15,158 research outputs found
Collapsing objects with the same gravitational trajectory can radiate away different amount of energy
We study radiation emitted during the gravitational collapse from two
different types of shells. We assume that one shell is made of dark matter and
is completely transparent to the test scalar (for simplicity) field which
belongs to the standard model, while the other shell is made of the standard
model particles and is totally reflecting to the scalar field. These two shells
have exactly the same mass, charge and angular momentum (though we set the
charge and angular momentum to zero), and therefore follow the same geodesic
trajectory. However, we demonstrate that they radiate away different amount of
energy during the collapse. This difference can in principle be used by an
asymptotic observer to reconstruct the physical properties of the initial
collapsing object other than mass, charge and angular momentum. This result has
implications for the information paradox and expands the list of the type of
information which can be released from a collapsing object.Comment: 5 pages, 5 figures, accepted by PLB. arXiv admin note: text overlap
with arXiv:1601.0792
Vacuum Solutions of Classical Gravity on Cyclic Groups from Noncommutative Geometry
Based on the observation that the moduli of a link variable on a cyclic group
modify Connes' distance on this group, we construct several action functionals
for this link variable within the framework of noncommutative geometry. After
solving the equations of motion, we find that one type of action gives
nontrivial vacuum solution for gravity on this cyclic group in a broad range of
coupling constants and that such solutions can be expressed with Chebyshev's
polynomials.Comment: Latex 7 pages; no figures. Significant modifications being given,
with references adde
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