3,339 research outputs found
Financial crises, unconventional monetary policy exit strategies, and agents' expectations
This paper considers a model with financial frictions and studies the role of expectations and unconventional monetary policy response to financial crises. During a financial crisis, the financial sector has reduced ability to provide credit to productive firms, and the central bank may help lessen the magnitude of the downturn by using unconventional monetary policy to inject liquidity into credit markets. The model allows parameters to change according to a Markov process, which gives agents in the economy expectation about the probability of the central bank intervening in response to a crises, as well as expectations about the central bank's exit strategy post-crises. Using this Markov regime switching specification, the paper addresses three issues. First, it considers the effects of different exit strategies, and shows that, after a crisis, if the central bank sells off its accumulated assets too quickly, the economy can experience a double-dip recession. Second, it analyzes the effects of expectations of intervention policy on pre-crises behavior. In particular, if the central bank increases the probability of intervening during crises, this increase leads to a loss of output in pre-crisis times. Finally, the paper considers the welfare implications of guaranteeing intervention during crises, and shows that providing a guarantee can raise or lower welfare depending upon the exit strategy used, and that committing before a crisis can be welfare decreasing but then welfare increasing once a crisis occurs.
Emergence of junction dynamics in a strongly interacting Bose mixture
We study the dynamics of a one-dimensional system composed of a bosonic
background and one impurity in single- and double-well trapping geometries. In
the limit of strong interactions, this system can be modeled by a spin chain
where the exchange coefficients are determined by the geometry of the trap. We
observe non-trivial dynamics when the repulsion between the impurity and the
background is dominant. In this regime, the system exhibits oscillations that
resemble the dynamics of a Josephson junction. Furthermore, the double-well
geometry allows for an enhancement in the tunneling as compared to the
single-well case.Comment: 20 pages, 9 figure
Dynamical realization of magnetic states in a strongly interacting Bose mixture
We describe the dynamical preparation of magnetic states in a strongly
interacting two-component Bose gas in a harmonic trap. By mapping this system
to an effective spin chain model, we obtain the dynamical spin densities and
the fidelities for a few-body system. We show that the spatial profiles transit
between ferromagnetic and antiferromagnetic states as the intraspecies
interaction parameter is slowly increased.Comment: 6 pages, 7 figure
Bethe ansatz solution of the anisotropic correlated electron model associated with the Temperley-Lieb algebra
A recently proposed strongly correlated electron system associated with the
Temperley-Lieb algebra is solved by means of the coordinate Bethe ansatz for
periodic and closed boundary conditions.Comment: 21 page
Realizing time crystals in discrete quantum few-body systems
The exotic phenomenon of time translation symmetry breaking under periodic
driving - the time crystal - has been shown to occur in many-body systems even
in clean setups where disorder is absent. In this work, we propose the
realization of time-crystals in few-body systems, both in the context of
trapped cold atoms with strong interactions and of a circuit of superconducting
qubits. We show how these two models can be treated in a fairly similar way by
adopting an effective spin chain description, to which we apply a simple
driving protocol. We focus on the response of the magnetization in the presence
of imperfect pulses and interactions, and show how the results can be
interpreted, in the cold atomic case, in the context of experiments with
trapped bosons and fermions. Furthermore, we provide a set of realistic
parameters for the implementation of the superconducting circuit.Comment: 6 pages, 4 figure
Magnetic Susceptibility of an integrable anisotropic spin ladder system
We investigate the thermodynamics of a spin ladder model which possesses a
free parameter besides the rung and leg couplings. The model is exactly solved
by the Bethe Ansatz and exhibits a phase transition between a gapped and a
gapless spin excitation spectrum. The magnetic susceptibility is obtained
numerically and its dependence on the anisotropy parameter is determined. A
connection with the compounds KCuCl3, Cu2(C5H12N2)2Cl4 and (C5H12N)2CuBr4 in
the strong coupling regime is made and our results for the magnetic
susceptibility fit the experimental data remarkably well.Comment: 12 pages, 12 figures included, submitted to Phys. Rev.
Universality class of quantum criticality for strongly repulsive spin-1 bosons with antiferromagnetic spin-exchange interaction
Using the thermodynamic Bethe ansatz equations we study the quantum phase
diagram, thermodynamics and criticality of one-dimensional spin-1 bosons with
strongly repulsive density-density and antiferromagnetic spin-exchange
interactions. We analytically derive a high precision equation of state from
which the Tomonaga-Luttinger liquid physics and quantum critical behavior of
the system are computed. We obtain explicit forms for the scaling functions
near the critical points yielding the dynamical exponent and correlation
length exponent for the quantum phase transitions driven by either
the chemical potential or the magnetic field. Consequently, we further
demonstrate that quantum criticality of the system can be mapped out from the
finite temperature density and magnetization profiles of the 1D trapped gas.
Our results provide the physical origin of quantum criticality in a 1D
many-body system beyond the Tomonaga-Luttinger liquid description.Comment: 12 pages, 11 figure
Classical and quantum dynamics of a model for atomic-molecular Bose--Einstein condensates
We study a model for a two-mode atomic-molecular Bose--Einstein condensate.
Starting with a classical analysis we determine the phase space fixed points of
the system. It is found that bifurcations of the fixed points naturally
separate the coupling parameter space into four regions. The different regions
give rise to qualitatively different dynamics. We then show that this
classification holds true for the quantum dynamics.Comment: 13 pages, 7 eps figure
A planar extrapolation of the correlation problem that permits pairing
It was observed previously that an SU(N) extension of the Hubbard model is
dominated, at large N, by planar diagrams in the sense of 't Hooft, but the
possibility of superconducting pairing got lost in this extrapolation. To allow
for this possibility, we replace SU(N) by U(N,q), the unitary group in a vector
space of quaternions. At the level of the free energy, the difference between
the SU(N)and U(N,q) extrapolations appears only to first nonleading order in N.Comment: 8 pages, 2 figure
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