Interacting Bosons at Finite Temperature: How Bogolubov Visited a Black Hole and Came Home Again

The structure of the thermal equilibrium state of a weakly interacting Bose gas is of current interest. We calculate the density matrix of that state in two ways. The most effective method, in terms of yielding a simple, explicit answer, is to construct a generating function within the traditional framework of quantum statistical mechanics. The alternative method, arguably more interesting, is to construct the thermal state as a vector state in an artificial system with twice as many degrees of freedom. It is well known that this construction has an actual physical realization in the quantum thermodynamics of black holes, where the added degrees of freedom correspond to the second sheet of the Kruskal manifold and the thermal vector state is a state of the Unruh or the Hartle-Hawking type. What is unusual about the present work is that the Bogolubov transformation used to construct the thermal state combines in a rather symmetrical way with Bogolubov's original transformation of the same form, used to implement the interaction of the nonideal gas in linear approximation. In addition to providing a density matrix, the method makes it possible to calculate efficiently certain expectation values directly in terms of the thermal vector state of the doubled system.Comment: 25 pages, LaTeX. To appear in a special issue of Foundations of Physics in honor of Jacob Bekenstei

Statistics of dressed modes in a thermal state

By a Wigner-function calculation, we evaluate the trace of a certain Gaussian operator arising in the theory of a boson system subject to both finite temperature and (weak) interaction. Thereby we rederive (and generalize) a recent result by Kocharovsky, Kocharovsky, and Scully [Phys. Rev. A, vol. 61, art. 053606 (2000)] in a way that is technically much simpler. One step uses a special case of the response of Wigner functions to linear transformations, and we demonstrate the general case by simple means. As an application we extract the counting statistics for each mode of the Bose gas.Comment: to appear in Optics Communications, 10 page

Expression and Purification of Z Protein from Junín Virus

Arenaviridae comprises 23 recognized virus species with a bipartite ssRNA genome and an ambisense coding strategy. The virions are enveloped and include nonequimolar amounts of each genomic RNA species, designated L and S, coding for four ORFs (N, GPC, L, and Z). The arenavirus Junín (JUNV) is the etiological agent of Argentine Hemorrhagic Fever, an acute disease with high mortality rate. It has been proposed that Z is the functional counterpart of the matrix proteins found in other negative-stranded enveloped RNA viruses. Here we report the optimized expression of a synthetic gene of Z protein, using three expression systems (two bacterial and a baculoviral one). One of these recombinant proteins was used to generate antibodies. A bioinformatic analysis was made where Z was subdivided into three domains. The data presented contributes methodologies for Z recombinant production and provides the basis for the development of new experiments to test its function

Dual-frequency optical pumping for spin-polarizing a lithium atomic beam

Baum G, Caldwell C, Schröder W. Dual-frequency optical pumping for spin-polarizing a lithium atomic beam. Appl.Phys. A. 1980;21(2):121-126

Market Structure after Horizontal Mergers: Evidence from the Banking Industry

Antitrust policy, Competition, Market structure, Banking industry mergers, G21, G28, G34, L11, L13,

The search for value: cross-border bank M&A in emerging markets

Between 1998 and 2005, we identify 74 cross-border M&A transactions in which international banks acquired ownership stakes in 46 listed banks in emerging market economies (EME). A total of $1,057,515 million of bank assets was acquired for$38,172 million in Latin America, Central and Eastern Europe, and Asia. Using an event study approach, there is scant evidence of win-win situations when joint abnormal return is positive. Whereas abnormal returns to targets are mostly positive and significant, they tend to be offset by negative returns to acquiring banks, which drives joint returns. Econometric results find no evidence that acquisition of majority control leads to higher abnormal returns to target banks; rather, the opposite holds in banking which is inconsistent with evidence from the non-financial sector. Our evidence implies there are considerable perceived risks associated with expanding banking operations into emerging markets, which affects stockmarket valuation of cross-border M&A. Thus, the evidence does not support suggestions of a transfer of wealth from shareholders in emerging markets to their counterparts in industrialised markets