6,091 research outputs found
Magnetic phase transition in coherently coupled Bose gases in optical lattices
We describe the ground state of a gas of bosonic atoms with two coherently
coupled internal levels in a deep optical lattice in a one dimensional
geometry. In the single-band approximation this system is described by a
Bose-Hubbard Hamiltonian. The system has a superfluid and a Mott insulating
phase which can be either paramagnetic or ferromagnetic. We characterize the
quantum phase transitions at unit filling by means of a density matrix
renormalization group technique and compare it with a mean-field approach. The
presence of the ferromagnetic Ising-like transition modifies the Mott lobes. In
the Mott insulating region the system maps to the ferromagnetic spin-1/2 XXZ
model in a transverse field and the numerical results compare very well with
the analytical results obtained from the spin model. In the superfluid regime
quantum fluctuations strongly modify the phase transition with respect to the
well established mean-field three dimensional classical bifurcation.Comment: 6 pages, 3 figure
TARGET2 Unlimited: monetary policy implications of asymmetric liquidity management within the Euro area. CEPS Policy Brief No. 248, 13 July 2011
This paper analyses the implications of a continued divergence of TARGET2 balances for monetary policy in the euro area. The accumulation of TARGET2 claims (liabilities) would make the ECBâs liquidity management asymmetric once the TARGET2 claims in core countries have crowded out central bank credit in those regions. Then while providing scarce liquidity to banks in countries with TARGET2 liabilities, the ECB will need to absorb excess liquidity in countries with TARGET2 claims. We discuss three alternatives and their implications for absorbing excess liquidity in core regions: 1) using market-based measures might accelerate the capital flight from periphery to core countries and would add to the accumulation of risky assets by the ECB; 2) conducting non-market based measures, such as imposing differential (unremunerated) reserve requirements, would distort banking markets and would support the development of shadow banking; and 3) staying passive would lead to decreasing interest rates in core Europe entailing inflationary pressure and overinvestment in those regions and possibly future instability of the banking system
Astrometry with "Carte du Ciel" plates, San Fernando zone. II. CdC-SF: a precise proper motion catalogue
The historic plates of the "Carte du Ciel", an international cooperative
project launched in 1887, offer valuable first-epoch material for the
determination of absolute proper motions. We present the CdC-SF, an astrometric
catalogue of positions and proper motions derived from the "Carte du Ciel"
plates of the San Fernando zone, photographic material with a mean epoch of
1901.4 and a limiting magnitude of V~16, covering the declination range of
-10deg < declination < -2deg. Digitization has been made using a conventional
flatbed scanner. Special techniques have been developed to handle the
combination of plate material and the large distortion introduced by the
scanner. The equatorial coordinates are on the ICRS defined by Tycho-2, and
proper motions are derived using UCAC2 as second-epoch positions. The result is
a catalogue with positions and proper motions for 560000 stars, covering 1080
degrees squared. The mean positional uncertainty is 0.20" (0.12" for
well-measured stars) and the proper-motion uncertainty is 2.0 mas/yr (1.2
mas/yr for well-measured stars). The proper motion catalogue CdC-SF is
effectively a deeper extension of Hipparcos, in terms of proper motions, to a
magnitude of 15.Comment: 10 pages, 13 figures, 6 tables. Accepted for publication in A&
TARGET2 Unlimited: Monetary Policy Implications of Asymmetric Liquidity Management within the Euro Area
This paper analyses the implications of a continued divergence of TARGET2 balances for monetary policy in the euro area. The accumulation of TARGET2 claims (liabilities) would make ECBâs liquidity management asymmetric once the TARGET2 claims in core countries have crowded out central bank credit in those regions. Then while providing scarce liquidity to banks in countries with TARGET2 liabilities, the ECB will need to absorb excess liquidity in countries with TARGET2 claims. We discuss three alternatives and its implications to absorb excess liquidity in core regions: (1) Using market based measures might accelerate the capital flight from periphery to core countries and would add to the accumulation of risky assets by the ECB. (2) Conducting non-market based measures such as imposing differential (unremunerated) reserve requirements would distort banking markets and would support the development of shadow banking. (3) Staying passive would lead to decreasing interest rates in core Europe entailing inflationary pressure and overinvestment in those regions and possibly future instability of the banking system.TARGET2 balances, monetary policy, euro area, Eurosystem, excess liquidity
Excitations and S-matrix for su(3) spin chain combining and ${3^{*}}
The associated Hamiltonian for a su(3) spin chain combining and
representations is calculated. The ansatz equations for this chain
are obtained and solved in the thermodynamic limit, and the ground state and
excitations are described. Thus, relations between the number of roots and the
number of holes in each level have been found . The excited states are
characterized by means of these quantum numbers. Finally, the exact S matrix
for a state with two holes is found.Comment: 17 pages, plaintex, harvmac (to be published in J. of Phys. A
Phase-slips and vortex dynamics in Josephson oscillations between Bose-Einstein condensates
We study the relation between Josephson dynamics and topological excitations
in a dilute Bose-Einstein condensate confined in a double-well trap. We show
that the phase slips responsible for the self-trapping regime are created by
vortex rings entering and annihilating inside the weak-link region or created
at the center of the barrier and expanding outside the system. Large amplitude
oscillations just before the onset of self-trapping are also strictly connected
with the dynamics of vortex rings at the edges of the inter-well barrier. Our
results extend and analyze the dynamics of the vortex-induced phase slippages
suggested a few decades ago in relation to the "ac" Josephson effect of
superconducting and superfluid helium systems.Comment: 6 pages, 5 figure
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