889 research outputs found
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
Tree FCNC and non-unitarity of CKM matrix
We discuss possible signatures of the tree level FCNC, which results from the
non-unitarity of CKM matrix. We first define the unitaity step-by-step, and
possible test of the non-unitaity through the 4-value-KM parametrization. We,
then, show how the phase angle of the unitary triangle would change in case of
the vector-like down quark model. As another example of tree FCNC, we
investigate the leptophobic model and its application to the recent
mixing measurements.Comment: Talk given at Neutrino Masses and Mixings 2006 (NMM2006), Shizuoka,
Japan (December 2006
Quark mixings and flavor changing interactions with singlet quarks
Aspects of the quark mixings and flavor changing interactions are
investigated in electroweak models with singlet quarks. The effects on the
ordinary quark mixing are determined in terms of the quark masses and the
parameters describing the mixing between the ordinary quarks q and the singlet
quarks Q (q-Q mixing). Some salient features arise in the flavor changing
interactions through the q-Q mixing. The unitarity of the
Cabibbo-Kobayashi-Maskawa (CKM) matrix within the ordinary quark sector is
violated, and the flavor changing neutral currents (FCNC's) appear both in the
gauge and scalar couplings. The flavor changing interactions are calculated
appropriately in terms of the q-Q mixing parameters and the quark masses, which
really exhibit specific flavor structures. It is found that there are
reasonable ranges of the model parameters to reproduce the ordinary quark mass
hierarchy and the actual CKM structure even in the presence of q-Q mixing. Some
phenomenological effects of the singlet quarks are also discussed. In
particular, the scalar FCNC's may be more important in some cases, if the
singlet quarks as well as the extra scalar particles from the singlet Higgs
fields have masses 100 GeV -- 1 TeV.Comment: 32 pages, 7 figures, added reference
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
The Effective Lagrangian for Bulk Fermions in Models with Extra Dimensions
We compute the dimension 6 effective Lagrangian arising from the tree level
integration of an arbitrary number of bulk fermions in models with warped extra
dimensions. The coefficients of the effective operators are written in terms of
simple integrals of the metric and are valid for arbitrary warp factors, with
or without an infrared brane, and for a general Higgs profile. All relevant
tree level fermion effects in electroweak and flavor observables can be
computed using this effective Lagrangian.Comment: 22 pages. V2: typos corrected, matches published versio
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
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
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
Top effective operators at the ILC
We investigate the effect of top trilinear operators in t tbar production at
the ILC. We find that the sensitivity to these operators largely surpasses the
one achievable by the LHC either in neutral or charged current processes,
allowing to probe new physics scales up to 4.5 TeV for a centre of mass energy
of 500 GeV. We show how the use of beam polarisation and an eventual energy
upgrade to 1 TeV allow to disentangle all effective operator contributions to
the Ztt and gamma tt vertices.Comment: LaTeX 13 pages. Typos corrected. Final version in JHE
Top effective operators at the ILC
We investigate the effect of top trilinear operators in t tbar production at
the ILC. We find that the sensitivity to these operators largely surpasses the
one achievable by the LHC either in neutral or charged current processes,
allowing to probe new physics scales up to 4.5 TeV for a centre of mass energy
of 500 GeV. We show how the use of beam polarisation and an eventual energy
upgrade to 1 TeV allow to disentangle all effective operator contributions to
the Ztt and gamma tt vertices.Comment: LaTeX 13 pages. Typos corrected. Final version in JHE
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