31,382 research outputs found
Near infra-red spectroscopy of V838 Monocerotis
Near IR, multi-epoch, spectroscopic and photometric observations of the
enigmatic, eruptive variable V838 Mon in JHK bands are reported. One of the
unusual features is the detection of several strong neutral TiI lines in
emission in the K band. From the strength of these lines, the mass of the
ejected envelope is estimated to be in the range 10e-7 to 10e-5 M(sun). The
spectra also show the strong presence of the first and second overtones of 12CO
bands seen in the K and H bands. The CO bands show a complex evolution. Deep
water bands at 1.4 and 1.9 micron are also seen later in the object's
evolution. Blackbody fits to the JHK photometric data show that V838 Mon has
evolved to temperatures between 2400 - 2600 K by approximately 130 days after
outburst. The spectra at this stage have the general characteristics of a very
cool M giant.Comment: 7 pages, 5 figures, to appear in Astronomy and Astrophysic
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
Qubit rotation and Berry Phase
A quantized fermion can be represented by a scalar particle encircling a
magnetic flux line. It has the spinor structure which can be constructed from
quantum gates and qubits. We have studied here the role of Berry phase in
removing dynamical phase during one qubit rotation of a quantized fermion. The
entanglement of two qubit inserting spin-echo to one of them results the change
of Berry phase that can be considered as a measure of entanglement. Some effort
is given to study the effect of noise on the Berry phase of spinor and their
entangled states.Comment: 12 page
A Note on Charged Black Holes in AdS space and the Dual Gauge Theories
We study the thermodynamics and the phase structures of Reissner-Nordstrom
and Born-Infeld black holes in AdS space by constructing ``off-shell'' free
energies using thermodynamic quantities derived directly from the action. We
then use these results to propose ``off-shell'' effective potentials for the
respective boundary gauge theories. The saddle points of the potentials
describe all the equilibrium phases of the gauge theories.Comment: LaTeX, 21+1 pages, 7 figure
Volatility and growth: credit constraints and productivity-enhancing investment
We examine how credit constraints affect the cyclical behavior of productivity-enhancing investment and thereby volatility and growth. We first develop a simple growth model where firms engage in two types of investment: a short-term one and a long-term productivity-enhancing one. Because it takes longer to complete, long-term investment has a relatively less procyclical return but also a higher liquidity risk. Under complete financial markets, long-term investment is countercyclical, thus mitigating volatility. But when firms face tight credit constraints, long-term investment turns procyclical, thus amplifying volatility. Tighter credit therefore leads to both higher aggregate volatility and lower mean growth for a given total investment rate. We next confront the model with a panel of countries over the period 1960-2000 and find that a lower degree of financial development predicts a higher sensitivity of both the composition of investment and mean growth to exogenous shocks, as well as a stronger negative effect of volatility on growth
Electric field control of spin lifetimes in Nb-SrTiO by spin-orbit fields
We show electric field control of the spin accumulation at the interface of
the oxide semiconductor Nb-SrTiO with Co/AlO spin injection
contacts at room temperature. The in-plane spin lifetime as
well as the ratio of the out-of-plane to in-plane spin lifetime
is manipulated by the built-in electric field at
the semiconductor surface, without any additional gate contact. The origin of
this manipulation is attributed to Rashba Spin-Orbit Fields (SOFs) at the
Nb-SrTiO surface and shown to be consistent with theoretical model
calculations based on SOF spin flip scattering. Additionally, the junction can
be set in a high or low resistance state, leading to a non-volatile control of
, consistent with the manipulation of the Rashba SOF
strength. Such room temperature electric field control over the spin state is
essential for developing energy-efficient spintronic devices and shows promise
for complex oxide based (spin)electronicsComment: 5 pages, 4 figure
SO(3) "Nuclear Physics" with ultracold Gases
An ab initio calculation of nuclear physics from Quantum Chromodynamics
(QCD), the fundamental SU(3) gauge theory of the strong interaction, remains an
outstanding challenge. Here, we discuss the emergence of key elements of
nuclear physics using an SO(3) lattice gauge theory as a toy model for QCD. We
show that this model is accessible to state-of-the-art quantum simulation
experiments with ultracold atoms in an optical lattice. First, we demonstrate
that our model shares characteristic many-body features with QCD, such as the
spontaneous breakdown of chiral symmetry, its restoration at finite baryon
density, as well as the existence of few-body bound states. Then we show that
in the one-dimensional case, the dynamics in the gauge invariant sector can be
encoded as a spin S=3/2 Heisenberg model, i.e., as quantum magnetism, which has
a natural realization with bosonic mixtures in optical lattices, and thus sheds
light on the connection between non-Abelian gauge theories and quantum
magnetism.Comment: 34 pages, 9 figure
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