332 research outputs found
The Effective Actions of Pseudoscalar and Scalar Particles in Theories with Gauge and Conformal Anomalies
We review recent work on the effective field theory description and the
phenomenology of axion-like and scalar particles in models characterized by
gauge and/or conformal anomalies.Comment: Presented by C. Coriano at the 9th Hellenic Workshop on Elementary
Particle Physics and Gravity, Corfu Summer Institute, Greece August 30
September 20, 200
Scale Invariant Lipatov Kernels at Non-Zero Momentum Transfer
We summarize recent work on the evaluation of the scale invariant
next-to-leading order Lipatov kernel, constructed via transverse momentum
diagrams. At zero momentum transfer the square of the leading-order kernel
appears together with an additional component, now identified as a new
partial-wave amplitude, having a separate, holomorphically factorizable,
spectrum. We present a simplified expression for the full kernel at non-zero
momentum transfer and give a complete analysis of its infrared properties. We
also construct a non-forward extension of the new amplitude which is infra-red
finite and satifies Ward identity constraints. We conjecture that this new
kernel has the conformal invariance properties corresponding to the holomorphic
factorization of the forward spectrum.Comment: 26 pages in latex, 4 uu-encoded ps-fig
Stability Analysis of Sum Rules for Compton Scattering
We perform a stability analysis of a recently proposed sum rule for pion
Compton scattering at fixed angle and moderate Mandelstam invariants. The sum
rule is found to be sensitive to the parameter , the contour radius
of a generalized Borel transform. A modified phenomenological model for the
continuum contribution is proposed to remove this dependence. It is shown that
the best value of the quark-hadron duality interval GeV is close
to that in the form factor case ( GeV). The application of this
new model to the pion form factor is examined. A comparison of our predictions
with those derived from a modified perturbative calculation including Sudakov
suppression is also briefly considered.Comment: 11 pages (latex), (CCUTH-93-1 preprint) 4 figs. availiable upon
request (email:[email protected]
Axions from Intersecting Branes and Decoupled Chiral Fermions at the Large Hadron Collider
We present a study of a class of effective actions which show typical
axion-like interactions, and of their possible effects at the Large Hadron
Collider. One important feature of these models is the presence of one
pseudoscalar which is a generalization of the Peccei-Quinn axion. This can be
very light and very weakly coupled, with a mass which is unrelated to its
couplings to the gauge fields, described by Wess Zumino interactions.
We discuss two independent realizations of these models, one derived from the
theory of intersecting branes and the second one obtained by decoupling one
chiral fermion per generation (one right-handed neutrino) from an anomaly-free
mother theory. The key features of this second realization are illustrated
using a simple example.
Charge assignments of intersecting branes can be easily reproduced by the
chiral decoupling approach, which remains more general at the level of the
solution of its anomaly equations. Using considerations based on its lifetime,
we show that in brane models the axion can be dark matter only if its mass is
ultralight ( eV), while in the case of fermion decoupling it can
reach the GeV region, due to the absence of fermion couplings between the heavy
Higgs and the light fermion spectrum. For a GeV axion derived from brane models
we present a detailed discussion of its production rates at the LHC.Comment: 64 pages, 15 Fig
Windows over a New Low Energy Axion
We outline some general features of possible extensions of the Standard Model
that include anomalous U(1) gauge symmetries, a certain number of axions and
their mixings with the CP-odd Higgs sector. As previously shown, after the
mixing one of the axions becomes a physical pseudoscalar (the axi-Higgs) that
can take the role of a modified QCD axion. It can be driven to be very light by
the same non-perturbative effects that are held responsible for the solution of
the strong CP-problem. At the same time the axi-Higgs has a sizeable gauge
interaction, which is not allowed to the Peccei-Quinn axion, possibly
explaining the PVLAS results. We point out that the Wess-Zumino term, typical
of these models, can be both interpreted as an anomaly inflow from higher
dimensional theories (second window) but also as a result of partial decoupling
of an extra Higgs sector (and of a fermion) that leaves behind an effective
anomalous abelian theory (first window) in a broken St\"{u}ckelberg phase. The
possibility that the axi-Higgs can be heavy, of the order of the Higgs mass or
larger, however, can't be excluded. The potentialities for the discovery of
this particle and of anomaly effects in the neutral current sector at the LHC
are briefly discussed in the context of a superstring inspired model (second
window), but with results that remain valid also if any of the two
possibilities is realized in Nature.Comment: 17 pages, 8 Figs, replaced with revised final version, to appear on
Phys.Lett.
