201 research outputs found
Measurements of neutral vector resonance in Higgsless models at the LHC
In Higgsless models, new vector resonances appear to restore the unitarity of
the W_L W_L scattering amplitude without the Higgs boson. In the ideal
delocalized three site Higgsless model, one of large prodcution cross section
of the neutral vector resonance (Z') at the Large Hadron Collider is the
W-associated production, pp \to Z'W \to WWW. Although the dileptonic decay
channnel, l\nu l'\nu 'jj, is experimentally clean to search for the Z' signals,
it is difficult to reconstruct the Z' invariant mass due to the two neutrinos
in the final state. We study collider signatures of Z' using the
M_{T2}-Assisted On-Shell (MAOS) reconstruction of the missing neutrino momenta.
We show the prospect of the Z' mass determination in the channel, l\nu l'\nu
'jj, at the Large Hadron Collider.Comment: 16 pages, 6 figures, 5 tables; v2: references added, minor
corrections, version published in JHE
R-parity violating resonant stop production at the Large Hadron Collider
We have investigated the resonant production of a stop at the Large Hadron
Collider, driven by baryon number violating interactions in supersymmetry. We
work in the framework of minimal supergravity models with the lightest
neutralino being the lightest supersymmetric particle which decays within the
detector. We look at various dilepton and trilepton final states, with or
without b-tags. A detailed background simulation is performed, and all possible
decay modes of the lighter stop are taken into account. We find that higher
stop masses are sometimes easier to probe, through the decay of the stop into
the third or fourth neutralino and their subsequent cascades. We also comment
on the detectability of such signals during the 7 TeV run, where, as expected,
only relatively light stops can be probed. Our conclusion is that the resonant
process may be probed, at both 10 and 14 TeV, with the R-parity violating
coupling {\lambda}"_{312} as low as 0.05, for a stop mass of about 1 TeV. The
possibility of distinguishing between resonant stop production and
pair-production is also discussed.Comment: 20 pages, 4 figures, 6 tables; Version accepted by JHE
Light neutralino dark matter in the MSSM and its implication for LHC searches for staus
It was shown in a previous study that a lightest neutralino with mass below
30 GeV was severely constrained in the minimal supersymmetric standard model
(MSSM), unless it annihilates via a light stau and thus yields the observed
dark matter abundance. In such a scenario, while the stau is the
next-to-lightest supersymmetric particle (NLSP), the charginos and the other
neutralinos as well as sleptons of the first two families are also likely to be
not too far above the mass bounds laid down by the Large Electron Positron
(LEP) collider. As the branching ratios of decays of the charginos and the
next-to-lightest neutralino into staus are rather large, one expects
significant rates of tau-rich final states in such a case. With this in view,
we investigate the same-sign ditau and tri-tau signals of this scenario at the
Large Hadron Collider (LHC) for two MSSM benchmark points corresponding to
light neutralino dark matter. The associated signal rates for these channels
are computed, for the centre-of-mass energy of 14 TeV. We find that both
channels lead to appreciable rates if the squarks and the gluino are not too
far above a TeV, thus allowing to probe scenarios with light neutralinos in the
14 TeV LHC run with 10-100 fb^{-1}.Comment: 19p, 4 Fig
Muon to electron conversion in the Littlest Higgs model with T-parity
Little Higgs models provide a natural explanation of the little hierarchy
between the electroweak scale and a few TeV scale, where new physics is
expected. Under the same inspiring naturalness arguments, this work completes a
previous study on lepton flavor-changing processes in the Littlest Higgs model
with T-parity exploring the channel that will eventually turn out to be the
most sensitive, \mu-e conversion in nuclei. All one-loop contributions are
carefully taken into account, results for the most relevant nuclei are provided
and a discussion of the influence of the quark mixing is included. The results
for the Ti nucleus are in good agreement with earlier work by Blanke et al.,
where a degenerate mirror quark sector was assumed. The conclusion is that,
although this particular model reduces the tension with electroweak precision
tests, if the restrictions on the parameter space derived from lepton flavor
violation are taken seriously, the degree of fine tuning necessary to meet
these constraints also disfavors this model.Comment: 26 pages, 7 figures, 4 tables; discussion improved, results
unchanged, one reference added, version to appear in JHE
Bridging flavour violation and leptogenesis in SU(3) family models
We reconsider basic, in the sense of minimal field content, Pati-Salam x
SU(3) family models which make use of the Type I see-saw mechanism to reproduce
the observed mixing and mass spectrum in the neutrino sector. The goal of this
is to achieve the observed baryon asymmetry through the thermal decay of the
lightest right-handed neutrino and at the same time to be consistent with the
expected experimental lepton flavour violation sensitivity. This kind of models
have been previously considered but it was not possible to achieve a
compatibility among all of the ingredients mentioned above. We describe then
how different SU(3) messengers, the heavy fields that decouple and produce the
right form of the Yukawa couplings together with the scalars breaking the SU(3)
