Regulation, competition and fraud: evidence from retail gas stations in Mexico

Mexican gas stations across the country buy and sell gasoline at regulated common prices. Therefore, authorities that set these prices do not take into account competition conditions of each market. In this paper we establish the effect of a regulated mark-up price as well as competition on the incentives that gas stations in Mexico have to dispense less amount of gasoline than what consumers pay for. The results of theoretical and empirical work indicate that a higher regulated mark-up price reduces the incentives of gas stations to cheat. Similarly, more intense competition among the retailers of a given market decreases the average shortage.gasoline pricing; regulation; competition; fraud

The isovector dipole strength in nuclei with extreme neutron excess

The E1 strength is systematically analyzed in very neutron-rich Sn nuclei, beyond $^{132}$Sn until $^{166}$Sn, within the Relativistic Quasiparticle Random Phase Approximation. The great neutron excess favors the appearance of a deformed ground state for $^{142-162}$Sn. The evolution of the low-lying strength in deformed nuclei is determined by the interplay of two factors, isospin asymmetry and deformation: while greater neutron excess increases the total low-lying strength, deformation hinders and spreads it. Very neutron rich deformed nuclei may not be as good candidates as stable spherical nuclei like $^{132}$Sn for the experimental study of low-lying E1 strength

Quantum Brownian representation for the quantum field modes

When analyzing the particle-like excitations in quantum field theory it is natural to regard the field mode corresponding to the particle momentum as an open quantum system, together with the opposite momentum mode. Provided that the state of the field is stationary, homogeneous and isotropic, this scalar two-mode system can be equivalently represented in terms of a pair of quantum Brownian oscillators under a Gaussian approximation. In other words, the two-mode system behaves as if it were interacting linearly with some effective environment. In this paper we build the details of the effective linear coupling and the effective environment, and argue that this quantum Brownian representation provides a simple, universal and non-perturbative characterization of any single particle-like excitation. As immediate applications of the equivalence, we reanalyse the interpretation of the self-energy in terms of decay rates in a general background state, and present the master equation for the field mode corresponding to the particle momentum.Comment: 25 pages, 1 figure. Motivations emphasized, new application, overall clarity improved. Version accepted for publication in AHE

Particle propagation in non-trivial backgrounds: a quantum field theory approach

The basic aim of the thesis is the study of the propagation of particles and quasiparticles in non-trivial backgrounds from the quantum field theory point of view. By "non-trivial background" we mean either a non-vacuum state in Minkowski spacetime or an arbitrary state in a curved spacetime. Starting with the case of a flat spacetime, the basic properties of the particle and quasiparticle propagation are analyzed using two different methods other than the conventional mean-field-based techniques: on the one hand, the quantum state corresponding to the quasiparticle excitation is explicitly constructed; on the other hand, the spectral representation of the two-point propagators is analyzed. Both methods lead to the same results: the energy and decay rate of the quasiparticles are determined by the real and imaginary parts of the retarded self-energy respectively. These general results are applied to two particular quantum systems: first, a scalar particle immersed in a thermal graviton bath; second, a simplified atomic model, seizing the opportunity to connect with other statistical and first-quantized approaches. In the second part of the thesis the results are extended to curved spacetime. Working with a quasilocal quasiparticle concept the flat-spacetime results are recovered. In cosmology, within the adiabatic approximation, it is possible to go beyond the flat spacetime results and find additional effects due to the universe expansion. The cosmologically-induced effects are analyzed, obtaining that there might be an additional contribution to the particle decay due to the universe expansion. In the de Sitter case, this additional contribution coincides with the decay rate in a thermal bath in a flat spacetime at the corresponding de Sitter temperature.Comment: 269 pages, 17 figures. PhD thesis, Universitat de Barcelona. One reference added, minor typos correcte

Power system controller tuning considering stochastic variations

Electrical power systems are vulnerable to external disturbances, such as short circuits, that can lead to damage on the equipments and even blackouts. In order to improve the system response to external disturbances, the generators of the power system are equipped with automatic controllers devised to maintain the generators working on a constant operating condition. The tuning of the controllers is performed assuming the system loads do not have time-dependent variations, but such assumption is not realistic as the power system loads are stochastically changing due to the switching on and o of every device (PCs, TVs, cellphones, etc.) connected to it. This work proposes two new methods for the tuning of the generator controllers which takes into account the stochastic nature of the system loads. More speci cally, this work proposes two new methods for the tuning of the governors and AVRs of the power system generators: one focused on the steady state response and the other focused on the fault response. First, the system response as a function of the controller parameters is calculated. As the power system is under the e ect of stochastic loads, the resulting system response is stochastic. Then, a stochastic objective function which measures the quality of the system response is de ned. Each tuning method uses a di erent objective function. Finally, the objective function is optimized using the metaheuristic Cuckoo Search, which is used for global optimization problems and can be used to optimize stochastic functions. The method was tested in di erent benchmark systems showing better system responses