753 research outputs found
Neutrino Oscillations and Collider Test of the R-parity Violating Minimal Supergravity Model
We study the R-parity violating minimal supergravity models accounting for
the observed neutrino masses and mixing, which can be tested in future collider
experiments. The bi-large mixing can be explained by allowing five dominant
tri-linear couplings and . The desired ratio
of the atmospheric and solar neutrino mass-squared differences can be obtained
in a very limited parameter space where the tree-level contribution is tuned to
be suppressed. In this allowed region, we quantify the correlation between the
three neutrino mixing angles and the tri-linear R-parity violating couplings.
Qualitatively, the relations , and are required by the large
atmospheric neutrino mixing angle and the small angle
, and the large solar neutrino mixing angle ,
respectively. Such a prediction on the couplings can be tested in the next
linear colliders by observing the branching ratios of the lightest
supersymmetric particle (LSP). For the stau or the neutralino LSP, the ratio
can be measured
by establishing or , respectively. The
information on the couplings can be drawn by measuring if the neutralino LSP is heavier than the top
quark.Comment: RevTex, 25 pages, 8 eps figure
A texture of neutrino mass matrix in view of recent neutrino experimental results
In view of recent neutrino experimental results such as SNO, Super-Kamiokande
(SK), CHOOZ and neutrinoless double beta decay , we
consider a texture of neutrino mass matrix which contains three parameters in
order to explain those neutrino experimental results. We have first fitted
parameters in a model independent way with solar and atmospheric neutrino mass
squared differences and solar neutrino mixing angle which satisfy LMA solution.
The maximal value of atmospheric neutrino mixing angle comes out naturally in
the present texture. Most interestingly, fitted parameters of the neutrino mass
matrix considered here also marginally satisfy recent limit on effective
Majorana neutrino mass obtained from neutrinoless double beta decay experiment.
We further demonstrate an explicit model which gives rise to the texture
investigated by considering an gauge group with two
extra real scalar singlets and discrete symmetry. Majorana
neutrino masses are generated through higher dimensional operators at the scale
. We have estimated the scales at which singlets get VEV's and M by
comparing with the best fitted results obtained in the present work.Comment: Journal Ref.: Phys. Rev. D66, 053004 (2002
The effect of grain size on electrical transport and magnetic properties of La0.9Te0.1MnO3
The effect of grain size on structural, magnetic and transport properties in
electron-doped manganites La0.9Te0.1MnO3 has been investigated. All samples
show a rhombohedral structure with the space group at room temperature. It
shows that the Mn-O-Mn bond angle decreases and the Mn-O bond length increases
with the increase of grain size. All samples undergo paramagnetic
(PM)-ferromagnetic (FM) phase transition and an interesting phenomenon that
both magnetization and the Curie temperature decrease with increasing grain
size is observed, which is suggested to mainly originate from the increase of
the Mn-O bond length . Additionally, obviously increases with decreasing grain
size due to the increase of both the height and width of tunneling barriers
with decreasing the grain size. The results indicate that both the intrinsic
colossal magnetoresistance (CMR) and the extrinsic the extrinsic interfacial
magnetoresistance (IMR) can be effectively tuned in La0.9Te0.1MnO3 by changing
grain size.Comment: 15 pages,4 figures. Solid state communications 132(2004)83-8
The origin of fracture in the I-ECAP of AZ31B magnesium alloy
Magnesium alloys are very promising materials for weight-saving structural applications due to their low density, comparing to other metals and alloys currently used. However, they usually suffer from a limited formability at room temperature and low strength. In order to overcome those issues, processes of severe plastic deformation (SPD) can be utilized to improve mechanical properties, but processing parameters need to be selected with care to avoid fracture, very often observed for those alloys during forming. In the current work, the AZ31B magnesium alloy was subjected to SPD by incremental equal-channel angular pressing (I-ECAP) at temperatures varying from 398 K to 525 K (125 °C to 250 °C) to determine the window of allowable processing parameters. The effects of initial grain size and billet rotation scheme on the occurrence of fracture during I-ECAP were investigated. The initial grain size ranged from 1.5 to 40 µm and the I-ECAP routes tested were A, BC, and C. Microstructures of the processed billets were characterized before and after I-ECAP. It was found that a fine-grained and homogenous microstructure was required to avoid fracture at low temperatures. Strain localization arising from a stress relaxation within recrystallized regions, namely twins and fine-grained zones, was shown to be responsible for the generation of microcracks. Based on the I-ECAP experiments and available literature data for ECAP, a power law between the initial grain size and processing conditions, described by a Zener–Hollomon parameter, has been proposed. Finally, processing by various routes at 473 K (200 °C) revealed that route A was less prone to fracture than routes BC and C
The effect of oxygen stoichiometry on electrical transport and magnetic properties of La0.9Te0.1MnOy
The effect of the variation of oxygen content on structural, magnetic and
transport properties in the electron-doped manganites La0.9Te0.1MnOy has been
investigated. All samples show a rhombohedral structure with the space group .
