311 research outputs found
Kahler Anomalies in Supergravity and Flux Vacua
We review the subject of Kahler anomalies in gauged supergravity, emphasizing
that field equations are inconsistent when the Kahler potential is
non-invariant under gauge transformations or when there are elementary
Fayet-Iliopoulos couplings. Flux vacua solutions of string theory with gauged
U(1) shift symmetries appear to avoid this problem. The covariant Kahler
anomalies involve tensors which are composite functions of the scalars as well
as the gauge field strength and space-time curvature tensors. Anomaly
cancellation conditions will be discussed in a sequel to this paper.Comment: 29 pages; v2: revised presentation, section on Fayet-Iliopoulos
couplings cut, effects of gauginos on anomalies included, references adde
Anomalies in field theories with extra dimensions
We give an overview of the issue of anomalies in field theories with extra
dimensions. We start by reviewing in a pedagogical way the computation of the
standard perturbative gauge and gravitational anomalies on non-compact spaces,
using Fujikawa's approach and functional integral methods, and discuss the
available mechanisms for their cancellation. We then generalize these analyses
to the case of orbifold field theories with compact internal dimensions,
emphasizing the new aspects related to the presence of orbifold singularities
and discrete Wilson lines, and the new cancellation mechanisms that are
becoming available. We conclude with a very brief discussion on global and
parity anomalies.Comment: Review article written for Int.J.Mod.Phys. A, 63 pages; v2: mistake
in subsection 4.3 corrected, some comments and references added, a few
misprints fixe
Reflections upon measurement and uncertainty in measurement
Measurements of physical quantities are the corner stone upon which we humans have built the scientific perception of the world. They characterize the scientific system of beliefs: measurements are the distinctive means to tell the scientific truth apart from any other kind of approach to knowledge. Moreover, measurements have been having a central part in the development of any sort of machine, instrument and artefact that humans have invented. Yet in industry, especially in small medium size enterprises (SMEâs), time and money spent in measurements is often seen as a necessary evil or, worst, as a waste of valuable resources. To contribute in contrasting this negative perception, a clarification of the fundamental concept of measurement is presented. The emphasis is in particular placed on uncertainty in measurement. The need for the introduction of the concept of uncertainty is justified. The theoretical implications attached to uncertainty of measurement are analyzed
Curing the Ills of Higgsless Models: the S Parameter and Unitarity
We consider various constraints on Higgsless models of electroweak symmetry
breaking based on a bulk SU(2)_L x SU(2)_R x U(1)_{B-L} gauge group in warped
space. First we show that the S parameter which is positive if fermions are
localized on the Planck brane can be lowered (or made vanishing) by changing
the localization of the light fermions. If the wave function of the light
fermions is almost flat their coupling to the gauge boson KK modes will be
close to vanishing, and therefore contributions to the S parameter will be
suppressed. At the same time the experimental bounds on such Z' and W' gauge
bosons become very weak, and their masses can be lowered to make sure that
perturbative unitarity is not violated in this theory before reaching energies
of several TeV. The biggest difficulty of these models is to incorporate a
heavy top quark mass without violating any of the experimental bounds on bottom
quark gauge couplings. In the simplest models of fermion masses a sufficiently
heavy top quark also implies an unacceptably large correction to the Zb\bar{b}
vertex and a large splitting between the KK modes of the top and bottom quarks,
yielding large loop corrections to the T-parameter. We present possible
directions for model building where perhaps these constraints could be obeyed
as well.Comment: 21 pages, LaTeX, 5 figures. References and acknowledgements adde
Anomalies on orbifolds with gauge symmetry breaking
We embed two 4D chiral multiplets of opposite representations in the 5D N=2
gauge theory compactified on an orbifold .
There are two types of orbifold boundary conditions in the extra dimension to
obtain the 4D N=1 gauge theory from the bulk: in
Type I, one has the bulk gauge group at and the unbroken gauge group at
while in Type II, one has the unbroken gauge group at both fixed
points. In both types of orbifold boundary conditions, we consider the zero
mode(s) as coming from a bulk -plet and brane fields at the fixed
point(s) with the unbroken gauge group. We check the consistency of this
embedding of fields by the localized anomalies and the localized FI terms. We
show that the localized anomalies in Type I are cancelled exactly by the
introduction of a bulk Chern-Simons term. On the other hand, in some class of
Type II, the Chern-Simons term is not enough to cancel all localized anomalies
even if they are globally vanishing. We also find that for the consistent
embedding of brane fields, there appear only the localized log FI terms at the
fixed point(s) with a U(1) factor.Comment: LaTeX file of 19 pages with no figure, published versio
Anomalies in orbifold field theories
We study the constraints on models with extra dimensions arising from local
anomaly cancellation. We consider a five-dimensional field theory with a U(1)
gauge field and a charged fermion, compactified on the orbifold S^1/(Z_2 x
Z_2'). We show that, even if the orbifold projections remove both fermionic
zero modes, there are gauge anomalies localized at the fixed points. Anomalies
naively cancel after integration over the fifth dimension, but gauge invariance
is broken, spoiling the consistency of the theory. We discuss the implications
for realistic supersymmetric models with a single Higgs hypermultiplet in the
bulk, and possible cancellation mechanisms in non-minimal models.Comment: 10 pages, 2 figures, LaTex; v2: final version to be published in
Phys. Lett.
Vector/tensor duality in the five dimensional supersymmetric Green-Schwarz mechanism
The five dimensional version of the Green-Schwarz mechanism can be invoked to
cancel U(1) anomalies on the boundaries of brane world models. In five
dimensions there are two dual descriptions that employ either a two-form tensor
field or a vector field. We present the supersymmetric extensions of these dual
theories using four dimensional N=1 superspace. For the supersymmetrization of
the five dimensional Chern-Simons three form this requires the introduction of
a new chiral Chern-Simons multiplet. We derive the supersymmetric vector/tensor
duality relations and show that not only is the usual one/two-form duality
modified, but that there is also an interesting duality relation between the
scalar components. Furthermore, the vector formulation always contains singular
boundary mass terms which are absent in the tensor formulation. This apparent
inconsistency is resolved by showing that in either formulation the four
dimensional anomalous U(1) mass spectrum is identical, with the lowest lying
Kaluza-Klein mode generically obtaining a finite nonzero mass.Comment: 1+35 pages, LaTeX, 1 figure, references added, typos correcte
Non-local symmetry breaking in Kaluza-Klein theories
Scherk-Schwarz gauge symmetry breaking of a D-dimensional field theory model
compactified on a circle is analyzed. It is explicitly shown that forbidden
couplings in the unbroken theory appear in the one-loop effective action only
in a non-local way, implying that they are finite at all orders in perturbation
theory. This result can be understood as a consequence of the local gauge
symmetry, but it holds true also in the global limit.Comment: v2: Wilson loop contributions and generalization to SU(N) included;
references added. v3: version to appear in Phys. Rev. Let
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