12452533
Tree level spontaneous R-symmetry breaking in O'Raifeartaigh models
We show that in O'Raifeartaigh models of spontaneous supersymmetry breaking, R-symmetries can be broken by non-zero values of fields at tree level, rather than by vacuum expectation values of pseudomoduli at loop level. As a complement of the recent result by Shih, we show that there must be a field in the theory with R-charge different from zero and two in order for R-symmetry breaking to occur, no matter whether the breaking happens at tree or loop level. We review the example by CDFM, and construct two types of tree level R-symmetry breaking models with a wide range of parameters and free of runaway problem. And the R-symmetry is broken everywhere on the pseudomoduli space in these models. This provides a rich set of candidates for SUSY model building and phenomenology.
119022393
R symmetries in the landscape
In the landscape, states with R symmetries at the classical level form a distinct branch, with a potentially interesting phenomenology. Some preliminary analyses suggested that the population of these states would be significantly suppressed. We survey orientifolds of IIB theories compactified on Calabi-Yau spaces based on vanishing polynomials in weighted projective spaces, and find that the suppression is quite substantial. On the other hand, we find that a Z2 R-parity is a common feature in the landscape. We discuss whether the cosmological constant and proton decay or cosmology might select the low energy branch. We include also some remarks on split supersymmetry.
119163417
Low energy supersymmetry from R-symmetries
Abstract In a generic setting of Wess–Zumino models, we prove that the existence of a supersymmetric vacuum with a vanishing superpotential can be a consequence of a continuous or discrete R-symmetry when invariant fields are not less than fields transforming in the same way as the superpotential under the R-symmetry. The realization in string theory is discussed. We show that a rich landscape of low energy supersymmetric vacua can be found in the Type IIB flux compactification setup ready for the KKLT construction of de Sitter vacua in string theory.
119110201
Vacuum statistics and parameter tuning for F-term supersymmetry breaking
We carry out a model-independent EFT method study on the vacuum statistics of general F-term SUSY breaking models. Assuming a smooth distribution of Lagrangian parameters, SUSY breaking vacua are rare in global SUSY models with a canonical Kähler potential, and have a peaked distribution near the cut-off of the SUSY breaking scale in both global SUSY and SUGRA models with a general Kähler potential. After including different mass scales in the Lagrangian, we compare the total number of SUSY and non-SUSY vacua and estimate quantitatively the rareness of SUSY breaking. The EFT method provides a general view to the amount of parameter tuning needed for a metastable SUSY breaking vacuum. The tuning also indicates the importance of R-symmetries in SUSY breaking even for metastable SUSY breaking.
119281514
The Nelson-Seiberg theorem revised
A bstractThe well-accepted Nelson-Seiberg theorem relates R-symmetries to supersymmetry (SUSY) breaking vacua, and provides a guideline for SUSY model building which is the most promising physics beyond the Standard Model. In the case of Wess-Zumino models with perturbative superpotentials, we revise the theorem to a combined necessary and sufficient condition for SUSY breaking which can be easily checked before solving the vacuum. The revised theorem provides a powerful tool to construct either SUSY breaking or SUSY vacua, and offers many practicable applications in low energy SUSY model building and string phenomenology.
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.
118473314
Isospin diffusion and equilibration for Sn+Sn collisions at E/A=35 MeV
Equilibration and equilibration rates have been measured by colliding Sn nuclei with different isospin asymmetries at beam energies of E/A=35 MeV. Using the yields of mirror nuclei of {sup 7}Li and {sup 7}Be, we have studied the diffusion of isospin asymmetry by combining data from asymmetric {sup 112}Sn+{sup 124}Sn and {sup 124}Sn+{sup 112}Sn collisions with those from symmetric {sup 112}Sn+{sup 112}Sn and {sup 124}Sn+{sup 124}Sn collisions. We use these measurements to probe isospin equilibration in central collisions where nucleon-nucleon collisions are strongly blocked by the Pauli exclusion principle. The results are consistent with transport theoretical calculations that predict a degree of transparency in these collisions, but inconsistent with the emission of intermediate mass fragments by a single chemically equilibrated source. Comparisons with quantum molecular dynamics calculations are consistent with results obtained at higher incident energies that provide constraints on the density dependence of the symmetry energy.
123261615
Holographic Dark Energy in Induced Gravity
Many astrophysics data show that our universe has a critical energy density, and 73% of it is dark energy, which drives the accelerating expansion of the universe. We consider the holographic dark energy in induced gravity by taking the Hubble scale, particle horizon and event horizon as the infrared cutoff. We find that only the event horizon can give accelerating expansion of our universe.
119540567
Dark Energy Cosmology with Spinor Field
Recent observations have shown that our universe is currently undergoing a period of accelerating expansion. In view of the astrophysical data we find that the equation of state of the dark energy lies in a narrow range around w = −1. In this paper we discuss the possibility of treating a spinor field as dark energy to realize the equation of state parameter w < −1 or w > −1. We derive the main equations which govern the evolution of the universe and then discuss the evolution and attractor property of this model, and show a late time de Sitter attractor. Finally we rewrite them with the observable quantities.
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.
121556817
Experimental study of two-proton correlated emission from S 29 excited states
An experiment of a {sup 29}S beam bombarding a {sup 197}Au target at an energy of 49.2 MeV/u has been performed to study the two-proton correlated emission from {sup 29}S excited states. Complete-kinematics measurements were carried out in the experiment. The relative momentum, opening angle, and relative energy of two protons, as well as the invariant mass of the final system, were deduced by relativistic-kinematics reconstruction. The {sup 27}Si-p-p coincident events were picked out under strict conditions and the phenomenon of p-p correlations was observed among these events. The mechanisms of two-proton emission were analyzed in a simple schematic model, in which the extreme decay modes like {sup 2}He cluster emission, three-body phase-space decay, and two-body sequential emission were taken into account. Associated with the Monte Carlo simulations, the present results show that two protons emitted from the excited states between 9.6 MeV and 10.4 MeV exhibit the features of {sup 2}He cluster decay with a branching ratio of 29{sub -11}{sup +10}%.