1,086 research outputs found
The Interface between Quantum Mechanics and General Relativity
The generation, as well as the detection, of gravitational radiation by means
of charged superfluids is considered. One example of such a "charged
superfluid" consists of a pair of Planck-mass-scale, ultracold "Millikan oil
drops," each with a single electron on its surface, in which the oil of the
drop is replaced by superfluid helium. When levitated in a magnetic trap, and
subjected to microwave-frequency electromagnetic radiation, a pair of such
"Millikan oil drops" separated by a microwave wavelength can become an
efficient quantum transducer between quadrupolar electromagnetic and
gravitational radiation. This leads to the possibility of a Hertz-like
experiment, in which the source of microwave-frequency gravitational radiation
consists of one pair of "Millikan oil drops" driven by microwaves, and the
receiver of such radiation consists of another pair of "Millikan oil drops" in
the far field driven by the gravitational radiation generated by the first
pair. The second pair then back-converts the gravitional radiation into
detectable microwaves. The enormous enhancement of the conversion efficiency
for these quantum transducers over that for electrons arises from the fact that
there exists macroscopic quantum phase coherence in these charged superfluid
systems.Comment: 22 pages, 7 figures; Lamb medal lecture on January 5, 2006 at the
Physics of Quantum Electronics Winter Colloquium at Snowbird, Utah; accepted
for publication in J. Mod. Optic
Calculation of permittivity tensors for invisibility devices by effective medium approach in general relativity
Permittivity tensors of arbitrary shaped invisibility devices are obtained
using effective medium approach in general relativity. As special cases,
analytical expressions for the permittivity tensors of invisibility cloaks for
the elliptic cylinder, prolate spheroid, and the confocal paraboloid geometry
are derived. In the case of elliptic cylinder, we found that the point of
infinite light speed in the electromagnetic space becomes two points in the
physical space in the zz component of the permittivity tensor. This result is
different from the case of perfect cylinder in which there is a line of cloak
at which the speed of light becomes infinite. In the cases of prolate spheroid
and confocal paraboloid, the point of infinite light speed in the
electromagnetic space becomes line in the physical space for the first two
tensor components and the third component of the permittivity tensor becomes
singular at the line of cloak
Possible alternative mechanism to SUSY: conservative extensions of the Poincar\'e group
A group theoretical mechanism is outlined, which can indecomposably extend
the Poincar\'e group by the compact internal (gauge) symmetries at the price of
allowing some nilpotent (or, more precisely: solvable) internal symmetries in
addition. Due to the presence of this nilpotent part, the prohibitive argument
of the well known Coleman-Mandula and McGlinn no-go theorems do not go through.
In contrast to SUSY or extended SUSY, in our construction the symmetries
extending the Poincar\'e group will be all internal, i.e. they do not act on
the spacetime, merely on some internal degrees of freedom -- hence the name:
conservative extensions of the Poincar\'e group. Using the Levi decomposition
and O'Raifeartaigh theorem, the general structure of all possible conservative
extensions of the Poincar\'e group is outlined, and a concrete example group is
presented with U(1) being the compact gauge group component. It is argued that
such nilpotent internal symmetries may be inapparent symmetries of some more
fundamental field variables, and therefore do not carry an ab initio
contradiction with the present experimental understanding in particle physics.
The construction is compared to (extended) SUSY, since SUSY is somewhat
analogous to the proposed mechanism. It is pointed out, however, that the
proposed mechanism is less irregular in comparison to SUSY, in certain aspects.
