4,306 research outputs found
Reconstruction of the Extended Gauge Structure from Observables at Future Colliders
The discovery of a new neutral gauge boson with a mass in the TeV region
would allow for determination of gauge couplings of the 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 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, and
, which fully specify the nature of the within . If the
is part of the gauge structure, then for TeV and
could be determined to around at the future colliders. The NLC
provides a unique determination of the two constraints as well as of and , 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
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
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.
Electroweak constraints on new physics
We briefly review the limits on new interactions implied by electroweak
precision data. Special attention is payed to the bounds on the Higgs boson
mass. We also comment on the required cancellation among the new contributions
to precisely measured electroweak observables in any Standard Model extension,
if the new particles have to evade the indirect constraints on their couplings
and masses but still remain at the LHC reach.Comment: Latex 4 pages, 1 table, 2 figures. To appear in the proceedings of
10th Hellenic School and Workshops on Elementary Particle Physics and Gravity
(Corfu 2010), Corfu, Greece, Aug 29 - Sep 19, 201
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
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
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
Neutrino physics beyond neutrino masses
We briefly summarise the current status of neutrino masses and mixing, paying
special attention to the prospects for observing new leptonic interactions.Comment: Latex 6 pages. To appear in the proceedings of 9th Hellenic School
and Workshops on Elementary Particle Physics and Gravity (CORFU2009), Corfu,
Greece, August 30-September 20, 2009
Combined analysis of Z' -> t tbar and Z' -> t tbar j production for vector resonance searches at LHC
We have implemented a code for Z' + n jets production in ALPGEN, with Z'
decays into several final states, including l+ l- and t tbar. The MLM
prescription is used for matching the matrix element with the parton shower,
including in this way the leading soft and collinear corrections. In order to
demonstrate its capabilities, we perform a combined analysis of Z' -> t tbar
and Z' -> t tbar j production for a heavy leptophobic gauge boson. It is found
that the effect of the extra jet cannot only be accounted for by a K factor
multiplying the leading-order cross section. In fact, the combined analysis for
Z' -> t tbar and Z' -> t tbar j presented improves the statistical significance
of the signal by 25% (8.55 sigma versus 6.77 sigma for a Z' mass of 1 TeV),
compared with the results of an inclusive analysis carried out on the same
sample of t tbar + t tbar j events.Comment: LaTeX 17 pages, 13 PS figure
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
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