Experimentos com nêutrons e gravidade modificada

Abstract

In recent decades, several proposals for modifying gravitational theory have emerged. In this context, we highlight the large extra dimensions theory, originally developed as an attempt to explain why gravity is significantly weaker compared to the other fundamental forces. Evidently, any new theoretical formulation must undergo experimental scrutiny. One of the interesting consequences of the large extra dimensions theory is the predicted enhancement of the gravitational force at short distances. In this work, we focus on some neutron-based experiments. Due to its electrically neutral nature, the neutron proves to be particularly useful in the search for anomalous gravitational interactions at short distances. We begin our discussion by considering the neutron boundstate experiment, in which slow neutrons are vertically confined between a perfectly reflective mirror and the Earth’s gravitational field. In the extradimensional scenario, we investigate how the gravitational interaction between the neutron and the mirror could influence the neutron’s bound states. Based on this analysis, we derive new constraints on the free parameters of the extradimensional model. Our results are based on the thick-brane model, which allows us to avoid divergence issues in the calculation of the anomalous gravitational potential and extend previous results in the literature, whose analysis is restricted to codimensions smaller than five. We also consider neutron scattering experiments involving heavy nuclei, which aim to determine the neutron’s polarizability. We show that such experiments enable the study of the gravitational interaction between the neutron and a non-baryonic source—namely, the energy of the electric field generated by the heavy nucleus. As we will see, this analysis allows us to establish new experimental constraints on the behavior of certain post-Newtonian parameters associated with the ability of pressure and internal energy to generate gravity. This method provides a significantly more stringent constraint, in the sub-picometer scale domain, compared to previous limits derived from other experiments. Finally, we analyze reflectometry experiments commonly used to determine the neutron scattering length. By studying this experiment within the thick-brane scenario, we derive new constraints on the free parameters of the model. The obtained constraints are comparable in order of magnitude to the experimental limits recently extracted from the spectroscopy of certain exotic atoms.