The Curie temperature decreases and the paramagnetic-ferromagnetic (PM-FM)
transition becomes broader with the reduction of oxygen content. The
resistivity of the annealed samples increases slightly with a small reduction
of oxygen content. Further reduction in the oxygen content, the resistivity
maximum increases by six orders of magnitude compared with that of the
as-prepared sample, and the r(T) curves of samples with y = 2.86 and y = 2.83
display the semiconducting behavior () in both high-temperature PM phase and
low-temperature FM phase, which is considered to be related to the appearance
of superexchange ferromagnetism (SFM) and the localization of carriers. The
results are discussed in terms of the combined effects of the increase in the
Mn2+/(Mn2++Mn3+) ratio, the partial destruction of double exchange (DE)
interaction, and the localization of carriers due to the introduction of oxygen
vacancies in the Mn-O-Mn network.Comment: 20 pages, 8 figure
Quark-lepton complementarity, neutrino and standard model data predict
The complementarity between the quark and lepton mixing matrices is shown to
provide a robust prediction for the neutrino mixing angle .
We obtain this prediction by first showing that the matrix , product of
the CKM and PMNS mixing matrices, may have a zero (1,3) entry which is favored
by experimental data. Hence models with bimaximal or tribimaximal forms of the
correlation matrix are quite possible. Any theoretical model with a
vanishing (1,3) entry of that is in agreement with quark data, solar, and
atmospheric mixing angle leads to .
This value is consistent with the present 90% CL experimental upper limit.Comment: 15 pages, 7 figures. Final version to appear in the journa
Plasma Wakefield Acceleration with a Modulated Proton Bunch
The plasma wakefield amplitudes which could be achieved via the modulation of
a long proton bunch are investigated. We find that in the limit of long bunches
compared to the plasma wavelength, the strength of the accelerating fields is
directly proportional to the number of particles in the drive bunch and
inversely proportional to the square of the transverse bunch size. The scaling
laws were tested and verified in detailed simulations using parameters of
existing proton accelerators, and large electric fields were achieved, reaching
1 GV/m for LHC bunches. Energy gains for test electrons beyond 6 TeV were found
in this case.Comment: 9 pages, 7 figure
The energy dependence of angular correlations inferred from mean- fluctuation scale dependence in heavy ion collisions at the SPS and RHIC
We present the first study of the energy dependence of angular
correlations inferred from event-wise mean transverse momentum
fluctuations in heavy ion collisions. We compare our large-acceptance
measurements at CM energies $\sqrt{s_{NN}} =$ 19.6, 62.4, 130 and 200 GeV to
SPS measurements at 12.3 and 17.3 GeV. $p_t$ angular correlation structure
suggests that the principal source of $p_t$ correlations and fluctuations is
minijets (minimum-bias parton fragments). We observe a dramatic increase in
correlations and fluctuations from SPS to RHIC energies, increasing linearly
with $\ln \sqrt{s_{NN}}$ from the onset of observable jet-related
fluctuations near 10 GeV.Comment: 10 pages, 4 figure
Partonic flow and -meson production in Au+Au collisions at = 200 GeV
We present first measurements of the -meson elliptic flow
() and high statistics distributions for different
centralities from = 200 GeV Au+Au collisions at RHIC. In
minimum bias collisions the of the meson is consistent with the
trend observed for mesons. The ratio of the yields of the to those of
the as a function of transverse momentum is consistent with a model
based on the recombination of thermal quarks up to GeV/,
but disagrees at higher momenta. The nuclear modification factor () of
follows the trend observed in the mesons rather than in
baryons, supporting baryon-meson scaling. Since -mesons are
made via coalescence of seemingly thermalized quarks in central Au+Au
collisions, the observations imply hot and dense matter with partonic
collectivity has been formed at RHIC.Comment: 6 pages, 4 figures, submit to PR
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