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Exploring Physics Beyond the Standard Electroweak Model in the Light of Supersymmetry
No full textWeak scale supersymmetry has perhaps become the most popular choice for explaining new physics beyond the standard model. An extension beyond the standard model was essential to explain issues like gauge-hierarchy problem or non-vanishing neutrino mass. With the initiation of the large hadron collider era at CERN, discovery of weak-scale supersymmetric particles and, of course, Higgs boson are envisaged. In this thesis we try to discuss certain phenomenological aspects of an R,-violating non-minimal supersymmetric model, called pvSSM. We show that pvSSM can provide a solution to the p-problem of supersymmetry and can simultaneously accommodate the existing three flavour global data from neutrino experiments even at the tree level with the simple choice of flavour diagonal neutrino Yukawa couplings. We show that it is also possible to achieve different mass hierarchies for light neutrinos at the tree level itself. In pvSSM, the effect of R-parity violation together with a seesaw mechanism with TeV scale right-handed neutrinos are instrumental for light neutrino mass generation. We also analyze the stability of tree level neutrino masses and mixing with the inclusion of one-loop radiative corrections. In addition, we investigate the sensitivity of the one-loop corrections to different light neutrino mass orderings. Decays of the lightest supersymmetric particle were also computed and ratio of certain decay branching ratios was observed to correlate with certain neutrino mixing angle. We extend our analysis for different natures of the lightest supersymmetric particle as well as with various light neutrino mass hierarchies. We present estimation for the length of associated displaced vertices for various natures of the lightest supersymmetric particle which can act as a discriminating feature at a collider experiment. We also present an unconventional signal of Higgs boson in supersymmetry which can lead to a discovery, even at the initial stage of the large hadron collider running. Besides, we show that a signal of this kind can also act as a probe to the seesaw scale. Certain other phenomenological issues have also been addressed.Research was carried out under the supervision of Prof. Utpal Chattopadhyay and Prof. Sourov Roy of the Theoretical Physics Division under SPS [School of Physical Sciences]Research was conducted under the CSIR financial research gran
The Study Of The Physics Beyond The SM At The LHC In The Light Of Dark Matter Searches
No full textThe newly discovered particle at the Large Hadron Collider (LHC) [1,2] has very close resemblance with the Standard Model (SM) Higgs boson and thus the search for the SM parameters seems to be apparently completed. However, the precise determination of the Higgs boson couplings with other SM particles as well as with itself is very important to conclude if the observed particle is the SM Higgs boson or it belongs to some extended Higgs scenario with additional heavy scalar particles which can be probed at the LHC. One should note that even with the discovery of the Higgs boson, the SM is not a complete theory for the following reasons:
• The SM is incapable of maintaining a stable vacuum until the ultimate Planck scale (M, ~ 1019 GeV) because the Higgs has its favored mass range around 125 GeV. Only the intervention of new physics at an intermediate scale will make the vacuum stable.
• The SM is unable to explain the tiny nonzero mass of neutrinos. But the present experimental data on neutrino oscillations with solar and atmospheric neutrinos clearly points toward the existence of neutrino mass and establish the mixing among the various flavors of neutrinos.
• The SM does not offer any viable ‘dark matter’ DM candidate. Although a variety of cosmological and astrophysical observation provide us substantial evidences of the presence of DM and so new physics is inevitable.
• Furthermore, the SM does not explain the prevalence of matter over antimatter in the universe and also does not include the effect of gravity.
In my thesis, I have studied some simple extensions of the SM that can easily resolve some of the above problems. To begin with, we look at the vacuum instability problem in the SM. The measured value of the Higgs mass at My, = 125.15 + 0.24 GeV is special because it corresponds to a unstable vacuum when the top quark pole mass (M,) and the strong coupling constant (as) reside in the upper sides of their uncertainties band. Taking all these uncertainties into account, it has been observed that the SM scalar potential becomes unstable at some scale in between 108-10!° GeV [3-6].The research was conducted under the supervision of Prof. Dilip Kumar Ghosh of the Theoretical Physics Division under SPS [School of Physical Sciences]The research was carried out under IACS research grant and fellowshi
Synthesis of Carbohydrate Functionalized Nanomaterials for Biomedical Application
No full textThe research was conducted under the supervision of Prof. N R Jana of SMS [School of Materials Sciences]The research was carried out under CSIR fellowshi
STUDY OF ELECTRICAL,MAGNETIC, MAGNETODIELECTRIC PROPERTIES OF NANODIMENSIONAL GLASSES AND THEIR NANOCOMPOSITES
No full textThe thesis deals with the synthesis of nanodimensional silica based glasses
containing either lithium ions or iron ions. The effect of nanosize on the ionic
conductivity and /or magnetic behaviour of the glass concerned have been
investigated. Also, the magnetodielectric properties resulting from these structural
peculiarities have been delineated.The research was carried out under the supervision of Prof. D Chakraborty, MLS and Prof. A K Nandi, PSU under SMS [School of Materials Sciences]The research was conducted under CSIR fellowship and research grant. Instrumental facilities was extended from Nano Science and Technology
Initiative program of the Department of Science and Technology, New Delh
Rectifiers formed between Organic and Inorganic Semiconductors: Characterization by Scanning Tunneling Spectroscopy
Full text linkRectifying junctions are fundamental building blocks for basic electronics. In traditional rectifiers
based on inorganic semiconductors, directionality of current flow arises due to the depletion layer or
potential barrier developed at the junction. In organic rectifiers, molecular orbitals, namely lowest
unoccupied molecular orbital (LUMO) and highest occupied molecular orbital (HOMO), enforce
directional flow of carriers. Hence assemblies of organic molecules as well as junctions between two
nanostructures are of utmost importance for both molecular and nanoscale electronic research.
