244 research outputs found
Bulk and brane radiative effects in gauge theories on orbifolds
We have computed one-loop bulk and brane mass renormalization effects in a
five-dimensional gauge theory compactified on the M_4 \times S^1/Z_2 orbifold,
where an arbitrary gauge group G is broken by the orbifold action to its
subgroup H. The space-time components of the gauge boson zero modes along the H
generators span the gauge theory on the orbifold fixed point branes while the
zero modes of the higher-dimensional components of the gauge bosons along the
G/H generators play the role of Higgs fields with respect to the gauge group H.
No quadratic divergences in the mass renormalization of the gauge and Higgs
fields are found either in the bulk or on the branes. All brane effects for the
Higgs field masses vanish (only wave function renormalization effects survive)
while bulk effects are finite and can trigger, depending on the fermionic
content of the theory, spontaneous Hosotani breaking of the brane gauge group
H. For the gauge fields we do find logarithmic divergences corresponding to
mass renormalization of their heavy Kaluza-Klein modes. Two-loop brane effects
for Higgs field masses are expected from wave function renormalization brane
effects inserted into finite bulk mass corrections.Comment: 31 pages, uses axodraw.sty and mcite.st
New Form of the T-Duality Due to the Stability of a Compact Dimension
We study behaviors of a compact dimension and the -duality, in the
presence of the wrapped closed bosonic strings. When the closed strings
interact and form another system of strings, the radius of compactification
increases. This modifies the -duality, which we call it as -duality-like.
Some effects of the -duality-like will be studied.Comment: 12 pages, Latex, no figur
Localized anomalies in orbifold gauge theories
We apply the path-integral formalism to compute the anomalies in general
orbifold gauge theories (including possible non-trivial Scherk-Schwarz boundary
conditions) where a gauge group G is broken down to subgroups H_f at the fixed
points y=y_f. Bulk and localized anomalies, proportional to \delta(y-y_f), do
generically appear from matter propagating in the bulk. The anomaly zero-mode
that survives in the four-dimensional effective theory should be canceled by
localized fermions (except possibly for mixed U(1) anomalies). We examine in
detail the possibility of canceling localized anomalies by the Green-Schwarz
mechanism involving two- and four-forms in the bulk. The four-form can only
cancel anomalies which do not survive in the 4D effective theory: they are
called globally vanishing anomalies. The two-form may cancel a specific class
of mixed U(1) anomalies. Only if these anomalies are present in the 4D theory
this mechanism spontaneously breaks the U(1) symmetry. The examples of five and
six-dimensional Z_N orbifolds are considered in great detail. In five
dimensions the Green-Schwarz four-form has no physical degrees of freedom and
is equivalent to canceling anomalies by a Chern-Simons term. In all other
cases, the Green-Schwarz forms have some physical degrees of freedom and leave
some non-renormalizable interactions in the low energy effective theory. In
general, localized anomaly cancellation imposes strong constraints on model
building.Comment: 30 pages, 4 figures. v2: reference adde
Minimal gauge-Higgs unification with a flavour symmetry
We show that a flavour symmetry a la Froggatt-Nielsen can be naturally
incorporated in models with gauge-Higgs unification, by exploiting the heavy
fermions that are anyhow needed to realize realistic Yukawa couplings. The case
of the minimal five-dimensional model, in which the SU(2)_L x U(1)_Y
electroweak group is enlarged to an SU(3)_W group, and then broken to U(1)_em
by the combination of an orbifold projection and a Scherk-Schwarz twist, is
studied in detail. We show that the minimal way of incorporating a U(1)_F
flavour symmetry is to enlarge it to an SU(2)_F group, which is then completely
broken by the same orbifold projection and Scherk-Schwarz twist. The general
features of this construction, where ordinary fermions live on the branes
defined by the orbifold fixed-points and messenger fermions live in the bulk,
are compared to those of ordinary four-dimensional flavour models, and some
explicit examples are constructed.Comment: LaTex, 37 pages, 2 figures; some clarifying comments and a few
references adde
The development of the gut microbiota in rainbow trout (<em>Oncorhynchus mykiss</em>) is affected by first feeding and diet type
