1,101 research outputs found

### Reconstruction of the Extended Gauge Structure from $Z'$ Observables at Future Colliders

The discovery of a new neutral gauge boson $Z'$ with a mass in the TeV region
would allow for determination of gauge couplings of the $Z'$ to ordinary quarks
and leptons in a model independent way. We show that these couplings in turn
would allow us to determine the nature of the extended gauge structure. As a
prime example we study the $E_6$ group. In this case two discrete constraints
on experimentally determined couplings have to be satisfied. If so, the
couplings would then uniquely determine the two parameters, $\tan \beta$ and
$\delta$, which fully specify the nature of the $Z'$ within $E_6$. If the $Z'$
is part of the $E_6$ gauge structure, then for $M_{Z'}=1$ TeV $\tan \beta$ and
$\delta$ could be determined to around $10\%$ at the future colliders. The NLC
provides a unique determination of the two constraints as well as of $\tan
\beta$ and $\delta$, though with slightly larger error bars than at the LHC. On
the other hand, since the LHC primarily determines three out of four normalized
couplings, it provides weaker constraints for the underlying gauge structure.Comment: 14 pages LaTeX using RevTeX and psfig.sty. TeX source and 3 PS
figures, tarred, compressed and uuencoded; also available via anonymous ftp
to ftp://dept.physics.upenn.edu/pub/Cvetic/UPR-636-T

### Impact of extra particles on indirect Z' limits

We study the possibility of relaxing the indirect limits on extra neutral
vector bosons by their interplay with additional new particles. They can be
systematically weakened, even below present direct bounds at colliders, by the
addition of more vector bosons and/or scalars designed for this purpose.
Otherwise, they appear to be robust.Comment: Latex 23 pages, 8 eps figures. Minor changes, version published in
Phys. Rev.

### Quark mixing: determination of top couplings

The top flavour-changing neutral couplings can be large in extended models
with vector-like quarks. In the next decade(s) the CERN Large Hadron Collider
will allow to measure (bound) them with a precision of few per cent.Comment: LaTeX 15 pages,19 PS figures, uses epsfig.sty. To be published in
Acta Physica Polonica

### Discrete regularisation of localised kinetic terms

We investigate the behaviour of 5d models with general brane kinetic terms by
discretising the extra dimension. We show that in the continuum limit the
Kaluza-Klein masses and wave functions are in general nonanalytic in the
coefficients of brane terms.Comment: Presented at the 7th DESY Workshop on Elementary Particle Theory
``Loops and Legs in Quantum Field Theory'', Zinnowitz, April 25-30, 200

### Light neutrino propagation in matter without heavy neutrino decoupling

We review the propagation of light neutrinos in matter assuming that their
mixing with heavy neutrinos is close to present experimental limits. The
phenomenological implications of the non-unitarity of the light neutrino mixing
matrix for neutrino oscillations are discussed. In particular we show that the
resonance effect in neutrino propagation in matter persists, but for slightly
modified values of the parameters and with the maximum reduced by a small
amount proportional to the mixing between light and heavy neutrinos squared.Comment: 11 pages, 1 figure, contribution to Stefan Pokorski 60th birthda

### Physical Parameters and Renormalization of U(1)_a x U(1)_b Models

We analize the structure of models with unbroken and spontaneously broken
U(1)_a x U(1)_b gauge symmetry. We show that the quantum corrections to the 2N
gauge charges, with N = #fermions + #scalars, can be absorbed in the
redefinition of three independent gauge couplings (g_a,g_b and g_ab). We
establish the (one-loop) conditions on the matter cotent for g_ab= = 0 (a value
usually assumed in the literature) and we show that in the minimal extensions
of the Standard Model with an extra U(1) symmetry the choice g_ab = 0 is not
stable under radiative corrections induced by the standard Higgs fields.
Moreover, g_ab = 0 to all orders seems to require an exact symmetry. The
spontaneous breaking of the gauge symmetry induces further mixing between the
two gauge bosons and introduces a fourth independent physical parameter. A
consequence of our analysis is that the usual tree-level description with only
three physical parameters (i.e., two gauge couplings and one gauge boson mixing
angle) is not in general a justified zero order limit of the treatment
including radiative corrections.Comment: 24 pages, tex, 1 figur

### Low energy constraints on orbifold models

We review the low energy limits on Kaluza-Klein excitations in orbifold
models. New vector-like quarks, as well as new Z' gauge bosons, can be
accommodated with masses observable at large colliders.Comment: Presented at RADCOR 2002, to appear in the proceeding

### Differential Renormalization of Gauge Theories

The scope of constrained differential renormalization is to provide
renormalized expressions for Feynman graphs, preserving at the same time the
Ward identities of the theory. It has been shown recently that this can be done
consistently at least to one loop for abelian and non-abelian gauge theories.
We briefly review these results, evaluate as an example the gluon selfenergy in
both coordinate and momentum space, and comment on anomalies.Comment: LaTex, 8 pages with 1 ps figures, talk given at the Zeuthen Workshop
on Elementary Particle Physics "Loops and Legs in Gauge Theories",
Rheinsberg, Germany, April 19-24, 1998, to appear in Acta Physica Polonica

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