162 research outputs found
A T-odd observable sensitive to CP violating phases in squark decay
We present a new observable sensitive to a certain combination of CP
violating phases in supersymmetric extensions of the Standard Model, viz. a
triple product of momenta in the cascade decay of a heavy squark via an
on-shell neutralino and off-shell slepton. We investigate the regions of
parameter space in which the signal is strong enough to be detectable at the
LHC with identified events,
where is a certain combination of phases in the MSSM presented in
the text.Comment: Several references adde
Do solar neutrinos decay?
Despite the fact that the solar neutrino flux is now well-understood in the
context of matter-affected neutrino mixing, we find that it is not yet possible
to set a strong and model-independent bound on solar neutrino decays. If
neutrinos decay into truly invisible particles, the Earth-Sun baseline defines
a lifetime limit of \tau/m \agt 10^{-4} s/eV. However, there are many
possibilities which must be excluded before such a bound can be established.
There is an obvious degeneracy between the neutrino lifetime and the mixing
parameters. More generally, one must also allow the possibility of active
daughter neutrinos and/or antineutrinos, which may partially conceal the
characteristic features of decay. Many of the most exotic possibilities that
presently complicate the extraction of a decay bound will be removed if the
KamLAND reactor antineutrino experiment confirms the large-mixing angle
solution to the solar neutrino problem and measures the mixing parameters
precisely. Better experimental and theoretical constraints on the B
neutrino flux will also play a key role, as will tighter bounds on absolute
neutrino masses. Though the lifetime limit set by the solar flux is weak, it is
still the strongest direct limit on non-radiative neutrino decay. Even so,
there is no guarantee (by about eight orders of magnitude) that neutrinos from
astrophysical sources such as a Galactic supernova or distant Active Galactic
Nuclei will not decay.Comment: Very minor corrections, corresponds to published versio
Determining the Higgs Boson Self Coupling at Hadron Colliders
Inclusive Standard Model Higgs boson pair production at hadron colliders has
the capability to determine the Higgs boson self-coupling, lambda. We present a
detailed analysis of the gg\to HH\to (W^+W^-)(W^+W^-)\to
(jjl^\pm\nu)(jj{l'}^\pm\nu) and gg\to HH\to (W^+W^-)(W^+W^-)\to
(jjl^\pm\nu)({l'}^\pm\nu {l''}^\mp\nu) (l, {l'}, {l''}=e, \mu) signal channels,
and the relevant background processes, for the CERN Large Hadron Collider, and
a future Very Large Hadron Collider operating at a center-of-mass energy of 200
TeV. We also derive quantitative sensitivity limits for lambda. We find that it
should be possible at the LHC with design luminosity to establish that the
Standard Model Higgs boson has a non-zero self-coupling and that lambda /
lambda_{SM} can be restricted to a range of 0-3.8 at 95% confidence level (CL)
if its mass is between 150 and 200 GeV. At a 200 TeV collider with an
integrated luminosity of 300 fb^{-1}, lambda can be determined with an accuracy
of 8 - 25% at 95% CL in the same mass range.Comment: 28 pages, Revtex3, 9 figures, 3 table
Neutrino Observatories Can Characterize Cosmic Sources and Neutrino Properties
Neutrino telescopes that measure relative fluxes of ultrahigh-energy
can give information about the location and
characteristics of sources, about neutrino mixing, and can test for neutrino
instability and for departures from CPT invariance in the neutrino sector. We
investigate consequences of neutrino mixing for the neutrino flux arriving at
Earth, and consider how terrestrial measurements can characterize distant
sources. We contrast mixtures that arise from neutrino oscillations with those
signaling neutrino decays. We stress the importance of measuring fluxes in neutrino observatories.Comment: 9 RevTeX pages, 4 figure
Matter effects and CP violating neutrino oscillations with non-decoupling heavy neutrinos
The evolution equation for active and sterile neutrinos propagating in
general anisotropic or polarized background environment is found and solved for
a special case when heavy neutrinos do not decouple, resulting in non-unitary
mixing among light neutrino states. Then new CP violating neutrino oscillation
effects appear. In contrast to the standard unitary neutrino oscillations these
effects can be visible even for two flavour neutrino transitions and even if
one of the elements of the neutrino mixing matrix is equal to zero. They do not
necessarily vanish with and they are different for various