In forming donor/acceptor assemblies that act as molecular rectifiers, we have introduced magnetic
organic molecules as electron-donating and electron-accepting moieties. We have characterized the
molecular assemblies formed on an electrode with a scanning tunneling microscope tip. Such
donor/acceptor assemblies with a control over the orientation of moments of the components provided
unique systems to study the effect of the nature of alignment on molecular rectifiers. We have
observed that the rectification ratio increased in junctions with moments of the components being
parallel to each other.
We have formed pn- and np-junctions between monolayers of p- and n-type nanocrystals that exhibit
current rectification in the nanodiodes when characterized with a scanning tunneling microscope
(STM) tip. With the use of ferromagnetic nanocrystals, we study the effect of mutual alignment of
magnetization vectors on current rectification in the junction between the two nanocrystals. We show
that when the magnetization vectors of the p- and of the n-type nanocrystals are parallel to each other
(and both face toward the apex of the STM tip), tunneling current in both bias modes increases with
correspondingly a higher rectification ratio.
We have also formed hybrid nanodiodes with magnetic organic molecules and diluted magnetic
semiconductors. The rectification ratio was enhanced when the magnetic moment of the component
materials align along a particular direction with the application of magnetic field. The current as well
as rectification ratio became enhanced due to the flow of spin polarized electron flow along a particular direction.
We have mapped band-edges across pn-junction that was formed as an heterostructure in a single nanorod or in a heterodimers system in an ultrahigh vacuum scanning tunneling microscope (UHVSTM) at 77 K. From scanning tunneling spectroscopy and correspondingly the density of states (DOS) spectra, we determined the conduction and valence band-edges at different points across the
junction and also the individual materials. We could map the band-diagram of the heterostructure junctions
to bring out the salient features of a diode, such as p- and n-sections, band-bending, depletion region in the nanoscale. The width (of the depletion region) and the energy-offset at the interface depended on the size of the semiconductors.Research was carried out under the supervision of Prof. A J Pal of Solid State Physics division under SPS [School of Physical Sciences]Research was conducted under CSIR fellowshi
Investigation of ion dynamics in mixed network former glasses
Full text linkThe work of this thesis is mainly based on the study of structure and ion dynamics of
several new ion conducting glasses and to correlate the macroscopic ion transport
properties to the glass network structure and the microscopic lengths. The organization
of the thesis is as follows
Chapter 1 of this thesis deals with the literature review in the field of glasses. A
brief introduction to glasses is presented and their exotic features are discussed. The
network structures of different type of glasses are briefly discussed. Several theoretical
models and concepts used to explain and understand the ion dynamics are pointed out.
Finally the scope of the thesis is presented.
In chapter 2 a brief description of the preparation technique of glasses and glassnanocomposites
and various experimental methods used to characterize them are
presented. In the initial part of the chapter the structural characterization such as
density, x-ray diffraction (XRD), differential scanning calorimetry (DSC), transmission
electron microscopy (TEM), field emission scanning electron microscopy (FESEM) and
Fourier transform infrared (FTIR) spectroscopy techniques are discussed. In the later
part, electrical characterization techniques used to study the ion dynamics are presented.
In Chapter 3 the structural and electrical properties of xAgI-(1-x)(0.3Ag2O-
0.7(0.5SeO2-0.5MoO3)) glasses have been investigated. The structural characterizations of
these glasses have been carried out using XRD, FTIR spectroscopy etc. and the thermal
study has been done using Differential Scanning Calorimeter. The Ag+ ion dynamics in
the glasses has been investigated in a broad frequency range from 10Hz – 2MHz and in
wide temperature range. The dc conductivity and the microscopic lengths obtained from
the linear response theory have been correlated to the glass network structure.
