The Supersymmetric Fine-Tuning Problem and TeV-Scale Exotic Scalars

A general framework is presented for supersymmetric theories that do not suffer from fine-tuning in electroweak symmetry breaking. Supersymmetry is dynamically broken at a scale \Lambda \approx (10 - 100) TeV, which is transmitted to the supersymmetric standard model sector through standard model gauge interactions. The dynamical supersymmetry breaking sector possesses an approximate global SU(5) symmetry, whose SU(3) x SU(2) x U(1) subgroup is explicitly gauged and identified as the standard model gauge group. This SU(5) symmetry is dynamically broken at the scale \Lambda, leading to pseudo-Goldstone boson states, which we call xyons. We perform a detailed estimate for the xyon mass and find that it is naturally in the multi-TeV region. We study general properties of xyons, including their lifetime, and study their collider signatures. A generic signature is highly ionizing tracks caused by stable charged bound states of xyons, which may be observed at the LHC. We also consider cosmology in our scenario and find that a consistent picture can be obtained. Our framework is general and does not depend on the detailed structure of the Higgs sector, nor on the mechanism of gaugino mass generation.Comment: 53 pages, 7 figure

Variations on Supersymmetry Breaking and Neutrino Spectra

The problem of generating light neutrinos within supersymmetric models is discussed. It is shown that the hierarchy of scales induced by supersymmetry breaking can give rise to suppression factors of the correct order of magnitude to produce experimentally allowed neutrino spectra.Comment: 18 pages, LaTeX, Contribution to "Neutrino Workshop", Fuji-Yoshida, Japan, August 200

Magnetization Plateau of an S=1 Frustrated Spin Ladder

We study the magnetization plateau at 1/4 of the saturation magnetization of the S=1 antiferromagnetic spin ladder both analytically and numerically, with the aim of explaining recent experimental results on BIP-TENO by Goto et al. We propose two mechanisms for the plateau formation and clarify the plateau phase diagram on the plane of the coupling constants between spins

How to distinguish the Haldane/Large-D state and the intermediate-D state in an S=2 quantum spin chain with the XXZ and on-site anisotropies

We numerically investigate the ground-state phase diagram of an S=2 quantum spin chain with the $XXZ$ and on-site anisotropies described by ${\mathcal H}=\sum_j (S_j^x S_{j+1}^x+S_j^y S_{j+1}^y+\Delta S_j^z S_{j+1}^z) + D \sum_j (S_j^z)^2$, where $\Delta$ denotes the XXZ anisotropy parameter of the nearest-neighbor interactions and $D$ the on-site anisotropy parameter. We restrict ourselves to the $\Delta>0$ and $D>0$ case for simplicity. Our main purpose is to obtain the definite conclusion whether there exists or not the intermediate-$D$ (ID) phase, which was proposed by Oshikawa in 1992 and has been believed to be absent since the DMRG studies in the latter half of 1990's. In the phase diagram with $\Delta>0$ and $D>0$ there appear the XY state, the Haldane state, the ID state, the large-$D$ (LD) state and the N\'eel state. In the analysis of the numerical data it is important to distinguish three gapped states; the Haldane state, the ID state and the LD state. We give a physical and intuitive explanation for our level spectroscopy method how to distinguish these three phases.Comment: Proceedings of "International Conference on Frustration in Condensed Matter (ICFCM)" (Jan. 11-14, 2011, Sendai, Japan

Increased tolerance to humans among disturbed wildlife.

Human disturbance drives the decline of many species, both directly and indirectly. Nonetheless, some species do particularly well around humans. One mechanism that may explain coexistence is the degree to which a species tolerates human disturbance. Here we provide a comprehensive meta-analysis of birds, mammals and lizards to investigate species tolerance of human disturbance and explore the drivers of this tolerance in birds. We find that, overall, disturbed populations of the three major taxa are more tolerant of human disturbance than less disturbed populations. The best predictors of the direction and magnitude of bird tolerance of human disturbance are the type of disturbed area (urbanized birds are more tolerant than rural or suburban populations) and body mass (large birds are more tolerant than small birds). By identifying specific features associated with tolerance, these results guide evidence-based conservation strategies to predict and manage the impacts of increasing human disturbance on birds

More Visible Effects of the Hidden Sector

There is a growing appreciation that hidden sector dynamics may affect the supersymmetry breaking parameters in the visible sector (supersymmetric standard model), especially when the dynamics is strong and superconformal. We point out that there are effects that have not been previously discussed in the literature. For example, the gaugino masses are suppressed relative to the gravitino mass. We discuss their implications in the context of various mediation mechanisms. The issues discussed include anomaly mediation with singlets, the mu (B mu) problem in gauge and gaugino mediation, and distinct mass spectra for the superparticles that have not been previously considered.Comment: 25 pages; small clarifications and corrections, version to appear in Phys. Rev.

Comparison of crystal structures and effects of Co substitution in a new member of Fe-1111 superconductor family AeFeAsF(Ae = Ca and Sr): a possible candidate for higher Tc superconductor

We refined crystal structures of newly found members of the Fe-1111 superconductor family, CaFe\_{1-x}Co\_{x}AsF and SrFe\_{1-x}Co\_{x}AsF (x = 0, 0.06, 0.12) by powder synchrotron X-ray diffraction analysis. The tetragonal to orthorhombic phase transitions were observed at ~120 K for unsubstituted CaFeAsF and at ~180 K for unsubstituted SrFeAsF, the transition temperatures agreeing with kinks observed in temperature-dependent resistivity curves. Although the transition temperature decreases, the structural phase transitions were observed below 100 K in both samples of x = 0.06, and finally they were suppressed in the doping level of x = 0.12. The refined structures reveal that distortions of the FeAs4 tetrahedron from the regular tetrahedron likely originate from mismatches in atomic radii among the constituent elements. In this system, the enlarged FeAs4 tetrahedron resulting from larger radius of Sr than that of Ca is flattened along a-b plane, whereas the smaller radius of Ca makes the tetrahedron closer to regular one, and their characteristic shapes are further enhanced by Co substitution. These results suggest that the CaFeAsF compound is a promising candidate for higher-Tc superconductor.Comment: 17 pages, 8 figures, 2 tables, Supplementary information is included at the end of the documen

Incommensurability and edge states in the one-dimensional S=1 bilinear-biquadratic model

Commensurate-incommensurate change on the one-dimensional S=1 bilinear-biquadratic model (${\cal H}(\alpha)=\sum_i \{{\bf S}_i\cdot {\bf S}_{i+1} +\alpha ({\bf S}_i\cdot{\bf S}_{i+1})^2\}$) is examined. The gapped Haldane phase has two subphases (the commensurate Haldane subphase and the incommensurate Haldane subphase) and the commensurate-incommensurate change point (the Affleck-Kennedy-Lieb-Tasaki point, $\alpha=1/3$). There have been two different analytical predictions about the static structure factor in the neighborhood of this point. By using the S{\o}rensen-Affleck prescription, these static structure factors are related to the Green functions, and also to the energy gap behaviors. Numerical calculations support one of the predictions. Accordingly, the commensurate-incommensurate change is recognized as a motion of a pair of poles in the complex plane.Comment: 29 pages, 15 figure