3,376 research outputs found
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
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