1,160 research outputs found
Effective description of brane terms in extra dimensions
We study how theories defined in (extra-dimensional) spaces with localized
defects can be described perturbatively by effective field theories in which
the width of the defects vanishes. These effective theories must incorporate a
``classical'' renormalization, and we propose a renormalization prescription a
la dimensional regularization for codimension 1, which can be easily used in
phenomenological applications. As a check of the validity of this setting, we
compare some general predictions of the renormalized effective theory with
those obtained in a particular ultraviolet completion based on deconstruction.Comment: 28 page
Heavy neutrino signals at large hadron colliders
We study the LHC discovery potential for heavy Majorana neutrino singlets in
the process pp -> W+ -> l+ N -> l+ l+ jj (l=e,mu) plus its charge conjugate.
With a fast detector simulation we show that backgrounds involving two
like-sign charged leptons are not negligible and, moreover, they cannot be
eliminated with simple sequential kinematical cuts. Using a likelihood analysis
it is shown that, for heavy neutrinos coupling only to the muon, LHC has 5
sigma sensitivity for masses up to 200 GeV in the final state mu+- mu+- jj.
This reduction in sensitivity, compared to previous parton-level estimates, is
driven by the ~ 10^2-10^3 times larger background. Limits are also provided for
e+- e+- jj and e+- mu+- jj final states, as well as for Tevatron. For heavy
Dirac neutrinos the prospects are worse because backgrounds involving two
opposite charge leptons are much larger. For this case, we study the
observability of the lepton flavour violating signal e+- mu-+ jj. As a
by-product of our analysis, heavy neutrino production has been implemented
within the ALPGEN framework.Comment: Latex 36 pages, 49 PS figures. Major extension incorporating analysis
for e+- e+-, e+- mu+- and e+- mu-+ final states. Final version to appear in
JHE
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
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
Antisymmetric tensor unparticle and the radiative lepton flavor violating decays
We study the contribution of the tensor unparticle mediation to the branching
ratios of the radiative lepton flavor violating decays and predict a
restriction region for free parameters of the scenario by using experimental
upper limits. We observe that the branching ratios of the radiative lepton
flavor violating decays are sensitive to the fundamental mass scales of the
scenario and to the scale dimension of antisymmetric tensor unparticle. We
obtain a more restricted set for the free parameters in the case of the
\mu\rightarrow e \gamma decayComment: 15 pages, 10 figure
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
Leptophobic U(1)'s and the R_b - R_c Crisis
In this paper, we investigate the possibility of explaining both the R_b
excess and the R_c deficit reported by the LEP experiments through Z-Z' mixing
effects. We have constructed a set of models consistent with a restrictive set
of principles: unification of the Standard Model (SM) gauge couplings, vector-
like additional matter, and couplings which are both generation-independent and
leptophobic. These models are anomaly-free, perturbative up to the GUT scale,
and contain realistic mass spectra. Out of this class of models, we find three
explicit realizations which fit the LEP data to a far better extent than the
unmodified SM or MSSM and satisfy all other phenomenological constraints which
we have investigated. One realization, the \eta-model coming from E_6, is
particularly attractive, arising naturally from geometrical compactifications
of heterotic string theory. This conclusion depends crucially on the inclusion
of a U(1) kinetic mixing term, whose value is correctly predicted by
renormalization group running in the E_6 model given one discrete choice of
spectra.Comment: LaTeX, 26 pages, 5 embedded EPSF figures. Version to be published in
Phys. Rev.
Understanding Radiatively Induced Lorentz-CPT Violation in Differential Regularization
We have investigated the perturbative ambiguity of the radiatively induced
Chern-Simons term in differential regularization. The result obtained in this
method contains all those obtained in other regularization schemes and the
ambiguity is explicitly characterized by an indefinite ratio of two
renormalization scales. It is argued that the ambiguity can only be eliminated
by either imposing a physical requirement or resorting to a more fundamental
principle. Some calculation techniques in coordinate space are developed in the
appendices.Comment: RevTex, 14 pages, one figure drawn by FEYNMAN, several references are
modified and a paragraph about a general choice on the mass scales is added
in page
The lepton flavor violating decays in the simplest little Higgs model
In the simplest little Higgs model the new flavor-changing interactions
between heavy neutrinos and the Standard Model leptons can generate
contributions to some lepton flavor violating decays of -boson at one-loop
level, such as , , and . We examine the decay modes, and find that the branching
ratios can reach for the three decays, which should be accessible at
the Giga option of the ILC.Comment: 12 pages, 9 figure
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