160 research outputs found
Baryon inhomogeneity generation via cosmic strings at QCD scale and its effects on nucleosynthesis
We have earlier shown that cosmic strings moving through the plasma at the
time of a first order quark-hadron transition in the early universe can
generate large scale baryon inhomogeneities. In this paper, we calculate
detailed structure of these inhomogeneities at the quark-hadron transition. Our
calculations show that the inhomogeneities generated by cosmic string wakes can
strongly affect nucleosynthesis calculations. A comparison with observational
data suggests that such baryon inhomogeneities should not have existed at the
nucleosynthesis epoch. If this disagreement holds with more accurate
observations, then it will lead to the conclusions that cosmic string formation
scales above GeV may not be consistent with nucleosynthesis
and CMBR observations. Alternatively, some other input in our calculation
should be constrained, for example, if the average string velocity remains
sufficiently small so that significant density perturbations are never produced
at the QCD scale, or if strings move ultra-relativistically so that string
wakes are very thin, trapping negligible amount of baryons. Finally, if
quark-hadron transition is not of first order then our calculations do not
apply.Comment: 24 pages, 5 figures, minor changes, version to appear in Phys. Rev.
Heavy ion physics
The 8th workshop on high energy physics phenomenology (WHEPP-8) was held at the Indian Institute of Technology, Mumbai, India during January 5-16, 2004. One of the four working groups, group III was dedicated to QCD and heavy ion physics (HIC). The present manuscript gives a summary of the activities of group III during the workshop (see also [1] for completeness). The activities of group III were focused to understand the collective behaviours of the system formed after the collisions of two nuclei at ultra-relativistic energies from the interactions of the elementary degrees of freedom, i.e. quarks and gluons, governed by non-abelian gauge theory, i.e. QCD. This was initiated by two plenary talks on experimental overview of heavy ion collisions and lattice QCD and several working group talks and discussions
Cosmic string induced sheet like baryon inhomogeneities at quark-hadron transition
Cosmic strings moving through matter produce wakes where density is higher
than the background density. We investigate the effects of such wakes occurring
at the time of a first order quark-hadron transition in the early universe and
show that they can lead to separation of quark-gluon plasma phase in the wake
region, while the region outside the wake converts to the hadronic phase.
Moving interfaces then trap large baryon densities in sheet like regions which
can extend across the entire horizon. Typical separation between such sheets,
at formation, is of the order of a km. Regions of baryon inhomogeneity of this
nature, i.e. having a planar geometry, and separated by such large distance
scales, appear to be well suited for the recent models of inhomogeneous
nucleosynthesis to reconcile with the large baryon to photon ratio implied by
the recent measurements of the cosmic microwave background power spectrum.Comment: 8 pages, 3 figure
Measuring Cosmic Defect Correlations in Liquid Crystals
From the theory of topological defect formation proposed for the early
universe, the so called Kibble mechanism, it follows that the density
correlation functions of defects and anti-defects in a given system should be
completely determined in terms of a single length scale , the relevant
domain size. Thus, when lengths are expressed in units of , these
distributions should show universal behavior, depending only on the symmetry of
the order parameter, and space dimensions. We have verified this prediction by
analyzing the distributions of defects/anti-defects formed in the
isotropic-nematic phase transition in a thin layer of nematic liquid crystals.
Our experimental results confirm this prediction and are in reasonable
agreement with the results of numerical simulations.Comment: 15 pages, 4 figures, minor changes, few new references adde
Effect of pre-existing baryon inhomogeneities on the dynamics of quark-hadron transition
Baryon number inhomogeneities may be generated during the epoch when the
baryon asymmetry of the universe is produced, e.g. at the electroweak phase
transition. The regions with excess baryon number will have a lower temperature
than the background temperature of the universe. Also the value of the quark
hadron transition temperature will be different in these regions as
compared to the background region. Since a first-order quark hadron transition
is very susceptible to small changes in temperature, we investigate the effect
of the presence of such baryonic lumps on the dynamics of quark-hadron
transition. We find that the phase transition is delayed in these lumps for
significant overdensities. Consequently, we argue that baryon concentration in
these regions grows by the end of the transition. We briefly discuss some
models which may give rise to such high overdensities at the onset of the
quark-hadron transition.Comment: 16 pages, no figures, minor changes, version to appear in Phys. Rev.