The only exoticity needed in comparison to a traditional gauge theory setting
is that the full group of internal symmetries is not purely compact, but is a
semi-direct product of a nilpotent and of a compact part.Comment: 10 pages, contribution to Proceedings of X. International Symposium
on Quantum Theory and Symmetries, Springer (2018
Wormhole Cosmic Censorship
We analyze the properties of a Kerr-like wormhole supported by phantom
matter, which is an exact solution of the Einstein-phantom field equations. It
is shown that the solution has a naked ring singularity which is unreachable to
null geodesics falling freely from the outside. Similarly to Roger Penrose's
cosmic censorship, that states that all naked singularities in the Universe
must be protected by event horizons, here we conjecture from our results that a
naked singularity can also be fully protected by the intrinsic properties of a
wormhole's throat
Gravitational Chern-Simons Lagrangians and black hole entropy
We analyze the problem of defining the black hole entropy when Chern-Simons
terms are present in the action. Extending previous works, we define a general
procedure, valid in any odd dimensions both for purely gravitational CS terms
and for mixed gauge-gravitational ones. The final formula is very similar to
Wald's original formula valid for covariant actions, with a significant
modification. Notwithstanding an apparent violation of covariance we argue that
the entropy formula is indeed covariant.Comment: 39 page
On the Origin of Gravity and the Laws of Newton
Starting from first principles and general assumptions Newton's law of
gravitation is shown to arise naturally and unavoidably in a theory in which
space is emergent through a holographic scenario. Gravity is explained as an
entropic force caused by changes in the information associated with the
positions of material bodies. A relativistic generalization of the presented
arguments directly leads to the Einstein equations. When space is emergent even
Newton's law of inertia needs to be explained. The equivalence principle leads
us to conclude that it is actually this law of inertia whose origin is
entropic.Comment: 29 pages, 6 figure
Remarks on matter-gravity entanglement, entropy, information loss and events
I recall my 'matter-gravity entanglement hypothesis' and briefly review the
evidence for it, based partly on its seeming ability to resolve a number of
puzzles related to quantum black holes including the black hole information
loss puzzle. I point out that, according to this hypothesis, there is a
quantity, i.e. the universe's 'matter-gravity entanglement entropy' -- which
deserves to be considered the 'entropy of the universe' and which, with
suitable initial conditions, will plausibly increase monotonically with
cosmological time. In the last section, which is more tentative and raises a
number of further puzzles and open questions, I discuss the prospects for a
notion of 'events' which 'happen' whose statistical properties are described by
this entropy of the universe. It is hoped that such a theory of events may be a
step on the way towards explaining how initial quantum fluctuations convert
themselves into inhomogeneities in a seemingly classical universe.Comment: 17 pages, 7 figures. Invited contribution to the proceedings of the
conference "Progress and Visions in Quantum Theory in View of Gravity",
Leipzig, Germany, October 2018, based on part of a talk at the workshop "The
Mysterious Universe: Dark Matter -- Dark Energy -- Cosmic Magnetic Fields"
MITP, Mainz, Germany, June 4, 2019. (v2 No change) v3: References added v4:
typos etc. correcte
symmetry and quasi-normal modes in the BTZ black hole
With the help of two new intrinsic tensor fields associated with the
quadratic Casimir of Killing fields, we uncover the
symmetry satisfied by the solutions to the equations of motion for various
fields in the BTZ black hole in a uniform way by performing tensor and spinor
analysis without resorting to any specific coordinate system. Then with the
standard algebraic method developed recently, we determine the quasi-normal
modes for various fields in the BTZ black hole. As a result, the quasi-normal
modes are given by the infinite tower of descendants of the chiral highest
weight mode, which is in good agreement with the previous analytic result
obtained by exactly solving equations of motion instead.Comment: JHEP style, 1+13 pages, version to appear in JHE
Large entropy production inside black holes: a simple model
Particles dropped into a rotating black hole can collide near the inner
horizon with enormous energies. The entropy produced by these collisions can be
several times larger than the increase in the horizon entropy due to the
addition of the particles. In this paper entropy is produced by releasing large
numbers of neutrons near the outer horizon of a rotating black hole such that
they collide near the inner horizon at energies similar to those achieved at
the Relativistic Heavy Ion Collider. The increase in horizon entropy is
approximately 80 per dropped neutron pair, while the entropy produced in the
collisions is 160 per neutron pair. The collision entropy is produced inside
the horizon, so this excess entropy production does not violate Bousso's bound
limiting the entropy that can go through the black hole's horizon. The
generalized laws of black hole thermodynamics are obeyed. No individual
observer inside the black hole sees a violation of the second law of
thermodynamicsComment: 10 page
Energy's and amplitudes' positivity
In QFT, the null energy condition (NEC) for a classical field configuration
is usually associated with that configuration's stability against small
perturbations, and with the sub-luminality of these. Here, we exhibit an
effective field theory that allows for stable NEC-violating solutions with
exactly luminal excitations only. The model is the recently introduced
`galileon', or more precisely its conformally invariant version. We show that
the theory's low-energy S-matrix obeys standard positivity as implied by
dispersion relations. However we also show that if the relevant NEC-violating
solution is inside the effective theory, then other (generic) solutions allow
for superluminal signal propagation. While the usual association between
sub-luminality and positivity is not obeyed by our example, that between NEC
and sub-luminality is, albeit in a less direct way than usual.Comment: 21 pages. v2: Typos in eq. (2.41) and (2.41) corrected; discussion of
section 2.3 modified accordingly. Other sections and conclusions unchanged.
Matches the Erratum published in JHE
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