Probing the composition of sub-millisecond rotating compact stars by r-modes instability

We investigate the implications of the r-modes instability on the composition of a compact star rotating at a sub-millisecond period. In particular, the only viable astrophysical scenario for such an object, wich might present inside the Low Mass X-ray Binary associated with the x-ray transient XTE J1739-285, is that it has a strangeness content. Since previous analysis indicate that hyperonic stars or stars containing a kaon condensate are unlikely because of the mass-shedding constraint, the only remaining possibility is that such an object is either a strange quark star or a hybrid quark-hadron star

Combustion of a hadronic star into a quark star: the turbulent and the diffusive regimes

We argue that the full conversion of a hadronic star into a quark or a hybrid star occurs within two different regimes separated by a critical value of the density of the hadronic phase $\overline{n_h}$. The first stage, occurring for $n_h>\overline{n_h}$, is characterized by turbulent combustion and lasts typically a few ms. During this short time-scale neutrino cooling is basically inactive and the star heats up thanks to the heat released in the conversion. In the second stage, occurring for $n_h<\overline{n_h}$, turbulence is not active anymore, and the conversion proceeds on a much longer time scale (of the order of tens of seconds), with a velocity regulated by the diffusion and the production of strange quarks. At the same time, neutrino cooling is also active. The interplay between the heating of the star due to the slow conversion of its outer layers (with densities smaller than $\overline{n_h}$) and the neutrino cooling of the forming quark star leads to a quasi-plateau in the neutrino luminosity which, if observed, would possibly represent a unique signature for the existence of quark matter inside compact stars. We will discuss the phenomenological implications of this scenario in particular in connection with the time structure of long gamma-ray-bursts.Comment: 12 pages, 5 figure

Influence of the measurement on the decay law: the bang-bang case

After reviewing the description of an unstable state in the framework of nonrelativistic Quantum Mechanics (QM) and relativistic Quantum Field Theory (QFT), we consider the effect of pulsed, ideal measurements repeated at equal time intervals on the lifetime of an unstable system. In particular, we investigate the case in which the `bare' survival probability is an exact exponential (a very good approximation in both QM and QFT), but the measurement apparatus can detect the decay products only in a certain energy range. We show that the Quantum Zeno Effect can occur in this framework as well.Comment: 8 pages, 1 figure. Contribution to the 3rd International Conference on New Frontiers in Physics, ICNFP 2014, 31/7/2014-6/8/2014, Crete (Greece

Eco-friendly countermeasures for enlarged basins erosion

Eco-friendly hydraulic structures (such as block ramps, rock weirs and stepped gabion weir) are generally made of rocks placed in two or more layers on a sloped bed. They are usually used in mountainous rivers to control sediment transport. The downstream stilling basin plays an important role in terms of both energy dissipation and erosion control. In addition, a correct design of the downstream stilling basin can create an optimal habitat for fish species in the river. Therefore, in the present work, an attempt was made to control the scour depth downstream of a block ramp using rock structures. In particular, the analysis was focused on scour characteristics in the presence of a protected and enlarged downstream channel. Namely, an abrupt symmetrically enlarged channel was simulated downstream of block ramps. Eco-friendly protection structures, such as rock sills, were tested to limit the erosive process. Rock sills were placed transversally at different longitudinal and vertical positions in the stilling basin and scour morphology variations were investigated. Experiments were carried out for two different ratios of the width of the channel to the width of the ramp and three different ramp slopes. Several scour morphologies were distinguished and classified. In addition, empirical relationships were derived, by which it is possible to estimate the main scour geometry characteristics

(Oscillating) non-exponential decays of unstable states

We discuss deviations from the exponential decay law which originate when going beyond the Breit-Wigner distribution for an unstable state. In particular, we concentrate on an oscillating behavior, reminiscent of the Rabi-oscillations, in the short-time region. We propose that these oscillations can explain the GSI experiment, which measured superimposed oscillations on top of the exponential law for hydrogen-like nuclides decaying via electron-capture (the so-called GSI anomaly). Moreover, we discuss the possibility, that the deviations from the Breit-Wigner distribution in the case of the GSI anomaly are (predominantly) caused by the interaction of the unstable state with the measurement apparatus. The consequences of this scenario, such as the non-existence of oscillations in an analogous experiment performed at the Berkeley Lab, are investigated.Comment: 10 pages, 2 figures, revised version in print in the Proceedings of the "50th International Winter Meeting on Nuclear Physics", 23-27 January 2012, Bormio, Ital

Anomalies in weak decays of H-like ions

We investigate the emergence of oscillations in the decay law of unstable systems. We discuss in particular the case of the so-called GSI anomaly seen in the electron capture decays of H-like ions and prove that such oscillations cannot be explained by neutrino oscillations. We then discuss how such anomalies could be intimately related to the decay law of unstable systems in the case in which their spectral function deviates from a Breit-Wigner shape.Comment: 6 pages. Based on the poster presentation given at the 18th International Conference 'Physics of Highly Charged Ions' HCI 2016, 11-16 September 2016, Kielce, Polan

Spectral function of a scalar boson coupled to fermions

We present the calculation of the spectral function of an unstable scalar boson coupled to fermions as resulting from the resummation of the one loop diagrams in the scalar particle self energy. We work with a large but finite high-energy cutoff: in this way, the spectral function of the scalar field is always correctly normalized to unity, independently on the value of the cutoff. We show that this high energy cutoff affects the Breit-Wigner width of the unstable particle: the larger the cutoff, the smaller is the width at fixed coupling. Thus, the existence of a high energy cutoff (alias minimal length), and for instance the possible opening of new degrees of freedom beyond that energy scale, could then be in principle proven by measuring, at lower energy scales, the line shape of the unstable scalar state. Although the Lagrangian here considered represents only a toy-model, we discuss possible future extensions of our work which could be relevant for particle physics phenomenology.Comment: 25 pages, 6 figure

Pulsed and continuous measurements of exponentially decaying systems

We study the influence of a detector on the decay law of a quantum state whose "undisturbed" survival probability is purely exponential. In particular, we consider a detector with a finite energy band of detection, i.e. it interacts only with decay products having an energy within a certain range of values. In one case, we assume that the detector performs many repeated measurements at short time intervals in all of which a collapse of the wave function occurs (bang-bang or pulsed-type measurements). In the second case, we assume a continuous measurement which preserves unitarity. We confirm the slowing down of the decay in presence of a measuring apparatus, the Quantum Zeno effect, but the outcomes of the detector are in general qualitatively and quantitatively different in the two cases. In turn, this implies that the so-called Schulman relation (the equivalence of pulsed and continuous measurements) does not hold in general and that it is in principle possible to experimentally access how a certain detector performs a measurement.Comment: 5 pages, 3 figure