A Holographic P-wave Superconductor Model

We study a holographic p-wave superconductor model in a four dimensional Einstein-Maxwell-complex vector field theory with a negative cosmological constant. The complex vector field is charged under the Maxwell field. We solve the full coupled equations of motion of the system and find black hole solutions with the vector hair. The vector hairy black hole solutions are dual to a thermal state with the U(1) symmetry as well as the spatial rotational symmetry breaking spontaneously. Depending on two parameters, the mass and charge of the vector field, we find a rich phase structure: zeroth order, first order and second order phase transitions can happen in this model. We also find "retrograde condensation" in which the hairy black hole solution exists only for the temperatures above a critical value with the free energy much larger than the black hole without hair. We construct the phase diagram for this system in terms of the temperature and charge of the vector field.Comment: v3: 26 pages, 15 figures, references added, extra arguments added, to appear in JHE

Entanglement entropy in a holographic p-wave superconductor model

In a recent paper, arXiv:1309.4877, a holographic p-wave model has been proposed in an Einstein-Maxwell-complex vector field theory with a negative cosmological constant. The model exhibits rich phase structure depending on the mass and the charge of the vector field. We investigate the behavior of the entanglement entropy of dual field theory in this model. When the above two model parameters change, we observe the second order, first order and zeroth order phase transitions from the behavior of the entanglement entropy at some intermediate temperatures. These imply that the entanglement entropy can indicate not only the occurrence of the phase transition, but also the order of the phase transition. The entanglement entropy is indeed a good probe to phase transition. Furthermore, the "retrograde condensation" which is a sub-dominated phase is also reflected on the entanglement entropy.Comment: figures added; accepted by Nuclear Physics

Competition between s-wave order and d-wave order in holographic superconductors

We study competition between s-wave order and d-wave order through two holographic superconductor models. We find that once the coexisting phase appears, it is always thermodynamically favored, and that the coexistence phase is narrow and one condensate tends to kill the other. The phase diagram is constructed for each model in terms of temperature and the ratio of charges of two orders. We further compare the behaviors of some thermodynamic quantities, and discuss the different aspects and identical ones between two models.Comment: 3 figures added, accepted by JHE

China's economic reforms : pointers for other economies in transition?

China's two main economic problems before reform were low incentives to workers and the misallocation of resources among sectors. These problems were theresult of a development strategy oriented toward heavy industry. By improving material incentives, China's reforms created a flow of new resources and allowed them to be allocated to sectors suppressed under pre-reform strategies. The onset of reform in China was not allowed to disrupt production from existing resources. Instead, the newly created resources were permitted to accrue and to flow into the more productive, often light industrial sectors, thus stimulating continuous growth of the national economy during reform. Low incentives and the suppression of nonpriority sectors are common features of the legacy of economies in transition from central planning that based their development on the rapid growth of heavy industry. China's approach may be of interest to them. Among lessons China learned are that: (a) Autonomy must be granted to micromanagement units and preserved to improve the incentive structure and create a new flow of resources. (b) While maintaining essential minimum levels of production in the pre-reform priority sectors, autonomous enterprises must be permitted and encouraged to allocate new incremental resource flows to the previously suppressed sectors. (c) In parallel, the distorted policy environment and planned-allocation system must be progressively reformed to bring them into line with the new system of incentives and modus operandi of autonomous enterprises.Banks&Banking Reform,Municipal Financial Management,Water and Industry,Economic Theory&Research,Environmental Economics&Policies

Microinsurance, Trust and Economic Development: Evidence from a Randomized Natural Field Experiment

We report results from a large randomized natural field experiment conducted in southwestern China in the context of insurance for sows. Our study sheds light on two important questions about microinsurance. First, how does access to formal insurance affect farmers' production decisions? Second, what explains the low takeup rate of formal insurance, despite substantial premium subsidy from the government? We find that providing access to formal insurance significantly increases farmers' tendency to raise sows. We argue that this finding also suggests that farmers are not previously insured efficiently through informal mechanisms. We also provide several pieces of evidence suggesting that trust, or lack thereof, for government-sponsored insurance products is a significant barrier for farmers' willingness to participate in the insurance program.Microinsurance; Trust, Natural Field Experiment