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 $A.$ 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 $\sigma$ and Skyrme terms as small perturbations. For our special choice of mass term (or potential) $V$, 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 $B/A$ 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 $3\sigma$ and $5\sigma$ for exposures times of 3 months and 1.5 years, respectively, and cavity densities below 1 g cm$^{-3}$ or above 5 g cm$^{-3}$, 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 $2\sigma$ to $5\sigma$ 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

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

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

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