General structure of the graviton self-energy

The graviton self-energy at finite temperature depends on fourteen structure functions. We show that, in the absence of tadpoles, the gauge invariance of the effective action imposes three non-linear relations among these functions. The consequences of such constraints, which must be satisfied by the thermal graviton self-energy to all orders, are explicitly verified in general linear gauges to one loop order.Comment: 4 pages, minor corrections of typo

Light--like Wilson loops and gauge invariance of Yang--Mills theory in 1+1 dimensions

A light-like Wilson loop is computed in perturbation theory up to ${\cal O} (g^4)$ for pure Yang--Mills theory in 1+1 dimensions, using Feynman and light--cone gauges to check its gauge invariance. After dimensional regularization in intermediate steps, a finite gauge invariant result is obtained, which however does not exhibit abelian exponentiation. Our result is at variance with the common belief that pure Yang--Mills theory is free in 1+1 dimensions, apart perhaps from topological effects.Comment: 10 pages, plain TeX, DFPD 94/TH/

Conformal Supergravity in Twistor-String Theory

Conformal supergravity arises in presently known formulations of twistor-string theory either via closed strings or via gauge-singlet open strings. We explore this sector of twistor-string theory, relating the relevant string modes to the particles and fields of conformal supergravity. We also use the twistor-string theory to compute some tree level scattering amplitudes with supergravitons, and compare to expectations from conformal supergravity. Since the supergravitons interact with the same coupling constant as the Yang-Mills fields, conformal supergravity states will contribute to loop amplitudes of Yang-Mills gluons in these theories. Those loop amplitudes will therefore not coincide with the loop amplitudes of pure super Yang-Mills theory.Comment: 43 pages harvmac tex, added footnote to introductio

The 3-graviton vertex function in thermal quantum gravity

The high temperature limit of the 3-graviton vertex function is studied in thermal quantum gravity, to one loop order. The leading ($T^4$) contributions arising from internal gravitons are calculated and shown to be twice the ones associated with internal scalar particles, in correspondence with the two helicity states of the graviton. The gauge invariance of this result follows in consequence of the Ward and Weyl identities obeyed by the thermal loops, which are verified explicitly.Comment: 19 pages, plain TeX, IFUSP/P-100

Thermal one- and two-graviton Green's functions in the temporal gauge

The thermal one- and two-graviton Green's function are computed using a temporal gauge. In order to handle the extra poles which are present in the propagator, we employ an ambiguity-free technique in the imaginary-time formalism. For temperatures T high compared with the external momentum, we obtain the leading T^4 as well as the subleading T^2 and log(T) contributions to the graviton self-energy. The gauge fixing independence of the leading T^4 terms as well as the Ward identity relating the self-energy with the one-point function are explicitly verified. We also verify the 't Hooft identities for the subleading T^2 terms and show that the logarithmic part has the same structure as the residue of the ultraviolet pole of the zero temperature graviton self-energy. We explicitly compute the extra terms generated by the prescription poles and verify that they do not change the behavior of the leading and sub-leading contributions from the hard thermal loop region. We discuss the modification of the solutions of the dispersion relations in the graviton plasma induced by the subleading T^2 contributions.Comment: 17 pages, 5 figures. Revised version to be published in Phys. Rev.

The graviton self-energy in thermal quantum gravity

We show generally that in thermal gravity, the one-particle irreducible 2-point function depends on the choice of the basic graviton fields. We derive the relevant properties of a physical graviton self-energy, which is independent of the parametrization of the graviton field. An explicit expression for the graviton self-energy at high-temperature is given to one-loop order.Comment: 13 pages, 2 figure

Trace Anomaly and Backreaction of the Dynamical Casimir Effect

The Casimir energy for massless scalar field which satisfies priodic boundary conditions in two-dimensional domain wall background is calculated by making use of general properties of renormalized stress-tensor. The line element of domain wall is time dependent, the trace anomaly which is the nonvanishing $T^{\mu}_{\mu}$ for a conformally invariant field after renormalization, represent the back reaction of the dynamical Casimir effect.Comment: 8 pages, no figures, typos corrected, discussion added, has been accepted for the publication in GR

Cobalt ions recruit inflammatory cells in vitro through human Toll-like receptor 4

AbstractMetal-on-metal (MoM) hip replacements, often manufactured from a cobalt-chrome alloy, are associated with adverse reactions including soft tissue necrosis and osteolysis. Histopathological analysis of MoM peri-implant tissues reveals an inflammatory cell infiltrate that includes macrophages, monocytes and neutrophils.Toll-like receptor 4 (TLR4) is an innate immune receptor activated by bacterial lipopolysaccharide. Recent studies have demonstrated that cobalt ions from metal-on-metal joints also activate human TLR4, increasing cellular secretion of inflammatory chemokines including interleukin-8 (IL-8, CXCL8) and CCL2. Chemokines recruit immune cells to the site of inflammation, and their overall effect depends on the chemokine profile produced.This study investigated the effect of cobalt on the secretion of inflammatory cytokines CCL20 and IL-6. The chemotactic potential of conditioned media from a cobalt-stimulated human monocyte cell line on primary monocytes and neutrophils was investigated using an in vitro transwell migration assay. The role of TLR4 in observed effects was studied using a small molecule TLR4-specific antagonist.Cobalt ions significantly increased release of CCL2 and IL-6 by MonoMac 6 cells (P<0.001). Conditioned media from cobalt-stimulated cells significantly increased monocyte and neutrophil chemotaxis in vitro (P<0.001). These effects were abrogated by the TLR4 antagonist (P<0.001) suggesting that they occur through cobalt activation of TLR4.This study demonstrates the role of TLR4 in cobalt-mediated immune cell chemotaxis and provides a potential mechanism by which cobalt ions may contribute to the immune cell infiltrate surrounding failed metal hip replacements. It also highlights the TLR4 signalling pathway as a potential therapeutic target in preventing cobalt-mediated inflammation

General solutions of the Wess-Zumino consistency condition for the Weyl anomalies

The general solutions of the Wess-Zumino consistency condition for the conformal (or Weyl, or trace) anomalies are derived. The solutions are obtained, in arbitrary dimensions, by explicitly computing the cohomology of the corresponding Becchi-Rouet-Stora-Tyutin differential in the space of integrated local functions at ghost number unity. This provides a purely algebraic, regularization-independent classification of the Weyl anomalies in arbitrary dimensions. The so-called type-A anomaly is shown to satisfy a non-trivial descent of equations, similarly to the non-Abelian chiral anomaly in Yang-Mills theory.Comment: 9 pages. RevTeX fil