symmetry, can lead to different Yukawa couplings. This in turn implies
different consequences for flavour violation couplings and conditions for
realizing the right amount of baryon asymmetry through the decay of the
lightest right-handed neutrino. Also a highlight of the present work is a new
fit of the Yukawa textures traditionally embedded in SU(3) family models.Comment: 26 pages, 5 figures, Some typos correcte
Rare B Decays with a HyperCP Particle of Spin One
In light of recent experimental information from the CLEO, BaBar, KTeV, and
Belle collaborations, we investigate some consequences of the possibility that
a light spin-one particle is responsible for the three Sigma^+ -> p mu^+ mu^-
events observed by the HyperCP experiment. In particular, allowing the new
particle to have both vector and axial-vector couplings to ordinary fermions,
we systematically study its contributions to various processes involving
b-flavored mesons, including B-Bbar mixing as well as leptonic, inclusive, and
exclusive B decays. Using the latest experimental data, we extract bounds on
its couplings and subsequently estimate upper limits for the branching ratios
of a number of B decays with the new particle. This can serve to guide
experimental searches for the particle in order to help confirm or refute its
existence.Comment: 17 pages, 3 figures; discussion on spin-0 case modified, few errors
corrected, main conclusions unchange
Simultaneous Extraction of the Fermi constant and PMNS matrix elements in the presence of a fourth generation
Several recent studies performed on constraints of a fourth generation of
quarks and leptons suffer from the ad-hoc assumption that 3 x 3 unitarity holds
for the first three generations in the neutrino sector. Only under this
assumption one is able to determine the Fermi constant G_F from the muon
lifetime measurement with the claimed precision of G_F = 1.16637 (1) x 10^-5
GeV^-2. We study how well G_F can be extracted within the framework of four
generations from leptonic and radiative mu and tau decays, as well as from K_l3
decays and leptonic decays of charged pions, and we discuss the role of lepton
universality tests in this context. We emphasize that constraints on a fourth
generation from quark and lepton flavour observables and from electroweak
precision observables can only be obtained in a consistent way if these three
sectors are considered simultaneously. In the combined fit to leptonic and
radiative mu and tau decays, K_l3 decays and leptonic decays of charged pions
we find a p-value of 2.6% for the fourth generation matrix element |U_{e 4}|=0
of the neutrino mixing matrix.Comment: 19 pages, 3 figures with 16 subfigures, references and text added
refering to earlier related work, figures and text in discussion section
added, results and conclusions unchange
Constraints from muon g-2 and LFV processes in the Higgs Triplet Model
Constraints from the muon anomalous magnetic dipole moment and lepton flavor
violating processes are translated into lower bounds on v_Delta*m_H++ in the
Higgs Triplet Model by considering correlations through the neutrino mass
matrix. The discrepancy of the sign of the contribution to the muon anomalous
magnetic dipole moment between the measurement and the prediction in the model
is clarified. It is shown that mu to e gamma, tau decays (especially, tau to mu
e e), and the muonium conversion can give a more stringent bound on
v_Delta*m_H++ than the bound from mu to eee which is expected naively to give
the most stringent one.Comment: 18 pages, 16 figure
New physics searches at near detectors of neutrino oscillation experiments
We systematically investigate the prospects of testing new physics with tau
sensitive near detectors at neutrino oscillation facilities. For neutrino beams
from pion decay, from the decay of radiative ions, as well as from the decays
of muons in a storage ring at a neutrino factory, we discuss which effective
operators can lead to new physics effects. Furthermore, we discuss the present
bounds on such operators set by other experimental data currently available.
For operators with two leptons and two quarks we present the first complete
analysis including all relevant operators simultaneously and performing a
Markov Chain Monte Carlo fit to the data. We find that these effects can induce
tau neutrino appearance probabilities as large as O(10^{-4}), which are within
reach of forthcoming experiments. We highlight to which kind of new physics a
tau sensitive near detector would be most sensitive.Comment: 20 pages, 2 figures, REVTeX
Lepton Number Violation from Colored States at the LHC
The possibility to search for lepton number violating signals at the Large
Hadron Collider (LHC) in the colored seesaw scenario is investigated. In this
context the fields that generate neutrino masses at the one-loop level are
scalar and Majorana fermionic color-octets of SU(3). Due to the QCD strong
interaction these states may be produced at the LHC with a favorable rate. We
study the production mechanisms and decays relevant to search for lepton number
violation signals in the channels with same-sign dileptons. In the simplest
case when the two fermionic color-octets are degenerate in mass, one could use
their decays to distinguish between the neutrino spectra. We find that for
fermionic octets with mass up to about 1 TeV the number of same-sign dilepton
events is larger than the standard model background indicating a promising
signal for new physics.Comment: minor corrections, added reference
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