12,838 research outputs found
A semi-analytical approach to perturbations in mutated hilltop inflation
We study cosmological perturbations and observational aspects for mutated
hilltop model of inflation. Employing mostly analytical treatment, we evaluate
observable parameters during inflation as well as post-inflationary
perturbations. This further leads to exploring observational aspects related to
Cosmic Microwave Background (CMB) radiation. This semi-analytical treatment
reduces complications related to numerical computation to some extent for
studying the different phenomena related to CMB angular power spectrum for
mutated hilltop inflation.Comment: 7 pages, 2 figures. Improved version to appear in IJMP
Proton Decay and Related Processes in Unified Models with Gauged Baryon Number:
In unification models based on SU(15) or SU(16), baryon number is part of the
gauge symmetry, broken spontaneously. In such models, we discuss various
scenarios of important baryon number violating processes like proton decay and
neutron-antineutron oscillation. Our analysis depends on the effective operator
method, and covers many variations of symmetry breaking, including different
intermediate groups and different Higgs boson content. We discuss processes
mediated by gauge bosons and Higgs bosons parallely. We show how accidental
global or discrete symmetries present in the full gauge invariant Lagrangian
restrict baryon number violating processes in these models. In all cases, we
find that baryon number violating interactions are sufficiently suppressed to
allow grand unification at energies much lower than the usual GeV.Comment: (32 pages LATEX) [DOE-ER\,40757-022, CPP-93-22] {Small changes made
and two references added. This version will appear in Phys. Rev. D
A momentum-conserving, consistent, Volume-of-Fluid method for incompressible flow on staggered grids
The computation of flows with large density contrasts is notoriously
difficult. To alleviate the difficulty we consider a consistent mass and
momentum-conserving discretization of the Navier-Stokes equation.
Incompressible flow with capillary forces is modelled and the discretization is
performed on a staggered grid of Marker and Cell type. The Volume-of-Fluid
method is used to track the interface and a Height-Function method is used to
compute surface tension. The advection of the volume fraction is performed
using either the Lagrangian-Explicit / CIAM (Calcul d'Interface Affine par
Morceaux) method or the Weymouth and Yue (WY) Eulerian-Implicit method. The WY
method conserves fluid mass to machine accuracy provided incompressiblity is
satisfied which leads to a method that is both momentum and mass-conserving. To
improve the stability of these methods momentum fluxes are advected in a manner
"consistent" with the volume-fraction fluxes, that is a discontinuity of the
momentum is advected at the same speed as a discontinuity of the density. To
find the density on the staggered cells on which the velocity is centered, an
auxiliary reconstruction of the density is performed. The method is tested for
a droplet without surface tension in uniform flow, for a droplet suddenly
accelerated in a carrying gas at rest at very large density ratio without
viscosity or surface tension, for the Kelvin-Helmholtz instability, for a
falling raindrop and for an atomizing flow in air-water conditions
Magnetic field induced orientation of superconducting MgB crystallites determined by X-ray diffraction
X-ray diffraction studies of fine polycrystalline samples of MgB in the
superconducting state reveal that crystals orient with their \emph{c}-axis in a
plane normal to the direction of the applied magnetic field. The MgB
samples were thoroughly ground to obtain average grain size 5 - 10 m in
order to increase the population of free single crystal grains in the powder.