Chapter 4 deals with the study of mixed former effect and dynamics of Ag+ ions
of xAgI-(1-x)(0.3Ag2O-0.7(ySeO2-(1-y)MoO3)) glasses. The glass formation has been
confirmed using XRD. The thermodynamic properties of these glasses have been
explored using DSC. The modification of the glass network structure has been analyzed
using deconvolution of the FTIR spectra. The ionic conductivity of these glasses has been
compared to that of the undoped silver selenomolybdate glasses. The study of relaxation dynamics in these glasses has been performed in the framework of the conductivity and the electric modulus formalism. The characteristic lengths obtained from the
conductivity and dielectric spectra have been correlated to the modification of the glass
network structure.
In chapter 5 the study of mixed former effect and ion dynamics in silver ion
conducting mixed network former glasses of composition yAg2O-(1-y)(xSeO2-(1-y))TeO2
are presented in wide composition and temperature ranges. The glass network
structures and structural modification depending on composition has been investigated
using FTIR spectroscopy. The ion dynamics in these mixed former glasses has been
studied using the conductivity formalism as a function of frequency and temperature.
The correlation of ion transport properties to the microscopic length scales and the glass
network structure has been established.
In chapter 6 the Ag+ ion dynamics in xAgI-(1-x)(yAg2O-(1-y)(0.5SeO2-O.5TeO2))
mixed network former glasses for different modifier content is presented. The thermal
properties of these glasses have been studied using DSC. The relative concentrations of
different network structural units have been determined from the de-convolution of the
FTIR spectra. The ac conductivity has been investigated taking the contribution of the
electrode-sample interface. The length scales of ion dynamics, such as characteristic
mean square displacement and spatial extent of sub-diffusive motion of silver ions have been determined from the ac conductivity and dielectric spectra respectively in the framework of linear response theory. A direct correlation between the ion dynamics and the characteristic length scales and the glass network structure has been established for different compositions of the selenium-tellurite glasses. In Chapter 7 the summary of the thesis is presented. The possible future research in continuation of this work is also highlighted.Research was carried out under the supervision of Prof. Aswini Ghosh of Solid State Division under SPS [School of Physical Sciences]Research was conducted under DST grant and IACS fellowshi
Dynamics and Phases of Strongly Correlated Systems
Full text linkNon-equilibrium dynamics of an isolated quantum system driven through a quantum critical point
shows Kibble-Zurek scaling. This scaling form is controlled by the critical exponents of the universality
class of the quantum phase transition. We develop a projection operator formalism for studying both the
zero temperature equilibrium phase diagram and the non-equilibrium dynamics of the Bose-Hubbard
model. Our work shows that the method provides an accurate description of the equilibrium zero temperature
phase diagram of the Bose-Hubbard model for several lattices in two- and three-dimensions
(2D and 3D).We show that the accuracy of this method increases with the coordination number z0 of the
lattice and reaches to within 0:5% of quantum Monte Carlo data for lattices with z0 = 6. We compute
the excitation spectra of the bosons using this method in the Mott and the superfluid phases and compare
our results with mean-field theory. We also show that the same method may be used to analyze the
non-equilibrium dynamics of the model both in the Mott phase and near the superfluid-insulator quantum
critical point where the hopping amplitude J and the on-site interaction U satisfy z0J=U 1. In
particular, we study the non-equilibrium dynamics of the model, both subsequent to a sudden quench of
the hopping amplitude J and during a ramp from Ji to Jf characterized by a ramp time t and exponent
a: J(t) = Ji +(Jf Ji)(t=t)a. We compute the wave function overlap F, the residual energy Q, the
superfluid order parameter D(t), the equal-time order parameter correlation function C(t), and the defect
formation probability P for the above-mentioned protocols and provide a comparison of our results to
their mean-field counterparts. We find that Q, F, and P do not exhibit the expected universal scaling.
We explain this absence of universality and show that our results for linear ramps compare well with the
recent experimental observations.
We have generalized our above mentioned work to develop a time-dependent hopping expansion
technique for studying the non-equilibrium dynamics of strongly interacting bosons in an optical lattice
in the presence of a harmonic trap characterized by a force constant K. We show that after a sudden
quench of the hopping amplitude J across the superfluid (SF)-Mott insulator(MI) transition, the SF
order parameter jDr(t)j and the local density fluctuation dnr(t) exhibit sudden decoherence beyond a
trap-induced time scale T0 K 1=2. We also show that after a slow linear ramp down of J, jDrj and
the boson defect density Pr display a novel non-monotonic spatial profile. Both these phenomena can
be explained as consequences of trap-induced time and length scales affecting the dynamics and can be tested by concrete experiments.
