Modified Gravitational Waves Across Galaxies from Macroscopic Gravity

We analyze the propagation of gravitational waves in a medium containing bounded subsystems ("molecules"), able to induce significant Macroscopic Gravity effects. We establish a precise constitutive relation between the average quadrupole and the amplitudes of a vacuum gravitational wave, via the geodesic deviation equation. Then we determine the modified equation for the wave inside the medium and the associated dispersion relation. A phenomenological analysis shows that anomalous polarizations of the wave emerge with an appreciable experimental detectability if the medium is identified with a typical galaxy. Both the modified dispersion relation (wave velocity less than the speed of light) and anomalous oscillations modes could be detectable by the incoming LISA or pulsar timing arrays experiments, having the appropriate size to see the concerned wavelengths (larger than the molecular size) and the appropriate sensitivity to detect the expected deviation from vacuum General Relativity.Comment: 10 pages, comments are welcom

Optimally chosen small portfolios are better than large ones

One of the fundamental principles in portfolio selection models is minimization of risk through diversification of the investment. However, this principle does not necessarily translate into a request for investing in all the assets of the investment universe. Indeed, following a line of research started by Evans and Archer almost fifty years ago, we provide here further evidence that small portfolios are sufficient to achieve almost optimal in-sample risk reduction with respect to variance and to some other popular risk measures, and very good out-of-sample performances. While leading to similar results, our approach is significantly different from the classical one pioneered by Evans and Archer. Indeed, we describe models for choosing the portfolio of a prescribed size with the smallest possible risk, as opposed to the random portfolio choice investigated in most of the previous works. We find that the smallest risk portfolios generally require no more than 15 assets. Furthermore, it is almost always possible to find portfolios that are just 1% more risky than the smallest risk portfolios and contain no more than 10 assets. Furthermore, the optimal small portfolios generally show a better performance than the optimal large ones. Our empirical analysis is based on some new and on some publicly available benchmark data sets often used in the literature

Low Complexity WMMSE Power Allocation In NOMA-FD Systems

In this paper we study the problem of power and channel allocation with the objective of maximizing the system sum-rate for multicarrier non-orthogonal multiple access (NOMA) full duplex (FD) systems. Such an allocation problem is non-convex and, thus, with the goal of designing a low complexity solution, we propose a scheme based on the minimization of the weighted mean square error, which achieves performance reasonably close to the optimum and allows to clearly outperforms a conventional orthogonal multiple access approach. Numerical results assess the effectiveness of our algorithm.Comment: 5 pages conference paper, 3 figures. Submitted on ICASSP 202

NLO matching for ttbb production with massive b-quarks

Theoretical uncertainties in the simulation of ttbb production represent one of the main obstacles that still hamper the observation of Higgs-boson production in association with top-quark pairs in the H->bb channel. In this letter we present a next-to-leading order (NLO) simulation of ttbb production with massive b-quarks matched to the Sherpa parton shower. This allows one to extend NLO predictions to arbitrary ttbb kinematics, including the case where one or both b-jets arise from collinear g->bb splittings. We find that this splitting mechanism plays an important role for the ttH(bb) analysis.Comment: 4 pages, 3 figures. v2: b-jet momenta replaced by b-quark momenta in the dynamical QCD scale; related technical cut removed; numerical results updated accordingly and conclusions unchanged. References and various comments on the resummation of b-mass logarithms and on the consistency of double-splitting contributions added. Version to appear in Phys. Lett

Higgs Boson Production in Association with a Photon in Vector Boson Fusion at the LHC

