48,202 research outputs found
Muon (g-2) from the bulk neutrino field in a warped extra dimensional model
In the Randall-Sundrum model, a bulk neutrino field in the 5-dimensional
space-time can give rise to tiny Dirac masses to neutrinos. In such a scenario,
we have computed the contribution of the bulk neutrino field to the anomalous
magnetic moment of muon. We have computed this contribution in the
't Hooft-Feynman gauge and have found that the contribution has the right sign
to fit the current discrepancy between the experiment and the standard model
value of . We have also studied possible constraints on the model
parameters by including contributions to from other sources such as
bulk gravitons.Comment: 18 pages, 3 figures, 2 tables, minor changes, this version has been
published in Physical Review
Study on Gait Efficiency and Energy Cost of Below Knee Amputees After Therapeutic Practices
An earlier research advocated that a below knee amputee (BK) with conventional trans-tibial prosthesis attains higher gait efficiency at lower energy cost with therapeutic practices of proper time and co-ordination in compare to normal subjects of similar physical parameters and quality of life. The present study focused on comparative analysis of energy cost and gait efficiency between a group of below knee amputees and a control group (normal subjects without amputation) to indicate the consistency of the earlier findings. The subjects were selected with similar physical parameters and quality of life. Oxygen Uptake (VO2) and Heart Rate (HR) were measured by Cosmed® k4 b2 analyzer system. Gait efficiency (p < 0.0001) was found higher with lower energy cost for BK amputees after therapeutic practices than control group. The therapeutic activities contributed to efficient gait pattern for amputees ensuring proper time and co-ordination with balance in consistence to the earlier research
Testing Reionization with Gamma Ray Burst Absorption Spectra
We propose to study cosmic reionization using absorption line spectra of
high-redshift Gamma Ray Burst (GRB) afterglows. We show that the statistics of
the dark portions (gaps) in GRB absorption spectra represent exquisite tools to
discriminate among different reionization models. We then compute the
probability to find the largest gap in a given width range [Wmax, Wmax + dW] at
a flux threshold Fth for burst afterglows at redshifts 6.3 < z < 6.7. We show
that different reionization scenarios populate the (Wmax, Fth) plane in a very
different way, allowing to distinguish among different reionization histories.
We provide here useful plots that allow a very simple and direct comparison
between observations and model results. Finally, we apply our methods to GRB
050904 detected at z = 6.29. We show that the observation of this burst
strongly favors reionization models which predict a highly ionized
intergalactic medium at z~6, with an estimated mean neutral hydrogen fraction
xHI = 6.4 \pm 0.3 \times 10^-5 along the line of sight towards GRB 050904.Comment: 5 pages, 3 figures, revised to match the accepted version; major
change: gap statistics is now studied in terms of the flux threshold Fth,
instead of the observed J-band flux FJ; MNRAS in pres
Detecting extra dimensions with gravity wave spectroscopy: the black string brane-world
Using the black string between two branes as a model of a brane-world black
hole, we compute the gravity wave perturbations and identify the features
arising from the additional polarizations of the graviton. The standard
four-dimensional gravitational wave signal acquires late-time oscillations due
to massive modes of the graviton. The Fourier transform of these oscillations
shows a series of spikes associated with the masses of the Kaluza-Klein modes,
providing in principle a spectroscopic signature of extra dimensions.Comment: 4 pages, 5 figures. Comments on the frequency and detectability of
the massive mode signal added, and title modified. Version accepted for
publication in Phys. Rev. Let
The pion-pion scattering amplitude. III: Improving the analysis with forward dispersion relations and Roy equations
We complete and improve the fits to experimental scattering
amplitudes, both at low and high energies, that we performed in the previous
papers of this series. We then verify that the corresponding amplitudes satisfy
analyticity requirements, in the form of partial wave analyticity at low
energies, forward dispersion relations (FDR) at all energies, and Roy equations
below threshold; the first by construction, the last two, inside
experimental errors. Then we repeat the fits including as constraints FDR and
Roy equations. The ensuing central values of the various scattering amplitudes
verify very accurately FDR and, especially, Roy equations, and change very
little from what we found by just fitting data, with the exception of the D2
wave phase shift, for which one parameter moves by . These improved
parametrizations therefore provide a reliable representation of pion-pion
amplitudes with which one can test various physical relations. We also present
a list of low energy parameters and other observables. In particular, we find
,
and .Comment: Plain TeX. 29 figures. Version to be published in PRD, with improved
P and F wave
Unification, Multiplets and Proton Decay
We make a detailed analysis of gauge coupling unification in supersymmetry.
When the Standard Model gauge group is embedded in a Grand Unified Theory, new
particles often appear below the GUT scale in order to predict the right
phenomenology at low energy. While these new particles are beyond the reach of
accelerator experiments, they change the prediction of \alpha_s. Here we
classify all the (SU(3)_C,SU(2)_L,U(1)_Y) representations which improve or
worsen the prediction. Running experimentally determined values of the coupling
constants at two loops we calculate the allowed range of masses of fields in
these representations. We explore the implication of these results in SU(5) and
SU(3)^3 (trinification) models. We discover that minimal trinification predicts
light triplet Higgs particles which lead to proton decay with a lifetime in the
vicinity of the current experimental bound.Comment: figures replaced, new calculations and references added. A
quantitative description of dependence of unification on varying input
parameters as well as varying the sparticle spectrum is added. This version
to appear in PR
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