341 research outputs found
Subtleties in the beta function calculation of N=1 supersymmetric gauge theories
We investigate some peculiarities in the calculation of the two-loop
beta-function of supersymmetric models which are intimately related to
the so-called "Anomaly Puzzle". There is an apparent paradox when the
computation is performed in the framework of the covariant derivative
background field method. In this formalism, it is obtained a finite two-loop
effective action, although a non-null coefficient for the beta-function is
achieved by means of the renormalized two-point function in the background
field. We show that if the standard background field method is used, this
two-point function has a divergent part which allows for the calculation of the
beta-function via the renormalization constants, as usual. Therefore, we
conjecture that this paradox has its origin in the covariant supergraph
formalism itself, possibly being an artifact of the rescaling anomaly.Comment: Few misprintings corrected and comments added. To meet the version to
be published at European Physical Journal
Advances towards the systematization of calculations with Implicit Regularization
There is currently a high demand for theoretical predictions for processes at
next-to-next-to-leading order (NNLO) and beyond, mainly due to the large amount
of data which has already been collected at LHC. This requires practical
methods that meet the physical requirements of the models under study. We
develop a new procedure for applying Constrained Implicit Regularization which
simplifies the calculation of amplitudes, including finite parts. The algebraic
identities to separate the divergent parts free from the external momenta are
used after the Feynman parametrization. These algebraic identities establish a
set of scale relations which are always the same and do not need to be
calculated in each situation. This procedure unifies the calculations in
massive and non-massive models in an unique procedure. We establish a
systematization of the calculation of one-loop amplitudes and extend the
procedure for higher-loop orders.Comment: 25 pages, 4 figure
Ultraviolet and Infrared Divergences in Implicit Regularization: a Consistent Approach
Implicit Regularization is a 4-dimensional regularization initially conceived
to treat ultraviolet divergences. It has been successfully tested in several
instances in the literature, more specifically in those where Dimensional
Regularization does not apply. In the present contribution we extend the method
to handle infrared divergences as well. We show that the essential steps which
rendered Implicit Regularization adequate in the case of ultraviolet
divergences have their counterpart for infrared ones. Moreover we show that a
new scale appears, typically an infrared scale which is completely independent
of the ultraviolet one. Examples are given.Comment: 9 pages, version to appear in Mod. Phys. Lett.
Residual gauge-invariance in a massive Lorentz-violating extension of QED
We reassess an alternative CPT-odd electrodynamics obtained from a
Palatini-like procedure. Starting from a more general situation, we analyze the
physical consistency of the model for different values of the parameter
introduced in the mass tensor. We show that there is a residual gaugeinvariance
in the model if the local transformation is taken to vary only in the direction
of the Lorentz-breaking vector
Regularization Independent Analysis of the Origin of Two Loop Contributions to N=1 Super Yang-Mills Beta Function
We present a both ultraviolet and infrared regularization independent
analysis in a symmetry preserving framework for the N=1 Super Yang-Mills beta
function to two loop order. We show explicitly that off-shell infrared
divergences as well as the overall two loop ultraviolet divergence cancel out
whilst the beta function receives contributions of infrared modes.Comment: 7 pages, 2 figures, typos correcte
Chiral Anomaly and CPT invariance in an implicit momentum space regularization framework
This is the second in a series of two contributions in which we set out to
establish a novel momentum space framework to treat field theoretical
infinities in perturbative calculations when parity-violating objects occur.
Since no analytic continuation on the space-time dimension is effected, this
framework can be particularly useful to treat dimension-specific theories.
Moreover arbitrary local terms stemming from the underlying infinities of the
model can be properly parametrized. We (re)analyse the undeterminacy of the
radiatively generated CPT violating Chern-Simons term within an extended
version of and calculate the Adler-Bardeen-Bell-Jackiw triangle anomaly
to show that our framework is consistent and general to handle the subtleties
involved when a radiative corretion is finite.Comment: 16 pages, LaTeX, version to appear in PR
Consistency analysis of a nonbirefringent Lorentz-violating planar model
In this work analyze the physical consistency of a nonbirefringent
Lorentz-violating planar model via the analysis of the pole structure of its
Feynman propagators. The nonbirefringent planar model, obtained from the
dimensional reduction of the CPT-even gauge sector of the standard model
extension, is composed of a gauge and a scalar fields, being affected by
Lorentz-violating (LIV) coefficients encoded in the symmetric tensor
. The propagator of the gauge field is explicitly evaluated
and expressed in terms of linear independent symmetric tensors, presenting only
one physical mode. The same holds for the scalar propagator. A consistency
analysis is performed based on the poles of the propagators. The isotropic
parity-even sector is stable, causal and unitary mode for .
On the other hand, the anisotropic sector is stable and unitary but in general
noncausal. Finally, it is shown that this planar model interacting with a
Higgs field supports compactlike vortex configurations.Comment: 11 pages, revtex style, final revised versio
Induced Lorentz- and CPT-violating Chern-Simons term in QED: Fock-Schwinger proper time method
Using the Fock-Schwinger proper time method, we calculate the induced
Chern-Simons term arising from the Lorentz- and CPT-violating sector of quantum
electrodynamics with a term. Our
result to all orders in coincides with a recent linear-in- calculation
by Chaichian et al. [hep-th/0010129 v2]. The coincidence was pointed out by
Chung [Phys. Lett. {\bf B461} (1999) 138] and P\'{e}rez-Victoria [Phys. Rev.
Lett. {\bf 83} (1999) 2518] in the standard Feynman diagram calculation with
the nonperturbative-in- propagator.Comment: 11 pages, no figur
Aspects of Causality and Unitarity and Comments on Vortex-like Configurations in an Abelian Model with a Lorentz-Breaking Term
The gauge-invariant Chern-Simons-type Lorentz- and CPT-breaking term is here
reassessed and a spin-projector method is adopted to account for the breaking
(vector) parameter. Issues like causality, unitarity, spontaneous
gauge-symmetry breaking and vortex formation are investigated, and consistency
conditions on the external vector are identified.Comment: 12 pages, late
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