24,299 research outputs found
Global monopole in scalar tensor theory
The well known monopole solution of Barriola and Vilenkin (BV) resulting from
the breaking of a global SO(3) symmetry is extended in general relativity along
with a zero mass scalar field and also in Brans-Dicke(BD) theory of gravity.In
the case of BD theory, the behaviour of spacetime and other variables such as
BD scalar field and the monopole energy density have been studied
numerically.For monopole along with a zero mass scalar field, exact solutions
are obtained and depending upon the choice of arbitary parameters, the
solutions either reduce to the BV case or to a pure scalar field solution as
special cases.It is interesting to note that unlike the BV case the global
monopole in the BD theory does exert gravitational pull on a test particle
moving in its spacetime.Comment: 12 pages LaTex, 3 postscript figures, Communicated to
Class.Quant.Gra
Self dual models and mass generation in planar field theory
We analyse in three space-time dimensions, the connection between abelian
self dual vector doublets and their counterparts containing both an explicit
mass and a topological mass. Their correspondence is established in the
lagrangian formalism using an operator approach as well as a path integral
approach. A canonical hamiltonian analysis is presented, which also shows the
equivalence with the lagrangian formalism. The implications of our results for
bosonisation in three dimensions are discussed.Comment: 15 pages,Revtex, No figures; several changes; revised version to
appear in Physical Review
I-V-T analysis of radiation damage in high efficiency Si solar cells
A detailed analysis of current-voltage characteristics of N(+)-P/P solar cells indicate that there is a combination of different mechanisms which results in an enhancement in the dark current and in turn deteriorates the photovoltaic performance of the solar cells after 1 MeV e(-) irradiation. The increase in the dark current is due to three effects, i.e., bulk recombination, space charge recombination by deep traps and space charge recombination through shallow traps. It is shown that the increase in bulk recombination current is about 2 to 3 orders of magnitude whereas space charge recombination current due to shallow traps increases only by an order or so and no space charge recombination through deep traps was observed after irradiation. Thus, in order to improve the radiation hardness of these devices, bulk properties should be preserved
Influence of design variables on radiation hardness of silicon MINP solar cells
Metal-insulator-N/P silicon (MINP) solar cells were fabricated using different substrate resistivity values, different N-layer designs, and different I-layer designs. A shallow junction into an 0.3 ohm-cm substrate gave best efficiency whereas a deeper junction into a 1 to 4 ohm-cm substrate gave improved radiation hardness. I-layer design variation did little to influence radiation hardness
Dirac Point Degenerate with Massive Bands at a Topological Quantum Critical Point
The quasi-linear bands in the topologically trivial skutterudite insulator
CoSb are studied under adiabatic, symmetry-conserving displacement of the
Sb sublattice. In this cubic, time-reversal and inversion symmetric system, a
transition from trivial insulator to topological point Fermi surface system
occurs through a critical point in which massless (Dirac) bands are {\it
degenerate} with massive bands. Spin-orbit coupling does not alter the
character of the transition. The mineral skutterudite (CoSb) is very near
the critical point in its natural state.Comment: 5 pages, 3 figure
Effect of control procedures on the evolution of entanglement in open quantum systems
The effect of a number of mechanisms designed to suppress decoherence in open
quantum systems are studied with respect to their effectiveness at slowing down
the loss of entanglement. The effect of photonic band-gap materials and
frequency modulation of the system-bath coupling are along expected lines in
this regard. However, other control schemes, like resonance fluorescence,
achieve quite the contrary: increasing the strength of the control kills
entanglement off faster. The effect of dynamic decoupling schemes on two
qualitatively different system-bath interactions are studied in depth. Dynamic
decoupling control has the expected effect of slowing down the decay of
entanglement in a two-qubit system coupled to a harmonic oscillator bath under
non-demolition interaction. However, non-trivial phenomena are observed when a
Josephson charge qubit, strongly coupled to a random telegraph noise bath, is
subject to decoupling pulses. The most striking of these reflects the resonance
fluorescence scenario in that an increase in the pulse strength decreases
decoherence but also speeds up the sudden death of entanglement. This
demonstrates that the behaviour of decoherence and entanglement in time can be
qualitatively different in the strong-coupling non-Markovian regime
Quasi-static probes of the QCD plasma
Screening correlators and masses were studied at finite temperature in QCD
with two flavours of dynamical staggered quarks on a lattice. The spectrum of
screening masses show a hierarchical approach to chiral symmetry restoration.
Control of explicit chiral symmetry breaking through the quark mass was shown
to be an important step to understanding this phenomenon. No sign of decays was
found in the finite temperature scalar meson-like correlators in the confined
phase
NaAlSi: a self-doped semimetallic superconductor with free electrons and covalent holes
The layered ternary sp conductor NaAlSi, possessing the iron-pnictide "111"
crystal structure, superconducts at 7 K. Using density functional methods, we
show that this compound is an intrinsic (self-doped) low-carrier-density
semimetal with a number of unusual features. Covalent Al-Si valence bands
provide the holes, and free-electron-like Al 3s bands, which propagate in the
channel between the neighboring Si layers, dip just below the Fermi level to
create the electron carriers. The Fermi level (and therefore the
superconducting carriers) lies in a narrow and sharp peak within a pseudogap in
the density of states. The small peak arises from valence bands which are
nearly of pure Si, quasi-two-dimensional, flat, and coupled to Al conduction
bands. Isostructural NaAlGe, which is not superconducting above 1.6 K, has
almost exactly the same band structure except for one missing piece of small
Fermi surface. Certain deformation potentials induced by Si and Na
displacements along the c-axis are calculated and discussed. It seems likely
that the mechanism of pairing is related to that of several other lightly doped
two-dimensional nonmagnetic semiconductors (TiNCl, ZrNCl, HfNCl), which is not
well understood but apparently not of phonon origin.Comment: 9 pages, 7 figures, 1 tabl
Coupling polynomial Stratonovich integrals : the two-dimensional Brownian case
We show how to build an immersion coupling of a two-dimensional Brownian motion (W1,W2) along with (n2)+n=12n(n+1). integrals of the form ∫Wi1Wj2∘dW2, where j=1,…,n and i=0,…,n−j for some fixed n. The resulting construction is applied to the study of couplings of certain hypoelliptic diffusions (driven by two-dimensional Brownian motion using polynomial vector fields). This work follows up previous studies concerning coupling of Brownian stochastic areas and time integrals (Ben Arous, Cranston and Kendall (1995), Kendall and Price (2004), Kendall (2007), Kendall (2009), Kendall (2013), Banerjee and Kendall (2015), Banerjee, Gordina and Mariano (2016)) and is part of an ongoing research programme aimed at gaining a better understanding of when it is possible to couple not only diffusions but also multiple selected integral functionals of the diffusions
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