pairs of flavour neutrino transitions (), (), (). Neutrino oscillations in vacuum and Earth's
matter are calculated for some fixed baseline experiments and a comparison
between unitary and non-unitary oscillations are presented. It is shown, taking
into account the present experimental constraints, that heavy neutrino states
can affect CP and T asymmetries. This is especially true in the case of
oscillations.Comment: 18 pages, 6 fig
Solar neutrino oscillation parameters after first KamLAND results
We analyze the energy spectrum of reactor neutrino events recently observed
in the Kamioka Liquid scintillator Anti-Neutrino Detector (KamLAND) and combine
them with solar and terrestrial neutrino data, in the context of two- and
three-family active neutrino oscillations. In the 2-neutrino case, we find that
the solution to the solar neutrino problem at large mixing angle (LMA) is
basically split into two sub-regions, that we denote as LMA-I and LMA-II. The
LMA-I solution, characterized by lower values of the squared neutrino mass gap,
is favored by the global data fit. This picture is not significantly modified
in the 3-neutrino mixing case. A brief discussion is given about the
discrimination of the LMA-I and LMA-II solutions with future KamLAND data. In
both the 2- and 3-neutrino cases, we present a detailed analysis of the
post-KamLAND bounds on the oscillation parameters.Comment: Revised version. Two figures adde
Zee Model Confronts SNO Data
We reexamine the solution of the minimal Zee model by comparing with the data
of the SNO experiment, and conclude that the model is strongly disfavored but
not yet excluded by the observations. Two extensions of the Zee model are
briefly discussed both of which introduce additional freedom and can
accommodate the data.Comment: 16 pages LaTeX including 7 figure
A study of semi-inclusive charmless decays
We study semi-inclusive charmless decays in detail, such as
, , , where does not contain a charm (anti)quark. We find that
the process () can be particularly
useful for determination of the CKM matrix element . We calculate and
present the branching ratio (BR) of as a function of
, with an estimate of possible uncertainties. It is expected that the
BR is an order of . Our estimation indicates that one can
phenomenologically determine with reasonable accuracy by measuring
the BR of ().Comment: 18 pages, 7 figures; Revtex; version accepted for publication in Eur.
Phys. J.
Spin Measurements in Cascade Decays at the LHC
We systematically study the possibility of determining the spin of new
particles after their discovery at the LHC. We concentrate on angular
correlations in cascade decays. Motivated by constraints of electroweak
precision tests and the potential of providing a Cold Dark Matter candidate, we
focus on scenarios of new physics in which some discrete symmetry guarantees
the existence of stable neutral particles which escape the detector. More
specifically, we compare supersymmetry with another generic scenario in which
new physics particles have the same spin as their Standard Model partners. A
survey of possibilities of observing spin correlations in a broad range of
decay channels is carried out, with interesting ones identified. Rather than
confining ourselves to one "collider friendly" benchmark point (such as SPS1a),
we describe the parameter region in which any particular decay channel is
effective. We conduct a more detailed study of chargino's spin determination in
the decay channel . A scan
over the chargino and neutralino masses is performed. We find that as long as
the spectrum is not too degenerate the prospects for spin determination in this
channel are rather good.Comment: 36 pages, references added, 1 figure modifie
Oscillation Induced Neutrino Asymmetry Growth in the Early Universe
We study the dynamics of active-sterile neutrino oscillations in the early
universe using full momentum-dependent quantum-kinetic equations. These
equations are too complicated to allow for an analytical treatment, and
numerical solution is greatly complicated due to very pronounced and narrow
structures in the momentum variable introduced by resonances. Here we introduce
a novel dynamical discretization of the momentum variable which overcomes this
problem. As a result we can follow the evolution of neutrino ensemble
accurately well into the stable growing phase. Our results confirm the
existence of a "chaotic region" of mixing parameters, for which the final sign
of the asymmetry, and hence the SBBN prediction of He(4)-abundance cannot be
accurately determined.Comment: 23 pages, 9 eps-figs, Latex, uses JHEP clas
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