An Anomalous Extra Z Prime from Intersecting Branes with Drell-Yan and Direct Photons at the LHC
We quantify the impact of gauge anomalies at the Large Hadron Collider by
studying the invariant mass distributions in Drell-Yan and in double prompt
photon, using an extension of the Standard Model characterized by an additional
anomalous U(1) derived from intersecting branes. The approach is rather general
and applies to any anomalous abelian gauge current. Anomalies are cancelled
using either the Wess-Zumino mechanism with suitable Peccei-Quinn-like
interactions and a Stueckelberg axion, or by the Green-Schwarz mechanism. We
compare predictions for the corresponding extra Z-prime to anomaly-free
realizations such as those involving U(1)_{B-L}. We identify the leading
anomalous corrections to both channels, which contribute at higher orders, and
compare them against the next-to-next-to-leading order (NNLO) QCD background.
Anomalous effects in these inclusive observables are found to be very small,
far below the percent level and below the size of the typical QCD corrections
quantified by NNLO K-factors.Comment: 46 pages, 36 figures, comments and citations adde
Power Corrections to QCD Sum Rules for Compton Scattering
We extend previous work on sum rules for the invariant amplitudes of pion
Compton scattering by deriving a complete lowest order perturbative spectral
function - and its leading non perturbative power corr ections - for a specific
combination of the two helicities of this process. Using some
properties of a modified version of the Borel transform, we develop a method of
calculation of the gluonic corrections which can be easily extended to other
similar reactions, such as proton Compton scattering. A preliminary comparison
of the new sum rule with the pion form factor sum rule is made.Comment: 24 pages in latex 5 figures not includes availiable upon request
(email: [email protected]), ITP-US-93-3 preprin
Drell-Yan Non-Singlet Spin Cross Sections and Spin Asymmetry to (II)
We present predictions for the non-singlet Drell-Yan longitudinal spin cross
sections and spin asymmetry, , in proton-proton collisions at large
at the RHIC energy of 200\gev at next-to-leading order QCD. The higher
order corrections to the non-singlet polarized cross section,
, are sizeable and similar to those found for the unpolarized
cross section. The non-singlet asymmetry parameter, , is very
stable against higher order corrections and is a direct measurement of the
non-singlet (i.e. valence) polarized quark distributions within the proton.Comment: 24 pages, 13 figure
The Generalized Hypergeometric Structure of the Ward Identities of CFT's in Momentum Space in
We review the emergence of hypergeometric structures (of Appell
functions) from the conformal Ward identities (CWIs) in conformal field
theories (CFTs) in dimensions . We illustrate the case of scalar 3- and
4-point functions. 3-point functions are associated to hypergeometric systems
with 4 independent solutions. For symmetric correlators they can be expressed
in terms of a single 3K integral - functions of quadratic ratios of momenta -
which is a parametric integral of three modified Bessel functions. In the
case of scalar 4-point functions, by requiring the correlator to be conformal
invariant in coordinate space as well as in some dual variables (i.e. dual
conformal invariant), its explicit expression is also given by a 3K integral,
or as a linear combination of Appell functions which are now quartic ratios of
momenta. Similar expressions have been obtained in the past in the computation
of an infinite class of planar ladder (Feynman) diagrams in perturbation
theory, which, however, do not share the same (dual conformal/conformal)
symmetry of our solutions. We then discuss some hypergeometric functions of 3
variables, which define 8 particular solutions of the CWIs and correspond to
Lauricella functions. They can also be combined in terms of 4K integral and
appear in an asymptotic description of the scalar 4-point function, in special
kinematical limits.Comment: 31 pages, 1 figure. Invited contribution to appear in: Axioms (MDPI)
"Geometric Analysis and Mathematical Physics" Ed. Sorin Dragomir, revised
final version, typos correcte
NNLO Logarithmic Expansions and Exact Solutions of the DGLAP Equations from x-Space: New Algorithms for Precision Studies at the LHC
A NNLO analysis of certain logarithmic expansions, developed for precision
studies of the evolution of the QCD parton distributions (pdf) at the Large
Hadron Collider, is presented. We elaborate on their relations to all the
solutions of the DGLAP equations that have been hitherto obtained from Mellin
space, to which are equivalent. Exact expansions, equivalent to exact solutions
of the equations, are constructed in the non-singlet sector. The algorithmic
features of our approach are also emphasized, since this method allows to
obtain numerical solutions of the evolution equations with the same accuracy of
other methods, based on Mellin space, and of brute force methods, which solve
the equations by finite differences. The implementation of our analysis allows
to compare with existing benchmarks for the evolution of the pdf's, useful for
applications at the LHC, and to extend them significantly in a systematic
fashion, especially when solutions that retain logarithmic corrections only of
a certain accuracy are searched for.Comment: 56 pages, no figure
- …