Performance of soybean (Glycine max) intercropped with different cereals under varying levels of nitrogen
A field experiment conducted during 2009 and 2010 at the research farm of the Indian Agricultural Research Institute, New Delhi to study the performance of soybean as influenced by the intercropping of cereals, viz. maize (Zea mays L.), sorghum [Sorghum bicolor (L.) Moench.] and pearl millet (Pennisetum glaucum L.) with 0, 50, 75 and 100% of their respective recommended dose of N (RDN) levels. In all 12 intercropping systems in 2:1 ratio of soybean+ maize, soybean+sorghum and soybean+pearl millet with 4 levels of RDN to cereal component crops along with sole soybean were carried out in a randomized block designand replicated thrice. The performance of soybean was greatly influenced by the intercrops as well as N levels. The sole crop of soybean recorded higher number of branches, drymatter accumulation, root biomass; leaf area index, crop growth rate and relative growth rate as compared to soybean grown in intercropping systems. Likewise the yield attributes, yield and harvest index were also higher with sole soybean. Among the intercropping systems, soybean+pearl millet had greater negative impact on performance of soybean as compared to soybean+maize and soybean+sorghum system. The increase in N levels to cereal crops in intercropping systems showed negative impact on the growth and yield attributes, and yield of soybean. The 100% RDN to intercropped cereals had the highest negative effect while the control had the least. The highest gross returns, net returns, B: C ratio and soybean equivalent yield (SEY) were observed under soybean+maize intercropping system along with 100% RDN to intercropped maize in both the years of experimentation. Among the intercropping systems, soybean+maize intercropping systems recorded higher returns and SEY than others
Working Group Report: Neutrino and Astroparticle Physics
This is the report of neutrino and astroparticle physics working group at
WHEPP-8. We present the discussions carried out during the workshop on selected
topics in the above fields and also indicate progress made subsequently. The
neutrino physics subgroup studied the possibilites of constraining neutrino
masses, mixing and CPT violation in lepton sector from future experiments.
Neutrino mass models in the context of abelian horizontal symmetries, warped
extra dimensions and in presence of triplet Higgs were studied. Effect of
threshold corrections on radiative magnification of mixing angles was
investigated. The astroparticle physics subgroup focused on how various
particle physics inputs affect the CMBR fluctuation spectrum, and on brane
cosmology. This report also contains an introduction on how to use the publicly
available code CMBFAST to calculate the CMBR fluctuations.Comment: Prepared for the 8th Workshop on High-Energy Physics Phenomenology
(WHEPP-8), IIT Mumbai, India, 5-16 Jan 200
Electromagnetic probes
We introduce the seminal developments in the theory and experiments of
electromagnetic probes for the study of the dynamics of relativistic heavy ion
collisions and quark gluon plasma.Comment: 47 pages, 33 Figures; Lectures delivered by Dinesh K. Srivastava at
QGP Winter School (QGPWS08) at Jaipur, India, February 1-3, 200
Magnetic and structural properties of the iron silicide superconductor LaFeSiH
The magnetic and structural properties of the recently discovered
pnictogen/chalcogen-free superconductor LaFeSiH (~K) have been
investigated by Fe synchrotron M{\"o}ssbauer source (SMS) spectroscopy,
x-ray and neutron powder diffraction and Si nuclear magnetic resonance
spectroscopy (NMR). No sign of long range magnetic order or local moments has
been detected in any of the measurements and LaFeSiH remains tetragonal down to
2 K. The activated temperature dependence of both the NMR Knight shift and the
relaxation rate is analogous to that observed in strongly overdoped
Fe-based superconductors. These results, together with the
temperature-independent NMR linewidth, show that LaFeSiH is an homogeneous
metal, far from any magnetic or nematic instability, and with similar Fermi
surface properties as strongly overdoped iron pnictides. This raises the
prospect of enhancing the of LaFeSiH by reducing its carrier
concentration through appropriate chemical substitutions. Additional SMS
spectroscopy measurements under hydrostatic pressure up to 18.8~GPa found no
measurable hyperfine field
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