Dynamics of Gravity in a Higgs Phase

We investigate the universal low-energy dynamics of the simplest Higgs phase for gravity, `ghost condensation.' We show that the nonlinear dynamics of the `ghostone' field dominate for all interesting gravitational sources. Away from caustic singularities, the dynamics is equivalent to the irrotational flow of a perfect fluid with equation of state p \propto \rho^2, where the fluid particles can have negative mass. We argue that this theory is free from catastrophic instabilities due to growing modes, even though the null energy condition is violated. Numerical simulations show that solutions generally have singularities in which negative energy regions shrink to zero size. We exhibit partial UV completions of the theory in which these singularities are smoothly resolved, so this does not signal any inconsistency in the effective theory. We also consider the bounds on the symmetry breaking scale M in this theory. We argue that the nonlinear dynamics cuts off the Jeans instability of the linear theory, and allows M \lsim 100MeV.Comment: 54 pages, 15 figures; postscript figures downloadable from http://schwinger.harvard.edu/~wiseman/Ghost/ghostepsfigs.tar.gz ; v2: substantial revision to section 5 on bound

Infrared Gluon and Ghost Propagators from Lattice QCD. Results from large asymmetric lattices

We report on the infrared limit of the quenched lattice Landau gauge gluon and ghost propagators as well as the strong coupling constant computed from large asymmetric lattices. The infrared lattice propagators are compared with the pure power law solutions from Dyson-Schwinger equations (DSE). For the gluon propagator, the lattice data is compatible with the DSE solution. The preferred measured gluon exponent being $\sim 0.52$, favouring a null zero momentum propagator. The lattice ghost propagator shows finite volume effects and, for the volumes considered, the propagator does not follow a pure power law. Furthermore, the strong coupling constant is computed and its infrared behaviour investigated.Comment: Talk given at QNP06; final version with improved english, accepted for publication at EPJ

The Infrared Behaviour of the Pure Yang-Mills Green Functions

We review the infrared properties of the pure Yang-Mills correlators and discuss recent results concerning the two classes of low-momentum solutions for them reported in literature; i.e. decoupling and scaling solutions. We will mainly focuss on the Landau gauge and pay special attention to the results inferred from the analysis of the Dyson-Schwinger equations of the theory and from "{\it quenched}" lattice QCD. The results obtained from properly interplaying both approaches are strongly emphasized.Comment: Final version to be published in FBS (54 pgs., 11 figs., 4 tabs

The minimal structure containing the band 3 anion transport site. A 35Cl NMR study

35Cl NMR, which enables observation of chloride binding to the anion transport site on band 3, is used in the present study to determine the minimal structure containing the intact transport site. Removal of cytoskeletal and other nonintegral membrane proteins, or removal of the 40-kDa cytoskeletal domain of band 3, each leave the transport site intact. Similarly, cleavage of the 52-kDa transport domain into 17- and 35-kDa fragments by chymotrypsin leaves the transport site intact. Extensive proteolysis by papain reduces the integral red cell membrane proteins to their transmembrane segments. Papain treatment removes approximately 60% of the extramembrane portion of the transport domain and produces small fragments primarily in the range 3-7 kDa, with 5 kDa being most predominant. Papain treatment damages, but does not destroy, chloride binding to the transport site; thus, the minimal structure containing the transport site is composed solely of transmembrane segments. In short, the results are completely consistent with a picture in which the transport site is buried in the membrane where it is protected from proteolysis; the transmembrane segments that surround the transport site are held together by strong attractive forces within the bilayer; and the transport site is accessed by solution chloride via an anion channel leading from the transport site to the solution

On the massive gluon propagator, the PT-BFM scheme and the low-momentum behaviour of decoupling and scaling DSE solutions

We study the low-momentum behaviour of Yang-Mills propagators obtained from Landau-gauge Dyson-Schwinger equations (DSE) in the PT-BFM scheme. We compare the ghost propagator numerical results with the analytical ones obtained by analyzing the low-momentum behaviour of the ghost propagator DSE in Landau gauge, assuming for the truncation a constant ghost-gluon vertex and a simple model for a massive gluon propagator. The asymptotic expression obtained for the regular or decoupling ghost dressing function up to the order ${\cal O}(q^2)$ is proven to fit pretty well the numerical PT-BFM results. Furthermore, when the size of the coupling renormalized at some scale approaches some critical value, the numerical PT-BFM propagators tend to behave as the scaling ones. We also show that the scaling solution, implying a diverging ghost dressing function, cannot be a DSE solution in the PT-BFM scheme but an unattainable limiting case.Comment: 16 pages, 2 figs., 2 tabs (updated version to be published in JHEP

Strong interactions and exact solutions in non-linear massive gravity

We investigate strong coupling effects in a covariant massive gravity model, which is a candidate for a ghost free non-linear completion of Fierz-Pauli. We analyse the conditions to recover general relativity via Vainshtein mechanism in the weak field limit, and find three main cases depending on the choice of parameters. In the first case, the potential is such that all non-linearities disappear and the vDVZ discontinuity cannot be avoided. In the second case, the Vainshtein mechanism allows to recover general relativity within a macroscopic radius from a source. In the last case, the strong coupling of the scalar graviton completely shields the massless graviton, and weakens gravity when approaching the source. In the second part of the paper, we explore new exact vacuum solutions, that asymptote de Sitter or anti de Sitter space depending on the parameter choice. The curvature of the space is proportional to the mass of the graviton, thus providing a cosmological background which may explain the present day acceleration in terms of the graviton mass. Moreover, by expressing the potential for non-linear massive gravity in a convenient form, we also suggest possible connections with a higher dimensional framework.Comment: 20 pages, no figures. Version accepted by PR