We also study the statistics of the work distribution P(w) in a d dimensional closed quantum system with linear dimension L subjected to a periodic drive with frequency w0. We show that the corresponding rate function I(w) = ln[P(w)=L0]=Ld after a drive period satisfies an universal lower bound I(0) nd and has a zero at w = QLd=N, where nd and Q are the excitation and the residual energy densities generated during the drive, L0 is a constant fixed by the normalization of P(w), and N is the total number of constituent particles/spins in the system. We supplement our results by calculating I(w) for a class of
d-dimensional integrable models and show that I(w) has oscillatory dependence on w0 originating from Stuckelberg interference generated due to double passage through critical point/region during the drive.
We suggest experiments to test our theory.Research was conducted under the supervision of Prof. Krishnendu Sengupta of the Theoretical Physics division under the SPS [School of Physical Sciences]Research was carried out under IACS fellowship and gran
Graphene Based Nanomaterials for Biosensing and Catalytic Application
Full text linkThe work presented in this thesis entitled “Graphene Based Nanomaterials for Biosensing and Catalytic Application” was initiated by the author in July, 2011 in Centre for Advanced Materials, Indian Association for the Cultivation of Science, Kolkata, under the supervision of Dr. Nikhil Ranjan Jana.
Currently, nanomaterials have wide applications owing to their structural properities. Commonly used nanoparticles include metal/metal oxide (e.g. Pt, Pd, Co3O4, Au, Ag), semiconductor nanoparticle (e.g. TiO2, CdSe, ZnS, ZnO) and magnetic nanoparticle (e.g. Fe2O3, Fe3O4). Similarly, variety of polymers (polyaniline, dextran), molecules (cyclodextrin), dendrimers have great impact in the energy-based and biomedical applications. However, scientists are exploring materials with improved physicochemical features that are dimensionally more appropriate in the field of nanoscience and nanotechnology. In this aspect, graphene and graphene based nanomaterials are valuable addition in the field of nanoscience, playing important role in recent development of science and technology. These graphene based hybrid materials offer the property of both component, removes some of the limitations of individual components and in some cases enhances the performance of individual component. In particular graphene based nanocomposites with Ag, Au, Pt are widely used in biosensing application; nanocomposites with Pt, Pd, Si, SnO2, MnO2, Ni(OH)2 are widely used in energy based application; nanocomposites with TiO2 and ZnO are used in photocatalytic application; nanocomposites with Fe3O4, γ-Fe2O3 are used in magnetic separation application and nanocomposites with dextran, cyclodextrin, polyaniline etc. are used in biomedical, energy based applications. Detection and quantification of biomolecules such as amino acid, vitamin, hormone, neurotransmitter, lipid, protein are very important as they control every activity of organisms and their altered concentration or structure leads to various diseases. The sensing capacity of the detection systems is being improved by using nanomaterials and the unique optical and electronic properties of nanoparticles have been used for sensitive and selective detection of DNA, proteins, pathogens or biomolecules. There is still challenge to develop easy and cost effective techniques by using nanomaterials in biosensor applications. Graphene surface has terrific ability to decorate different molecules or nanoparticles to combine the both property of graphene and as well as molecules/nanoparticles. Two principle aspect such as quenching efficiency and high conductivity are playing significant role for placing graphene based nanomaterials an important position in the field of optical and electrochemical sensing of biomolecules. However, graphene is actually hydrophobic in nature that limits its application in biomedical field. Thus preparation of soluble graphene is challenging for optical and electrochemical based biosensing.Research was conducted under the supervision of Prof. N R Jana of CAM under SPS [School of Physical Sciences]Research was carried out under CSIR fellowship and gran
Current-voltage characteristics of semiconducting nanostructures and organic molecules by scanning tunneling microscopy
Full text linkThe discovery and use of scanning probe techniques have changed the roadmap of research
work during the last two decades. With scanning tunneling microscopy (STM) and spectroscopy
(STS), electronic properties of various nanostructures and organic molecules are being explored in
details. Manipulating a single atom or a molecule or a quantum dot (QD) is now a reality. In our
work, we aimed to use STM to understand the electronic properties of (magnetic) organic
molecules and semiconducting nanostructures in a monolayer or in an isolated form. To form such a
monolayer of organic molecules or semiconducting nanostructures on suitable substrates, we have
used conventional layer-by-layer (LbL) electrostatic self assembly process. Earlier in our lab, we
showed the route to orient molecular plane of planar magnetic organic molecules in a monolayer
with magnetic field assisted LbL electrostatic assembly process. As a continuation to such research
progress, transport properties (transport gap) of such oriented molecules in a monolayer have
been studied by STS. We also showed the route to tune transport gap through time restricted
assembly process, where sub-monolayers of organic molecules were formed on suitable electrode substrates.
