Non-Newtonian Gravity, Fluctuative Hypothesis and the Sizes of Astrophysical Structures

We show that the characteristic sizes of astrophysical and cosmological structures, where gravity is the only overall relevant interaction assembling the system, have a phenomenological relation to the microscopic scales whose order of magnitude is essentially ruled by the Compton wavelength of the proton. This result agrees with the absence of screening mechanisms for the gravitational interaction and could be connected to the presence of Yukawa correcting terms in the Newtonian potential which introduce typical interaction lengths. Furthermore, we are able to justify, in a straightforward way, the Sanders--postulated mass of a vector boson considered in order to obtain the characteristic sizes of galaxies.Comment: 11 pages. to appear in Mod. Phys. Lett.

Can Lightcone Fluctuations be Probed with Cosmological Backgrounds?

Finding signatures of quantum gravity in cosmological observations is now actively pursued both from the theoretical and the experimental side. Recent work has concentrated on finding signatures of light-cone fluctuations in the CMB. Because in inflationary scenarios a Gravitational Wave Background (GWB) is always emitted much before the CMB, we can ask, in the hypothesis where this GWB could be observed, what is the imprint of light cone fluctuations on this GWB. We show that due to the flat nature of the GWB spectrum, the effect of lightcone fluctuations are negligible.Comment: 10 pages, references adde

Astrophysical structures from primordial quantum black holes

The characteristic sizes of astrophysical structures, up to the whole observed Universe, can be recovered, in principle, assuming that gravity is the overall interaction assembling systems starting from microscopic scales, whose order of magnitude is ruled by the Planck length and the related Compton wavelength. This result agrees with the absence of screening mechanisms for the gravitational interaction and could be connected to the presence of Yukawa corrections in the Newtonian potential which introduce typical interaction lengths. This result directly comes out from quantization of primordial black holes and then characteristic interaction lengths directly emerge from quantum field theory.Comment: 11 page

SUPER-Screening

We present a framework for embedding scalar-tensor models of screened modifed gravity such as chameleons, symmetrons and environmental dilatons into global supersymmetry. This achieved by secluding the dark sector from both the observable and supersymmetry breaking sectors. We examine the resulting supersymmetric features in a model-independent manner and find that, when the theory follows from an underlying supergravity, the mediation of supersymmetry breaking to the dark sector induces a soft mass for the scalar of order the gravitino mass. This is enough to forbid the construction of supersymmetric symmetrons and ensures that when other screening mechanisms operate, no object in the universe is unscreened thereby precluding any observable signatures. In view of a possible origin of modifed gravity within fundamental physics, we find that no-scale models are the only ones that can circumvent these features. We also present a novel mechanism where the coupling of the scalar to two other scalars charged under U(1) can dynamically generate a small cosmological constant at late times in the form of a Fayet-Iliopoulos term.Comment: 10 pages, 1 figur

Lorentz and CPT Invariance Violation In High-Energy Neutrinos

High-energy neutrino astronomy will be capable of observing particles at both extremely high energies and over extremely long baselines. These features make such experiments highly sensitive to the effects of CPT and Lorentz violation. In this article, we review the theoretical foundation and motivation for CPT and Lorentz violating effects, and then go on to discuss the related phenomenology within the neutrino sector. We describe several signatures which might be used to identify the presence of CPT or Lorentz violation in next generation neutrino telescopes and cosmic ray experiments. In many cases, high-energy neutrino experiments can test for CPT and Lorentz violation effects with much greater precision than other techniques.Comment: 27 pages, 8 figure