5,542 research outputs found
Semiclassical geons as solitonic black hole remnants
We find that the end state of black hole evaporation could be represented by
non-singular and without event horizon stable solitonic remnants with masses of
the order the Planck scale and up to 16 units of charge. Though these objects
are locally indistinguishable from spherically symmetric, massive electric (or
magnetic) charges, they turn out to be sourceless geons containing a wormhole
generated by the electromagnetic field. Our results are obtained by
interpreting semiclassical corrections to Einstein's theory in the first-order
(Palatini) formalism, which yields second-order equations and avoids the
instabilities of the usual (metric) formulation of quadratic gravity. We also
discuss the potential relevance of these solutions for primordial black holes
and the dark matter problem.Comment: 9 pages, 1 figur
An anti-Schwarzshild solution: wormholes and scalar-tensor solutions
We investigate a static solution with an hyperbolic nature, characterised by
a pseudo-spherical foliation of space. This space-time metric can be perceived
as an anti-Schwarzschild solution, and exhibits repulsive features. It belongs
to the class of static vacuum solutions termed "a degenerate static solution of
class A". In the present work we review its fundamental features, discuss the
existence of generalised wormholes, and derive its extension to scalar-tensor
gravity theories in general.Comment: 3 pages, contribution to the proceedings of the Spanish Relativity
Meeting-ERE200
Microscopic wormholes and the geometry of entanglement
It has recently been suggested that Einstein-Rosen (ER) bridges can be
interpreted as maximally entangled states of two black holes that form a
complex Einstein-Podolsky-Rosen (EPR) pair. This relationship has been dubbed
as the ER = EPR correlation. In this work, we consider the latter conjecture in
the context of quadratic Palatini theory. An important result, which stems from
the underlying assumptions about the geometry on which the theory is
constructed, is the fact that all the charged solutions of the quadratic
Palatini theory possess a wormhole structure. Our results show that spacetime
may have a foam-like microstructure with wormholes generated by fluctuations of
the quantum vacuum. This involves the spontaneous creation/annihilation of
entangled particle-antiparticle pairs, existing in a maximally entangled state
connected by a non-traversable wormhole. Since the particles are produced from
the vacuum and therefore exist in a singlet state, they are necessarily
entangled with one another. This gives further support to the ER=EPR claim.Comment: 5 pages. V2: minor changes and references adde
f(R,T) gravity
We consider f(R,T) modified theories of gravity, where the gravitational
Lagrangian is given by an arbitrary function of the Ricci scalar R and of the
trace of the stress-energy tensor T. We obtain the gravitational field
equations in the metric formalism, as well as the equations of motion for test
particles, which follow from the covariant divergence of the stress-energy
tensor. Generally, the gravitational field equations depend on the nature of
the matter source. The field equations of several particular models,
corresponding to some explicit forms of the function f(R,T), are also
presented. An important case, which is analyzed in detail, is represented by
scalar field models. We write down the action and briefly consider the
cosmological implications of the models, where is
the trace of the stress-energy tensor of a self-interacting scalar field. The
equations of motion of the test particles are also obtained from a variational
principle. The motion of massive test particles is non-geodesic, and takes
place in the presence of an extra force orthogonal to the four-velocity. The
Newtonian limit of the equation of motion is further analyzed. Finally, we
provide a constraint on the magnitude of the extra-acceleration by analyzing
the perihelion precession of the planet Mercury in the framework of the present
model.Comment: 14 pages. V2: minor corrections, to appear in PR
Correlation between Local Structure Distortions and Martensitic Transformation in Ni-Mn-In alloys
The local structural distortions arising as a consequence of increasing Mn
content in Ni_2Mn_1+xIn_1-x (x=0, 0.3, 0.4, 0.5 and 0.6) and its effect on
martensitic transformation have been studied using Extended X-ray Absorption
Fine Structure (EXAFS) spectroscopy. Using the room temperature EXAFS at the Ni
and Mn K-edges in the above compositions, the changes associated with respect
to the local structure of these absorbing atoms are compared. It is seen that
in the alloys exhibiting martensitic transformation () there is a
significant difference between the Ni-In and Ni-Mn bond lengths even in the
austenitic phase indicating atomic volume to be the main factor in inducing
martensitic transformation in Ni-Mn-In Heusler alloys.Comment: 8 pages, 2 figure
Dynamical generation of wormholes with charged fluids in quadratic Palatini gravity
The dynamical generation of wormholes within an extension of General
Relativity (GR) containing (Planck's scale-suppressed) Ricci-squared terms is
considered. The theory is formulated assuming the metric and connection to be
independent (Palatini formalism) and is probed using a charged null fluid as a
matter source. This has the following effect: starting from Minkowski space,
when the flux is active the metric becomes a charged Vaidya-type one, and once
the flux is switched off the metric settles down into a static configuration
such that far from the Planck scale the geometry is virtually indistinguishable
from that of the standard Reissner-Nordstr\"om solution of GR. However, the
innermost region undergoes significant changes, as the GR singularity is
generically replaced by a wormhole structure. Such a structure becomes
completely regular for a certain charge-to-mass ratio. Moreover, the nontrivial
topology of the wormhole allows to define a charge in terms of lines of force
trapped in the topology such that the density of lines flowing across the
wormhole throat becomes a universal constant. To the light of our results we
comment on the physical significance of curvature divergences in this theory
and the topology change issue, which support the view that space-time could
have a foam-like microstructure pervaded by wormholes generated by quantum
gravitational effects.Comment: 14 pages, 3 figures, revtex4-1 style. New content added on section
VI. Other minor corrections introduced. Final version to appear in Phys. Rev.
- …