Intoduction of magnetic dopants in a semiconducting quantum dot leads to dilute magnetic
semiconductor (DMS). Such room temperature ferromagnetic QDs (with high Curie temperature Tc)
have been predicted by theoreticians in the early 1990’s. Experimental procedures to synthesize
cobalt doped ZnO QDs were first realized by Gamlein et.al. We followed such reported procedures to grow ferromagnetic QDs and measured their electronic properties in a monolayer with the magnetic domains being aligned to a particular direction.
In addition we have made in depth studies with spin polarized scanning tunneling
microscopy (SP-STM) and spin polarized scanning tunneling spectroscopy (SP-STS) with magnetic organic molecules and DMS QDs. Spin of electrons has added an extra dimension in the field of modern electronics as it has been considered as the backbone of modern day computation. Such spin-electronics or spintronics is one of the most fascinating and emerging field of research. In this respect, measurement of spin transport through spin valve configuration, where a nonmagnetic spacer layer sandwiched between two ferromagnetic layers is being explored. SP-STM on the other
hand has given the possibility to manipulate spins of magnetic molecules or nanostructures in a monolayer or in an isolated form. We have emphasized tunneling of spin-polarized electrons through a monolayer of magnetic organic molecules or cobalt doped ZnO QDs.
The last part of this thesis focuses on memristive effect of metal semiconductor core-shell nanoparticles. Memristor is considered as the fourth circuit element as predicted first by Leon Chua in 1971. In memristors, electrical resistance of a system depends on the history of current that had
previously flew through the material and thus gave rise to resistive memory effect. We tested such behavior on individual metal or semiconducting nanoparticles and also on metal semiconductor core-shell nanostructures and showed multilevel memristor effect.Research was carried out under the supervision of Prof. A J Pal of the Solid State division of the SPS [School of Physical Sciences]Research was carried out under IACS fellowship & DST gran
Study of Improved Dielectric Properties of Some Technologically Important Flexible Inorganic Oxide-Polymer Composites
Full text linkThe rapid development of the electronics industry requires easily synthesized as well as
inexpensive electronic components which would offer higher performance yet with smaller
size. In this regard, ceramic polymer (C/P) composites with 0–3 connectivity are especially
attractive for various applications due to their ease of fabrication, and they have thus been
widely studied over the last couple of decades. In such composites, the 0–3 connectivity is
formed by suspending 0–dimensional ceramic particles within a 3–dimensional continuative
polymer matrix host. The ability to make a composite of a particular, bespoke permittivity and
permeability (albeit within certain limits) provides useful degrees of freedom in applications
and design. Additionally, 0–3 composites provide opportunities to develop materials with the
combined magnetic and dielectric properties desired for multifunctional components. The
principal advantage to be had is the downsizing of telecommunication devices. By combining
high-permittivity ceramic powders with ductile polymers, composites with good dielectric
properties can be developed. In general, the properties achievable with composites depend on
the initial matrix and filler properties. With 0–3 type composites, their dielectric and magnetic
properties are dominated by the guest material.
In this respect, ferroelectric high- εr ceramic or conductive fillers have been widely studied,
because of their potential applications such as high charge-storage capacitors, artificial muscles,
smart skins, and apparatus used in high-speed integrated circuits. Even though many ceramic materials like BaTiO3, Ba(Sr, Ti)O3, Pb(Zr, Ti)O3, Pb(Mg, Nb)O3 etc. that have a high dielectric permittivity and a low dielectric loss are presently used in electronic fields, they are generally brittle in nature, sintered at high temperature and entail a complicated fabrication process. To
overcome these disadvantages, C/P composites are better alternatives and offer excellent material characteristics, such as flexibility, machinabilty, low-temperature process ability and tailored dielectric properties. Such flexibility in the fabrication of inductive and capacitive
circuit elements would be highly advantageous in telecommunication and related applications. Generally polymers offer good mechanical flexibility and high electrical breakdown strength but suffer from low dielectric permittivity (low- εr). Many efforts have been devoted to achieve enhanced εr values with low dielectric loss.Research was conducted under the supervision of Prof. B K Chowdhury of the Solid State Physics division under SPS [School of Physical Sciences]Research was carried out under DST & CSIR gran