71,209 research outputs found

    Symmetry-protected many-body Aharonov-Bohm effect

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    It is known as a purely quantum effect that a magnetic flux affects the real physics of a particle, such as the energy spectrum, even if the flux does not interfere with the particle's path - the Aharonov-Bohm effect. Here we examine an Aharonov-Bohm effect on a many-body wavefunction. Specifically, we study this many-body effect on the gapless edge states of a bulk gapped phase protected by a global symmetry (such as ZN\mathbb{Z}_{N}) - the symmetry-protected topological (SPT) states. The many-body analogue of spectral shifts, the twisted wavefunction and the twisted boundary realization are identified in this SPT state. An explicit lattice construction of SPT edge states is derived, and a challenge of gauging its non-onsite symmetry is overcome. Agreement is found in the twisted spectrum between a numerical lattice calculation and a conformal field theory prediction.Comment: 5 pages main text + 8 pages appendix, 3 figures. v2: nearly PRB versio

    Open String Descriptions of Space-like Singularities in Two Dimensional String Theory

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    The matrix model formulation of two dimensional string theory has been shown to admit time dependent classical solutions whose closed string duals are geodesically incomplete space-times with space-like boundaries. We investigate some aspects of the dynamics of fermions in one such background. We show that even though the background solution appears pathological, the time evolution of the system is smooth in terms of open string degrees of freedom, viz. the fermions. In particular, an initial state of fermions evolves smoothly into a well defined final state over an infinite open string time interval, while the time perceived by closed strings appears to end abruptly. We outline a method of calculating fermion correlators exactly using symmetry properties. The result for the two point function is consistent with the semiclassical picture.Comment: LaTeX 8 eps figures, referenced adde

    Keynesian Theorizing During Hard Times: Stock-Flow Consistent Models as an Unexplored 'Frontier' of Keynesian Macroeconomics

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    This paper argues that the Stock-Flow Consistent Approach to macroeconomic modeling can be seen as a natural outcome of the path taken by Keynesian macroeconomic thought in the 1960s and 1970s, a theoretical frontier that remained largely unexplored with the end of Keynesian academic hegemony. The representative views of Davidson, Godley, Minsky, and Tobin as different closures of the same SFC accounting framework are presented, and similarities and problems discussed.Post-Keynesian Models, Stock-Flow Consistency, Pitfalls Approach

    Optimal Supervisory Policies and Depositor-Preferences Laws.

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    When supervisors have imperfect information about the soundness of banks, they may be unaware of insolvency problems that develop in the interval between on-site examinations. Supervising banks more often will alleviate this problem but will increase the costs of supervision. This paper analyzes the trade-offs that supervisors face between the cost of supervision and their need to monitor banks effectively. We first characterize the optimal supervisory policy, in terms of the time between examinations and the closure rule at examinations, and compare it with the policy of an independent supervisor. We then show that making this supervisor accountable for deposit insurance losses in general reduces the excessive forbearance of the independent supervisor and may also improve on the time between examinations. Finally, we extend our analysis to the impact of depositor-preference laws on supervisors' monitoring incentives and show that these laws may lead to conflicting effects on the time between examinations and closure policy vis-a-vis the social optimum.Deposit Insurance; Depositor Preference; Supervision.
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