28 research outputs found
On the Treatment of Neutrino Oscillations Without Resort to Weak Eigenstates
We discuss neutrino oscillations in the framework of the quantum field theory
without introducing the concept of neutrino weak eigenstates. The external
particles are described by wave packets and the different mass eigenstate
neutrinos propagate between the production and detection interactions, which
are macroscopically localized in space-time. The time-averaged cross section,
which is the measurable quantity in the usual experimental setting, is
calculated. It is shown that only in the extremely relativistic limit the usual
quantum mechanical oscillation probability can be factored out of the cross
section.Comment: LaTeX-18pages, JHU-TIPAC-930011,DFTT 22/9
Limits on the Neutrino Mass and Mixing Angle from Pion and Lepton Decays
Motivated by a recent rather surprising conclusion based on the 1992 PDG data
on the pion, kaon and lepton decays that if three generations of neutrinos are
assumed to be massive and mixed, the heaviest neutrino, , could have a
mass in the range, 155~\mbox{MeV} \lsim m_3 \lsim 225~\mbox{MeV}, we have
analyzed the latest 1995 data on the leptonic decays of pion, and
with the assumption that three generations of neutrinos are massive and mixed.
It is shown that when the radiative corrections are included and the constraint
{}from partial decay widths is imposed, the 1995 data are consistent with three
massless neutrinos with no mixing. Various limits on the neutrino mass and
mixing angle implied by the 1995 data are presented together with a critique of
the previous analysis.Comment: REVTeX file, 20 pages and 10 figures (not included). Revision of the
analysis and inclusion of the latest data. The TeX file and the figures
(uuencoded, compressed, tarred file) are available at
http://fermi.pha.jhu.edu/personnel/fornengo/fornengo.htm
Nonperturbative Corrections to the Heavy Lepton Energy Distribution in the Inclusive Decays H_b\ra \tau\bar\nu X.
Nonperturbative corrections up to to the heavy lepton energy
distributions are investigated in the inclusive semileptonic weak decays of
heavy flavors in QCD. In the case of -meson decays, for b \ra u\tau\bnu
transitions they decrease the decay rate by 6\% of its perturbative value,
while for b \ra c\tau\bnu they decrease it by 10\%.Comment: LaTeX, 10 pages, 4 postscript figures included. Few typos correcte
Decay of Z into Two Light Higgs Bosons
If the standard electroweak gauge model is extended to include two or more
Higgs doublets, there may be a neutral Higgs boson which is light (with a
mass of say 10 GeV) but the coupling is suppressed so that it has so far
escaped experimental detection. However, the effective coupling is
generally unsuppressed, hence the decay of Z into two light Higgs bosons plus a
fermion-antifermion pair may have an observable branching fraction, especially
if decays invisibly as for example in the recently proposed doublet Majoron
model.Comment: 10 pages, LaTex, figures available upon request to
[email protected]
The Noncommutative Standard Model and Forbidden Decays
In this contribution we discuss the Noncommutative Standard Model and the
associated Standard Model-forbidden decays that can possibly serve as an
experimental signature of space-time noncommutativity.Comment: 15 pages, 1 figure, Invited talk at 9th Adriatic Meeting and Central
European Symposia on Particle Physics and The Universe, Dubrovnik, Croatia,
4-14 Sep 200
Supersymmetry without R-parity : Constraints from Leptonic Phenomenology
R-parity conservation is an {\it ad hoc} assumption in the most popular
version of the supersymmetric standard model. Most studies of models which do
allow for R-parity violation have been restricted to various limiting
scenarios. The single-VEV parametrization used in this paper provides a
workable framework to analyze phenomenology of the most general theory of SUSY
without R-parity. We perform a comprehensive study of leptonic phenomenology at
tree-level. Experimental constraints on various processes are studied
individually and then combined to yield regions of admissible parameter space.
In particular, we show that large R-parity violating bilinear couplings are not
ruled out, especially for large .Comment: 56 pages Revtex with figures incorporated; typos (including
transcription typo in Table II) and minor corrections; proof-read version, to
appear in Phys. Rev.
