11,255 research outputs found
Little Higgs model effects in
Though the predictions of the Standard Model (SM) are in excellent agreement
with experiments there are still several theoretical problems associated with
the Higgs sector of the SM, where it is widely believed that some ``{\it new
physics}'' will take over at the TeV scale. One beyond the SM theory which
resolves these problems is the Little Higgs (LH) model. In this work we have
investigated the effects of the LH model on \gggg scattering
\cite{Choudhury:2006xa}.Comment: Talk given at LCWS06, Bangalore, 4 pages (style files included
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
High Power, Continuous-wave Supercontinuum Generation in Highly Nonlinear Fibers Pumped with High Order, Cascaded Raman Fiber Amplifiers
A novel method for efficient generation of high power, equalized
continuous-wave supercontinuum source in an all conventional silica fiber
architecture is demonstrated. Highly nonlinear fiber (HNLF) is pumped in its
anomalous dispersion region using a novel, high power, L-band laser. The L-band
laser encompasses a 6th order cascaded Raman amplifier which is pumped with a
high power Ytterbium doped fiber laser and amplifies a low-power, tunable
L-band seed source. The supercontinuum generated 35W of power with ~40%
efficiency. The Supercontinuum spectrum was measured to have a high degree of
flatness of better than 5 dB over 400 nm of bandwidth (1.3 - 1.7 micron,
limited by spectrum analyzer range) and a power spectral density in this region
of >50 mW/nm. The extent of the SC spectrum is estimated to be upto 2 micronComment: 6 pages, 5 figure
Probing large distance higher dimensional gravity from lensing data
The modifications induced in the standard weak-lensing formula if Newtonian
gravity differs from inverse square law at large distances are studied. The
possibility of putting bounds on the mass of gravitons from lensing data is
explored. A bound on graviton mass, esitmated to be about 100 Mpc is
obtained from analysis of some recent data on gravitational lensing.Comment: 6 pages, 1 figure, added reference
Unitarity constraints on the stabilized Randall-Sundrum scenario
Recently proposed stabilization mechanism of the Randall-Sundrum metric gives
rise to a scalar radion, which couples universally to matter with a weak
interaction ( TeV) scale. Demanding that gauge boson scattering as
described by the effective low enerrgy theory be unitary upto a given scale
leads to significant constraints on the mass of such a radion.Comment: 10 page Latex 2e file including 4 postscript figures. Accepted in
Journal of Physics
Total cross sections for neutron-nucleus scattering
Systematics of neutron scattering cross sections on various materials for
neutron energies up to several hundred MeV are important for ADSS applications.
Ramsauer model is well known and widely applied to understand systematics of
neutron nucleus total cross sections. In this work, we examined the role of
nuclear effective radius parameter (r) on Ramsauer model fits of neutron
total cross sections. We performed Ramsauer model global analysis of the
experimental neutron total cross sections reported by W. P. Abfalterer, F. B.
Bateman, {\it et. al.,}, from 20MeV to 550MeV for nuclei ranging from Be to U .
The global fit functions which can fit total cross section data over periodic
table are provided along with the required global set of parameters. The global
fits predict within deviation to data, showing the scope for
improvement. It has been observed that a finer adjustment of r parameter
alone can give very good Ramsauer model description of neutron total scattering
data within deviation. The required r values for Ramsauer model
fits are shown as a function of nuclear mass number and an empirical formula is
suggested for r values as a function of mass number. In optical model
approach for neutron scattering, we have modified the real part of
Koning-Deleroche potentails to fit the neutron total cross sections using SCAT2
code. The modified potentails have a different energy dependence beyond 200MeV
of neutron energy and fit the total cross sections from Al to Pb.Comment: 9 pages, 20figures, Poster number ND-1457, ND2010 Conference in Kore
The multi-frequency angular power spectrum of the epoch of reionization 21 cm signal
Observations of redshifted 21cm radiation from HI at high redshifts is an
important future probe of reionization. We consider the Multi-frequency Angular
Power Spectrum (MAPS) to quantify the statistics of the HI signal as a joint
function of the angular multipole l and frequency separation \Delta\nu. The
signal at two different frequencies is expected to get decorrelated as
\Delta\nu is increased, and quantifying this decorrelation is particularly
important in deciding the frequency resolution for future HI observations. This
is also expected to play a very crucial role in extracting the signal from
foregrounds as the signal is expected to decorrelate much faster than the
foregrounds (which are largely continuum sources) with increasing \Delta\nu. In
this paper we develop formulae relating the MAPS to different components of the
three dimensional HI power spectrum taking into account HI peculiar velocities.
We show that the flat-sky approximation provides a very good representation
over the angular scales of interest, and a final expression which is very
simple to calculate and interpret. We present results considering two models
for the HI distribution, namely, (i) DM: where the HI traces the dark matter
and (ii) PR: where the effects of patchy reionization are incorporated through
two parameters. We find that while the DM signal is largely featureless, the PR
signal peaks at the angular scales of the individual bubbles, and the signal is
considerably enhanced for large bubble size. For most cases of interest at l
\sim 100 the signal is uncorrelated beyond \Delta\nu \sim 1 MHz or even less,
whereas it occurs around \sim 0.1 MHz at l \sim 10^3. The \Delta\nu dependence
also carries an imprint of the bubble size and the bias, and is expected to be
an important probe of the reionization scenario (abridged).Comment: Accepted for publication in MNRAS. Revised to match the accepted
versio
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