119366741
IIA moduli stabilization with badly broken supersymmetry.
We generalize the concept of Scherk-Schwarz compactification in string theory to include orbifolding by any symmetry that acts differently on bosons and fermions, namely, an R-symmetry. Such a symmetry can arise in many situations, including toroidal and orbifold compactifications, as well as smooth Calabi-Yau spaces. If the symmetry acts freely then for large radius there are no tachyons in the spectrum. We give examples where the coupling is small, the internal manifold is large and all the moduli are stabilized by fluxes. Such models appear to be perturbatively stable with supersymmetry broken at the Kaluza-Klein scale. These are interesting laboratories for a variety of theoretical questions and provide models of a non-supersymmetric landscape.
17051829
Continuous degeneracy of non-supersymmetric vacua
Abstract In global supersymmetric Wess–Zumino models with minimal Kahler potentials, F-type supersymmetry breaking always yields instability or continuous degeneracy of non-supersymmetric vacua. As a generalization of the original O'Raifeartaigh's result, the existence of instability or degeneracy is true to any higher order corrections at tree level for models even with non-renormalizable superpotentials. The degeneracy generically coincides the R-axion direction under some assumptions of R-charge assignment, but generally requires neither R-symmetries nor any assumption of generic superpotentials. The result also confirms the well-known fact that tree level supersymmetry breaking is a very rare occurrence in global supersymmetric theories with minimal Kahler potentials. The implication for effective field theory method in the landscape is discussed and we point out that choosing models with minimal Kahler potentials may result in unexpected answers to the vacuum statistics. Supergravity theories or theories with non-minimal Kahler potentials in general do not suffer from the existence of instability or degeneracy. But very strong gauge dynamics or small compactification dimension reduces the Kahler potential from non-minimal to minimal, and gravity decoupling limit reduces supergravity to global supersymmetry. Instability or degeneracy may appear in these limits. Away from these limits, a large number of non-SUSY vacua may still be found in an intermediate region.
8346
Branches of the landscape
With respect to the question of supersymmetry breaking, there are three branches of the ∞ux landscape. On one of these, if one requires small cosmological con- stant, supersymmetry breaking is predominantly at the fundamental scale; on another, the distribution is roughly ∞at on a logarithmic scale; on the third, the preponderance of vacua are at very low scale. A priori, as we will explain, one can say little about the flrst branch. The vast majority of these states are not accessible even to crude, approximate analysis. On the other two branches one can hope to do better. But as a result of the lack of access to branch one, and our poor understanding of cosmology, we can at best conjecture about whether string theory predicts low energy supersymmetry or not. If we hypothesize that are on branch two or three, distinctive predictions may be possible. We comment of the status of naturalness within the landscape, deriving, for example, the statistics of the flrst branch from simple efiective fleld theory reasoning.
34544949
On Witten's instability and winding tachyons
We investigate, from a spacetime perspective, some aspects of Horowitz's re- cent conjecture that black strings may catalyze the decay of Kaluza-Klein spacetimes into a bubble of nothing. We identify classical configurations that interpolate between flat space and the bubble, and discuss the energetics of the transition. We investigate the effects of winding tachyons on the size and shape of the barrier and find no evidence at large com- pactification radius that tachyons enhance the tunneling rate. For the interesting radii, of order the string scale, the question is difficult to answer due to the failure of the ® 0 expansion.
118075063
Supersymmetry breaking from string landscape
124471759
Neutron spectroscopic factors of Ar34 and Ar46 from (p,d) transfer reactions
Single-neutron-transfer measurements using (p,d) reactions have been performed at 33 MeV per nucleon with proton-rich Ar-34 and neutron-rich Ar-46 beams in inverse kinematics. The extracted spectroscopic factors are compared to the large-basis shell-model calculations. Relatively weak quenching of the spectroscopic factors is observed between Ar-34 and Ar-46. The experimental results suggest that neutron correlations have a weak dependence on the asymmetry of the nucleus over this isotopic region. The present results are consistent with the systematics established from extensive studies of spectroscopic factors and dispersive optical-model analyses of Ca40-49 isotopes. They are, however, inconsistent with the trends obtained in knockout-reaction measurements.
53341830
Thermoelectric DC conductivities with momentum dissipation from higher derivative gravity
A bstractWe present a mechanism of momentum relaxation in higher derivative gravity by adding linear scalar fields to the Gauss-Bonnet theory. We analytically computed all of the DC thermoelectric conductivities in this theory by adopting the method given by Donos and Gauntlett in [arXiv:1406.4742]. The results show that the DC electric conductivity is not a monotonic function of the effective impurity parameter β: in the small β limit, the DC conductivity is dominated by the coherent phase, while for larger β, pair creation contribution to the conductivity becomes dominant, signaling an incoherent phase. In addition, the DC heat conductivity is found independent of the Gauss-Bonnet coupling constant.
123570279
Investigation of two-proton emission from excited states of the odd-Z nucleus P-28 by complete-kinematics measurements
An experiment to study exotic two-proton emission from excited levels of the odd-Z nucleus {sup 28}P was performed at the National Laboratory of Heavy Ion Research-Radioactive Ion Beam Line (HIRFL-RIBLL) facility. The projectile {sup 28}P at the energy of 46.5 MeV/u was bombarding a {sup 197}Au target to populate the excited states via Coulomb excitation. Complete-kinematics measurements were realized by the array of silicon strip detectors and the CsI+PIN telescope. Two-proton events were selected and the relativistic-kinematics reconstruction was carried out. The spectrum of relative momentum and opening angle between two protons was deduced from Monte Carlo simulations. Experimental results show that two-proton emission from {sup 28}P excited states less than 17.0 MeV is mainly two-body sequential emission or three-body simultaneous decay in phase space. The present simulations cannot distinguish these two decay modes. No obvious diproton emission was found.
88507575
Projectile fragmentation of Kr86 at 64 MeV/nucleon
We measured fragmentation cross sections produced using the primary beam of 86 Kr at 64 MeV/nucleon on 9 Be and 181 Ta targets. The cross sections were obtained by integrating the momentum distributions of isotopes with 25 ≤ Z < 36 measured using the RIPS fragment separator at RIKEN. The cross-section ratios obtained with the 181 Ta and 9 Be targets depend on the fragment masses, contrary to the simple geometrical models. We compared the extracted cross sections to EPAX; an empirical parametrization of fragmentation cross sections. Predictions from current EPAX parametrization severely overestimate the production cross sections of very neutron-rich isotopes. Attempts to obtain another set of EPAX parameters specific to the reaction studied here to extrapolate the neutron-rich nuclei more accurately have not been very successful, suggesting that accurate predictions of production cross sections of nuclei far from the valley of stability require information of nuclear properties that are not present in EPAX.
123530541
Probing the equation of state of asymmetric nuclear matter with isospin diffusion and stopping in heavy-ion collisions
Results from the study of isospin asymmetric Sn+Sn collisions at E/A=35 MeV and 50 MeV, collected with the LASSA and the Chimera detectors at the NSCL of MSU, respectively, are shown. The diffusion of neutrons and protons between projectiles and targets with different N/Z-asymmetries is studied by means of imbalance ratios measurements. The obtained results and their comparison to transport model simulations provide constraints on the density dependence of the symmetry energy. The systematic study of these phenomena at different impact parameters also allows us to explore isospin transparency and stopping phenomena in more central collisions, with important implications about the attainment of chemical equilibrium in central collisions at 35 MeV/nucleon.