94 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
Trace Anomaly, Massless Scalars and the Gravitational Coupling of QCD
The anomalous effective action describing the coupling of gravity to a
non-abelian gauge theory can be determined by a variational solution of the
anomaly equation, as shown by Riegert long ago. It is given by a nonlocal
expression, with the nonlocal interaction determined by the Green's function of
a conformally covariant operator of fourth order. In recent works it has been
shown that this interaction is mediated by a simple pole in an expansion around
a Minkowski background, coupled in the infrared in the massless fermion limit.
This result relies on the local formulation of the original action in terms of
two auxiliary fields, one physical scalar and one ghost, which take the role of
massless composite degrees of freedom. In the gravity case, the two scalars
have provided ground in favour of some recent proposals of an infrared approach
to the solution of the dark energy problem, entirely based on the behaviour of
the vacuum energy at the QCD phase transition. As a test of this general
result, we perform a complete one-loop computation of the effective action
describing the coupling of a non-abelian gauge theory to gravity. We confirm
the appearance of an anomaly pole which contributes to the trace part of the
correlator and of extra poles in its trace-free part, in the quark and
gluon sectors, describing the coupling of the energy momentum tensor () to
two non abelian gauge currents ().Comment: 25 pages, 9 figures. Revised final version, to be published on Phys.
Rev.
Inflation, Leptogenesis, and Yukawa Quasi-Unification within a Supersymmetric Left-Right Model
A simple extension of the minimal left-right symmetric supersymmetric grand
unified theory model is constructed by adding two pairs of superfields. This
naturally violates the partial Yukawa unification predicted by the minimal
model. After including supergravity corrections, we find that this extended
model naturally supports hilltop F-term hybrid inflation along its trivial
inflationary path with only a very mild tuning of the initial conditions. With
a convenient choice of signs of the terms in the Kahler potential, we can
reconcile the inflationary scale with the supersymmetric grand unified theory
scale. All the current data on the inflationary observables are readily
reproduced. Inflation is followed by non-thermal leptogenesis via the decay of
the right-handed neutrinos emerging from the decay of the inflaton and any
possible washout of the lepton asymmetry is avoided thanks to the violation of
partial Yukawa unification. The extra superfields also assist us in reducing
the reheat temperature so as to satisfy the gravitino constraint. The observed
baryon asymmetry of the universe is naturally reproduced consistently with the
neutrino oscillation parameters.Comment: 20 pages including 4 figure
Trilinear Gauge Interactions in Extensions of the Standard Model and Unitarity
We summarize recent work on the characterization of anomaly poles in
connection with the field-theory interpretation of the Green-Schwarz mechanism
of anomaly cancellation and on their effective field theories, stressing on the
properties of the anomaly vertex in two representations, the Rosenberg and the
Longitudinal/Transverse. The presence of polar amplitudes in these theories
causes a violation of unitarity at high energy which is cured by the exchange
of the axion. We comment on the possible physical implications of this
mechanism.Comment: 5 pages, 6 Figs. Presented at IFAE 2009, Bari, 15-17 April 2009,
Ital
Anomaly Poles as Common Signatures of Chiral and Conformal Anomalies
One feature of the chiral anomaly, analyzed in a perturbative framework, is
the appearance of massless poles which account for it. They are identified by a
spectral analysis of the anomaly graph and are usually interpreted as being of
an infrared origin. Recent investigations show that their presence is not just
confined in the infrared, but that they appear in the effective action under
the most general kinematical conditions, even if they decouple in the infrared.
Further studies reveal that they are responsible for the non-unitary behaviour
of these theories in the ultraviolet (UV) region. We extend this analysis to
the case of the conformal anomaly, showing that the effective action describing
the interaction of gauge fields with gravity is characterized by anomaly poles
that give the entire anomaly and are decoupled in the infrared (IR), in
complete analogy with the chiral case. This complements a related analysis by
Giannotti and Mottola on the trace anomaly in gravity, in which an anomaly pole
has been identified in the corresponding correlator using dispersion theory in
the IR. Our extension is based on an exact computation of the off-shell
correlation function involving an energy-momentum tensor and two vector
currents (the gauge-gauge-graviton vertex) which is responsible for the
appearance of the anomaly.Comment: 13 pages, 4 figures revised final version, to appear on Phys. Lett.
The Trace Anomaly and the Gravitational Coupling of an Anomalous U(1)
We extend a previous computation of the TJJ correlator, involving the
energy-momentum tensor of an abelian gauge theory and two vector currents, to
the case of mixed axial-vector/vector currents. The study is performed in
analogy to the case of the vertex for the chiral anomaly. We derive the
general structure of the anomalous Ward identities and provide explicit tests
of their consistency using Dimensional Reduction. Mixed massive correlators of
the form are shown to vanish both by Ward identities and by
C-invariance. The result is characterized by the appearance of massless scalar
degrees of freedom in the coupling of chiral and vector theories to gravity,
affecting both the soft and the ultraviolet region of the vertex. This is in
agreement with previous studies of the effective action of gauge and conformal
anomalies in QED and QCD.Comment: 30 pages, 3 figure
Dilaton Interactions and the Anomalous Breaking of Scale Invariance of the Standard Model
We discuss the main features of dilaton interactions for fundamental and
effective dilaton fields. In particular, we elaborate on the various ways in
which dilatons can couple to the Standard Model and on the role played by the
conformal anomaly as a way to characterize their interactions. In the case of a
dilaton derived from a metric compactification (graviscalar), we present the
structure of the radiative corrections to its decay into two photons, a photon
and a , two gauge bosons and two gluons, together with their
renormalization properties. We prove that, in the electroweak sector, the
renormalization of the theory is guaranteed only if the Higgs is conformally
coupled. For such a dilaton, its coupling to the trace anomaly is quite
general, and determines, for instance, an enhancement of its decay rates into
two photons and two gluons. We then turn our attention to theories containing a
non-gravitational (effective) dilaton, which, in our perturbative analysis,
manifests as a pseudo-Nambu Goldstone mode of the dilatation current ().
The infrared coupling of such a state to the two-photons and to the two-gluons
sector, and the corresponding anomaly enhancements of its decay rates in these
channels, is critically analyzed.Comment: Revised version, 42 pages, 5 figure
Anomalous U(1) Models in Four and Five Dimensions and their Anomaly Poles
We analyze the role played by anomaly poles in an anomalous gauge theory by
discussing their signature in the corresponding off-shell effective action. The
origin of these contributions, in the most general kinematical case, is
elucidated by performing a complete analysis of the anomaly vertex at
perturbative level. We use two independent (but equivalent) representations:
the Rosenberg representation and the longitudinal/transverse (L/T)
parameterization, used in recent studies of of the muon and in the proof
of non-renormalization theorems of the anomaly vertex. The poles extracted from
the L/T parameterization do not couple in the infrared for generic anomalous
vertices, as in Rosenberg, but we show that they are responsible for the
violations of unitarity in the UV region, using a class of pole-dominated
amplitudes. We conclude that consistent formulations of anomalous models
require necessarily the cancellation of these polar contributions. Establishing
the UV significance of these terms provides a natural bridge between the
anomalous effective action and its completion by a nonlocal theory. Some
additional difficulties with unitarity of the mechanism of inflow in extra
dimensional models with an anomalous theory on the brane, due to the presence
of anomaly poles, are also pointed out.Comment: Revised final version, to appear on JHE
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
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