339 research outputs found
Mu + N --> Tau + N at a Muon or Neutrino Factory
The experimental discovery of large nu_mu-nu_tau mixing indicates that
analogous mixing in the charged lepton sector could be substantial. We consider
the possibility that if a high intensity muon beam, perhaps at the early stages
of a muon or neutrino factory, strikes a nuclear target, then conversion of
some of the muons into tau leptons could occur (similar to the conversion of
muons to electrons at MECO). Using current experimental limits on rare tau
decays to bound the size of the relevant operators, we find that a 50 GeV muon
beam, with 10^20 muons on target per year, could yield as many as 10^7 mu + N
--> tau + N events per year. Backgrounds could be substantial, and we comment
on the possibility of detection of this process.Comment: Paragraph on theoretical models added. Version to be published in
Phys. Rev.
Production and Decays of bosons at the LHC
With the advent of the LHC, it is important to devise clear tests for Physics
Beyond the Standard Model. Such physics could manifest itself in the form of
new charged bosons, whose presence is most naturally occurring in left-right
symmetric models (LRSM). We analyze the single boson production in an
asymmetric left-right model, where the left and right quark mixing matrices are
not constrained to be equal. We investigate the cross sections as well as
branching ratios of bosons at the LHC, including constraints from low
energy phenomenology. We then look for most likely signals in production. Including the background, we find that LHC could
show significant signals for the new charged bosons. We compare our results
throughout with the manifest left-right symmetric model and comment on
similarities and differences.Comment: 22 pages, 9 figure
Neutrino Masses in the Effective Rank-5 Subgroups of E_6 I: Non-supersymmetric Case
The neutral fermion sectors of E_6-inspired low energy models, in particular
the Alternative Left-Right and Inert models, are considered in detail within
the non-supersymmetric scenario. We show that in their simplest form, these
models always predict, for each generation, the lightest neutrino to be an
SU(2)_L singlet, as well as two extra neutrinos with masses of the order of the
up-quark mass. In order to recover Standard Model phenomenology, additional
assumptions in the form of discrete symmetries and/or new interactions are
needed. These are classified as the Discrete Symmetry (DS), Higher Dimensional
Operators (HDO), and Additional Neutral Fermion (ANF) methods. The DS method
can solve the problem, but requires additional Higgs doublets that do not get
vacuum expectation values. The HDO method predicts no sterile neutrino, and
that the active neutrinos mix with a heavy isodoublet neutrino, thus slightly
suppressing the couplings of active neutrinos, with interesting
phenomenological implications. The ANF method also predicts this suppression,
and also naturally includes one or more "sterile" neutrinos. This scenario
allows the existence of sterile neutrino(s) in either a 3+1 or 2+2 structure at
low energies, which are favored by the LSND result.Comment: 25 pages, 1 figure; typos corrected, version to be published in
Physical Review
Neutrino Masses in the Effective Rank-5 Subgroups of E_6 II: Supersymmetric Case
We present a complete analysis of the neutral fermion sector of
supersymmetric E_6-inspired low energy models containing an extra SU(2),
concentrating on the Alternate Left-Right and Inert models. We show that the
R-parity conserving scenario always exhibits a large Dirac mass for \nu_L with
maximal mixing with an isosinglet neutrino, and that R-parity violating
scenarios do not change the picture other than allowing further mixing with
another isosinglet. In order to recover Standard Model phenomenology,
additional assumptions in the form of discrete symmetries and/or new
interactions are needed. We introduce and investigate Discrete Symmetry method
and Higher Dimensional Operators as mechanisms for solving the neutrino mass
and mixing problems in these models.Comment: 27 pages, 2 figures; typos correted, version to be published in
Physical Review
Collider Effects of Unparticle Interactions in Multiphoton Signals
A new model of physics, with a hidden conformal sector which manifests itself
as an unparticle coupling to Standard Model particles effectively through
higher dimensional operators, predicts strong collider signals due to
unparticle self-interactions. We perform a complete analysis of the most
spectacular of these signals at the hadron collider, pp -> 4photon and pp
->2photon,2gluon. These processes can go through the three-point unparticle
self interactions as well as through some s and t channel diagrams with one
and/or two unparticle exchanges. We study the contributions of individual
diagrams classified with respect to the number of unparticle exchanges and
discuss their effect on the cross sections at the Tevatron and the LHC. We also
restrict the Tevatron bound on the unknown coefficient of the three-point
unparticle correlator. With the availability of data from Tevatron, and the
advent of the data emerging from the LHC, these interactions can provide a
clear and strong indication of unparticle physics and distinguish this model
from other beyond the standard model scenarios.Comment: 28 pages, 16 figure
Lorentz and CPT Violation in the Higgs Sector
Colladay and Kostelecky have proposed a framework for studying Lorentz and
CPT violation in a natural extension of the Standard Model. Although numerous
bounds exist on the Lorentz and CPT violating parameters in the gauge boson and
fermion sectors, there are no published bounds on the parameters in the Higgs
sector. We determine these bounds. The bounds on the CPT-even asymmetric
coefficients arise from the one-loop contributions to the photon propagator,
those from the CPT-even symmetric coefficients arise from the equivalent
c_{\mu\nu} coefficients in the fermion sector, and those from the CPT-odd
coefficient arise from bounds on the vacuum expectation value of the Z-boson.Comment: 17 pages, 1 figure, 1 table; Clarifications and changes to text,
results unchanged. References added. Version to be published in Physical
Review
Neutralino Dark Matter in the Left-Right Supersymmetric Model
We study the neutralino sector of the left-right supersymmetric model. In
addition to the possibilities available in the minimal supersymmetric model,
the neutralino states can be superpartners of the U(1)_{B-L} gauge boson, the
neutral SU(2)_R neutral gauge boson, or of the Higgs triplets. We analyze
neutralino masses and determine the parameter regions for which the lightest
neutralino can be one of the new pure states. We then calculate the relic
density of the dark matter for each of these states and impose the constraints
coming from the rho parameter, the anomalous magnetic moment of the muon, b ->
s gamma, as well as general supersymmetric mass bounds. The lightest neutralino
can be the bino, or the right-wino, or the neutral triplet higgsino, all of
which have different couplings to the standard model particles from the usual
neutralinos. A light bino satisfies all the experimental constraints and would
be the preferred dark matter candidate for light supersymmetric scalar masses,
while the right-wino would be favored by intermediate supersymmetric mass
scales. The neutral triplet Higgs fermion satisfies the experimental bounds
only in a small region of the parameter space, for intermediate to heavy
supersymmetric scalar masses.Comment: 31 pages, 8 figures, one table and references added, to be published
in Phys. Rev.
B Decays in an Asymmetric Left-Right Model
Motivated by recently observed disagreements with the SM predictions in
decays, we study transitions in an asymmetric class of models, with a simple one-parameter structure
of the right handed mixing matrix for the quarks, which obeys the constraints
from kaon physics. We use experimental constraints on the branching ratios of
, , and
mixing to restrict the parameters of the model: as well as the elements of the right-handed
quark mixing matrix . We present a comparison with the more commonly
used (manifest) left-right symmetric model. Our analysis exposes the parameters
most sensitive to transitions and reveals a large parameter space where
left- and right-handed quarks mix differently, opening the possibility of
observing marked differences in behaviour between the standard model and the
left-right model.Comment: 32 pages and 8 figure
- …