1,849 research outputs found
Sharpening up the Charged Higgs Boson Signature using Tau Polarization at LHC
The opposite states of the polarization resulting from the charged
Higgs boson and the boson decays can be exploited to enhance the
signal in the inclusive 1-prong hadronic decay channel of . We suggest
practical methods of sharpening up the signature in the top quark decay
at LHC using this idea. As a result one can carry on the charged Higgs boson
search to within of the parent top quark mass over the full
parameter space of the MSSM.Comment: 14 pages, 4 figures available on reques
Decay and Decoupling of heavy Right-handed Majorana Neutrinos in the L-R model
Heavy right-handed neutrinos are of current interest. The interactions and
decay of such neutrinos determine their decoupling epoch during the evolution
of the universe. This in turn affects various observable features like the
energy density, nucleosynthesis, CMBR spectrum, galaxy formation, and
baryogenesis. Here, we consider reduction of right-handed electron-type
Majorana neutrinos, in the left-right symmetric model, by the WR+ - WR- channel
and the channel originating from an anomaly, involving the SU(2)R gauge group,
as well as decay of such neutrinos. We study the reduction of these neutrinos
for different ranges of left-right model parameters, and find that, if the
neutrino mass exceeds the right-handed gauge boson mass, then the neutrinos
never decouple for realistic values of the parameters, but, rather, decay in
equilibrium. Because there is no out-of-equilibrium decay, no mass bounds can
be set for the neutrinos.Comment: Latex, 16 pages, No figures. Some additions in the text and
references. Conclusions unaffected. To appear in Eur. Phys. J.
Temperature dependent electrical resistivity of a single strand of ferromagnetic single crystalline nanowire
We have measured the electrical resistivity of a single strand of a
ferromagnetic Ni nanowire of diameter 55 nm using a 4-probe method in the
temperature range 3 K-300 K. The wire used is chemically pure and is a high
quality oriented single crystalline sample in which the temperature independent
residual resistivity is determined predominantly by surface scattering. Precise
evaluation of the temperature dependent resistivity () allowed us to
identify quantitatively the electron-phonon contribution (characterized by a
Debye temperature ) as well as the spin-wave contribution which is
significantly suppressed upon size reduction
New Variables For Neutrino Oscillation Diagnostics at Superkamiokande and the Sudbury Neutrino Observatory
The SuperKamiokande collaboration has presented results on the observation of solar neutrinos. The Sudbury Neutrino Observatory (SNO) is also expected to go on-line in the near future. We propose several new variables, insensitive to the absolute flux of the initial solar neutrino beam, which probe the shape of the observed spectrum at these experiments and can sensitively signal neutrino oscillations. One class of such variables involves normalised moments of the distributions recorded at the two facilities while another variable, specific to SNO, depends on the integrated charged and neutral current signals. The utility of these variables in the context of supernova neutrinos, both from the collapse epoch and the post-bounce era, is also emphasised. It is shown that, notwithstanding the imprecise nature of the information about the initial neutrino spectra from a supernova, oscillations can be detected using these variables and it will be possible to distinguish between the alternatives of oscillation to a sequential neutrino {\em vis-a-vis} that to a sterile neutrino
Temperature dependence of the resistance of metallic nanowires (diameter 15 nm): Applicability of Bloch-Gr\"{u}neisen theorem
We have measured the resistances (and resistivities) of Ag and Cu nanowires
of diameters ranging from 15nm to 200nm in the temperature range 4.2K-300K with
the specific aim to assess the applicability of the Bloch-Gr\"{u}neisen formula
for electron phonon resistivity in these nanowires. The wires were grown within
polymeric templates by electrodeposition. We find that in all the samples the
resistance reaches a residual value at T=4.2K and the temperature dependence of
resistance can be fitted to the Bloch-Gr\"{u}neisen formula in the entire
temperature range with a well defined transport Debye temperature
(). The value of Debye temperature obtained from the fits lie
within 8% of the bulk value for Ag wires of diameter 15nm while for Cu
nanowires of the same diameter the Debye temperature is significantly lesser
than the bulk value. The electron-phonon coupling constants (measured by
or ) in the nanowires were found to have the same
value as that of the bulk. The resistivities of the wires were seen to increase
as the wire diameter was decreased. This increase in the resistivity of the
wires may be attributed to surface scattering of conduction electrons. The
specularity p was estimated to be about 0.5. The observed results allow us to