By monitoring Bragg reflections in a plane normal to an applied magnetic field
we find that the powder is textured with significantly stronger (\emph{0,0,l})
reflections in comparison to (\emph{h,k,0}), which remain essentially
unchanged. The orientation of the crystals with the \emph{ab}-plane parallel to
the magnetic field at all temperatures below demonstrates that the sign
of the torque under magnetic field does not alter, in disagreement with current
theoretical predictions
Non-relativistic CFT and Semi-classical Strings
We study different features of 3D non-relativistic CFT using gravity
description. As the corresponding gravity solution can be embedded into the
type IIB string theory, we study semi-classical closed/open strings in this
background. In particular we consider folded rotating and circular pulsating
closed strings where we find the anomalous dimension of the dual operators as a
function of their quantum numbers. We also consider moving open strings in this
background which can be used to compute the drag force. In particular we find
that for slowly moving particles, the energy is lost exponentially and the
characteristic time is given in terms of the temperature, while for fast moving
particles the energy loss goes as inverse of the time and the characteristic
time is independent of the temperature.Comment: 20 pages, Latex file; V2: typos corrected, ref. adde
To freeze or not to: Quantum correlations under local decoherence
We provide necessary and sufficient conditions for freezing of quantum
correlations as measured by quantum discord and quantum work deficit in the
case of bipartite as well as multipartite states subjected to local noisy
channels. We recognize that inhomogeneity of the magnetizations of the shared
quantum states plays an important role in the freezing phenomena. We show that
the frozen value of the quantum correlation and the time interval for freezing
follow a complementarity relation. For states which do not exhibit "exact"
freezing, but can be frozen "effectively", by having a very slow decay rate
with suitable tuning of the state parameters, we introduce an index -- the
freezing index -- to quantify the goodness of freezing. We find that the
freezing index can be used to detect quantum phase transitions and discuss the
corresponding scaling behavior.Comment: 14 pages, 9 figures, close to published version, title changed by
Phys. Rev. A. to 'Freezing of quantum correlations under local decoherence
Quantum phase transition in a Dp-Dq system
Using the top-down approach, we study intersecting Dp-Dq brane configuration
in string theory and find examples, where there can be a quantum phase
transition at zero temperature induced by the violation of the
Breitenlohner-Freedman (BF) bound at IR, which is done essentially by a
combination of charge density and magnetic fields. In particular, there exists
a Berezinskii-Kosterlitz-Thouless (BKT) type of transition for D3-D5 and D5-D5
systems. The study of the BKT type of transition is initiated by Jensen et al.
[Phys. Rev. Lett. {\bf 105}, 041601 (2010) ] for a D3-D5 system with nonzero
charge density and a magnetic field. Here, we show that one can have the BKT
transition for a D3-D5 system even in the absence of charge density but
requires multiple magnetic fields. In this case the field theory lives in 2+1
dimensions, whereas for the D5-D5 type, the transition requires the presence of
both the charge density and magnetic fields and the dual field theory lives on
a 3+1 dimensional spacetime. We also study the D3-D7 system but it does not
show the BKT type of transition.Comment: 1+37 pages; v2 Chern-Simon term for D3-D5 case presented, typos fixed
and a reference added; v3 Minor corrections, Chern-Simon term for D2-D4,
D4-D6, and D5-D7 added, also an appendix and few references added; v4 Journal
versio
The Nature of Electronic States in Atomically Thin MoS2 Field-Effect Transistors
We present low temperature electrical transport experiments in five field
effect transistor devices consisting of monolayer, bilayer and trilayer MoS2
films, mechanically exfoliated onto Si/SiO2 substrate. Our experiments reveal
that the electronic states in all films are localized well up to the room
temperature over the experimentally accessible range of gate voltage. This
manifests in two dimensional (2D) variable range hopping (VRH) at high
temperatures, while below \sim 30 K the conductivity displays oscillatory
structures in gate voltage arising from resonant tunneling at the localized
sites. From the correlation energy (T0) of VRH and gate voltage dependence of
conductivity, we suggest that Coulomb potential from trapped charges in the
substrate are the dominant source of disorder in MoS2 field effect devices,
which leads to carrier localization as well.Comment: 10 pages, 5 figures; ACS Nano (2011
Selection of longitudinal modes in a terahertz quantum cascade laser via narrow-band injection seeding
A terahertz quantum cascade laser is injection seeded with narrow-band seed pulses generated from a periodically poled lithium niobate crystal. The spectral emission of the quantum cascade laser is controlled by the seed spectra
Generalized particle dynamics in anti de Sitter spaces: A source for dark energy
We consider the generalized particle dynamics, proposed by us, in brane world
formalisms for an asymptotically anti de Sitter background. The present
framework results in a new model that accounts for the late acceleration of the
universe. An effective Dark Energy equation of state, exhibiting a phantom like
behaviour, is generated. The model is derived by embedding the physical FRW
universe in a -dimensional effective space-time, induced by the
generalized particle dynamics. We corroborate our results with present day
observed cosmological parameters.Comment: 18 pages, 6 figures. Final version to appear in IJMP
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