292 research outputs found
Wormholes and Child Universes
Evidence to the case that classical gravitation provides the clue to make
sense out of quantum gravity is presented. The key observation is the existence
in classical gravitation of child universe solutions or "almost" solutions,
"almost" because of some singularity problems. The difficulties of these child
universe solutions due to their generic singularity problems will be very
likely be cured by quantum effects, just like for example "almost" instanton
solutions are made relevant in gauge theories with breaking of conformal
invariance. Some well motivated modifcations of General Relativity where these
singularity problems are absent even at the classical level are discussed. High
energy density excitations, responsible for UV divergences in quantum field
theories, including quantum gravity, are likely to be the source of child
universes which carry them out of the original space time. This decoupling
could prevent these high UV excitations from having any influence on physical
amplitudes. Child universe production could therefore be responsible for UV
regularization in quantum field theories which take into account
semiclassically gravitational effects. Child universe production in the last
stages of black hole evaporation, the prediction of absence of tranplanckian
primordial perturbations, connection to the minimum length hypothesis and in
particular the connection to the maximal curvature hypothesis are discussed.
Some discussion of superexcited states in the case these states are Kaluza
Klein excitations is carried out. Finally, the posibility of obtaining "string
like" effects from the wormholes associated with the child universes is
discussed.Comment: Talk presented at the IWARA 2009 Conference, Maresias, Brazil,
October 2009, accepted for publication in the proceedings, World Scientific
format, 8 page
Black Holes and Photons with Entropic Force
We study entropic force effects on black holes and photons. We find that
application of an entropic analysis restricts the radial change of a
black hole of radius , due to a test particle of a
Schwartzchild radius moving towards the black hole by near
black body surface, to be given by a relation , or {\Delta R}/{\lambdabar_M} = {\Delta x}/{2 \lambdabar_m}. We
suggest a new rule regarding entropy changes in different dimensions, \Delta
S= 2\pi k D \Delta l /\lambdabar, which unifies Verlinde's conjecture and the
black hole entropy formula. We also propose to extend the entropic force idea
to massless particles such as a photon. We find that there is an entropic force
on a photon of energy , with , and therefore
the photon has an effective gravitational mass .Comment: 4 Latex pages, no figure
Standard Model Parameters and the Cosmological Constant
Simple functional relations amongst standard model couplings, including
gravitional, are conjectured. Possible implications for cosmology and future
theory are discussed.Comment: submitted to Physical Review
A Curvature Principle for the interaction between universes
We propose a Curvature Principle to describe the dynamics of interacting
universes in a multi-universe scenario and show, in the context of a simplified
model, how interaction drives the cosmological constant of one of the universes
toward a vanishingly small value. We also conjecture on how the proposed
Curvature Principle suggests a solution for the entropy paradox of a universe
where the cosmological constant vanishes.Comment: Essay selected for an honorable mention by the Gravity Research
Foundation, 2007. Plain latex, 8 page
A model of radiating black hole in noncommutative geometry
The phenomenology of a radiating Schwarzschild black hole is analyzed in a
noncommutative spacetime. It is shown that noncommutativity does not depend on
the intensity of the curvature. Thus we legitimately introduce noncommutativity
in the weak field limit by a coordinate coherent state approach. The new
interesting results are the following: i) the existence of a minimal non-zero
mass to which black hole can shrink; ii) a finite maximum temperature that the
black hole can reach before cooling down to absolute zero; iii) the absence of
any curvature singularity. The proposed scenario offers a possible solution to
conventional difficulties when describing terminal phase of black hole
evaporation.Comment: 10 pages, 4 figure
Microbial Symbionts and Ecological Divergence of Caribbean Sponges: A New Perspective on an Ancient Association
Marine sponges host diverse communities of microbial symbionts that expand the metabolic capabilities of their host, but the abundance and structure of these communities is highly variable across sponge species. Specificity in these interactions may fuel host niche partitioning on crowded coral reefs by allowing individual sponge species to exploit unique sources of carbon and nitrogen, but this hypothesis is yet to be tested. Given the presence of high sponge biomass and the coexistence of diverse sponge species, the Caribbean Sea provides a unique system in which to investigate this hypothesis. To test for ecological divergence among sympatric Caribbean sponges and investigate whether these trends are mediated by microbial symbionts, we measured stable isotope (δ13C and δ15N) ratios and characterized the microbial community structure of sponge species at sites within four regions spanning a 1700 km latitudinal gradient. There was a low (median of 8.2 %) overlap in the isotopic niches of sympatric species; in addition, host identity accounted for over 75% of the dissimilarity in both δ13C and δ15N values and microbiome community structure among individual samples within a site. There was also a strong phylogenetic signal in both δ15N values and microbial community diversity across host phylogeny, as well as a correlation between microbial community structure and variation in δ13C and δ15N values across samples. Together, this evidence supports a hypothesis of strong evolutionary selection for ecological divergence across sponge lineages and suggests that this divergence is at least partially mediated by associations with microbial symbionts
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