Higgs boson production in association with two forward jets and a central photon at the CERN Large Hadron Collider is analyzed, for the Higgs boson decaying into a b bbar pair in the m_H <= 140 GeV mass region. We study both irreducible and main reducible backgrounds at parton level. Compared to the Higgs production via vector-boson fusion, the request of a further photon at moderate rapidities dramatically enhances the signal/background ratio. Inclusive cross sections for p_T^\gamma >= 20 GeV can reach a few tens of fb's. After a suitable choice of kinematical cuts, the cross-section ratio for signal and irreducible-background can be enhanced up to >= ~1/10, with a signal cross section of the order of a few fb's, for m_H ~ 120 GeV. The request of a central photon radiation also enhances the relative signal sensitivity to the WWH coupling with respect to the ZZH coupling. Hence, a determination of the cross section for the associated production of a Higgs boson decaying into a b bbar pair plus a central photon in vector-boson fusion could help in constraining the b bbar H coupling, and the WWH coupling as well. A preliminary study of QCD showering effects points to a further significant improvement of the signal detectability over the background.Comment: 30 pages, 8 figures, 8 tables; minor corrections to the text; version appeared in Nuclear Physics

Gravitational Landau Damping for massive scalar modes

We establish the possibility of Landau damping for gravitational scalar waves which propagate in a non-collisional gas of particles. In particular, under the hypothesis of homogeneity and isotropy, we describe the medium at the equilibrium with a J\"uttner-Maxwell distribution, and we analytically determine the damping rate from the Vlasov equation. We find that damping occurs only if the phase velocity of the wave is subluminal throughout the propagation within the medium. Finally, we investigate relativistic media in cosmological settings by adopting numerical techniques.Comment: 11 pages, 4 figures. Comments are welcom

Operating times and users' behavior at urban road intersections

The safety of at grade road intersections is a relevant issue with social, economic, and environmental implications. It is related to the behavior of a driver approaching an intersection that, in its turn, is affected by kinematic and physiological variables. This study proposes a model to calculate the intersection operation time (IOT) for typical non-signalized 4-leg and 3-leg (or T-leg) urban intersections. Data available in the literature have been considered in order to identify the points of interest and assess the number and the time of a driver's eye fixation on them. When approaching an intersection, the probability of glancing in a particular area changes with the distance to the yield or stop line; for this reason, a probabilistic approach was used to model the phenomenon. All possible maneuvers have been considered: left turning, right turning, and through-movement. The proposed model allowed an objective comparison between time spent by drivers for various maneuvers and layout conditions, and identification of the critical conditions. Indeed, significant differences in terms of IOT were found: they could lead to modification of the traffic management considering different needs of road users, traffic demand, and geometrical and functional constraints

Contribution to the assessment of CFD codes for in-vessel flow investigation

The present research aims at contributing to the CFD code assessment process for nuclear reactor applications, and particularly for the predictive analysis of the fluid dynamic phenomena occurring inside the reactor pressure vessel of a pressurized water reactor. The importance of such phenomena relies, for instance, on the influence that they can have on the spatial and temporal distribution of coolant properties (such as temperature or boron concentration) at the core inlet during certain accident transients involving perturbations of such properties with respect to nominal conditions; furthermore, in-vessel mixing phenomena can also affect the thermal interaction between coolant and pressure vessel during pressurized thermal shock scenarios. The contribution provided by this work consists in the proposal of a general and systematic methodology to be applied in the CFD code assessment for in-vessel flow investigations. Within the proposed approach, the relevant modelling issues are identified and discussed, so as to point out the main capabilities and limitations in the present state-of-the-art tools and methods. Then, the main steps of the code application procedure are described and discussed analytically, thus providing guidance for a quality-oriented use of the codes, and complementing the existing best practice guidelines for this specific problem. Furthermore, the research addresses the problem of the quantification of the accuracy for numerical predictions (both from CFD and integral codes) about coolant properties perturbations at the core inlet. As a result, a methodology is proposed based on a set of accuracy indicators, which can represent a means for judging whether the code results are sufficiently close to experimental data, once acceptance thresholds have been defined and the method has been completely assessed. The work is supported by extensive CFD code validation and application results obtained in the frame of several international research projects and co-operations, and by a continuous interaction with the involved International scientific community