Recovering a MOND-like acceleration law in mimetic gravity

We reconsider the recently proposed mimetic gravity, focusing in particular on whether the theory is able to reproduce the inferred flat rotation curves of galaxies. We extend the theory by adding a non-minimal coupling between matter and mimetic field. Such coupling leads to the appearance of an extra force which renders the motion of test particles non-geodesic. By studying the weak field limit of the resulting equations of motion, we demonstrate that in the Newtonian limit the acceleration law induced by the non-minimal coupling reduces to a Modified Newtonian Dynamics (MOND)-like one. In this way, it is possible to reproduce the successes of MOND, namely the explanation for the flat galactic rotation curves and the Tully-Fisher relation, within the framework of mimetic gravity, without the need for particle dark matter. The scale-dependence of the recovered acceleration scale opens up the possibility of addressing the missing mass problem not only on galactic but also on cluster scales: we defer a full study of this issue, together with a complete analysis of fits to spiral galaxy rotation curves, to an upcoming companion paper.Comment: 11 pages, accepted for publication in Class. Quant. Gra

New solar metallicity measurements

In the past years, a systematic downward revision of the metallicity of the Sun has led to the "solar modeling problem", namely the disagreement between predictions of standard solar models and inferences from helioseismology. Recent solar wind measurements of the metallicity of the Sun, however, provide once more an indication of a high-metallicity Sun. Because of the effects of possible residual fractionation, the derived value of the metallicity $Z_{\odot} = 0.0196 \pm 0.0014$ actually represents a lower limit to the true metallicity of the Sun. However, when compared with helioseismological measurements, solar models computed using these new abundances fail to restore agreement, owing to the implausibly high abundance of refractory (Mg, Si, S, Fe) elements, which correlates with a higher core temperature and hence an overproduction of solar neutrinos. Moreover, the robustness of these measurements is challenged by possible first ionization potential fractionation processes. I will discuss these solar wind measurements, which leave the "solar modeling problem" unsolved.Comment: 6 pages, extended version of contribution to proceedings of the 51st Rencontres de Moriond, Cosmology Session, published as communication in Atom

Sales online of Health Products: Economical and Administrative Perspective

The continuing decline in the pharmaceutical expenditure deduction, the increasing fees paid by pharmacies in favor of the NHS and the crisis that reduces the spending power of the citizen, triggered a huge drop in the profitability of the Italian pharmacies. However the crisis can also be positive because it forces the companies to deploy all the resources needed to invert the situation, changing certain vicious behaviors in favor of virtuous ones. But if on the one hand, it is the single pharmacist who should implement corrective measures, on the other hand some problems must be solved by the entire distribution system in order to prevent the marginalization of the pharmacy. A good solution might be represented by the emerging tendency of the online sale of OTC pharmaceuticals, already recognized by the market trends and regulated at the European Law level, and almost completely implemented by the Italian legislation . This opportunity might increase the health related products demand whereas an optimal marketing and administrative strategy is executed. Nevertheless, the strategy should be designed to create the prospective for the pharmacy to re-achieve the distribution that has been lost; with a direct distribution the pharmacy loses and the intermediate distribution channel as well, with an higher number of losers than winners, in the end. Hence, the technological solution proposition i.e. the web pharmacy, has to take into consideration this disintermediation problem that should be strengthened instead of weakened, at least to some degrees. It can be already anticipated that the Italian normative alignment with the European directive proposes to solve the problem of the disintermediation naturally related to the e-commerce adoption, with the possibility for the E-pharmacy to exist only if a physical shop already exists behind it

Static spherically symmetric solutions in mimetic gravity: rotation curves & wormholes

In this work, we analyse static spherically symmetric solutions in the framework of mimetic gravity, an extension of general relativity where the conformal degree of freedom of gravity is isolated in a covariant fashion. Here we extend previous works by considering in addition a potential for the mimetic field. An appropriate choice of such potential allows for the reconstruction of a number of interesting cosmological and astrophysical scenarios. We explicitly show how to reconstruct such a potential for a general static spherically symmetric space-time. A number of applications and scenarios are then explored, among which traversable wormholes. Finally, we analytically reconstruct potentials which leads to solutions to the equations of motion featuring polynomial corrections to the Schwarzschild spacetime. Accurate choices for such corrections could provide an explanation for the inferred flat rotation curves of spiral galaxies within the mimetic gravity framework, without the need for particle dark matter.Comment: Version accepted for publication in Class. Quant. Gra

Black holes with scalar hair in light of the Event Horizon Telescope

Searching for violations of the no-hair theorem (NHT) is a powerful way to test gravity, and more generally fundamental physics, particularly with regards to the existence of additional scalar fields. The first observation of a black hole (BH) shadow by the Event Horizon Telescope (EHT) has opened a new direct window onto tests of gravity in the strong-field regime, including probes of violations of the NHT. We consider two scenarios described by the Einstein-Maxwell equations of General Relativity and electromagnetism, to which we add a scalar field. In the first case we consider a minimally-coupled scalar field with a potential, whereas in the second case the field is conformally-coupled to curvature. In both scenarios we construct charged BH solutions, which are found to carry primary scalar hair. We then compute the shadows cast by these two BHs as a function of their electric charge and scalar hair parameter. Comparing these shadows to the shadow of M87* recently imaged by the EHT collaboration, we set constraints on the amount of scalar hair carried by these two BHs. The conformally-coupled case admits a regime for the hair parameter, compatible with EHT constraints, describing a so-called mutated Reissner-Nordstr\"{o}m BH: this solution was recently found to effectively mimic a wormhole. Our work provides novel constraints on fundamental physics, and in particular on violations of the no-hair theorem and the existence of additional scalar fields, from the shadow of M87*.Comment: 33 pages, 6 figures, 1 table, references added, version accepted for publication in JCA