obtain the resistivities exactly from the resistance and gives us a method of
obtaining the exact numbers of wires within the measured array (grown within
the template).Comment: 9 pages, 10 figure
A Minimal Model of Signaling Network Elucidates Cell-to-Cell Stochastic Variability in Apoptosis
Signaling networks are designed to sense an environmental stimulus and adapt
to it. We propose and study a minimal model of signaling network that can sense
and respond to external stimuli of varying strength in an adaptive manner. The
structure of this minimal network is derived based on some simple assumptions
on its differential response to external stimuli. We employ stochastic
differential equations and probability distributions obtained from stochastic
simulations to characterize differential signaling response in our minimal
network model. We show that the proposed minimal signaling network displays two
distinct types of response as the strength of the stimulus is decreased. The
signaling network has a deterministic part that undergoes rapid activation by a
strong stimulus in which case cell-to-cell fluctuations can be ignored. As the
strength of the stimulus decreases, the stochastic part of the network begins
dominating the signaling response where slow activation is observed with
characteristic large cell-to-cell stochastic variability. Interestingly, this
proposed stochastic signaling network can capture some of the essential
signaling behaviors of a complex apoptotic cell death signaling network that
has been studied through experiments and large-scale computer simulations. Thus
we claim that the proposed signaling network is an appropriate minimal model of
apoptosis signaling. Elucidating the fundamental design principles of complex
cellular signaling pathways such as apoptosis signaling remains a challenging
task. We demonstrate how our proposed minimal model can help elucidate the
effect of a specific apoptotic inhibitor Bcl-2 on apoptotic signaling in a
cell-type independent manner. We also discuss the implications of our study in
elucidating the adaptive strategy of cell death signaling pathways.Comment: 9 pages, 6 figure
Self-gravitating spheres of anisotropic fluid in geodesic flow
The fluid models mentioned in the title are classified. All characteristics
of the fluid are expressed through a master potential, satisfying an ordinary
second order differential equation. Different constraints are imposed on this
core of relations, finding new solutions and deriving the classical results for
perfect fluids and dust as particular cases. Many uncharged and charged
anisotropic solutions, all conformally flat and some uniform density solutions
are found. A number of solutions with linear equation among the two pressures
are derived, including the case of vanishing tangential pressure.Comment: 21 page
Magnetoresistance of metallic perovskite oxide LaNiO
We report a study of the magnetoresistance (MR) of the metallic perovskite
oxide LaNiO as a function of the oxygen stoichiometry
( 0.14), magnetic field (H ) and temperature (1.5K T 25K). We find a strong dependence of the nature of MR on the oxygen
stoichiometry. The MR at low temperatures change from positive to negative as
the sample becomes more oxygen deficient (i.e, increases). Some of the
samples which are more resistive, show a resistivity minima at
20K. We find that in these samples the MR is positive at T >
and negative for T < . We conclude that in the absence of
strong magnetic interaction, the negative MR in these oxides can arise from
weak localisation effects.Comment: 10 pages in REVTeX format, 4 eps fig
A GEANT-based study of atmospheric neutrino oscillation parameters at INO
We have studied the dependence of the allowed space of the atmospheric
neutrino oscillation parameters on the time of exposure for a magnetized Iron
CALorimeter (ICAL) detector at the India-based Neutrino Observatory (INO). We
have performed a Monte Carlo simulation for a 50 kTon ICAL detector generating
events by the neutrino generator NUANCE and simulating the detector response by
GEANT. A chi-square analysis for the ratio of the up-going and down-going
neutrinos as a function of is performed and the allowed regions at 90%
and 99% CL are displayed. These results are found to be better than the current
experimental results of MINOS and Super-K. The possibilities of further
improvement have also been discussed.Comment: 8 pages, 13 figures, a new figure added, version accepted in IJMP
Vortex matching effect in engineered thin films of NbN
We report robust vortex matching effects in antidot arrays fabricated on thin
films of NbN. The near absence of hysteresis between field sweep directions
indicates a negligible residual pinning in the host thin film. Owing to the
very small coherence length of NbN thin films (), the observations
suggests the possibility of probing physics of vortices at true nanometer
length scales in suitably fabricated structures.Comment: Submitted to Appl. Phys. Let
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