Bounds on the tau and muon neutrino vector and axial vector charge radius
A Majorana neutrino is characterized by just one flavor diagonal
electromagnetic form factor: the anapole moment, that in the static limit
corresponds to the axial vector charge radius . Experimental information
on this quantity is scarce, especially in the case of the tau neutrino. We
present a comprehensive analysis of the available data on the single photon
production process off Z-resonance, and we
discuss the constraints that these measurements can set on for the tau
neutrino. We also derive limits for the Dirac case, when the presence of a
vector charge radius is allowed. Finally, we comment on additional
experimental data on scattering from the NuTeV, E734, CCFR and
CHARM-II collaborations, and estimate the limits implied for and
for the muon neutrino.Comment: 20 pages, 2 eps figures. CCFR data included in the analysis.
Conclusion unchange
Towards an Asymptotic-Safety Scenario for Chiral Yukawa Systems
We search for asymptotic safety in a Yukawa system with a chiral
symmetry, serving as a toy model for the
standard-model Higgs sector. Using the functional RG as a nonperturbative tool,
the leading-order derivative expansion exhibits admissible non-Ga\ssian
fixed-points for which arise from a conformal threshold
behavior induced by self-balanced boson-fermion fluctuations. If present in the
full theory, the fixed-point would solve the triviality problem. Moreover, as
one fixed point has only one relevant direction even with a reduced hierarchy
problem, the Higgs mass as well as the top mass are a prediction of the theory
in terms of the Higgs vacuum expectation value. In our toy model, the fixed
point is destabilized at higher order due to massless Goldstone and fermion
fluctuations, which are particular to our model and have no analogue in the
standard model.Comment: 16 pages, 8 figure
Invisible Z-Boson Decays at e+e- Colliders
The measurement of the invisible Z-boson decay width at e+e- colliders can be
done "indirectly", by subtracting the Z-boson visible partial widths from the
Z-boson total width, or "directly", from the process e+e- -> \gamma \nu
\bar{\nu}. Both procedures are sensitive to different types of new physics and
provide information about the couplings of the neutrinos to the Z-boson. At
present, measurements at LEP and CHARM II are capable of constraining the
left-handed Z\nu\nu-coupling, 0.45 <~ g_L <~ 0.5, while the right-handed one is
only mildly bounded, |g_R| <= 0.2. We show that measurements at a future e+e-
linear collider at different center-of-mass energies, \sqrt{s} = MZ and
\sqrt{s}s ~ 170 GeV, would translate into a markedly more precise measurement
of the Z\nu\nu-couplings. A statistically significant deviation from Standard
Model predictions will point toward different new physics mechanisms, depending
on whether the discrepancy appears in the direct or the indirect measurement of
the invisible Z-width. We discuss some scenarios which illustrate the ability
of different invisible Z-boson decay measurements to constrain new physics
beyond the Standard Model
Asymptotic safety of simple Yukawa systems
We study the triviality and hierarchy problem of a Z_2-invariant Yukawa
system with massless fermions and a real scalar field, serving as a toy model
for the standard-model Higgs sector. Using the functional RG, we look for UV
stable fixed points which could render the system asymptotically safe. Whether
a balancing of fermionic and bosonic contributions in the RG flow induces such
a fixed point depends on the algebraic structure and the degrees of freedom of
the system. Within the region of parameter space which can be controlled by a
nonperturbative next-to-leading order derivative expansion of the effective
action, we find no non-Gaussian fixed point in the case of one or more fermion
flavors. The fermion-boson balancing can still be demonstrated within a model
system with a small fractional flavor number in the symmetry-broken regime. The
UV behavior of this small-N_f system is controlled by a conformal Higgs
expectation value. The system has only two physical parameters, implying that
the Higgs mass can be predicted. It also naturally explains the heavy mass of
the top quark, since there are no RG trajectories connecting the UV fixed point
with light top masses.Comment: 14 pages, 3 figures, v2: references added, typos corrected, minor
numerical correction