Recent results in the infrared sector of QCD

We review the most recent results, derived within the combined framework of the pinch technique and the background field method, describing certain QCD nonperturbative properties.Comment: 8 pages, 3 figures. Talk presented at the International Meeting "Excited QCD", Peniche, Portugal, 6 - 12 May, 201

On the dynamics of the Kugo-Ojima function

In this talk, after reviewing the dynamical gluon mass generation mechanism within the pinch technique framework and its phenomenological predictions, we will introduce the modern formulation of the pinch technique which makes extensive use of the Batalin-Vilkovisky quantization formalism. In this framework a certain auxiliary function \Lambda_{\mu\nu}(q) - and its associated form factors G(q^2) and L(q^2) -play a prominent role. After showing that in the (background) Landau gauge \Lambda_{\mu\nu}(q) fully constrains the QCD ghost sector, we show that G(q^2) coincides with the Kugo-Ojima function u(q^2), whose infrared behavior has traditionally served as the standard criterion for the realization of the Kugo-Ojima confinement mechanism. The determination of the behavior of G(q^2) (and therefore of the Kugo-Ojima function) for all momenta through a combination of the available lattice data on the gluon and ghost propagators as well as the dynamical equation G(q^2) satisfies, will be then discussed. In particular we will show that (i) in the deep infrared the function deviates considerably from the value associated with the realization of the Kugo-Ojima confinement scenario, and (ii) establish the dependence on the renormalization point of u(q^2), and especially of its value at q^2=0.Comment: 12 pages, 7 figures. Talk presented at the International Workshop on QCD Green's Functions, Confinement, and Phenomenology - QCD-TNT09, September 07 - 11 2009, ECT* Trento, Ital

The Cosmological Slavnov-Taylor Identity from BRST Symmetry in Single-Field Inflation

The cosmological Slavnov-Taylor (ST) identity of the Einstein-Hilbert action coupled to a single inflaton field is obtained from the Becchi-Rouet-Stora-Tyutin (BRST) symmetry associated with diffeomorphism invariance in the Arnowitt-Deser-Misner (ADM) formalism. The consistency conditions between the correlators of the scalar and tensor modes in the squeezed limit are then derived from the ST identity, together with the softly broken conformal symmetry. Maldacena's original relations connecting the 2- and 3-point correlators at horizon crossing are recovered, as well as the next-to-leading corrections, controlled by the special conformal transformations.Comment: 38 pages, no figures. Corrected an error in the bispectrum relations, so that original Maldacena's results are now recovered. Added new sections on the extended discussions of the in-in formalism in the BRST approach and higher order corrections in the squeezed limit (special conformal transformations). Revised version accepted for publication in JCA

JaxoDraw: A graphical user interface for drawing Feynman diagrams

JaxoDraw is a Feynman graph plotting tool written in Java. It has a complete graphical user interface that allows all actions to be carried out via mouse click-and-drag operations in a WYSIWYG fashion. Graphs may be exported to postscript/EPS format and can be saved in XML files to be used in later sessions. One of the main features of JaxoDraw is the possibility to produce LaTeX code that may be used to generate graphics output, thus combining the powers of TeX/LaTeX with those of a modern day drawing program. With JaxoDraw it becomes possible to draw even complicated Feynman diagrams with just a few mouse clicks, without the knowledge of any programming language.Comment: 15 pages, no figures; typos corrected; visit the JaxoDraw home page at http://altair.ific.uv.es/~JaxoDraw/home.htm

JaxoDraw: A graphical user interface for drawing Feynman diagrams. Version 2.0 release notes

A new version of the Feynman graph plotting tool JaxoDraw is presented. Version 2.0 is a fundamental re-write of most of the JaxoDraw core and some functionalities, in particular importing graphs, are not backward-compatible with the 1.x branch. The most prominent new features include: drawing of Bezier curves for all particle modes, on-the-fly update of edited objects, multiple undo/redo functionality, the addition of a plugin infrastructure, and a general improved memory performance. A new LaTeX style file is presented that has been written specifically on top of the original axodraw.sty to meet the needs of this this new version.Comment: 17 pages, 1 figur

Scalar Resonances in the Non-linearly Realized Electroweak Theory

We introduce a physical scalar sector in a SU(2)xU(1) electroweak theory in which the gauge group is realized non linearly. By invoking theoretical as well as experimental constraints, we build a phenomenologically viable model in which a minimum of four scalar resonances appear, and the mass of the CP even scalar is controlled by a vacuum expectation value; however, the masses of all other particles (both matter as well as vector boson fields) are unrelated to spontaneous symmetry breaking and generated by the St\"uckelberg mechanism. We evaluate in this model the CP-even scalar decay rate to two photons and use this amplitude to perform a preliminary comparison with the recent LHC measurements. As a result, we find that the model exhibits a preference for a negative Yukawa coupling between the top quark and the CP-even resonance.Comment: 21 pages, 3 figures; typos correcte

Renormalization Group Equation for Weakly Power Counting Renormalizable Theories

We study the renormalization group flow in weak power counting (WPC) renormalizable theories. The latter are theories which, after being formulated in terms of certain variables, display only a finite number of independent divergent amplitudes order by order in the loop expansion. Using as a toolbox the well-known SU(2) non linear sigma model, we prove that for such theories a renormalization group equation holds that does not violate the WPC condition: that is, the sliding of the scale $\mu$ for physical amplitudes can be reabsorbed by a suitable set of finite counterterms arising at the loop order prescribed by the WPC itself. We explore in some detail the consequences of this result; in particular, we prove that it holds in the framework of a recently introduced beyond the Standard Model scenario in which one considers non-linear St\"uckelberg-like symmetry breaking contributions to the fermion and gauge boson mass generation mechanism.Comment: 32 pages, 5 figure

BRST-driven cancellations and gauge invariant Green's functions

We study a fundamental, all order cancellation operating between graphs of distinct kinematic nature, which allows for the construction of gauge-independent effective self-energies, vertices, and boxes at arbitrary order.Comment: 4 pages, 3 figures. Contributed to QCD 03: High-Energy Physics International Conference in Quantum Chromodynamics, Montpellier, France, 2-9 July 200

The neutrino charge radius in the presence of fermion masses

We show how the crucial gauge cancellations leading to a physical definition of the neutrino charge radius persist in the presence of non-vanishing fermion masses. An explicit one-loop calculation demonstrates that, as happens in the massless case, the pinch technique rearrangement of the Feynman amplitudes, together with the judicious exploitation of a fundamental current relation leads to a completely gauge independent definition of the effective neutrino charge radius. Using the formalism of the Nielsen identities it is further proved that the same cancellation mechanism operates unaltered to all orders in perturbation theory.Comment: 26 pages, 8 figure

The QCD Effective Charge to All Orders

Using the pinch technique, we show how to construct the QCD effective charge to all orders.Comment: 4 pages, no figures. Contributed to QCD 02: High-Energy Physics International Conference in Quantum Chromodynamics, Montpellier, France, 2-9 July 200