Phase Diagram for a Luttinger Liquid coupled to Phonons in one dimension

The Green function and the ordering correlation functions of a system of electrons coupled to acoustic phonons are calculated explicitly. The sensitivity of the correlation function exponents to the Wentzel-Bardeen singularity is discussed. A phase diagram is established for the Hubbard model coupled to phonons, using the integral equations of Lieb and Wu. By increasing the filling factor towards half filling, the Wentzel-Bardeen singularity can be reached for arbitrary phonon coupling. This suppresses antiferromagnetic fluctuations and drives the system in a metallic phase, and ultimately in the triplet superconducting regime.Comment: 33 pages, REVTex, 6 figures upon request ([email protected]

Are lives a substitute for livelihoods ? Terrorism, security, and U.S. bilateral imports

What is the impact of terrorism on trade through higher security at the borders? The authors set up a theory which shows that the impact goes not only from terrorism to trade. Higher trade with a partner might, in turn, increase the probability of terrorism acts and make security measures more costly for total welfare. To identify the true impact of terrorism, their theory allows for a strategy to condition out the latter mechanism. The authors show in particular how past incidents perpetrated in third countries (anywhere in the world except the origin or targeted country) constitute good exogenous factors for current security measures at the borders. Their tests suggest that terrorist incidents have a small effect on U.S. imports on average, but a much higher effect for those origin countries at the top of the distribution of incidents. In addition, the level of the impact is up to three times higher when the acts result ina relatively high number of victims, the products are sensitive to shipping time, and the size of the partner is small. The authors further show how terrorism affects the number of business visas given by the United States, thereby affecting significantly U.S. imports in differentiated products. These results suggest that security to prevent terrorism does matter for trade.International Terrorism&Counterterrorism,Transport Security,Economic Theory&Research,Country Strategy&Performance,Free Trade

Debt, debt relief, and growth : a bargaining approach

This report compares and identifies two ways that Governments can"up-front"the adjustment effort: accumulating reserves; and engaging in an equity swap. The authors compare these methods with a constant rescheduling agreement which assumes that no reserves can be accumulated and that tax collections go to the creditors. The paper analyzes the outcome of a"memoryless"rescheduling agreement. The model exhibits two potential Laffer curves effects. In one, the lenders would want to reduce the vulnerability of the debtor to their sanctions (that is, required taxation). In the other, the debtor would actually prefer less growth than more. The role of reserves is studied and it is determined that their use can improve a country's welfare, over the case of the rescheduling agreement. The country must, however, be able to commit itself to a tax rate before negotiations start. Otherwise, reserves are useless. Debt-equity swaps are also studied. The outcome - always Pareto - dominates the outcome of the rescheduling equilibrium. Banks always gain a fraction of the country's capital above the share of output that they gain in the rescheduling equilibrium. Thus, banks are relatively less"impatient"than the country to reach a debt-relief agreement.Economic Theory&Research,Banks&Banking Reform,Environmental Economics&Policies,Financial Intermediation,Strategic Debt Management

Experimental investigations of the dipolar interactions between single Rydberg atoms

This review summarizes experimental works performed over the last decade by several groups on the manipulation of a few individual interacting Rydberg atoms. These studies establish arrays of single Rydberg atoms as a promising platform for quantum state engineering, with potential applications to quantum metrology, quantum simulation and quantum information

Phase space density limitation in laser cooling without spontaneous emission

We study the possibility to enhance the phase space density of non-interacting particles submitted to a classical laser field without spontaneous emission. We clearly state that, when no spontaneous emission is present, a quantum description of the atomic motion is more reliable than semi-classical description which can lead to large errors especially if no care is taken to smooth structures smaller than the Heisenberg uncertainty principle. Whatever the definition of position - momentum phase space density, its gain is severely bounded especially when started from a thermal sample. More precisely, the maximum phase space density, can only be improved by a factor M for M-level atoms. This bound comes from a transfer between the external and internal degrees of freedom. To circumvent this limit, one can use non-coherent light fields, informational feedback cooling schemes, involve collectives states between fields and atoms, or allow a single spontaneous emission evenComment: 3 figures, 4 page