We present the first Dyson-Schwinger equation calculation of the light hadron spectrum that simultaneously correlates the masses of meson and baryon ground-and excited-states within a single framework. At the core of our analysis is a symmetry-preserving treatment of a vector-vector contact interaction. In comparison with relevant quantities the root-mean-square-relative-error/degreeof freedom is 13%. Notable amongst our results is agreement between the computed baryon masses and the bare masses employed in modern dynamical coupled-channels models of pion-nucleon reactions. Our analysis provides insight into numerous aspects of baryon structure; e.g., relationships between the nucleon and ∆ masses and those of the dressed-quark and diquark correlations they contain.

We present a unified Dyson-Schwinger equation treatment of static and electromagnetic properties of pseudoscalar and vector mesons, and scalar and axial-vector diquark correlations, based upon a vector-vector contact-interaction. A basic motivation for this study is the need to document a comparison between the electromagnetic form factors of mesons and those diquarks which play a material role in nucleon structure. A notable result, therefore, is the large degree of similarity between related meson and diquark form factors. The simplicity of the interaction enables computation of the form factors at arbitrarily large spacelike-Q 2 , which enables us to expose a zero in the ρ-meson electric form factor at z, where rρ, rD are, respectively, the electric radii of the ρ-meson and deuteron.

We show that in fully-self-consistent treatments of the pion; namely, its static properties and elastic and transition form factors, the asymptotic limit of the product Q^2 G_{\gamma * \gamma \pi ^0}(Q^2), determined a priori by the interaction employed, is not exceeded at any finite value of spacelike momentum transfer. Furthermore, in such a treatment of a vector-vector contact-interaction one obtains a \gamma * \gamma -> \pi ^0 transition form factor that disagrees markedly with all available data. We explain that the contact interaction produces a pion distribution amplitude which is flat and nonvanishing at the endpoints. This amplitude characterises a pointlike pion bound-state. Such a state has the hardest possible form factors; i.e., form factors which become constant at large momentum transfers and hence are in striking disagreement with completed experiments. On the other hand, interactions with QCD-like behaviour produce soft pions, a valence-quark distribution amplitude that vanishes as ~(1-x)^2 for x~1, and results that agree with the bulk of existing data. Our analysis supports a view that the large-Q^2 data obtained by the BaBar Collaboration is not an accurate measure of the \gamma * \gamma -> \pi ^0 form factor.Comment: 11 pages, 6 figure

Recent LHC data, together with the electroweak naturalness argument, suggest that the top squarks may be significantly lighter than the other sfermions. We present supersymmetric models in which such a split spectrum is obtained through "geometries": being "close to" electroweak symmetry breaking implies being "away from" supersymmetry breaking, and vice versa. In particular, we present models in 5D warped spacetime, in which supersymmetry breaking and Higgs fields are located on the ultraviolet and infrared branes, respectively, and the top multiplets are localized to the infrared brane. The hierarchy of the Yukawa matrices can be obtained while keeping near flavor degeneracy between the first two generation sfermions, avoiding stringent constraints from flavor and CP violation. Through the AdS/CFT correspondence, the models can be interpreted as purely 4D theories in which the top and Higgs multiplets are composites of some strongly interacting sector exhibiting nontrivial dynamics at a low energy. Because of the compositeness of the Higgs and top multiplets, Landau pole constraints for the Higgs and top couplings apply only up to the dynamical scale, allowing for a relatively heavy Higgs boson, including m h = 125 GeV as suggested by the recent LHC data. We analyze electroweak symmetry breaking for a well-motivated subset of these models, and find that fine-tuning in electroweak symmetry breaking is indeed ameliorated. We also discuss a flat space realization of the scenario in which supersymmetry is broken by boundary conditions, with the top multiplets localized to a brane while other matter multiplets delocalized in the bulk.

We explore supersymmetric theories in which the Higgs mass is boosted by the non-decoupling D-terms of an extended U (1)X gauge symmetry, defined here to be a general linear combination of hypercharge, baryon number, and lepton number. Crucially, the gauge coupling, gX , is bounded from below to accommodate the Higgs mass, while the quarks and leptons are required by gauge invariance to carry non-zero charge under U (1)X . This induces an irreducible rate, σBR, for pp → X → relevant to existing and future resonance searches, and gives rise to higher dimension operators that are stringently constrained by precision electroweak measurements. Combined, these bounds define a maximally allowed region in the space of observables, (σBR, mX ), outside of which is excluded by naturalness and experimental limits. If natural supersymmetry utilizes non-decoupling D-terms, then the associated X boson can only be observed within this window, providing a model independent 'litmus test' for this broad class of scenarios at the LHC. Comparing limits, we find that current LHC results only exclude regions in parameter space which were already disfavored by precision electroweak data.

Recently, a new framework for describing the multiverse has been proposed which is based on the principles of quantum mechanics. The framework allows for well-defined predictions, both regarding global properties of the universe and outcomes of particular experiments, according to a single probability formula. This provides complete unification of the eternally inflating multiverse and many worlds in quantum mechanics. In this paper we elucidate how cosmological parameters can be calculated in this framework, and study the probability distribution for the value of the cosmological constant. We consider both positive and negative values, and find that the observed value is consistent with the calculated distribution at an order of magnitude level. In particular, in contrast to the case of earlier measure proposals, our framework prefers a positive cosmological constant over a negative one. These results depend only moderately on how we model galaxy formation and life evolution therein.

We provide a glimpse of recent progress in hadron physics made using QCD's Dyson-Schwinger equations, reviewing: the notion of in-hadron condensates and a putative solution of a gross problem with the cosmological constant; the dynamical generation of quark anomalous chromo- and electro-magnetic moments, and their material impact upon the proton's electric/magnetic form factor ratio; a computation that simultaneously correlates the masses of meson and baryon ground- and excited-states; and a prediction for the x->1 value of the ratio of neutron/proton distribution functions.Comment: 7 pages, 3 figures. Contribution to the proceedings of "T(r)opical QCD 2010: Cairns CSSM 2010 Workshop," Cairns Colonial Club, Cairns, Australia, 26 September - 1 Octobe

Abstract. A Dyson-Schwinger equation calculation of the light hadron spectrum, which correlates the masses of meson and baryon ground-and excited-states within a single framework, produces a description of the Roper resonance that corresponds closely with conclusions drawn recently by EBAC. Namely, the Roper is a particular type of radial excitation of the nucleon's dressed-quark core augmented by a material meson cloud component. There are, in addition, some surprises. . DCSB is an essentially quantum field theoretical effect. In quantum field theory a meson appears as a pole in the four-point quark-antiquark Green function. From this observation one can derive the Bethe-Salpeter equation. It is therefore unsurprising that a baryon appears as a pole in a six-point quark Green function; and one can derive a Poincaré covariant Faddeev equation to describe the associated bound state [4]. The Faddeev equation sums all possible exchanges and interactions that can take place between three dressedquarks. These dressed-quarks are one of the basic consequences of DCSB in QCD. A tractable Faddeev equation, Fig. 1, follows from the observation that an interaction which describes color-singlet mesons also generates quark-quark (diquark) correlations in the color-antitriplet channel [5].It should be emphasized that the diquark correlations within baryons are nonpointlike. They have a nonzero extent, which can be characterized by a charge radius. One finds, e.g., that isoscalar-scalar diquark correlations have a charge radius commensurate with that of the pion and the analogous axial-vector diquarks have radii similar to those of the ρ-meson [7]. Quantum mechanical models that employ pointlike diquark degrees of freedom have no relation to the Faddeev equation description of baryons in quantum field theory.