Electrovac Universes with a Cosmological Constant

We present the extension of the Einstein-Maxwell system called electrovac universes by introducing a cosmological constant $\Lambda$. In the absence of the $\Lambda$ term, the crucial equation in solving the Einstein-Maxwell system is the Laplace equation. The cosmological constant modifies this equation to become in a non-linear partial differential equation which takes the form $\Delta U=2\Lambda U^3$. We offer special solutions of this equation.Comment: 7 page

Universal quantum computation with the Orbital Angular Momentum of a single photon

We prove that a single photon with quantum data encoded in its orbital angular momentum can be manipulated with simple optical elements to provide any desired quantum computation. We will show how to build any quantum unitary operator using beamsplitters, phase shifters, holograms and an extraction gate based on quantum interrogation. The advantages and challenges of these approach are then discussed, in particular the problem of the readout of the results.Comment: First version. Comments welcom

The impact of the ECB´s targeted long-term refinancing operations on banks´ lending policies : the role of competition

El presente artículo evalúa el impacto de las operaciones de refinanciación a largo plazo con objetivo específico (TLTRO, por sus siglas en inglés) en las políticas crediticias de los bancos del área del euro. Para guiar la investigación empírica, construimos un modelo teórico en el que los bancos compiten a la Cournot en los mercados de crédito y depósito. Distinguimos entre efectos directos y efectos indirectos. Los efectos directos ocurren porque los bancos que participan en las TLTRO expanden su oferta de crédito gracias a los menores costes marginales que conllevan estas operaciones. Los efectos indirectos en los bancos que no participan operan a través de cambios en la estructura competitiva de los mercados de crédito y depósito, y su efecto es ambiguo a priori. Tras este análisis, examinamos estas predicciones teóricas con una muestra de 130 bancos de 13 países y las respuestas confidenciales a la Encuesta de Préstamos Bancarios del Banco Central Europeo. Respecto a los efectos directos, encontramos que las TLTRO contribuyeron a reducir los márgenes sobre préstamos relativamente seguros, pero que no tuvieron impacto en los criterios de aprobación de préstamos. Respecto a los efectos indirectos, la transmisión de las TLTRO tuvo lugar a través de la relajación de los criterios de aprobación de préstamos, y estuvo concentrada principalmente en los bancos expuestos a altas presiones competitivas. También hallamos evidencia de externalidades positivas en los mercados de financiaciónWe assess the impact of the Eurosystem’s Targeted Long-Term Refinancing Operations (TLTROs) on the lending policies of euro area banks. To guide our empirical research, we build a theoretical model in which banks compete à la Cournot in the credit and deposit markets. According to the model, we distinguish between direct and indirect effects. Direct effects take place because bidding banks expand their loan supply due to the lower marginal costs implied by the TLTROs. Indirect effects on non-bidders operate via changes in the competitive environment in banks’ credit and deposit markets and are a priori ambiguous. We then test these theoretical predictions with a sample of 130 banks from 13 countries and the confidential answers to the ECB’s Bank Lending Survey. Regarding direct effects on bidders, we find an easing impact on margins on loans to relatively safe borrowers, but no impact on credit standards. Regarding indirect effects, there is a positive impact on the loan supply on non-bidders but, contrary to the direct effects, the transmission of the TLTROs takes place through an easing of credit standards, and it is mainly concentrated in banks facing high competitive pressures. We also find evidence of positive funding externalitie

Discurso de investidura como Doctor Honoris Causa del Prof. C. Tiao

Investido Doctor Honoris Causa en el acto del día de la Universidad del curso 02/0

Delayed commutation in quantum computer networks

In the same way that classical computer networks connect and enhance the capabilities of classical computers, quantum networks can combine the advantages of quantum information and communications. We propose a non-classical network element, a delayed commutation switch, that can solve the problem of switching time in packet switching networks. With the help of some local ancillary qubits and superdense codes we can route the information after part of it has left the network node.Comment: 4 pages. 4 figures. Preliminar versio