Gravitational Waves from Coalescing Binary Sources

Coalescing binary systems (eg pulsars, neutron stars and black holes) are the most likely sources of gravitational radiation, yet to be detected on or near Earth, where the local gravitational field is negligible and the Poincar\'e symmetry rules. On the other hand, the general theory of gravitational waves emitted by axially symmetric rotating sources predicts the existence of a non-vanishing news function. The existence of such function implies that, for a distant observer, the asymptotic group of isometries, the BMS group, has a translational symmetry that depends on the orbit periodicity of the source, thus breaking the isotropy o the Poincar\'e translations. These results suggest the application of the asymptotic BMS-covariant wave equation to obtain a proper theoretical basis for the gravitational waves observations.Comment: 4 pages, awarded a honorable mention from the Gravity Research Foundation 201

Dynamical Casimir effect with cylindrical waveguides

I consider the quantum electromagnetic field in a coaxial cylindrical waveguide, such that the outer cylindrical surface has a time-dependent radius. The field propagates parallel to the axis, inside the annular region between the two cylindrical surfaces. When the mechanical frequency and the thickness of the annular region are small enough, only Transverse Electromagnetic (TEM) photons may be generated by the dynamical Casimir effect. The photon emission rate is calculated in this regime, and compared with the case of parallel plates in the limit of very short distances between the two cylindrical surfaces. The proximity force approximation holds for the transition matrix elements in this limit, but the emission rate scales quadratically with the mechanical frequency, as opposed to the cubic dependence for parallel plates.Comment: 6 page

Reheating in the Presence of Noise

Explosive particle production due to parametric resonance is a crucial feature of reheating in inflationary cosmology. Coherent oscillations of the inflaton field act as a periodically varying mass in the evolution equation for matter fields which couple to the inflaton. This in turn results in the parametric resonance instability. Thermal and quantum noise will lead to a nonperiodic perturbation in the mass. We study the resulting equation for the evolution of matter fields and demonstrate that noise (at least if it is temporally uncorrelated) will increase the rate of particle production. We also estimate the limits on the magnitude of the noise for which the resonant behavior is qualitatively unchanged.Comment: 26 pages, 2 figures, uses LATE

Intergenerational Mobility and the Informative Content of Surnames

We propose an alternative method for measuring intergenerational mobility. Traditional methods based on panel data provide measurements that are scarce, difficult to compare across countries and almost impossible to get across time. In particular this means that we do not know how intergenerational mobility is correlated with growth, income or the degree of inequality. Our proposal is to measure the informative content of surnames in one census. The more information does the surname have on the income of an individual, the more important is background in determining outcomes; and thus, the less mobility there is. The reason for this is that surnames inform on family relationships because the distribution of surnames is necessarily much skewed. A large percentage of the population is bound to have a very unfrequent surname. For them the partition generated by surnames is very informative on family linkages. First, we develop a model whose endogenous variable is the joint distribution of surnames and income. Then we explore the relationship between mobility and the informative content of surnames. We allow for assortative mating to be a determinant of both. Then, we use our methodology to show that in a large Spanish region the informative content of surnames is large and consistent with the model. We also show that it has increased over time, indicating a substantial drop in the degree of mobility. Finally, using the peculiarities of the Spanish surname convention we show that the degree of assortative mating has also increased over time, in such a manner that might explain the decrease in mobility observed. Our method allows us to provide measures of mobility comparable across time. It should also allow us to study other issues related to inheritance.inheritance, birth-death processes, cross-sectional data, population genetics

Cash-Flow Risks, Financial Leverage and the Cross Section of Equity Returns

What is the cross-sectional relationship between financial leverage and expected equity returns? How is the empirical relationship associated with firm\u27s financial decisions? This dissertation investigates the potential explanations for the flatness relation between financial leverage and expected equity returns, and its link to firms’ capital structure determinants. Empirical evidence contradicts the theoretical prediction that leverage amplifies the equity risks. I decompose expected equity returns of book leverage portfolios according to their exposure to cash flow and discount rate risk. I find that low leverage firms have lower cash-flow beta and higher discount-rate beta than firms with high leverage. Although cash flow beta typically has a higher price of risk, book leverage portfolios load disproportionately on discount-rate beta, generating an essentially flat relation. Moreover, the main determinants of firms’ capital structures are related to firms’ sensitivities to these systematic sources of risk and have different importance for low and high leverage firms. I show that temporary shocks are relatively more important for low leverage firms, and that financial distress risk seems to be captured by the sensitivity of firms\u27 cash flow innovations to market discount rate news

Quantum radiation in a plane cavity with moving mirrors

We consider the electromagnetic vacuum field inside a perfect plane cavity with moving mirrors, in the nonrelativistic approximation. We show that low frequency photons are generated in pairs that satisfy simple properties associated to the plane geometry. We calculate the photon generation rates for each polarization as functions of the mechanical frequency by two independent methods: on one hand from the analysis of the boundary conditions for moving mirrors and with the aid of Green functions; and on the other hand by an effective Hamiltonian approach. The angular and frequency spectra are discrete, and emission rates for each allowed angular direction are obtained. We discuss the dependence of the generation rates on the cavity length and show that the effect is enhanced for short cavity lengths. We also compute the dissipative force on the moving mirrors and show that it is related to the total radiated energy as predicted by energy conservation.Comment: 17 pages, 1 figure, published in Physical Review

Inertial forces in the Casimir effect with two moving plates

We combine linear response theory and dimensional regularization in order to derive the dynamical Casimir force in the low frequency regime. We consider two parallel plates moving along the normal direction in $D-$dimensional space. We assume the free-space values for the mass of each plate to be known, and obtain finite, separation-dependent mass corrections resulting from the combined effect of the two plates. The global mass correction is proportional to the static Casimir energy, in agreement with Einstein's law of equivalence between mass and energy for stressed rigid bodies.Comment: 9 pages, 1 figure; title and abstract changed; to appear in Physical Review

Particle Creation by a Moving Boundary with Robin Boundary Condition

We consider a massless scalar field in 1+1 dimensions satisfying a Robin boundary condition (BC) at a non-relativistic moving boundary. We derive a Bogoliubov transformation between input and output bosonic field operators, which allows us to calculate the spectral distribution of created particles. The cases of Dirichlet and Neumann BC may be obtained from our result as limiting cases. These two limits yield the same spectrum, which turns out to be an upper bound for the spectra derived for Robin BC. We show that the particle emission effect can be considerably reduced (with respect to the Dirichlet/Neumann case) by selecting a particular value for the oscillation frequency of the boundary position