348 research outputs found
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
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
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 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
- …