potentials
Nuclear interactions evolved via renormalization group methods to lower
resolution become increasingly non-local (off-diagonal in coordinate space) as
they are softened. This inhibits both the development of intuition about the
interactions and their use with some methods for solving the quantum many-body
problem. By applying "local projections", a softened interaction can be reduced
to a local effective interaction plus a non-local residual interaction. At the
two-body level, a local projection after similarity renormalization group (SRG)
evolution manifests the elimination of short-range repulsive cores and the flow
toward universal low-momentum interactions. The SRG residual interaction is
found to be relatively weak at low energy, which motivates a perturbative
treatment
Recommended from our members
Neutron Capture by 94,96Zr and the Decays of 97Zr and 97Nb
Cross sections for radiative neutron capture have been determined for ⁹⁴Zr and ⁹⁶Zr using the activation technique with samples of naturally occurring Zr metal. The sensitivity to the correction for epithermal neutrons in the determination of small thermal cross sections is discussed, particularly in view of the variation in the resonance integral at different sites in the reactor. Gamma-ray spectroscopic studies of the decays of ⁹⁷Zr and its daughter ⁹⁷Nb have been performed, leading to improved values of the energies and intensities of the emitted γ rays, and correspondingly improved values for the energy levels and β feedings of excited states populated in ⁹⁷Nb and ⁹⁷Mo.KEYWORDS: [superscript 94,96]Zr neutron capture cross sections, ⁹⁷Zr, ⁹⁷Nb γ ray spectroscopy, ⁹⁷Nb, ⁹⁷Mo energy level
Recommended from our members
Neutron capture cross sections of 184,189,190,192Os and the decays of 185Os,190Osm, 191Os, and 193Os
Radiative neutron capture cross sections have been measured for the stable isotopes of natural Os with mass numbers 184, 189, 190, and 192 by observing radioactive decays of the activation products following neutron irradiation of naturally occurring Os. From irradiations of Os samples separately with thermal and epithermal neutrons, independent values of the thermal cross sections and resonance integrals have been deduced. By observing the gamma rays emitted by the activation products Os-185, Os-190(m), Os-191, and Os-193, improved values for the energies and intensities of the gamma rays and the decay half-lives have been obtained, enabling corresponding improvements in the energy values and beta-decay feedings of levels in the daughter nuclei.Keywords: gamma rays, Emission probabilities, Energy, Nuclear data sheets, Compilation, IR-19
Sensitivity of low energy neutrino experiments to physics beyond the standard model
We study the sensitivity of future low energy neutrino experiments to extra
neutral gauge bosons, leptoquarks and R-parity breaking interactions. We focus
on future proposals to measure coherent neutrino-nuclei scattering and
neutrino-electron elastic scattering. We introduce a new comparative analysis
between these experiments and show that in different types of new physics it is
possible to obtain competitive bounds to those of present and future collider
experiments. For the cases of leptoquarks and R-parity breaking interactions we
found that the expected sensitivity for most of the future low energy
experimental setups is better than the current constraints.Comment: 21 pages, 5 figures. A more detailed analysis of systematic errors is
done. Final version to be published in PR
Recommended from our members
Neutron capture cross sections of 136,138,140,142Ce and the decays of 137Ce
The activation method has been used to measure the cross sections for radiative capture of neutrons by all isotopes of stable Ce (mass numbers 136, 138, 140, and 142). Both the thermal cross sections and the resonance integrals have been determined from separate irradiations with thermal and epithermal neutrons, wherever possible cross-checking results from different irradiation facilities with different flux distributions. Because determination of precise cross sections by activation requires equally precise values of the decay half-lives, we have remeasured decay half-lives of ¹³⁷Ce[superscript g], ¹³⁷Ce[superscript m], ¹³⁹Ce[superscript m], ¹⁴¹Ce, and ¹⁴³Ce. Improved values for the energies and intensities of the γrays in the decays of ¹³⁷Ce[superscript g] and ¹³⁷Ce[superscript m] have also been determined, along with corresponding values for the βdecay feedings and energies of excited states in ¹³⁷La..Keywords: LA-137,
Isotopes,
Half lives,
Nuclei,
142CE,
Dilution resonance integrals,
Nuclides,
N, Gamma,
Ratio
- …