940 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
Constraining differential renormalization in abelian gauge theories
We present a procedure of differential renormalization at the one loop level
which avoids introducing unnecessary renormalization constants and
automatically preserves abelian gauge invariance. The amplitudes are expressed
in terms of a basis of singular functions. The local terms appearing in the
renormalization of these functions are determined by requiring consistency with
the propagator equation. Previous results in abelian theories, with and without
supersymmetry, are discussed in this context.Comment: 13 pages, LaTeX. Some equations corrected and a reference added.
Complete ps paper also available at http://www-ftae.ugr.es/papiros.html or
ftp://ftae3.ugr.es/pub/rmt/ugft73.p
Lorentz Violation in Extra Dimensions
In theories with extra dimensions it is well known that the Lorentz
invariance of the -dimensional spacetime is lost due to the compactified
nature of the dimensions leaving invariance only in 4d. In such theories
other sources of Lorentz violation may exist associated with the physics that
initiated the compactification process at high scales. Here we consider the
possibility of capturing some of this physics by analyzing the higher
dimensional analog of the model of Colladay and Kostelecky. In that scenario a
complete set of Lorentz violating operators arising from spontaneous Lorentz
violation, that are not obviously Planck-scale suppressed, are added to the
Standard Model action. Here we consider the influence of the analogous set of
operators which break Lorentz invariance in 5d within the Universal Extra
Dimensions picture. We show that such operators can greatly alter the
anticipated Kaluza-Klein(KK) spectra, induce electroweak symmetry breaking at a
scale related to the inverse compactification radius, yield sources of parity
violation in, e.g., 4d QED/QCD and result in significant violations of
KK-parity conservation produced by fermion Yukawa couplings, thus destabilizing
the lightest KK particle. LV in 6d is briefly discussed.Comment: 26 pages, 2 figures; additional references and discussio
Looking for signals beyond the neutrino Standard Model
Any new neutrino physics at the TeV scale must include a suppression
mechanism to keep its contribution to light neutrino masses small enough. We
review some seesaw model examples with weakly broken lepton number, and comment
on the expected effects at large colliders and in neutrino oscillations.Comment: LaTeX 10 pages, 9 PS figures. Contribution to the Proceedings of the
XXXI International School of Theoretical Physics "Matter To The Deepest"
Ustron, Poland, September 5-11, 2007. Typos correcte
Z' Decays into Four Fermions
If a new is discovered with a mass at LHC/SSC, its (rare)
decays into two charged leptons plus missing transverse energy will probe the
coupling to the lepton doublet and to , allowing
further discrimination among extended electroweak models.Comment: 9 pages plus 1 figure (not included but available), UG-FT-22/9
Impact of right-handed interactions on the propagation of Dirac and Majorana neutrinos in matter
Dirac and Majorana neutrinos can be distinguished in relativistic neutrino
oscillations if new right-handed interactions exist, due to their different
propagation in matter. We review how these new interactions affect neutrino
oscillation experiments and discuss the size of this eventually observable
effect for different oscillation channels, baselines and neutrino energies.Comment: 26 pages, 5 figure
Model-Independent Searches for New Quarks at the LHC
New vector-like quarks can have sizable couplings to first generation quarks
without conflicting with current experimental constraints. The coupling with
valence quarks and unique kinematics make single production the optimal
discovery process. We perform a model-independent analysis of the discovery
reach at the Large Hadron Collider for new vector-like quarks considering
single production and subsequent decays via electroweak interactions. An early
LHC run with 7 TeV center of mass energy and 1 fb-1 of integrated luminosity
can probe heavy quark masses up to 1 TeV and can be competitive with the
Tevatron reach of 10 fb-1. The LHC with 14 TeV center of mass energy and 100
fb-1 of integrated luminosity can probe heavy quark masses up to 3.7 TeV for
order one couplings.Comment: 37 pages, 11 figures, 7 table
Identifying Unconventional E Models at Colliders
Recently it was shown that, in the framework of superstring inspired \E
models, the presence of generation dependent discrete symmetries allows us to
construct a phenomenologically viable class of models in which the three
generations of fermions do not have the same embedding within the fundamental
{\bf 27} dimensional representation of E. In this scenario, these different
embeddings of the conventional fermions imply that the left-handed charged
leptons and the right-handed -type quarks are coupled in a non--universal
way to the new neutral gauge bosons present in these models. It
was also shown that a unique signature for this scenario, would be a deviation
from unity for the ratio of cross sections for the production of two different
lepton species in annihilation. However, several different scenarios
are possible, depending on the particular assignment chosen for ,
and and for the right-handed -type quarks, as well as on the type
of boson. Such scenarios can not be disentangled from one another by
means of cross section measurements alone. In this paper we examine the
possibility of identifying the pattern of embeddings through measurements of
polarized and unpolarized asymmetries for fermion pair-production at the 500
GeV Next Linear Collider (NLC). We show that it will be possible to
identify the different patterns of unconventional assignments for the
left-handed leptons and for the quark, for masses as large as
TeV.Comment: Plain Tex, 15 pages, + 9 figure available upon request
([email protected] or [email protected]), UM-TH 93--1
Charged Higgs-boson production in association with an electron and a neutrino at electron-positron colliders
We present results of a calculation of the cross section for the production
of a charged Higgs boson in association with an electron and a neutrino at
electron-positron colliders (e+ e- -> H+ e- nu_e-bar, H- e+ nu_e). We study
predictions for the cross section in the Minimal Supersymmetric Standard Model
(MSSM) and the Two Higgs Doublet Model (THDM), highlighting possible
differences. The process is effectively loop-induced in both models. Hence, the
cross section is expected to be strongly model-dependent. Most notably, due to
the presence of superpartners, the MSSM amplitude contains Feynman graphs of
pentagon-type, which are not present in the THDM. This is the first complete
one-loop calculation of the cross section for this process in the THDM and the
MSSM. For both models, so far, only approximate results with limited ranges of
validity were available. Our main aim here is to clarify several open questions
in the existing literature on this process. Specifically, we will discuss the
validity of the Heavy Fermion loop approximation in both models, and of the
Fermion/Sfermion loop approximation in the MSSM.Comment: 21 pages, 8 figures, 1 tabl
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