The rationale for a safe asset and fiscal capacity for the Eurozone. LEQS Paper No. 144/2019 May 2019

The only way to share common liabilities in the Eurozone is to achieve full fiscal and political union, i.e. unity of liability and control. In the pursuit of that goal, there is a need to smooth the transition, avoid unnecessary strains to macroeconomic and financial stability and lighten the burden of stabilisation policies from national sovereigns and the European Central Bank, while preserving market discipline and avoiding moral hazard. Both fiscal and monetary policy face constraints linked to the high legacy debt in some countries and the zero-lower-bound, respectively, and thus introducing Eurozone ‘safe assets’ and fiscal capacity at the centre would strengthen the transmission of monetary and fiscal policies. The paper introduces a standard Mundell-Fleming framework adapted to the features of a closed monetary union, with a two-country setting comprising a ‘core’ and a ‘periphery’ country, to evaluate the response of policy and the economy in case of symmetric and asymmetric demand and supply shocks in the current situation and following the introduction of safe bonds and fiscal capacity. Under the specified assumptions, it concludes that a safe asset and fiscal capacity, better if in combination, would remove the doom loop between banks and sovereigns, reduce the loss in output for both economies and improve the stabilisation properties of fiscal policy for both countries, and thus is welfare enhancing

Solar System motions and the cosmological constant: a new approach

We use the corrections to the Newton-Einstein secular precessions of the longitudes of perihelia of some planets (Mercury, Earth, Mars, Jupiter, Saturn) of the Solar System, phenomenologically estimated as solve-for parameters by the Russian astronomer E.V. Pitjeva in a global fit of almost one century of data with the EPM2004 ephemerides, in order to put on the test the expression for the perihelion precession induced by an uniform cosmological constant Lambda in the framework of the Schwarzschild-de Sitter (or Kottler) space-time. We compare such an extra-rate to the estimated corrections to the planetary perihelion precessions by taking their ratio for different pairs of planets instead of using one perihelion at a time for each planet separately, as done so far in literature. The answer is neatly negative, even by further re-scaling by a factor 10 (and even 100 for Saturn) the errors in the estimated extra-precessions of the perihelia released by Pitjeva. Our conclusions hold also for any other metric perturbation having the same dependence on the spatial coordinates, as those induced by other general relativistic cosmological scenarios and by many modified models of gravity. Currently ongoing and planned interplanetary spacecraft-based missions should improve our knowledge of the planets' orbits allowing for more stringent constraints.Comment: LaTex, 12 pages, no figures, 2 tables. One reference and one WEBlink updated. To appear in Advances in Astronom

Some considerations on the present-day results for the detection of frame-dragging after the final outcome of GP-B

The cancelation of the first even zonal harmonic coefficient J2 of the multipolar expansion of the Newtonian part of the Earth's gravitational potential from the linear combination f(2L) of the nodes of LAGEOS and LAGEOS II used in the latest tests of the general relativistic Lense-Thirring effect cannot be perfect, as assumed so far. It is so, among other things, because of the uncertainties in the spatial orientation of the terrestrial spin axis as well. As a consequence, the coefficient c1 entering f(2L), which is not a solve-for parameter being theoretically computed from the analytical expressions of the classical node precessions due to J2, is, on average, uncertain at a 10-8 level over multi-decadal time spans DT comparable to those used in the data analyses performed so far. A further \simeq 20% systematic uncertainty in the theoretically predicted gravitomagnetic signal, thus, occurs. The shift due to the gravitomagnetic frame-dragging on the station-spacecraft range is numerically computed over DT = 15 d and DT = 1 yr. The need of looking at such a directly observable quantity is pointed out, along with some critical remarks concerning the methodology used so far to measure the Lense-Thirring effect with the LAGEOS satellites. Suggestions for a different, more trustable and reliable approach are offered.Comment: LaTex2e, 6 pages, 1 table, 5 figures, 36 references. Minor changes. Version matching the one at press in Europhysics Letters (EPL

Post-Keplerian perturbations of the orbital time shift in binary pulsars: an analytical formulation with applications to the Galactic Center

We develop a general approach to analytically calculate the perturbations $\Delta\delta\tau_\textrm{p}$ of the orbital component of the change $\delta\tau_\textrm{p}$ of the times of arrival of the pulses emitted by a binary pulsar p induced by the post-Keplerian accelerations due to the mass quadrupole $Q_2$, and the post-Newtonian gravitoelectric (GE) and Lense-Thirring (LT) fields. We apply our results to the so-far still hypothetical scenario involving a pulsar orbiting the Supermassive Black Hole in in the Galactic Center at Sgr A$^\ast$. We also evaluate the gravitomagnetic and quadrupolar Shapiro-like propagation delays $\delta\tau_\textrm{prop}$. By assuming the orbit of the existing S2 main sequence star and a time span as long as its orbital period $P_\textrm{b}$, we obtain $\left|\Delta\delta\tau_\textrm{p}^\textrm{GE}\right|\lesssim 10^3~\textrm{s},~\left|\Delta\delta\tau_\textrm{p}^\textrm{LT}\right|\lesssim 0.6~\textrm{s},\left|\Delta\delta\tau_\textrm{p}^{Q_2}\right|\lesssim 0.04~\textrm{s}$. Faster $\left(P_\textrm{b} = 5~\textrm{yr}\right)$ and more eccentric $\left(e=0.97\right)$ orbits would imply net shifts per revolution as large as $\left|\left\langle\Delta\delta\tau_\textrm{p}^\textrm{GE}\right\rangle\right|\lesssim 10~\textrm{Ms},~\left|\left\langle\Delta\delta\tau_\textrm{p}^\textrm{LT}\right\rangle\right|\lesssim 400~\textrm{s},\left|\left\langle\Delta\delta\tau_\textrm{p}^{Q_2}\right\rangle\right|\lesssim 10^3~\textrm{s}$, depending on the other orbital parameters and the initial epoch. For the propagation delays, we have $\left|\delta\tau_\textrm{prop}^\textrm{LT}\right|\lesssim 0.02~\textrm{s},~\left|\delta\tau_\textrm{prop}^{Q_2}\right|\lesssim 1~\mu\textrm{s}$. The expected precision in pulsar timing in Sgr A$^\ast$ is of the order of $100~\mu\textrm{s}$, or, perhaps, even $1-10~\mu\textrm{s}$.Comment: LaTex2e, 2 tables, 4 figures, 36 pages. Entirely rewritten version which corrects previous erroneous results concerning the orbital time delay

Some comments on a recently derived approximated solution of the Einstein equations for a spinning body with negligible mass

Recently, an approximated solution of the Einstein equations for a rotating body whose mass effects are negligible with respect to the rotational ones has been derived by Tartaglia. At first sight, it seems to be interesting because both external and internal metric tensors have been consistently found, together an appropriate source tensor; moreover, it may suggest possible experimental checks since the conditions of validity of the considered metric are well satisfied at Earth laboratory scales. However, it should be pointed out that reasonable doubts exist if it is physically meaningful because it is not clear if the source tensor related to the adopted metric can be realized by any real extended body. Here we derive the geodesic equations of the metric and analyze the allowed motions in order to disclose possible unphysical features which may help in shedding further light on the real nature of such approximated solution of the Einstein equations.Comment: Latex2e, 17 pages, no tables, 5 figures, minor typos corrected. To appear in general Relativity and Gravitatio