An influence of the intestinal microbiota in connection to first-feeding of rainbow trout (Oncorhynchus mykiss) fry was demonstrated using Illumina HiSeq sequencing. The period from the end of yolk-sac feeding and until seven weeks post first-feeding was examined after administration of either a marine- or plant based diet with or without the probiont Pediococcus acidilactici. Before first feeding the main part of the sequence reads grouped to the genus Sediminibacterium probably originating from the surrounding water. The microbial abundance and diversity increased after first-feeding and the microbiota then changed towards Firmicutes phylum dominance for plant based fed fish and towards dominance of phylum Proteobacteria for the marine fed fish. After first-feeding, there were significantly higher abundances of Streptococcus,Leuconostoc and Weissella in fish fed the plant-based diet. The microbiota clustered separately according to the diet type, but only minor effects were seen from the probiont when using PCAanalysis. The constitutive transcription level of most examined immune genes increased during the ontogenic shift, but the results could not explain the differences in the composition of the microbiota dependent on diet treatment after first-feeding. The results suggest that the intestine of rainbow trout is colonised at an early state, but is guided in new and different directions dependent on the diet type
Non-Perturbative Renormalization Group calculation of the scalar self-energy
We present the first numerical application of a method that we have recently
proposed to solve the Non Perturbative Renormalization Group equations and
obtain the n-point functions for arbitrary external momenta. This method leads
to flow equations for the n-point functions which are also differential
equations with respect to a constant background field. This makes them, a
priori, difficult to solve. However, we demonstrate in this paper that, within
a simple approximation which turns out to be quite accurate, the solution of
these flow equations is not more complicated than that of the flow equations
obtained in the derivative expansion. Thus, with a numerical effort comparable
to that involved in the derivative expansion, we can get the full momentum
dependence of the n-point functions. The method is applied, in its leading
order, to the calculation of the self-energy in a 3-dimensional scalar field
theory, at criticality. Accurate results are obtained over the entire range of
momenta.Comment: 29 page
Gauge-Higgs Unification in Orbifold Models
Six-dimensional orbifold models where the Higgs field is identified with some
internal component of a gauge field are considered. We classify all possible
T^2/Z_N orbifold constructions based on a SU(3) electroweak gauge symmetry.
Depending on the orbifold twist, models with two, one or zero Higgs doublets
can be obtained. Models with one Higgs doublet are particularly interesting
because they lead to a prediction for the Higgs mass, which is twice the W
boson mass at leading order: m_H=2 m_W. The electroweak scale is quadratically
sensitive to the cut-off, but only through very specific localized operators.
We study in detail the structure of these operators at one loop, and identify a
class of models where they do not destabilize the electroweak scale at the
leading order. This provides a very promising framework to construct realistic
and predictive models of electroweak symmetry breaking.Comment: 27 pages, uses axodraw.sty; v2: version to appear in JHE
Big Corrections from a Little Higgs
We calculate the tree-level expressions for the electroweak precision
observables in the SU(5)/SO(5) littlest Higgs model. The source for these
corrections are the exchange of heavy gauge bosons, explicit corrections due to
non-linear sigma-model dynamics and a triplet Higgs VEV. Weak isospin violating
contributions are present because there is no custodial SU(2) global symmetry.
The bulk of these weak isospin violating corrections arise from heavy gauge
boson exchange while a smaller contribution comes from the triplet Higgs VEV. A
global fit is performed to the experimental data and we find that throughout
the parameter space the symmetry breaking scale is bounded by f > 4 TeV at 95%
C.L. Stronger bounds on f are found for generic choices of the high energy
gauge couplings. We find that even in the best case scenario one would need
fine tuning of less than a percent to get a Higgs mass as light as 200 GeV.Comment: 20 pages, 5 figures included, typos fixed, comments on the effects of
extra vector-like heavy fermions adde
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